F&S International Edition 2018

D 11665 F

International Edition

2018

International Edition

MFP 3000 G for General Ventilation Filter Media Filter media test rig in accordance with ISO 16890

for Filtration and Separation Technologies

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info@jcem.ch www.jcem.ch

Highlights 2017

Dear Readers,

In Germany and the neighbouring countries, the magazine F&S has been quite an institution for the past 31 years – after all, it is the only German-speaking trade journal exclusively dedicated to filtration and separation technology but also to the treatment of disperse substance systems.

Our readers and advertisers especially value F&S because of the high quality of the published articles and essays that were often trendsetting and also describe today’s valid standards.

For the eighteenth time, we have now had a small part of our broad editorial spectrum translated into English. These are contributions that were published in the year 2017.

By doing so, we want to provide the contents of our magazine to process engineers in non-German-speaking countries as well.

As we said, this is only a small selection of our articles. With a complete translation of all the articles that were published in the year 2017, you would now hold a thick book of nearly 450 pages in your hands.

We would like to wish you a lot of reading pleasure and would be pleased to receive your feedback.

If you would like to find out more about the German F&S, please do not hesitate to contact us at the address listed below (also see imprint: page 63).

With best regards

Eckhard von der Lühe Publisher

VDL-Verlag GmbH Heinrich-Heine-Straße 5 D - 63322 Rödermark Phone: + 49 (0) 60 74 / 92 08 80 Fax:

+ 49 (0) 60 74 / 9 33 34

E-mail: vdl-verlag@t-online.de Internet: www.fs-journal.de

F & S International Edition

No. 18/2018

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EĞǁ ĮůƚĞƌ ŵĞĚŝĂ ƚĞƐƚ ƌŝŐ D&W ϯϬϬϬ ' ƚŽ ƚĞƐƚ ĮůƚĞƌ ŵĞĚŝĂ ŝŶ ĂĐĐŽƌĚĂŶĐĞ ǁŝƚŚ /^K ϭϲϴϵϬ dŚĞ ŝŶƚĞƌŶĂƟŽŶĂůůLJ ƉƌŽǀĞŶ D&W ĮůƚĞƌ ŵĞĚŝĂ ƚĞƐƚ ƌŝŐ ŐƌŽƵƉ ďLJ WĂůĂƐΠ ŚĂƐ ŐƌŽǁŶ͘ tŝƚŚ ƚŚĞ ŶĞǁ D&W ϯϬϬϬ '͕ ƚŚĞ ĂƉƉůŝĐĂƟŽŶ ƌĂŶŐĞ ĨŽƌ ƚŚĞ D&W ƐĞƌŝĞƐ ǁĂƐ ĞdžƚĞŶĚĞĚ ǁŝƚŚ ƌĞŐĂƌĚƐ ƚŽ ƚŚĞ ŶĞǁ /^K ϭϲϴϵϬ͘ tŝƚŚ ƚŚĞ ĐŽŶǀĞƌƐŝŽŶ ŽĨ ƚŚĞ ƚĞƐƚ ƐƚĂŶĚĂƌĚ ĨŽƌ ŐĞŶĞƌĂů ǀĞŶƟůĂƟŽŶ ĮůƚĞƌƐ ĨƌŽŵ E ϳϳϵ ƚŽ /^K ϭϲϴϵϬ͕ ĂŶ ĂĚĚŝƟŽŶĂů ƚĞƐƚ ĂĞƌŽƐŽů ;< ůͿ ǁŝƚŚ ƉĂƌƟĐůĞ ƐŝnjĞƐ ƵƉ ƚŽ ϭϬ ʅŵ ŝƐ ƌĞƋƵŝƌĞĚ ďĞƐŝĚĞƐ ƚŚĞ ǁĞůůͲŬŶŽǁŶ ƌĞƋƵŝƌĞŵĞŶƚƐ ĂĐĐŽƌĚŝŶŐ ƚŽ E ϳϳϵ ;ŐĞŶĞƌĂů ǀĞŶƟůĂƟŽŶ ĮůƚĞƌƐͿ͕ /^K ϱϬϭϭ ;ŵŽƚŽƌ ŝŶůĞƚ ĮůƚĞƌƐͿ Žƌ /^K ϭϭϭϱϱͲϭ ;ĐĂďŝŶ Ăŝƌ ĮůƚĞƌƐͿ͘ With the ŶĞǁ < ů ĂĞƌŽƐŽů ŐĞŶĞƌĂƚŽƌ >^W' ϭϲϴϵϬ͕ WĂůĂƐΠ ŝƐ ƚŚĞ ĮƌƐƚ ŵĂŶƵĨĂĐƚƵƌĞƌ ƚŽ ƉƌŽĚƵĐĞ Ă ƐƚĂďůĞ ĂĞƌŽƐŽů ĨŽƌ ƵƐĞ Ăƚ ůŽǁ ŇŽǁ ƌĂƚĞƐ ĂƐ ƌĞƋƵŝƌĞĚ ŝŶ ĮůƚĞƌ ŵĞĚŝĂ ƚĞƐƟŶŐ ĨŽƌ /^K ϭϲϴϵϬ͘ dŚĞ ŶĞǁ < ů ĂĞƌŽƐŽů ŐĞŶĞƌĂƚŽƌ >^W' ϭϲϴϵϬ ŵĞĞƚƐ ƚŚĞ ǀĞƌLJ ŚŝŐŚ WĂůĂƐΠ ƋƵĂůŝƚLJ ƌĞƋƵŝƌĞŵĞŶƚƐ ĂŶĚ ŝƐ ƵƐĞĚ ƌĞůŝĂďůLJ ĂƐ Ă ŐĞŶĞƌĂƚŽƌ ŝŶ ƚŚĞ ƚĞƐƚ ƌŝŐƐ ŽīĞƌĞĚ ďLJ WĂůĂƐΠ ŝŶ ĂĐĐŽƌĚĂŶĐĞ ǁŝƚŚ /^K ϭϲϴϵϬ͘ ĚĚŝƟŽŶĂůůLJ͕ ƚŚĞ D&W ϯϬϬϬ ' ŝƐ ĞƋƵŝƉƉĞĚ ǁŝƚŚ Ă ŶĞǁ ƐŽŌǁĂƌĞ ƚŽ ĨŽůůŽǁ ƚŚĞ ƚĞƐƚ ƉƌŽĐĞĚƵƌĞ ĂĐĐŽƌĚŝŶŐ ƚŽ /^K ϭϲϴϵϬ ĂŶĚ ĂƵƚŽŵĂƟĐĂůůLJ ĞǀĂůƵĂƚĞ ĞWDϭ͕ ĞWDϮ͘ϱ ĂŶĚ ĞWDϭϬ ĞĸĐŝĞŶĐŝĞƐ͘ dŚĞ D&W ϯϬϬϬ ŽīĞƌƐ ƉĂƌƟĐƵůĂƌ ƚĞĐŚŶŝĐĂů ĂĚǀĂŶƚĂŐĞƐ ŝŶ ƚŚĞ ĐŚŽŝĐĞ ŽĨ ƚĞƐƚ ĐŽŶĚŝƟŽŶƐ ĂŶĚ ĞĂƐLJ ŽƉĞƌĂƟŽŶ͗ ͻ t ŝĚĞƐƚ ƌĂŶŐĞ ŽĨ ĨĂĐĞ ǀĞůŽĐŝƟĞƐ ĨƌŽŵ ф Ϯ ĐŵͬƐ ƵƉ ƚŽ ϭ ŵͬƐ ŝŶ ƐƵĐƟŽŶ ŵŽĚĞ ͻ Y ƵĂƐŝͲƐŝŵƵůƚĂŶĞŽƵƐ ƉĂƌƟĐůĞ ĚĞƚĞĐƟŽŶ ŝŶ ƵƉƐƚƌĞĂŵ ĂŶĚ ĚŽǁŶƐƚƌĞĂŵ ǁŝƚŚ WƌŽŵŽΠ ϯϬϬϬ ǁŝƚŚŝŶ ŽŶĞ ŝŶƐƚƌƵŵĞŶƚ͕ ƚŚĞƌĞĨŽƌĞ ĞĂƐLJ ĐŽƌƌĞůĂƟŽŶ ĂĚũƵƐƚŵĞŶƚ ͻ t ŝĚĞ ŵĞĂƐƵƌĞŵĞŶƚ ƌĂŶŐĞ ĨƌŽŵ ϮϬϬ Ŷŵ ƵƉ ƚŽ ϰϬ ђŵ ǁŝƚŚ ŚŝŐŚ ƌĞƐŽůƵƟŽŶ ;ϯϮ ŝŶƚĞƌǀĂůƐ ƉĞƌ ĚĞĐĂĚĞͿ͘ dŚĞ WƌŽŵŽΠ ϯϬϬϬ ĂĞƌŽƐŽů ƐƉĞĐƚƌŽŵĞƚĞƌ ĨƵůĮůůƐ ƚŚĞ ƌĞƋƵŝƌĞŵĞŶƚƐ ĂĐĐŽƌĚŝŶŐ ƚŽ ^,Z ϱϮ͘Ϯ͕ E ϳϳϵ ĂŶĚ /^K ϭϲϴϵϬ ͻ t ŝĚĞ ƌĂŶŐĞ ŽĨ ĂĞƌŽƐŽů ĐŽŶĐĞŶƚƌĂƟŽŶƐ ĨƌŽŵ ф ϳ ŵŐͬŵϹ ƵƉ ƚŽ х ϭ ŐͬŵϹ ;/^K Ϯ &ŝŶĞͿ

Contents W Highlights 2017

6

Developments in the Filtration and Separation Technology Sectors S. Ripperger

6

New Developments in Membrane Technology Report from the DGMT conference in Kassel H. Lyko

12

Membranes for Sustainable Processes Report from the 16th Aachener Membran Kolloquium H. Lyko 20 Wastewater Treatment and the Reuse of Purified Wastewater: Hygienic Aspects H. Lyko

26

Phosphor Recovery from Sludge and Other Waste Streams – Conditions and Processes H. Lyko

32

Water Technology for the Beverage and Food Industries Report from the 14th VDMA Water and Wastewater Conference H. Lyko

37

Membrane Technology Used in Waterworks: Experience gained from removing ingredients H. Lyko

41

Biological Treatment of VOC contaminated Extracted Air or Wastewater by Using an Activated Carbon-Doped PU Carrier A report from centrotherm clean solutions GmbH & Co. KG

45

Development, Production and Testing of Nonwovens for Filtration Use Report from the 2017 Filtrex conference H. Lyko

47

ͻ , ŝŐŚĞƐƚ ƌĞƉƌŽĚƵĐŝďŝůŝƚLJ ŝŶ ƚĞƐƚ ƌĞƐƵůƚƐ ͻ / ŶƚĞŐƌĂƚĞĚ ĐŽƌŽŶĂ ĚŝƐĐŚĂƌŐŝŶŐ ƐLJƐƚĞŵ ͻ E t͗ > ϮϬϬϬ ĐŽŶĚŝƟŽŶƐ ĚŝƐƉĞƌƐŝŽŶ Ăŝƌ ĨŽƌ ƉŽǁĚĞƌ ŐĞŶĞƌĂƚŽƌ Z ' ϭϬϬϬ ƚŽ ϱϬ й ƌĞů͘ ŚƵŵŝĚŝƚLJ

ŽŶƚĂĐƚ ĂŶĚ ĨƵƌƚŚĞƌ ŝŶĨŽƌŵĂƟŽŶ WĂůĂƐ 'ŵď, 'ƌĞƐĐŚďĂĐŚƐƚƌĂƐƐĞ ϯ ď ͮ ϳϲϮϮϵ <ĂƌůƐƌƵŚĞ 'ĞƌŵĂŶLJ WŚŽŶĞ͗ нϰϵ ϳϮϭ ϵϲϮϭϯͲϬ &Ădž͗ нϰϵ ϳϮϭ ϵϲϮϭϯͲϯϯ ͲŵĂŝů͗ ŵĂŝůΛƉĂůĂƐ͘ĚĞ ǁǁǁ͘ƉĂůĂƐ͘ĚĞ

4

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Contents Highlights 2017

Air and Gas Filtration R&D Report from the 8th IUTA filtration day H. Lyko

54

Efficiency and Pressure Drop of Air Filters used in General Ventilation Systems F. Schmidt , T. Engelke , A. Breidenbach , E. Däuber

58

W New Developments in Membrane Technology – Report from the DGMT conference in Kassel

New Aspects Regarding the Testing of Air Filters Report from the Palas Air Filtration seminar H. Lyko 64 Separation Processes Used in the Treatment of Bulk Solids and Recycling Technologies H. Lyko

67

Powtech 2017: The Marketplace for Industrial Gas and Air Cleaning Systems H. Lyko

71

Imprint

63

This issue is accompanied by a brochure with information about the 17th Aachener Membran Kolloquium.

We ask for your attention.

W Wastewater Treatment and the Reuse of Purified Wastewater: Hygienic Aspects

W Efficiency and Pressure Drop of Air Filters used in General Ventilation Systems

W Separation Processes Used in the Treatment of Bulk Solids and Recycling Technologies

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Highlights 2017

Developments in the Filtration and Separation Technology Sectors S. Ripperger* In all areas of process and plant engineering, new, economical systems are being searched for, especially with regard to energy requirements and the necessary operating and auxiliary materials. The energy supplied should be used as much as possible and waste streams should be avoided as far as possible. With the higher demands on the separation process, the energy demand usually increases, and so do energy costs. The increasing use of renewable raw materials and the use of biotechnological processes also result in new requirements for separation technology and the associated systems and equipment. In the field of environmental technology, the increased implementation of European regulatory law has an impact on process and plant technology. In the following article, some developments, which are also of importance for the filtration and separation technology, are dealt with in more detail.

1. Introduction In a contribution to the 150th issue of this journal /1/ developments and trends in the field of separation and filter technology were treated. It was also pointed to the “compulsion to innovate and product development” due to the competition and the constant changes. In a later article /2/ the associated “challenge product development” was described in more detail.

Changes in a discipline arise on the one hand from new insights and technical possibilities and on the other hand from new social, political and economic challenges.

Both developments lead to new technical solutions and organizational forms.

In Germany, the research and development work of companies and public research institutions and universities stimulate each other. For example, in the specialist groups of ProcessNet, an organization of the VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurtechnik (GVC) and the DECHEMA Society for Chemical Engineering and Biotechnology, the universities and public research institutions work in different fields with the respective leading companies. In an article of the magazine, the specialist group from ProcessNet responsible for mechanical separation processes are presented /3/.

This article also describes the current developments in this special sector. Basic and “precompetitive” research undertaken at public institutions, which is funded by considerable resources from the state, forms an excellent basis for companies to build on. * Prof. Dr.-Ing. Siegfried Ripperger Editor-in-chief of the “Filtrieren und Separieren” magazine Former holder of the “Chair of Mechanical Process Engineering” at the Technische Universität Dresden and Technische Universität Kaiserslautern IES GmbH Luxstr. 1 67655 Kaiserslautern, Germany Tel: +49 (0) 6302 - 5707 Email: ripperger@mv.uni-kl.de

6

Fig. 1: Filtration simulation using DNSlab (Direct Numerical Simulation Laboratory) Recording the real filter media structure (e.g. using microtomography), b) Numerical flow calculation, c) Calculation of particle paths and possible contacts with the filter medium after taking into consideration the particle adhesion conditions

Mentioned in this context should be the AiF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen „Otto von Guericke“ e.V.). It enables small and medium-sized enterprises (SMEs) to participate directly in research projects and access to current research results. As part of AiF approximately 100 Research Associations, organized by sector and technology field, small and medium-sized enterprises jointly conduct pre-competitive research that benefits the industry as a whole /4/. The research projects are oriented directly to the needs. A committee consisting of company representatives from the research association supervises every project. This ensures the practical relevance of the results and also accelerates the transfer of knowledge to the economy.

In general it is important that the work is reported in a practical manner and that this information can be called up by the companies and evaluated with regard to their own activities. The findings can therefore be incorporated into the development of new products and processes.

Professional journals are taking over this important role as intermediaries in their respective sectors in addition to conferences and congresses. This magazine has been the only German-language professional journal over the last 30 years that covers the filtration and separation technologies

sector. Their development and the industries that they report to were presented on the occasion of the 25th anniversary of the magazine /5/. New processes, devices, apparatus and processing-chain developments and insights are presented and successful applications are also described in each issue. Some of the developments and trends applicable to the entire sector are covered in the following article.

2. Development trends in technical sectors 2.1 Virtual product development Modern research is increasingly using simulation technology and its software in order to design new products and determine their properties during an early phase.

These so-called “IT tools” are also used to interpret data and to facilitate workgroup coordination. For example, simulation programs enable flows to be displayed on virtual models and essential parameters can then be defined for using the products.

They also offer simultaneous options for visualising running processes. Computer programs for structure generation and numerical flow simulations are also used during the development of new, optimised filter media. Microcomputer tomography (μ-CT) is increasingly being used to take really complex porous structures, such as

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Highlights 2017

The PACO + HETA-Formula: those used as filter media, into consideration. The pressure drops that occur when using different fluid parameters can also be calculated in conjunction with the numerical flow simulation. Particle separation can also be calculated in advance. An important benefit here is that system performance can be determined through simulation before realisation of the filter media structure. The effects of structural changes can also be studied cost-effectively by using the generated virtual models.

Particle separation simulation occurs using a Lagrangian particle trajectory calculation, e.g. as in the DNSlab program (Fig. 1) /6, 7/. The flow field in the open pore space must be recalculated after a specific number of particles have been separated so that particle separation during filtration can be considered. The increase in the pressure drop as well as the change in separation efficiency during filtration can also be determined. The data obtained in this way then become the starting point for simulating filtration in filter units (e. g. filter cartridges, candle filters) or in filter devices that contain these elements. In such a way, virtual product development and filter designing can help to considerably reduce the cost of developments.

2.2 Product Data Management (PDM) The data volume that already exists in connection with product testing and usage is increasing significantly, so that electronic Product Data Management (PDM) is becoming more important in conjunction with the virtual product development and the associated experimental trials. Within the mechanical engineering and manufacturing engineering sectors this is seen as a concept whereby product-defining, representation and presentation data and documents are stored, managed and made available in downstream phases during the product’s life cycle. Electronic product data management (PDM) has become a new software category in the mechanical engineering sector, but previously it was only available or used to some extent in separation technology. It is very important that the product development data and data relating to product usage are recorded and stored in such a way that they can be interlinked and evaluated at any time for the further development and use of separation technology products. This will result in new options for product and process optimisation as well as for new or further developments as well as quality management options.

PACO Group means PACO + HETA as one technological authority when there is a need for rewarding solutions in the fields of

Filtration Separation Sieving Automation Loading Technology You can be confident that there is application know k how waiting for you matching your demands. And d you can be sure that there are understanding, creativity and nd solution skills which will exceed your expectations. Put ut into practice with an extraordinary chain of competencee from high quality f metal wire cloth to completely automated solutions. And the m almost endless number of convincing cin solutions between.

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2.3 Digitalisation and Industry 4.0 “Integrated industry”, “Digitalisation” and “Industry 4.0” are key words used to denote a development, which, with regard to the classic industries, will cause a revolutionary change in the associated production and system technologies used in industry.

One expects that many sectors will change due to the interlinking of information systems and software technology components with mechanical and electronic parts via the internet using wired or wireless communications (Fig. 2). Some of the production and process technology effects are discussed in /8/.

One development trend is that all mechatronic products will be given an IP address and networked into the internet. They will

Cloud Humans Computer

Machine 1

Find your local PACO and HETA partner: www.paco-online.com www.heta.de

Process 1

Abb. 2: Networked system as part of Industry 4.0

powered by .Ing – the German art of engineering F & S International Edition

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Highlights 2017

Excellent

Good

Average

Poor

Fig. 3: Assessment of the international competiveness of Germany as an IT location (Source: VDI)

become “smart products” in the “Internet of Things” or “cyber-physical systems with integrated, internet-based services”.

New options will arise in conjunction with the previously described PDM system.

For example, the use of the data collected via the internet can be used to optimise a filter automatically or to adapt it to meet the respective requirements. In the case of depth filter elements, the optimum time for an exchange can be determined and planned after the recorded in-line operational data is taken into consideration.

This results in new Product Lifecycle Management (PLM) options. This also gives the recorded product data a new significance. The manufacturer’s data recorded during the development and production of a product will be supplemented by the data obtained during product utilisation.

According to Ulrich Sendler, both types of data will play a major role in the industrial products business in the future /9/. As he wrote in an article: “The first data type is virtually the resources that the producer can throw into the balance, whereas the second data type can be a gateway for services provided by third parties for the respective products. Since the majority of the data generated from usage is measurable and ascertainable, it can be collected without the manufacturer having to make it available. However, if both can be interlinked and normally only the manufacturer can do this, then particularly interesting services can be derived from this.”

Data generated or collected whilst using a product also plays a major role in preventive maintenance. It is becoming increasingly recognised that efficient planning of the maintenance and repair work is necessary in order to minimise plant operating costs. Four basic maintenance strategies can be followed here: a) Running the plant until it fails: In this case, repairs will be carried out only after an error occurs or the system fails. This is the simplest maintenance method, but usually proves to be the most expensive. This maintenance method can be associated with defective batches,

8

Fig. 4: German exports of equipment for purifying water by region in 2016; Total export volume: 976.68 million euros; Source: Federal Statistics Office (Art-No. 842121) / VDMA

loss of production and long unscheduled downtimes. b) Preventative maintenance: This maintenance strategy includes regular maintenance according to a planned schedule. Parts are replaced before they fail. This means that unexpected failures are usually avoided, but some parts are unnecessarily replaced even though they have not yet reached their usable limits. c) Condition-based maintenance: In this case plant operation is monitored continuously and maintenance is carried out when specific conditions occur. The parameters that are compared against the generated data are normally defined in advance. Maintenance is initiated when specific data exceeds the defined limit parameters. Exceeding of the limit parameters usually indicates that operational safety can only be guaranteed to a limited extent. d) Predictive maintenance: Plant operation is also continuously monitored in this case, but it is based on the recorded data and used in conjunction with a calculation model, which is stored as software, and the highly probable time when a failure of the system can be expected is estimated beforehand. This means that it is possible to optimally plan plant utilisation as well as the associated maintenance.

Whereas data analysis has long been an integral part of manufacturing in mechanical engineering, predictive maintenance it is hardly being used in plant engineering.

Good opportunities exist here to improve existing maintenance routines, especially with regard to filters that have to be replaced at specific intervals. The necessary infrastructure has to be created for this in many sectors and the appropriate software modules also have to be developed. Optimum filter changes could be predictively determined using developed software and by monitoring the filtration pressure and substantial cost savings could be realised as part of the ongoing projects for optimising filter changing. This system

could also be used for filter cartridges for liquid filtration as well as storage filters used for dust separation /10/.

Many decision-makers distrust the possible benefits of digital transformation because of the risks associated with digital transformation. A survey conducted by the VDI among more than 600 IT experts from companies showed that Germany was generally rated as a rather average IT location with regard to international competition /11/. 62 per cent of respondents rated misuse or data manipulation as a high or very high-risk (see Fig. 3). IT security, big data and clouds are topics that concern many companies, but they still need to be persuaded in order to use the opportunities associated with the keyword “Industry 4.0”.

2.4 Modularisation used in plant engineering Module-based plants are now a global trend that shortens development times and also reduces development and manufacturing costs. A modularised plant consists of prefabricated, validated plant modules.

For example, these are processing stages for heating or cooling, pumping, mixing, filtering, centrifuging or complete functional units, such as flash heaters, water treatment systems and plant parts for CIP cleaning and plant sterilisation. Individual modules (units or skids) with defined dimensions have been designed and constructed so that they can be combined in compliance with the modular principle. They are fitted with the devices needed for implementing the measuring, control and management technology and are all electrically wired.

The modules are usually tested by the manufacturer before delivery and are integrated in the plant at the destination.

In a modularised plant concept: - production is transferred to an economical production environment - quality management is improved - planning time is reduced - transportation is simplified - on-site assembly time is considerably reduced

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- commissioning time is reduced - costs are reduced.

Validation work is carried out whenever necessary and the corresponding documentation is also created during the module development stage. This reduces having to work under critical conditions, e.g. on off-shore platforms, to a minimum.

Modularisation is usually simultaneously linked with standardisation, whereby in-house economic and technical advantages will emerge during the order processing, engineering, assembly and automation as well as purchasing and stocking of components.

In the “White Paper Modular Plants”, a ProcessNet working group has evaluated and summarised the current developments based on project results /12/. Experts from industry and the universities are calling for further harmonisation of the equipment used, in order to create a basis for broader use of this technology in industry.

Since customised products are becoming more and more important in the chemical and pharmaceutical industries, the life cycles and development times are also becoming shorter for these products. Module-based systems provide an opportunity to adapt and design processes flexibly under this context. It might also be possible to reuse specific parts and this will reduce the cost of the engineering process. The use of a standardised modular planning workflow is decisive with regard to reusing process engineering information and a continuous flow of data throughout all of the project phases. A processing stage can be subdivided into groups of components, which will produce reusable units. All of the module’s documents can be compiled into a database. A process should be comprised of at least one main component, which together with all the

peripheral components covers the required unit operation. The compatible modules should be designed as customisable units and assembled into multi-purpose plants.

3. Economic conditions 3.1 The industry’s economic environment Despite numerous political and economic uncertainties, many filtration and separation technology companies are expecting a good business result from the current year, even after considerable fluctuations in specific markets have been taken into consideration. Many of the companies in the industry are SMEs that, according to the EU definition, have no more than 249 employees and generate annual sales of no more than 50 million euros or a maximum balance sheet total of 43 million euros. The export quota is of great importance to many of the companies.

93 companies have been assigned to the “Water, Wastewater and Sludge Treatment” group within the VDMA. In 2016 the German manufacturers in this sector were able to maintain their exports virtually unchanged at the high level of the previous year. Exports fell from 977.2 million euros (2015) to 967.7 million euros (2016) /13/. The result was mainly driven by growth within the EU 28 core markets and in Russia. The ranking of the world’s strongest export markets is shown in the article by H. Lyko /14/. Despite some significant changes in specific markets, the EU 28 remain the most important purchasing region for German manufacturers of water and wastewater technologies (see Fig. 4). The exports to these countries increased by 3.5% to 412 million euros.

The production volume of the companies in the VDMA General Air Technology Association reached around 14 billion

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euros in 2016. 59% of the EU countries were the most important export sales markets again in 2016. Companies, like many others, consider the EU to be their home market. The basis for this was created by harmonising many of the technical regulations. The legal system created by this was previously addressed in some articles published in this magazine /16/. The realisation of this system came at great cost to the companies, but the advantages to the filtration and separation technology sector are now many.

The number of projects awarded to German companies in large plant construction has declined for several years.

The export quota from this sector lies at approx. 80% /17/. International customers frequently expect the contractor to assume the role of general contractor and to guarantee turnkey delivery at a fixed price. The ability to master the complexity as well as the various financial, technical and planning challenges of such projects is a fundamental requirement for continued existence in the market. With so-called EPC (Engineering, Procurement and Construction) projects, the contractor is obliged to provide a turnkey plant, usually at a fixed price and on a specific date that is subject to a contractual penalty. He also provides all the necessary services, especially the entire engineering service, procurement or production of all necessary plant components, on-site assembly and the commissioning. Therefore, all of the risks involved under these conditions must be thoroughly examined and evaluated during the tender phase. Accordingly, safeguarding exports under the so-called Hermes coverage scheme also plays an important role in this sector. Calls for tenders in developing and emerging countries can also ensure that a greater number of

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locally supplied parts are used. According to a statement from the VDMA, German suppliers subject to the OECD regulations are therefore at a disadvantage when compared to their Asian competitors, as protecting local services is severely restricted by the OECD regulations. Companies involved in large scale plant construction who are members of the VDMA do not expect any trend reversal during the current year because of this background.

3.2 Mergers and takeovers The growing challenges due to stringent legal requirements, strong competition and sharp price competition forced many companies to rethink their structuring and adapt to the current situation. This resulted in the filter and separation technology sector undergoing considerable structural changes in recent years due to mergers and acquisitions. It was mainly smaller companies that were incorporated into a larger group. This expanded the portfolio of processes within the company, improved the international product sales and ensured that the necessary service was available especially abroad.

The many medium-sized companies and their interrelationships with numerous large and small companies is a German location advantage. In many cases, it is still undecided as to whether the newly formed structures will prove themselves and strengthen the location or weaken it over the long term.

However, structural changes are often needed to improve the situation in which some companies find themselves.

4. Sociopolitical changes Socio-political changes have resulted in new or amended laws, many of which have direct repercussions regarding technology. Marginal economic conditions are often changed as well, which in turn also have an effect on the technology being used. Such as major changes in the energy technology sector resulting from the politically initiated energy transitions or the development of electric drives for passenger cars as a consequence of politically desired and promoted electromobility.

Both developments are linked to the political and international accords covering climate change.

Even though harmonisation of the technical regulations within the European Union (EU) for completing the single European market is already well advanced, it is still ongoing. Therefore it can be expected that this will also result in further changes that will influence the technical performance of plants and equipment.

Developments in the separation technology sector are also severely affected by environmental protection measures and a sustainable economy. The new or amended legal provisions as well as the changed economic conditions necessitate contin10

uous updating of the technology being used. R&D activities are needed for this because many of the new requirements are not fulfilled by the known technical systems. R&D activities in an engineering/ scientific discipline are therefore carried out in a political, economic, environmental and social environment, which in turn is influenced by the research results and findings (feedback). Which effects the legal regulations might have, are evident in the following examples.

4.1 Aftertreatment of exhaust gases from combustion engines The measures for reducing emissions from combustion engines are considered as examples here. The minimum standards to be complied with are defined by European regulations. The gradual tightening of the standards requires continual updating of the exhaust gas aftertreatment technology. The VW scandal revealed that compliance with the legal regulations, especially with regard to diesel engines, requires a lot of effort. The problem of exhaust gas aftertreatment was previously covered by an article in this magazine in 2004 /18/. Diesel engines provide an economical and reliable drive system for motor vehicles due to their high efficiency and their subsequent low fuel consumption. Solving the exhaust gas problem presented the manufacturers with a major challenge, which they countered with internal engine measures and an exhaust aftertreatment to reduce NOx- and particle emissions. Solving this problem is fraught with considerable technical and economic problems. The formation of nitrogen oxides can be reduced by low combustion temperatures and shorter retention times. However, this also creates conditions under which an increased number of particles are formed. Minimising particle emissions can be realised through combustion that is as complete as possible, but this abets the creation of nitrogen oxides.

A simultaneous reduction of both emission values through internal engine measures can only be realised to a certain extent, so that expensive exhaust gas aftertreatment becomes necessary. Discussions about the future of the diesel engine have shown that an entire technology will be questioned if the expenditure for exhaust gas cleaning exceeds a specific level. The decision that the expenditure is too high for small engines and therefore these engines will no longer be provided in the future.

Emissions immediately behind the engine are often partially re-combusted through exhaust gas recirculation in diesel and gasoline engines. In gasoline engines with fuel injection it is also expected that an additional particle filter will also be needed after the three-way catalytic converter in the future. An oxidation catalytic converter and a particle filter as well as an SCR catalytic converter with urea injec-

tion will be needed for diesel engines after exhaust gas recirculation.

Modern diesel engines also place high demands on the fuel quality at the injection nozzle inlet, both with regard to the particle concentrations of different size fractions as well as the proportion of water. This means that further fuel filtration developments are needed.

The absence of exhaust gas aftertreatment on inland vessels and high-sea ships has been increasingly reported. Mandatory regulations do not exist. Therefore it can be taken for granted that the fine dust guideline values stipulated by the EU are inadmissibly exceeded in cities with port facilities and on cruise liners (see /19/).

4.2 Increasing utilisation of biological substances With the increasing use of biogenic raw materials and the utilisation of the resulting coupling products, the demands placed on the process technology with regard to their preparation and treatment capabilities will continue to increase. The increasing importance of the resulting natural-product process technology developments for chemical production is covered in /20/. It is expected that this development will lead to further separation process applications. Many of the preparation and cleaning steps run as wet-chemical processes, so that solid/liquid separation and, if needed, drying the materials are also necessary. Processes such as centrifugation, filtration and substance separation using membranes are now used in many stations as part of the processes.

4.3 A sustainable economy It has long been recognized that to sustain the economic system in the industrialized world, human beings worldwide are massively intervening in the natural balance. These interventions are so great that researchers now find it justified to speak of a new geological age, the “Anthropocene,” in which life on earth is influenced in all areas by human action. Its influence is so great that for the first time even an manmade climate change begins.

This realisation supports many people’s desire for a sustainable economy. The aim here is to preserve the natural resources on which our existence is based over as many generations as possible and, if necessary, even to improve them. Developments in the industrialised countries show that process technology and separation technology in particular, often play a key role in them.

Although the criteria for a sustainable economy are adequately described in many publications the economy in the industrialised countries remains a long way away from meeting the criteria for sustainability. However, it is indisputable that permanently safeguarding the livelihoods of humanity can only be realised if the pressures on the environment and F & S International Edition

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the consumption of natural resources are drastically reduced.

According to the concept of sustainability, we no longer need to consume environmental resources over a given period of time as new ones will be created. Many processes and products will have to be improved in order to realise this balance. Moreover, energy use, mobility and food production will also have to meet the sustainability requirements. A more efďŹ cient material ďŹ&#x201A;ow management system must be installed. Much of this will only be possible through the use of separation technology.

However, sustainability also means that decisions and actions must not just be evaluated according to environmental considerations, but that the associated social effects are also considered.

Therefore permanent safeguarding of the livelihoods can only be realised if the severe social gaps within the countries and beyond the national borders diminish and the living standards of those people living in poverty are signiďŹ cantly improved. According to the â&#x20AC;&#x153;Guidelines on sustainability for the chemical industry in Germanyâ&#x20AC;?, which were compiled by the social partners in 2013, the decisions and actions should be linked to an improvement in competitiveness, good working conditions and positive contributions to society /21/.

5. Summary Some developments have been described here that are also of importance to the ďŹ ltration and separation technology sector. They show that this speciďŹ c sector will continue to evolve as a result of many further development changes that are expected and that the range of applications will be further expanded due to future tasks.

It is expected that these tasks will often be more complex and can only be solved in conjunction with other disciplines.

Literature: /1/ S. Ripperger: Entwicklungen und Trends auf dem Gebiet der Separations- und Filtertechnik.

Filtrieren und Separieren 25 (2011), Nr. 1, S. 7-16 /2/ S. Ripperger: Herausforderung Produktentwicklung. Filtrieren und Separieren 27 (2013), Nr. 1, S. 16-18 /3/ U. Esser: Die ProcessNet - Fachgruppe â&#x20AC;&#x17E;Mechanische FlĂźssigkeitsabtrennung (MFA)â&#x20AC;&#x153;.

Filtrieren und Separieren 31 (2017), Nr. 3, S. 158-160 /4/ Die Forschungsvereinigung Verfahrens-Technik (GVT) e. V.Filtrieren und Separieren 31 (2017), Nr. 3, S. 161-162 /5/ S. Ripperger: 25 Jahre Fachzeitschrift â&#x20AC;&#x17E;Filtrieren und Separierenâ&#x20AC;&#x153; â&#x20AC;&#x201C; Eine RĂźck- und Vorschau auf die Entwicklung einer interessanten verfahrenstechnischen Disziplin.

Filtrieren und Separieren 26 (2012), Nr. 5, S. 308-316 /6/ D. Hund, K. Schmidt, S. Ripperger: Numerische Berechnung der StrĂśmung und der Partikelabscheidung in Filtergeweben. Filtrieren und Separieren 28 (2014), Nr. 4, S. 221-225 /7/ S. Ripperger, K. Schmidt: Entwicklung von Geweben als Filtermedien unter BerĂźcksichtigung der numerischen StrĂśmungssimulation. Filtrieren und Separieren 29 (2015), Nr. 6, S. 378-381 /8/ S. Ripperger: Industrie 4.0 und mĂśgliche Auswirkungen auf die Produktions- und Prozesstechnik. Filtrieren und Separieren 30 (2016), Nr. 1, S. 6-12 /9/ U. Sendler: PLM und die Zukunft der digitalisierten Industrie. MĂźnchen, 1. September 2016; unter: www.plmportal.org; aufgerufen am 29.12.2016 /10/ â&#x20AC;&#x17E;IT Seminar Filtertechnikâ&#x20AC;&#x153;, Mannheim 23./24.5.2017; Seminarunterlagen, Hrsg.: IT for Engineering (it4e) GmbH /11/ Pressemitteilung des Verein Deutscher Ingenieure e. V. (VDI) vom 17. März 2017 (siehe www.vdi.de) /12/ â&#x20AC;&#x17E;White Paper Modular Plantsâ&#x20AC;&#x153;, Hrsg.: ProcessNet Arbeitskreis â&#x20AC;&#x17E;Modulare Anlagenâ&#x20AC;&#x153;, Januar 2017, abrufbar unter â&#x20AC;&#x17E;www.dechema.deâ&#x20AC;&#x153; /13/ â&#x20AC;&#x17E;Deutsche Wasser- und Abwassertechnik 2016â&#x20AC;&#x153;; Mitteilung des VDMA vom 28.04.2017 /14/ H. Lyko: Wasseraufbereitung fĂźr die Lebensmittel- und Getränkeindustrie - Bericht von der 14. Wasser- und Abwassertagung des VDMA. Filtrieren und Separieren 31 (2017), Nr. 3, S. 189-194 /15/ â&#x20AC;&#x17E;Geschäftsbericht 2015-2016 der Allgemeine Lufttechnikâ&#x20AC;&#x153; verĂśffentlicht zur Mitgliederversammlung am 30./31.03.2017 unter www.vdma.org /16/ S. Ripperger: Technisches Recht zur Anlagentechnik, Teil 1: Europäische Regelungen Filtrieren und Separieren 30 (2016), Nr. 4, S. 218-223, Teil 2: Deutsche Rechtsvorschriften Filtrieren und Separieren 30 (2016), Nr. 5, S. 303-308, Teil 3: Die neue Druckgeräterichtlinie und ihre Umsetzung in deutsches Recht, Filtrieren und Separieren 30 (2016), Nr. 6, S. 393397, Teil 4: Bedeutung des Qualitätsmanagements, Filtrieren und Separieren 31 (2017), Nr. 1, S. 20-26 /17/ â&#x20AC;&#x17E;Die Welt im Wandel â&#x20AC;&#x201C; GroĂ&#x;anlagenbau muss ďŹ&#x201A;exibel agieren kĂśnnenâ&#x20AC;&#x153;; Mitteilung des VDMA vom 27.03.2017 /18/ Ripperger, M. Stintz, L. Hillemann: Filtersysteme zur Abgasreinigung von Dieselmotoren.

Filtrieren und Separieren 18 (2004) 1, 6-12 /19/ S. Ripperger: Separationsverfahren auf Schiffen und Offshore-Einrichtungen. Filtrieren und Separieren 28 (2014), Nr. 2, S. 84-89 /20/ S. Ripperger: ZukĂźnftige Bedeutung der Naturstoff-Verfahrenstechnik fĂźr die chemische Produktion. Filtrieren und Separieren 28 (2014), Nr. 1, S. 25-28 /21/ â&#x20AC;&#x17E;Leitlinien zur Nachhaltigkeit fĂźr die chemische Industrie in Deutschlandâ&#x20AC;&#x153; 29. Mai 2013 abrufbar unter www.vci.de

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New Developments in Membrane Technology Report from the DGMT conference in Kassel H. Lyko* Membrane technology innovations do not play a major role in the markets in which membranes already have great importance and membranes, modules and membrane plants are all used in very large areas or in plants with very large capacities. This was reflected in the program for this year’s Kassel Conference held by the German Society for Membrane Technology (DGMT), which not only included presentations about membrane contactor processes, gas separation, process intensification and the elimination of trace elements, but also covered classic procedures such as reverse osmosis. Membrane bioreactor technology, which has become widely accepted in the meantime, can still continue to grow, especially in urban wastewater treatment and more so if it supports micro pollutants elimination.

With the help of one of the most experienced membrane experts in Germany, Prof. Heiner Strathmann, Emeritus and guest professor of the Institute of Chemical Process Engineering at Stuttgart university, everyone was able to gain an insight into the history of membrane technology with a bridging impact covering new materials and applications.

Membrane technology development Prof. Strathmann looked back over the time when the use of synthetic membranes started around the middle of last century and highlighted the most important membrane materials and membrane processes in use nowadays. The technologically and economically relevant processes include, in addition to the separation of substance mixtures, the controlled release of substances (in medicine and the dosing of pesticides or fertilizers) as well as the generation and storage of electrical energy (fuel cells and batteries). Amongst the multitude of different membrane applications there are some that are really outstanding because of their great technical and economic importance. Haemofiltration and haemodialysis (collectively >4 billion $/a) and reverse osmosis used for sea water desalination (>3 billion $/a) are at the forefront with regard to the volumes realised.

Reverse osmosis and electro-deionization for pure and high-purity water production, ultrafiltration and electrodialysis for wastewater treatment as well as electrodialysis for brackish desalination (each >100 million $/a) are more than one order of magnitude less. The entire process filtration (product preparation) range using electrodialysis and ultrafiltration was deemed to be a small market with a turnover >200 $/a. The reason for the prominent roles of seawater desalination and haemodialysis was mentioned as these processes only need to use one specific type of membrane. However, membranes adapted to the respective separation tasks (products, solvents as well as operating * Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696

12

temperatures and pressures) are needed for process filtration. Haemodialysis benefits from the fact that there are no alternative procedures.

Strathmann was relatively sceptical when he described the economic importance of membrane processes for energy generation and storage. In his opinion, some procedures such as reverse electro-enhanced dialysis (REED) or forward osmosis are wanted for political purposes, but the energy generated by them is not worthwhile. The hoped-for efficiency of fuel cells has still not been realised because of the internal resistance of the cells. All-in-all, it can be seen that this sector still needs a high level of R&D to improve available membranes.

Contactor processes Membrane contactors for specific applications have been well known for more than 30 years. Wolfgang Riedl, from

the University of Applied Sciences and Arts Northwestern Switzerland (FHNW), researches membrane-assisted liquid/liquid extraction as well as the gassing and degassing of liquids using membranes.

Despite their advantages over conventional processes such as extraction, absorption and desorption or distillation, some contactor applications fail due to the insufficient thermal or chemical resistance of the membrane materials. The LiquiCel module, which has been on the market for more than 20 years and is produced by 3M (formerly Membrana), contains 300 μm diameter PP hollow-fibre membranes with a porosity of around 30% and it has proven itself many times in gas/liquid applications. Contactor processes offer the advantage that emulsions cannot be formed during liquid/liquid extraction because of the phase separation that occurs when using membranes. Flat membranes made from PTFE and PVDF as well as PTFE

Fig. 1: Diagram of a two-stage membrane contactor process for decentralised biogas treatment (picture: 3M)

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capillaries and hydrophobised ceramic membranes were examined at FHNW during the search for membrane materials with a higher solvent resistance than PP. The performance of a contact membrane vis-à-vis the phases used on both sides is described by the overall substance transmission coefficient. The greater this value, the smaller the membrane area needed for the same drive forces. The PTFE capillaries that were studied have proven to be the best, mainly because of their high porosity of up to 80%. The inner diameter of the PTFE capillaries is 1.9 mm. This is larger when compared to the PP hollow fibres and results in a reduced membrane surface density. Whether the use of the correspondingly larger contactor module is economical depends on the value of the product. PTFE capillaries cannot be welded or glued and this has made the production of durable modules difficult for a long time.

This problem has now been solved by the Swiss MemO3 GmbH, who use a special thermal joining process. The contactors made by this company have been tested by Prof. Riedl and his team in various applications over the last three years. These include ozone dosing in waste water or drinking water as an alternative to chlorine disinfection and direct extraction from fermentation broths.

Mathias Leimbrink and his colleagues, from the Department of Fluid Mechanics at Dortmund TU, compared CO2 removal from exhaust gases using absorption in a membrane contactor against a conventional packed column and the RPB (Rotating Packed Bed) process developed at the institute. The operating windows (specific gas and liquid load values) were determined for all three types of apparatus here. Comparative experiments were carried out using parameters within the overlapping range of the operating windows of all three types of apparatus. Finally, it was found that when using a membrane contactor, the plant size can be reduced by 80% when compared to a packing column and by 50% when compared to a RPB. The contactor’s possible variation range is also much higher with regard to the fluid load than with the other processes.

For example, under these boundary conditions CO2 separation from the flue gas can be carried out using an alternative solvent instead of the known methanolamine solution (MEA). These alternative solvents (e.g. tertiary amines, potassium carbonate solutions /1/) can be regenerated with significantly less energy expenditure than with MEA, but they have a clearly lower absorption capacity.

The lower absorption capacity can be compensated for by the contactor’s higher volume-specific absorption capacity. Enzymes can be added to the absorption solution as another measure and they will accelerate substance transportation /1/.

CO2 separation from biogas or reformate gas using pressure washing with water (PWW) with the help of membrane contactors was the topic of the lecture given by Monika Vogt from the Institute for Environmental and Energy Technology (IUTA) in Duisburg. When using a PWW, carbon dioxide is dissolved under pressure in the water and then released again through pressure reduction. This is generally applicable when the raw gas is generated at a correspondingly high pressure or the producer gas is required at this pressure level. Whilst the conventional process is carried out at around 5 – 10 bar, the DWW tests using membrane contactors were conducted using pressures of up to 30 bar. The pressure-tight modules needed for this, i.e. with tube and capillary membranes made from PP, PVDF and PTFE, were purpose-built

by IUTA. Four different contactors using different membranes, packing densities, volume-specific exchange surfaces and value ranges for the water’s delay time were tested using gas mixture models. The PVDF membrane proved to be unsuitable very early on due to its unfavourable wetting behaviour. The module with the PTFE membranes exhibited the lowest total resistance to the mass transfer relative to the liquid phase.

According to the gas model measurements, DWW using membrane contactors was named as a suitable option for biogas treatment and the separation of CO2 from reformate gas. However,

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Fig. 2: Biogas filling station at the Weitenau energy plant (Image: Winfried Vees Energieproduktion)

it was also pointed out that the wetting behaviour may change when using real gas mixtures instead of the model mixtures, because real gases already have a certain water content. Also, the methane slip occurring with this method when using CO2 methane mixtures is still above the limit value of 0.2% vol. mentioned in the lecture.

Biogas treatment using water as the absorbent agent in a two-stage membrane contactor process was developed and patented by the Buse engineering bureau in Winsen / Luhe. Vera Krüger, from 3M, described the process in which LiquiCel membrane contactors are used (see Fig. 1). The membrane modules are symmetrically constructed with the so-called “extra-flow” design as special feature. A deflection barrier ensures that the liquid entering centrally in the jacket area flows radially outwards through the hollow fibre bundles in the first half of the module and flows radially inwards in the second half of the module. This results in the greatest possible and uniform hollow fibres

Fig. 3: Basic Memsys membrane module: Basic frame design (Image: memsys water technologies GmbH)

overflow, which results in a higher gas exchange being realised. In the process outlined in Fig. 1, the desulphurised biogas with about 50 - 55% methane and 45 - 50% CO2 passes through the hollow fibre bundles used in the absorption stage, whereby the CO2 is transferred into the liquid flow due to the existing difference in partial pressure and the high solubility of CO2 in water. In the desorption stage, the water loaded with CO2 is degassed by drawing vacuumised air through the lumens in the installed membranes. The CO2 enriched air is then discharged into the environment. It is important here to ensure that no methane is released during this process. This is virtually impossible as methane is not absorbed during the absorption stage because of its much lower solubility in water.

Membrane distillation In a membrane distillation process, the membrane separates the liquid and vapour phases from one another and this prevents

liquid droplets from being carried along into the vapour phase. A hydrophobic membrane material (contact angle to water >90°) is needed for this, so that no liquid water and only steam can enter through its pores. Memsys, a company from Grafing, has developed the Vacuum-Multi-EffektMembrane Distillation (V-MEMD) process. Christoph Maurer described the structuring and functioning of the modules and presented the concentrating of sugar solutions as an application example. The basic element of each effect (corresponds to a separation stage) is a frame made of polypropylene, which carries either a membrane for vapour permeation or a film for condensation (see Fig. 3). Several of these frames are linked to a block in an especially developed procedure. A single effect consists of 1 - 4 blocks. Vapour permeation through the membranes is produced by the vacuum in the vapour chamber. The solution to be concentrated is heated only once at the inlet, for which waste heat or solar-generated heat of about

Fig. 4: Test plant for combining a short-path evaporator (left) with organophile nanofiltration (right), with which a high-quality vegetable oil product can be obtained (Image: Evonik Technology & Infrastructure GmbH)

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Process intensiďŹ cation and coupled processes

60° - 90°C can be used, and is cooled down using a coolant (around 20° - 35°C) at the outlet of a multi-effect system. One of the intermediate effects is to use the heat released from the steam condensation during the previous stage to heat the liquid. The thermal efďŹ ciency factor increases with the number of effects, but is limited by the temperature difference between the heating and the cooling elements, since the temperature decreases by 6° - 8°C with each effect. As the concentration of the managed solution is increased by the effect, the boiling point also increases and this constitutes a further limitation applied to the possible concentration. The target applications for this technology are process water treatments using corrosive ingredients and high concentrations of salts (e.g. RO concentrates from seawater desalination) or other solutes (such as sugars in the present example) using economical low-temperature heat sources. The V-MEMD process is arranged between the clarifying ďŹ ltration (UF) and the desalination of the syrup (using an ion exchanger) in sugar production. It was shown that a sugar solution of up to 60° brix can be concentrated using an 80°C waste heat source.

Dr Peter Kreis develops membrane processes for internal applications to be used in his company, Evonik, i.e. chemical production processes become more efďŹ cient by using them. Membrane separation can contribute either as a single process or as an intelligent interconnection to thermal separation processes used for process intensiďŹ cation. A good example of this is the puriďŹ cation of high-quality vegetable oil. The combination of organophilic nanoďŹ ltration and short-path evaporators was studied in order to recover the target component from the oil as pure and colourless as possible. The required product quality was realised even when it was just the short-path evaporator that was used, but the yields were lower. The speciďŹ cations regarding colour and product composition have been achieved and kept constant as a result of the hybrid process (see Fig. 4 for the experimental plant), in which the feed is ďŹ rst evaporated and then continuously fed into the nanoďŹ ltration process. Another example of the use of membranes in hybrid processes is recovering helium by pressure swing adsorption, which was put into operation at the worldâ&#x20AC;&#x2122;s ďŹ rst large-scale plant of its

kind in August 2016 in Mankota, Canada.

Energy-intensive, multi-stage cryogenic distillation was previously needed to generate high-quality helium as a by-product of natural gas treatment. In the new plant, which has a capacity of 250,000 m3/d of raw gas, the helium is ďŹ rst recovered as a permeate using Sepuran hollow-ďŹ bre membrane modules from Evonik and then fed into the pressure swing adsorption plant, where it is reďŹ ned to an industrial grade (99.999%).

By coupling the processes, energy (e.g. in the form of waste heat) or mass ďŹ&#x201A;ows can be reused and resources can be saved.

Franziska Blauth, from IUTA, reported on two projects for coupling membrane-based desalination plants with energy generating processes. The suitability of the RO concentrate produced from seawater desalination was studied for use in sulphite oxidation and in power plant scrubbers as part of a material coupling project. This concentrate utilisation resulted in pumping power savings when removing seawater for the oxidation tank, provided the power station and the RO plant are installed relatively close to one another. In a second project, the coupling possibilities of desalination plants for generating drinking water to combined heat and power plants,

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Highlights 2017

Fig. 5: Zeolites used for membrane production (Top: Na-LTA type, pore width 0.45 nm, Lower: MFI type, pore width 0.55 nm, Source: International Zeolite Association database (http://www.iza-structure.org/databases/)

adsorption refrigeration plants, compression chilling machines as well as solar thermal systems and concentrating solar collectors and photovoltaics were studied.

Software has been developed that can be used to find the most economical component selections and interconnections for the decentralised supply to a building (a fictional hotel complex was used here). It was particularly evident that the coupling of solar energy use with drinking water generation has great potential here.

Membranes used for gas and vapour permeation Dr Marcus Weyd presented an overview of the development and testing of ceramic membranes for environmental applications being carried out at the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS). Various membranes with porous structures (non-porous, but suitable for selective, diffusive mass transport due to their internal structures) were applied to ceramic carriers. Specific membrane materials for the separation or drying of permanent gases are zeolite membranes or carbon membranes applied to porous, ceramic carrier tubes. Various zeolites are available for membrane production, but they differ with regard to their pore sizes and polarity (see Fig. 5 for examples).

Carbon membranes are formed by applying a polymeric precursor to the ceramic carrier and subsequent polymerisation and pyrolysis of the precursor under inert conditions. When carbon membranes were used, very good selectivities and permeances were determined during the separation of H2/C3H8-, H2/CO2- or CO2/CH4 mixtures. Excellent results were obtained using MFI zeolite membranes and car16

bon membranes for the removal of water vapour during the methanation of CH4 and H2 (power-to-gas).

Mixed conductive ceramic membranes (MIEC - Mixed Ionic Electronic Conductors) and relevant modules for the high-temperature recovery of oxygen were also used at IKTS. A number of demonstration plants of different sizes were built so that the feasibility and optimisation of the process parameters for the technical application could be verified. The most recent and largest of these is a plant for up to 10,000 l/h (see Fig. 6), which has a specific energy consumption of < 0.5 kWh/m3 of high-purity O2, which is clearly better than a pressure swing adsorption plant and comes close to cryogenic air separation, which consumes > 0.38 kWh/m3.

The regeneration of triethylene glycol (TEG) is an example for a technical application for IKTS zeolite membranes.

TEG is used as an absorbent agent for drying natural gas. Udo Lubenau, from IKTS, described the pilot plant at the gas reservoir in Staßfurt, where testing for economic evaluations and economic comparisons of membrane separation against normal TEG regeneration distillation were carried out until the middle of the year 2017.

A description of the process can be found in /2/.

Polymer gas separation membranes are being developed and tested at the Helmholtz Centre in Geesthacht. Dr Torsten Brinkmann described the development stages ranging from laboratory testing to application maturity of the polyethylene oxide-based membranes used for CO2 separation. Block copolymer made from PolyButylene Terephthalate (PBT) and PolyEthylene Oxide (PEO)

was studied in 2008. This resulted in creation of Polyactive multilayer composite membranes, which were integrated in the pocket module developed at the institute.

Between 2008 and 2015 the CO2 permeance selectivity of the finished membrane could be clearly increased with CO2/N2 selectivity remaining constant. In a pilot plant for concentrating CO2 from flue gas with a subsequent feed into algae bioreactors (see “Algenhaus” in Hamburg, /3/), stable membrane plant operation was demonstrated over a period of 12 months.

Pilot trials for CO2 separation from power plant flue gas were carried out in the successive METPORE II and MemKoR BMWi projects. The membranes had to prove their performance under typical power station application scenario conditions using consumption-related start-up and shut-down procedures.

Simulation used during membrane production The computer-assisted development of filter media is known from the fabrics and nonwovens sector and this saved time and materials during the product development.

Once again, the development of membranes was strongly influenced by empiricism. Manuel Hirschler, from the Institute for Chemical Process Engineering at Stuttgart university, is looking for an engineering gateway into the complex interrelationships that result in the formation of different pore structures in polymer membranes during the phase inversion process.

He presented a simplified model, in which the formation of foam and finger pores during diffusive processes was explained.

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process should exist by the end of the development, together with an extraction solution for use in osmosis, which can be returned to the fermenter afterwards.

Reverse osmosis: Surface layer control, module development and practical application

Fig. 6: CAD design for a demonstration plant for high-temperature air separation using MIEC membranes for the production of ultrapure O2 with a capacity of up to 10,000 l/h (Image: Fraunhofer IKTS, Hermsdorf)

mixtures are stable, if polymer, solvent and precipitant are brought together, i.e. only the polymer and solvent or the solvent and precipitant are mixable. The simulation includes component balances that are thermodynamically consistent to a nanoscale, and the inclusion of the surface energy at the phase interfaces. With this simplified and two-dimensional modelling being used up to now, ranges of values for the initial proportion of the polymer solution and the ratio of the solvent’s binary diffusion coefficients in the precipitation bath and in the polymer solution could be identified, in which either dense membranes, structured and unstructured sponge structures or finger-like pores occur.

Prof. Stefan Panglisch, from Duisburg-Essen university, presented the results of the doctoral thesis written by his colleague, Ben Mathis Keller /4/. A measuring method was developed for the thesis in which the resistance of nanoporous cover layers formed on desalination membranes can be clearly determined as it depends on the salt concentration in the raw water. The challenge facing the measurement technology was to be able to clearly distinguish between the hydraulic resistance that results from the change in the osmotic pressure difference caused by the concentration boundary layer and any possible friction losses resulting from the crossflow filtration. This was achieved by using a dead-end filtration arrangement whereby a state of equilibrium was attained between the salt concentrations in the in-feed and in the permeate so that any change in the transmembrane pressure difference would be attributable to the change in the hydraulic resistance of the colloidal cover layer. The latter was generated by using defined standard colloids so that the dependence on the particle size could be determined. The cover layer formation kinetics that depend on the salt concentration could be resolved by using time-resolved recording of the cover layer resistance when using different salt concentrations. It was also determined that the resistances of particularly small particles cannot be calculated using the CarmanKozeny equation.

Osmosis used in the production of biobutanol Biobutanol is considered to be a second generation biofuel (1st generation was bioethanol and biodiesel) that can also be produced from plant residues such as straw. However, the manufacturing process has not yet been optimised so that this alcohol can be considered as being competitive and environmentally compatible. At the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart, the combination of optimised gas stripping using (forward) osmosis is being tested in cooperation with the Institute for Environmental Process Engineering at Bremen University, in order enable biobutanol to be dewatered using reduced energy requirements. Dr Thomas Schiestel, from IGB, described the laboratory scale experiments in which wheat straw was converted into Acetone, Butanol and Ethanol (ABE) in a fermentation reactor. These three substances should be stripped from the fermentation medium by the gas stripping process, condensed as an aqueous solution and then fed into a (forward) osmosis unit so that the butanol contained in it can be concentrated. The butanol concentration should reach at least 7.3%, because phase separation occurs at this concentration. Commercial reverse osmosis membranes as well as self-produced cellulose acetate membranes or TFC membranes were used for the osmosis experiments, which were initially carried out using butanol/ water mixtures. The initial results showed that it is possible to concentrate butanol up to the phase separation limit. A circulation F & S International Edition

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tory setup that was initially used for this process. Determination of the membrane separation limit (in the range below 100 nm) is also possible if defined particle standards are used in addition to the online integrity measuring.

Wastewater treatment and trace element removal

Fig. 7: Changing the permeability and TS content in the MBR with PAC dosing at the Hünxe clarification plant (Image: Microdyn-Nadir)

The pressure loss from the overflow of the membrane surface as well as the tendency to accumulate fouling material in spiral winding modules was determined by the thickness and design of the spacers used. Lanxess, together with the manufacturer of the spacer material, has developed a spacer configuration for this purpose that reduces the pressure loss in spiral wound modules and the biomass concentration when compared to conventional modules.

Dr Jens Lipnitzki presented the development work and the results, which have already been described in F&S 5/2016 /5/.

Robert Reisewitz from Toray, Switzerland, presented a three-stage plant for the treatment of 15,000 m3/d highly salted mine water from an opencast mine in South Africa. This facility provides the purification of waste water that cannot be discharged into the environment without treatment due to its high salt content, whereas the provision of drinking water for the surrounding municipalities and the introduction of purified water arises from the nearby river suffering from a scarcity of water resulting from a groundwater reduction caused by mining. Before the raw water enters the first reverse osmosis system, it is pre-treated using multistage systems such as precipitation, sand filter and ultrafiltration and interim precipitation with subsequent ultrafiltration is also needed in-between the separate reverse osmosis stages in order to reduce the scaling potential. The yield obtained is greater than 97%. The sludge from all of the precipitation stages is partly recycled back to the initial precipitation stage in the plant inlet and some of it is also used for the production of high-purity gypsum. The reverse osmosis modules used in the first 18

two treatment stages are energy-saving elements with high permeability (brackish water elements). Elements with maximum salt retention properties are only used in the third stage. The energy consumption for the entire process is given as 1.8 to 2 kWh/ m3. The scaling and biofouling challenges were mastered by using optimised dosing of hardness stabilisers with regular measuring of critical water parameters and a comprehensive cleaning strategy.

Verification of nanoparticle retention by UF membranes Particle counting to verify particle retention by membranes, analogous to the determination of the retention capacity of air filter media, often fails because known laser-based nanoparticle measurement processes are not sensitive enough for the low concentrations downstream from an UF membrane. The LIBD process (Laser Induced Breakdown Detection), as explained by Dr Pia Lipp, from the DVGW Water Technology Centre in Karlsruhe, enables the detection of particles in the 20 nm - 500 nm size range even in concentrations of just a few ng/l.

This process, which was presented several years ago at the Aachen conference /6/, is based on the fact that when a laser pulse is applied to a particle, it triggers a plasma ignition that results in the destruction of the particle and this event can be measured as a sound signal. The particle size information is obtained from the laser pulse energy applied to trigger the event and the particle concentration can be determined by the frequency of these events.

A compact, transportable system, which has been tested in a waterworks, has been developed from the very complex labora-

The photocatalytic degradation of dissolved organic substances where TiO2 nanoparticles and a light source were used has been studied in various configurations in which attempts were made to immobilize the TiO2 particles on a carrier that also works as a particle filter. At the Fraunhofer Institute for Environmental, Security and Energy Technology (UMSICHT) in Oberhausen, extensive experience has been gained regarding the coating of purpose-made metallic microsieves with TiO2 nanoparticles. A suitable module was built for this purpose and a series of trials to eliminate organic dyes and pharmaceuticals were carried out (see /7/ as well). Dr Ilka Gehrke, from UMSICHT, described the production of the metallic microsieves and the various processes for applying the nanoparticle layer. Ultimately, the results obtained using the microsieves that were specially created to eliminate the trace substances showed that this microsieve system is less suitable for use as an effective broadband cleaning stage in clarification plants, but rather more suited for use as a compact system solution for specific cases.

Even though the proportion of clarification plants using membrane bioreactors is still very low amongst municipal wastewater treatment plants in Germany, these processes are often taken into consideration in preparation of future wastewater purification concepts, as in the case presented by Sven Theus, from TU Cologne. He prepared three scenarios for future wastewater treatment in the city of Bonn, whereby one case considered reducing the four currently operated wastewater treatment plants (WWTP) down to one by using submerged membrane modules at the largest of them, WWTP Bonn Salierweg. This would result in the 8,460 m3/h inflow being increased to 14,278 m3/h. The results presented here were based on the guidance notes in the DWA-M 227 leaflet and the ATV-A 198 and DWA-A 131 worksheets as well as the data sheets provided by the membrane module manufacturers were also taken into consideration.

Various plant configurations (installing the modules in one of the existing basins or in a separate filtration basin) and module types were compared and the expected costs were roughly estimated. The basic

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gross membrane flow used in the designs was considered to be independent from the module supplier. In this design, in which the operating parameters could only be partially estimated due to the absence of more detailed public information from the manufacturer, GE Water & Process’s hollow-fibre modules received the theoretical acceptance. A study into the integration of processes for adsorption on powdered activated carbon or granulated activated carbon was also undertaken in view of the need to eliminate micropollutants in the future wastewater treatment plants.

Measures to eliminate micropollutants have already been installed in some clarification plants belonging to the Emschergenossenschaft and Lippeverband (EGLV) wastewater associations in North Rhine-Westphalia and new processes are also being tested in cooperation with research institutes and various companies.

Combining adsorption on powdered active carbon (PAC) with membrane processes was the focus of the contribution presented

by Dr Ruben-Laurids Lange, from ELGV. The high PAC slippage of up to 20%, which was determined using conventional PAC dosing together with a subsequent sand filter, is the motivation for using membranes in conjunction with PAC. Since 2011, a clarification plant with MBR has been running in the grounds of the Marien hospital in Gelsenkirchen, where dosing PAC into the MBR has also been tested and found to be functional. A GE Water & Process pilot plant was operated in the test clarification plant in Duisburg for several months, whereby PAC was dosed into the membrane bioreactor. This showed that a relatively high elimination capacity for many pharmaceuticals was achieved using relatively low PAC concentrations of 10 mg/l. The behaviour of a membrane bioreactor with PAC dosing was studied in another project and the reactor was installed behind the conventionally operated treatment line at the Hünxe WWTP. The MBR was operated using Biocel modules from Microdyn-Nadir, the project partner. Werner Ruppricht, their representative, described this work in detail, which had been undertaken as part of a master thesis for Dresden TU. The PAC effect on the flow rate and service life of the membrane also had to be clarified in addition to answering the question as to how far combined MBR/PAC dosing effects elimination of micro pollutants. 10 to 20 mg PAC per litre of wastewater was added for the experiments. The activated

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carbon concentration in the filtration tank was increased to 6.5 g/l during the experiments. A positive effect from the active carbon particles on the filtration efficiency was seen from a concentration of about 1.2 g/l, (see Fig. 7). The membrane modules were operated using a stable net flow of 31 l/(m2 h) and even with a 50% reduction in the amount of purging air used they were still more efficient than the Biocel modules without PAC dosing used in the parallel wastewater line in the same clarification plant. Mr Ruppricht explicitly pointed out the additional effect of the membrane on the retention of microorganisms, which includes antibiotic-resistant microbes, in addition to the positive effect that PAC has on the filtration efficiency.

The retention of micropollutants, microplastic particles and microbes through membranes used in municipal clarification plants was also the main focus of the Micro Pollutants Working Group from DGMT, which was founded a year before this event at the Annual DGMT General Meeting in 2016. Hildegard Lyko introduced this working group and reported on previous and planned activities. These include explaining and publicising the possibilities of using membrane technology to optimise the processes used for the elimination of trace elements and to improve particle and microbial retention.

Literature: /1/ M. Leimbrink, K. Kupitz, K. Neumann, A. Górak, M. Skiborowski: Improving the Energy Efficiency of Carbon Capture Processes – Combining Enzyme Accelerated Solvent Systems and Improved Contacting Equipment; 2016 AIChE Annual Meeting, 13.-18. November 2016, San Francisco /2/ H. Lyko: Membranen für nachhaltige Prozesse – Bericht vom 16. Aachener Membran Kolloquium, F&S Filtrieren und Separieren 31(2017) Nr. 1, S. 6-10 /3/ H. Lyko: Stand und Perspektiven der Gastrennung mit Membranen; Welt-Handbuch der Filtrations- und Separationsindustrie 2016-2018; S. 303-312 /4/ B.M. Keller: Zur Bedeutung hydraulisch bedingter Deckschichtwiderstände beim Fouling Salz rückhaltender Membranen unter Berücksichtigung von Kopplungseffekten, Dissertation, Universität Duisburg-Essen, 2016 /5/ J. Kidwell, St. Tielen, B. Paesen, J. Ogier, St. Lehmann, C. Schellenberg: Innovative FeedspacerTechnologie bewirkt eine verbesserte Leistung von Umkehrosmosemodulen, F&S Filtrieren und Separieren 5(2015) Nr. 5, S. 323-326 /6/ P. Lipp, M. Tröster, K. Kreißel, P. Nagtegaele, S. Büchner: Charakterisierung des Partikelrückhalts von Ultrafiltrationsmembranen mittels LIBD, in J. Pinnekamp, M. Wessling (Hrsg): Membrantechnik in der Wasseraufbereitung und Abwasserbehandlung: 10. Aachener Tagung Wasser und Membranen, 29.-30.

Oktober 2013, S. 73-82, ISBN 3-8107-0178-5 /7/ H. Lyko: Status and perspectives of the production and application of microsieves, F&S Global Guide of the Filtration and Separation Industry 2014 -2016, pp. 210 – 219, VDL-Verlag GmbH (2014), ISBN 978-3-00-04 5566-7

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Highlights 2017

Membranes for Sustainable Processes Report from the 16th Aachener Membran Kolloquium H. Lyko* Aachen Verfahrenstechnik (formerly the Institute of Process Engineering) has been organizing the Aachen Membrane Kolloquium, which has been held every second year, for the last 30 years. The primary objective of this event has always been promoting discussions between users, technology providers and scientists about the latest developments in materials science and process engineering. The event has become somewhat smaller over the years. In November 2016, Prof. Matthias Wessling, Head of the Chair of Chemical Process Engineering at RWTH, welcomed a total of around 200 participants to 34 lectures and 39 poster presentations. In addition to the actual lecture program, both the creators of the posters as well as the companies that were present with a stand at the accompanying exhibition were also given the opportunity to present their content in a two-minute presentation.

In addition to the water treatment topics, the focus was also on new materials, gas separation processes as well as the use of membranes in biotechnology and process technology.

Key topic: capacitive deionization The functional principle of Membraneassisted Capacitive De-Ionization of water (MCDI), realized by the Dutch company Voltea, was presented several years ago in Aachen. This time, Piotr Dlugolecki, technology manager at Voltea, was invited to be the keynote speaker. He presented the path from the inception in R&D up to a large-scale industrial plant. As opposed to reverse osmosis, MCDI does not separate a large quantity of pure water from a comparatively small quantity of salt but separates the dissolved ions from the water.

This occurs during cyclic charging and discharging processes and is supported by ion-exchanging membranes. Microporous * Dr.-Ing. Hildegard Lyko Dortmund, Germany, Tel: +49 (0) 231-730696

carbon electrodes form the core of the system, in which the electrons are adsorbed during the charge phase. The module capacity depends on the ion storage capacity of the electrodes. In principle the process can run without a membrane, but a membrane also increases the charge efďŹ ciency by a factor of 2 with the same electric ďŹ eld strength as a result of which, the number of charge regeneration cycles can be increased and the pure water yield can also be increased. A single MCDI module produces approx. 0.5 m3/h of pure water.

A system for industrial water desalination is composed of a total of 12 modules and 3 of these systems ďŹ t into a container.

Such a container system is, for example, in operation for cooling water treatment.

With variable salt concentrations, such as those used for the treatment of surface

Fig. 1: Membrane plant for the regeneration of triethylene glycol (TEG), which is used as a sorbent for drying natural gas (Image: Innogy SE)

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water, which is stressed in the winter by strong scattered salt applications, the pure water concentration can be kept constant through dynamically controlling the applied voltage. For raw water with a low salt concentration (brackish water), the WCDI process with an energy requirement of about 0.3 KW/m3 is more economical than reverse osmosis. However, the latter is more useful for seawater desalination because the electricity consumption of the MCDI exceeds the reverse osmosis energy requirement due to the higher concentration of salt.

Processes that are on the threshold of commercialization At DSM, a Dutch chemical company, it is felt that those companies that have been involved in recycling management

Fig. 2: Complete plant including membrane system in a container, controller and tank for regenerating TEG (Image: Innogy SE)

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Fig. 3: a) Appling activated carbon / POMS suspension on the drainage layer of the substrate membrane (left); b) Mixed matrix membrane used as the roll material after cross-linking (right)

over the last 25 years are on the winning side. This was mentioned by Erik Hoving of DSM in his paper about the possibilities for membrane technology in recycling management. This was not just about the use of membranes in material recycling, which has long been known in water treatment processes. The topic included more than “just” the re-using of materials, which resulted in quality downgrades in many previously realized cascade processes. A typical example of a cascade process is the current practice of recycling plastic. Hoving presented the enterprise as two cycles, a “technosphere” in which all materials are used again and again, whereby the treatment uses regenerative energies and a “biosphere” in which the recycling is determined by processes such as growth, enrichment of valuable substances and disintegration. Splitting up the goods is also an important aspect in this type of recycling management.

With regard to designing the membrane modules and plant engineering, Hoving suggested that the plants should all be constructed in such a way to ensure that they are easy to assemble and disassemble and that they should consist exclusively of materials that are easy to recycle. A further step would be the possibility of not having to purchase a plant or a module, but leasing a specific filtration capacity or an entire plant as necessary. Organic Solvent Nanofiltration (OSN) processes using specific membrane technology applications in recycling management were also described. For example, OSN is used in the DSM process for converting biomass into levulinic acid as well as being used in the further conversion of levulinic acid into adipic acid. Membrane technology is used here for the recovery of the expensive and dissolved catalyst. Another very recent application is the dewatering of vitamin C by Forward Osmosis (FO) using a sodium chloride solution as the extraction solution.

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Fig. 4: Microscope image from a PVDF membrane with photocatalytically acting TiO2-nanoparticles (Image: Andrea Prager, IOM Leipzig)

Commercial processes that were previously established or have yet to be established commercially are also frequently used for gas treatment. Hartwig Voß has worked on the production of carbon membranes for gas separation at BASF for several years. In a joint project with the Fraunhofer Institute for Ceramic Technologies and Systems IKTS, ceramic membranes were coated with a thin polymer film that was subsequently carbonized in a pyrolysis process. The original motivation for this project was the separation of hydrogen from gas mixtures (e.g.

H2 /propane), where it was still unclear how a membrane behaves in the presence of water vapor. In the meantime, it has become possible to produce membranes that are not only stable to water vapor but with which the water vapor can also be very selectively removed from mixtures containing organic vapors at temperatures of up to or around 400°C. For example, a possible application for such membranes used in combination with chemical reactions is esterification, the production of alcoholate in the presence of NaOH or condensation reactions. The selective removal of water vapor can shift the balance and increase product yield.

Gas separation, pervaporation Whenever there is talk of the energy costs arising from the separation processes, membrane technology is mentioned as being advantageous to distillation and sorption processes and endless research work has been aimed at replacing thermal separation processes by new processes that use membranes. In a recently published article, David Sholl and Ryan Lively, researchers at the Georgia Institute of Technology, USA, reported that potential membranes would reduce energy consumption in some of the seven most important separation tasks used in the processing industry when alternatives to ther-

mal separation are available. Prof. Ingo Pinnau of the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia also pointed to this problem and repeated the possibility of reducing energy consumption by around 90% by replacing thermal separation processes with membranes. Admittedly, there has been little change with regard to the commercialization of new materials during the last 15 years. Academic research ends at the very latest when the first finished membrane is produced from a promising polymer on a laboratory scale. The frequently cited Robeson plot (see /2/), which shows the permeability and selectivity of materials against certain pairs of materials, is misleading in that it reflects individual gas measurements in which, for example, concentration polarization was not taken into consideration. According to Pinnau, the obstacles to the commercialization of new membrane materials are the material price as well as the difficulty involved in scaling up the production process.

Expensive materials are best processed only as extremely thin layers in TFC membranes with a substructure that is available as inexpensive bulk material. With largescale spinning processes for hollow fiber production, the challenge is to produce large quantities of spinning solution with a controlled molecular weight distribution and constant viscosity. Finally, there is the demand from industry, which must also be ready to use new materials.

Besides distillation, absorption is a competitive gas separation method that uses membranes. It is particularly suitable when low concentrations of impurities have to be removed from gases. A charged sorbent is then produced and thermal processes are normally used for its regeneration. A good example of this is the dehydration of natural gas taken from storage sites, which is necessary before the gas is transported into pipelines. Triethylene glycol (TEG) is generally used as the sorbent,

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which is usually reprocessed by distillation at 190° to 205°C. As an alternative to energy-intensive distillation, which also leads to aging and partial TEG decomposition, Dr Marcus Weyd of the Fraunhofer IKTS proposed dewatering the TEG by pervaporation using NaA zeolite membranes. These membranes were previously developed and tested for dewatering ethanol. During the experiments with TEG, the membrane was optimized once, i.e. they have less defects when compared to previous membranes, which significantly reduces the probability of TEG permeation. When the sorbent was charged with about 1.5% weight of H2O and at a temperature of 120°C, an economical water flow of 0.3 kg/.(m2 h) was realized.

The potential of such processing plants with around 50 underground gas storage sites would be more than 20 billion m3 of natural gas, which is relatively high.

These membranes are currently being produced by IKTS on a pilot scale.

A producer for large-scale membrane surfaces and modules has not yet been found at the time the lecture was given.

Gas separation membranes can also play an important role in developing new processes for the development of regenerative energy sources. The use of hydrogen as an energy carrier as well as a basic synthesis material is an example of this.

Photoelectrochemical processes (PEC) for the splitting of water were studied as an alternative to the costly and energy-intensive steam reformation of methane. In his poster presentation Sari Al-Sayegh, from RWTH Aachen, looked at a process in which water is split into a colloidal suspension with catalytic nanoparticles.

This resulted in the two hydrogen and oxygen products coming together, which

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means there is a considerable safety risk.

Nitrogen should be used as the diluent gas in order to curb the risk of an explosion.

Consequently, an economical process for the subsequent recovery of H2 from a H2 / N2 /O2 mixture was sought. This could be a gas separation using H2 selective polymer membranes. Such a process was previously studied in a simulation using a known commercial polyimide membrane (UBE, Japan) and new membrane materials to determine the input and processing conditions under which it can be economically carried out. An essential membrane material condition is extremely low O2/ N2 selectivity to keep the permeate free of oxygen.

Membrane materials An already known application of gas separation membranes is the separation of higher hydrocarbons, such as butane, from natural gas or other permanent gases, e.g. for monomer recovery during polymer synthesis. Dr Torsten Brinkmann, from the Helmholtz Center in Geesthacht, described the disadvantages of using PDMS (PolyDiMethylSiloxane) polymer and POMS (PolyOctylMethylSiloxane) membranes as they lose their selectivity regarding methane due to the higher fugacity of HHC (Higher HydroCarbon).

The HHC / methane selectivity was increased by using thin-layer composite membranes with an active layer prepared as a mixed-matrix POMS membrane containing 1.5 μm particles of an active carbon that is highly adsorptive for HHC. The particles were created by milling spherical adsorbents, which are produced from polymers by Blücher. A suspension from the POMS solution in isooctane

with the active carbon particles and a cross-linking agent was applied as a thin layer to a three-layered TFC membrane with a PDMS top layer (see Fig. 3a) and a thin PDMS protective layer was applied after hardening. By producing membranes of a width of 30 cm and a length of 250 m (see Fig. 3b), membrane areas were available for equipping an industrial pocket module. Extensive measurements were then carried out for the gas separation of both O2 /N2 mixtures and butane / methane mixtures. The O2 /N2 measurements were used for the quality control of membrane samples and finished membrane pockets.

The experimental studies with butane / methane mixtures as well as the process simulations showed higher selectivity when using a mixed-matrix membrane for butane as compared to the pure polymer membrane, which was associated with a lower permeance. The benefit of the mixed-matrix membrane is seen at higher pressures and higher concentrations of the preferably permeating component (HHC).

At the Institute of Surface Modification (IOM) in Leipzig, Kristina Fischer works with the direct synthesis of TiO2 nanoparticles on a commercial PVDF microfiltration membrane with a 0.22 μm nominal pore width (see Fig. 4). The photo-catalytic property of the particles facilitates the oxidation of the dissolved organic impurities in water. The nanoparticles are formed by direct hydrolysis of titanium tetraisopropoxide (TTIP) on the polymer surface and the subsequent crystallization.

The process was optimized by varying the TTIP concentration and the membrane wetting and drying stages. The photocatalytic effect was detected on a laboratory scale by determining the time-dependent degradation of methylene blue.

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Fig. 5: Diagram of the further digestate treatment using a MBR process (as presented by Tobias Steube, Microdyn-Nadir)

Applications in biotechnology The treatment of fermentation residues arising from biogas production represents a major challenge to membrane technology in so far as the fouling potential of the liquid fraction remaining after coarse particle separation is extremely high. This is why Tobias Steube, from Microdyn-Nadir GmbH, proposed using a membrane bioreactor instead of direct pressure-driven membrane filtration, in which aerobic degradation of organic substances takes place in addition to filtration. The membrane then retains the remaining suspended solids including all of the bacteria.

Fig. 5 shows a diagram of this process, in which the membrane module is directly immersed in activated sludge or is placed in a separate filtration tank. The Biocel module is equipped with ultrafiltration membranes made from polyethersulfone (PES). The permeate from this ultrafiltration process is concentrated by reverse osmosis and this results in a liquid fertilizer that is rich in nitrogen and potassium that can also be dried if necessary. The solids separated during the pre-sieving can be returned to the biogas plant to reset the P/N ratio or be used as a solid fertilizer with or without drying. The extent to which this treatment process is economical depends on the local conditions (i.e. operating parameters, availability of land).

Other presentations given under the “biotechnology” concept dealt with a completely different branch of biotechnology, namely the treatment of valuable sub-

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stances and sterile filtration in the biopharmaceutical industry. Microfiltration membranes are generally used for sterile filtration purposes. These sometimes exhibit increased permeation of viruses after a sudden pressure drop, which occurs, for example, with a flow interruption /3/. The manufacturer Sartorius Stedim Biotech has studied this phenomenon several times together with their university partners. Catharina Kars, from the University of Bremen, showed a poster with the results of studies into the influence of membrane properties (different pore size gradients and hydrophilicities using the same PES polymer membrane), pH values and salt concentrations on the retention capabilities of a bacteriophage model before and after flow interruption.

Christina Grote, from RWTH Aachen, carried out similar experiments but used mycoplasma (very small bacteria) instead, as well as gram-negative and gram-positive bacteria, which are larger than viruses, and polystyrene particles. PES membranes with different pore widths between 0.2 and 0.8 μm were used. Under which conditions sterile filtration is possible, even in the case of intermittent pressure drops, depends on the interaction between the membrane’s sieve effect (retention through size exclusion) and the adsorptive effects. It also appears possible that particles can penetrate more deeply into larger pores when pressure fluctuations occur and they can also be discharged from the permeate side during the next pressure drop.

Membrane extraction Membrane extraction is a much-discussed procedure used for process intensification, particularly in biotechnology.

Two studies covering the recovery of organic acids were presented in Aachen.

The production of bioethanol produces a slurry that contains dissolved organic hydrocarbons and nutrients. Generally known recycling processes are fermentation to biogas or concentrating (often thermally) for use as a nutrient, animal feed or as an additive to animal feed. A new utilization route is aimed at the fermentative conversion into volatile fatty acids (VFA) for use as basic chemicals. The Belgian research company VITO, which is participating in the EU Water4Crops project, is studying a process in which such fermentation is carried out in conjunction with integrated separation of the fatty acids. Linsey Garcie-Gonzalez described the experiments that were used to remove the carboxylic acids from the reaction mixture using reactive extraction, whereby a variety of solvent and diluent combinations were tested. However, the mixture of solvent and diluent that proved to be optimum for extraction turned out to be toxic to the microorganisms in the fermenter. Membrane extraction was tested as a separation process using PP hollow-fiber membranes, whereby the aqueous phase was outside the hollow fibers and the extract phase was inside the lumen. In laboratory experiments that used synthetic mixtures of carboxylic acids with different chain lengths in a real fer-

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mentation broth, steady-state operation with an overall extraction efficiency of 70% was achieved after about 3 hours and the effectiveness of the process was even higher when longer-chain carboxylic acids were used. During the installation of the membrane module directly into the process, in which the aqueous phase from the membrane module is fed back into the fermenter, these good results could not be repeated initially. It was assumed that the decreased performance was due to fouling.

Thus they increased the membrane area, which resulted in a significant decrease in the VFA concentration in the fermenter together with a shift in the quantity proportions to the shorter-chained acids.

Angelo Gössi from the University of Applied Science North-West Switzerland reported on his work on the extraction and backwashing of lactic acid as a product from the carbohydrate fermentation process. The optimal fermentation conditions

are with a pH 4.5 - 6, which is why the fermentation broth in a conventional process must be neutralized using calcium hydroxide (Ca (OH)2), when the yield of lactid acid increases. However, after fermentation it must be acidified using sulfuric acid in order to free the lactic acid from its salt. This results in costs for the consumption of Ca (OH)2 and sulfuric acid as well as large quantities of gypsum produced as a by-product. Neutralization can be dispensed with if the lactic acid is continuously removed from the reaction mixture. However, the trioctylamine extraction agent, which was tested previously, showed a tendency to form emulsions.

Membrane extraction makes it possible to prevent this. Experiments using PTFE and PP hollow fiber modules and different initial concentrations of lactic acid were carried out in a laboratory system in which membrane extraction could be operated both in the same and reverse flows. It

also showed that the contactors used are suitable for long-term operation without a performance loss. It was also seen that the solvent can be regenerated for reuse using a backwashing membrane contactor.

The relatively high membrane surface requirement for such treatment is disadvantageous: a production volume of 50 kg/d of lactic acid in an ideal case requires a contact surface of at least 205 m2.

Literature /1/ D.S. Sholl, R.P. Lively: Seven chemical separations to change the world; Nature Vol 532 (2016) /2/ H. Lyko: Stand und Perspektiven der Gastrennung mit Membranen; F&S Global Guide of the Filtration and Separation Industry 2016-2018, pp. 235-244, VDLVerlag, ISBN 978-3-00-052832-3 /3/ M.A.Woods, A.L. Zydney: Effects of a pressure release on virus retention with the ultipor DV20 membrane, Biotechnol. Bioeng. 111(2013) 545-551. Doi:10.1002/ bit.25112

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Wastewater Treatment and the Reuse of Purified Wastewater: Hygienic Aspects H. Lyko * The closing-off of water circulation circuits is an important condition for supplying people in many countries of the world and this includes the irrigation of farmland. This is the reason why treated water must not only be free of suspended and dissolved pollutants, but also be microbiologically harmless. With regard to the retention capacity of conventional clarification plants, it is not only bacteria and viruses that are generally discussed, but rather microbes that are resistant to antibiotics. Their emergence is generally discussed in connection with the misuse or excessive use of antibiotics. The contribution that clarification plants make to the spread of antibiotic-resistant microbes or resistance genes has been the subject of a large number of global research projects.

1. Introduction Water is a substance whose potential for reuse through purification, recovery of energy as well as dissolved or suspended substances recovered as valuable substances has been studied so intensively in the context of terms such as circular economy or resource efficiency that this is unlikely to occur with any other raw material. Allowing as much wastewater treatment as possible is an essential condition for the protection of surface waters, groundwater reservoirs and drinking water in water-rich countries such as Germany.

In countries where water is scarce, the reuse of treated wastewater together with the desalination of seawater constitute the vital basis for suppling many people, a functioning agriculture sector and the possibility of industrial production.

Municipal wastewater or agricultural wastewater contain not only organic substances but also microbiological residues from both humans and animals, especially from livestock with regard to the latter.

Organisms remain more or less viable and they can proliferate in the treated wastewater depending on the retention capacity of the clarification plants and the efficiency of disinfection processes. The transmission and proliferation of antibiotics-resistant microbes also plays a role against the background of excessive or incorrectly indicated use of antibiotics in human and veterinary medicine and the possibility that antibiotics might also pass through clarification plants as trace substances. The figures published about the spread of antibiotic-resistant microbes such as those from the European Centre for Disease Prevention and Control speak for themselves (see Fig. 1, www.ecdc. * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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europa.eu). The problem is intensified by the fact that newly developed antibiotics are on the market for shorter periods of time before initial resistance occurs, so that the number of pharmaceutical companies that are even prepared to develop new antibiotics has fallen dramatically /1/. The short periods between the market launch of an antibiotic and the emergence of resistance to it make it harder for research-based pharmaceutical companies to offset research spending against marketing profits.

Hygienic issues arising from the introduction of clarification plant effluents into surface waters or the reuse of purified wastewater are increasingly being discussed in conjunction with the emergence and spread of resistance to antibiotics.

The spread of pathogenic microbes and parasites through irrigation systems that use purified (insufficiently) wastewater or receive surface water is a topic in several countries and it is not just those with lower development levels that are included here.

Various risk identification, management

Fig. 1: ECDC info-graphic showing the increase and decrease in resistance of specific pathogenic microbes to certain antibiotics during the five-year period 2009 – 2013

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Tab. 1: Tab. 1: Correlation between the wastewater treatment efficiency and the exposure of the population to wastewater or wastewater substances as defined for monitoring SDGs 6.2.1 and 6.3.1 (see www.who.int)

Tab. 2: Classification of treatment levels for (sanitary) wastewater as defined for the monitoring SDGs 6.2.1 and 6.3.1

and communication projects have been implemented, some of which are described below, as part of the BMBF’s RiskWa (risk management of new pollutants and pathogenic microbes in water circuits) funding programme. The gist of the complete measure is published in the RiSKWa practice manual /2/. This manual leaves no doubt as to the role of clarification plants with regard to antibiotics-resistant microbes: “Wastewater systems are important sources of entry for facultative-pathogenic bacteria and clinically-relevant antibiotic resistances that enter directly into the aquatic environment. Suitable technical processes must be used to interrupt these distribution channels” /2/.

2. Spreading microbes through the use of surface water or the reuse of wastewater

Tab. 3: Micro-organism retention potential of various clarification plant components as per /6/

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The extent to which the reuse of purified, but not completely disinfected wastewater for irrigation in agriculture can actually be problematic, is shown by two examples from different countries. The first example comes from Ghana and was presented at World Water Week 2017 in Stockholm during the “Wastewater and health: managing risks, seizing opportunities” session and it was described by Dr Prince Antwi-Agyei from the London School of Hygiene and Tropical Medicine /3/. The irrigation water, soil samples from a vegetable field and salad samples taken directly from a field, a market and ready-to-eat street food were all examined for microbial contamination. More than 80% of the product samples were found to be contaminated with E.coli, with the salads directly available for consumption on the street having the highest contamination levels. The wastewater purification measures are not described in detail in the abstract. The following example from the USA shows how microbes from surface waters can continue to spread, regardless of how they entered the water. Ryan Blaustein et al. /4/ tested weekly water samples taken from irrigation pipelines at a research farm in Beltsville, Maryland, USA, and also took biofilm samples from the internal pipe walls using the same intervals. Water from a nearby stream was used for the irrigation. The irrigation was switched on at week intervals and the fresh water as well as the water in the pipeline and the biofilm were analysed before the next irrigation process was switched on. In general, it was found that not only did the number of heterotrophic microorganisms generally increase, but the number of col-

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The sixth of the UN’s 17 global Sustainable Development Goals (SDGs) is “Clean water and sanitary facilities”. Under Section 6.3, the sub-objective is formulated to halve the proportion of untreated wastewater that is discharged into the environment or surface water and to significantly increase the proportion of recycled wastewater [see www.sustainabledevelopment.un.org or www.bmz.de (Federal Ministry for Economic Cooperation and Development)]. It is explicitly stated as being “safe reuse”, i.e. harmless reuse. The proportion of “safely” treated wastewaters and the proportion of good quality water bodies were determined in order to assess the extent to which the sub-objective has been realised. Defining the procedures for “safe” wastewater treatment depends on whether purified wastewater is used or not (see Table 1 and focus on sanitary wastewater, www.who.int). The different treatment levels for faecal sludge were classified simultaneously.

With regard to the classifications listed in Table 1, it must be pointed out that tertiary purification should not be restricted to extended N, P elimination if wastewater treatment is to be assessed as being safe for food production.

The measures that should be used in specific purification stages are listed in Table 2.

The participants at the 1st DWA Hygiene Day, which was held in Düsseldorf in October 2016, were able to learn to what extent the separate purification stages of municipal clarification plants contribute to the reduction of microbes contained in municipal wastewater from Dr Andrea Rechenburg, who is researching this at the Institute for Hygiene and Public Health at the University of Bonn /6/. The microorganisms are killed off or prevented from proliferating by the effects of temperature, irradiation, the pH value, too much or too little oxygen, lack of nutrients, competition (i.e. from the beneficial bacteria in the biomass) and dryness. The capabilities of the separate purification stages for reducing wastewater microbes are shown in Table 3.

As most of the municipal clarification plants in Europe were not designed as MBR plants, their retention capacity regarding microorganisms is assessed as being moderate to low.

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3. Potential for using wastewater treatment processes for hygienisation

4. The role of clarification plants in the spread or emergence of antibiotics-resistant pathogenic germs The extent to which clarification plants actually retain antibiotics-resistant microbes or even support their proliferation through the prevailing conditions in biological wastewater purification processes is being intensively studied at various places in Europe and throughout the world. Antibiotics-resistant organisms form through mutation under evolutionary pressure, which builds up due to the presence of antibiotics and their subsequent proliferation.

Another possible reason for the spread of resistance is the horizontal transfer of resistance genes to other bacteria, which may be in addition to non-resistant pathogenic microbes and environmental microbes such as those found in masses in a bioreactor plant /7/.

A few years ago Schreiber undertook studies at the University of Bonn into the retention of antibiotics and antibiotics-resistant microbes in clarification plants /8/. An increase in resistance below a clarification plant inlet as compared to its headwaters was found for specific species of microorganisms and specific antibiotics.

Even though no generalised conclusion about the effect of municipal wastewater on the resistance situation in receiving surface waters can be drawn from this study, the proliferation of multi-resistance pathogenic microorganisms having increasing impact in municipal wastewater was determined.

The questions as to what extent clarification plants are disseminators of antibiotics-resistant microbes and which wastewater purification processes are best suited to prevent the spread of resistance are also the subjects of the extensive research being carried out

by Eawag in Dübendorf, Switzerland. The known and assumed microbe entry paths into surface waters are outlined in Fig. 2. In

SW IS

iform bacteria resistant to certain antibiotics also increased in the water in the pipeline and more particularly in the biofilm.

An up-to-date and comprehensive overview of the state of knowledge about the distribution of antibiotics as trace substances and antibiotics-resistant bacteria via the clarification plant outlet path into agricultural irrigation systems is provided in an overview article by Christou et al. /5/. The authors evaluated a vast number of experimental studies aimed at appraising the retention of antibiotics and possible degradation products in irrigation waters, plant parts and in the soil. They also looked at published studies covering the detection of Antibiotics-Resistant Bacteria (ARB) and Antibiotics-Resistance Genes (ARG) that exist in these media.

The studies published to date seem to provide controversial results, especially with regard to the survivability of ARB and ARG on arable land as well as on and in the irrigated plants. Some of the studies see an accumulation of specific resistance genes in areas irrigated with wastewater, whereas others found the same or even reduced frequencies when compared to areas irrigated with fresh water. All-in-all the problem also appears to lie in the relatively low concentrations of the components that were studied, in the small sample volumes and in the probable non-uniform distribution of these bacteria or genes.

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Fig. 2: Known (black lines) and suspected (red, dashed lines) inlet pathways of microbes into surface waters and back to humans and animals (free as per /9/)

a study involving a total of 13 clarification plants, of which 6 also collect waste water from hospitals or pharmaceutical production facilities, the concentrations of multi-resistant bacteria and ARGs were measured before and after the clarification plant /9/. In general, a reduction in concentration of 1 - 3 log stages was determined during the wastewater treatment, which corresponds approximately to 90% - 99% elimination. Selective processes, i.e. the preferential survival and possible proliferation of multi-resistant bacteria, were suspected in clarification plants with hospital or industrial input. These were traced back to the increase in micro-pollutants caused by the antibiotics.

Scientists at the University of Bonn are also co-ordinating the ongoing HyReKa interdisciplinary research project that focuses on the “biological and hygienic-medical relevance and control of antibiotics-resistant pathogenic microbes in

clinical, agricultural and municipal wastewaters and their importance in raw water” (see: www.hyreka.net).

Prof. Thomas Berendonk from the Institute of Hydrobiology at the TU in Dresden is participating in this as well as in other projects involving this topic.

He described the explosive nature of the problem in a lecture given during the forum organised by the DGMT micro-pollutants working group on the fringe of the Wasser Berlin event in 2017 (see: www. dgmt.org). In Berlin Berendonk presented the results from sampling clarification plant wastewater and sewage system sections, which were taken in Dresden as part of the ANTI-Resist project during 2012 2013. The antibiotics resistance of the E.coli bacterium, which is spread throughout the wastewater sewers, was phenotypically analysed and compared against the E.coli resistance patterns in the clarification plant during each quarter. An increase

Fig. 3: Possible locations for membrane technology in clarification plants (Image: M. Milovic, Cut Membrane Technology GmbH, DGMT’s AK Mikroschadstoffe working group)

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in the path from the wastewater sewer to the clarification plant was detected in the normalised number of tetM (against tetracycline) and CTX-M-32 (against ceftazidime) resistance genes. The possibility of verifying the ARG using molecular-biological processes that allow for faster studying than when using classical culture methods also plays an important role in the risk assessment of antibiotics-resistant microbes in this context.

5. Conclusions regarding “safe” wastewater treatment Pathogenic or possibly antibiotics-resistant microbes constitute another important argument for retrofitting clarification plants with one or more further purification or disinfection processes in addition to the micro-pollutants (residues from medicines and industrial chemicals that are not retained or degraded in a conventional clarification plant). In order to avoid conceptual confusion, it should be noted that the typical “4th cleaning stage” process discussed here already belongs to the tertiary wastewater treatment defined in Table 2.

The term “4th cleaning stage” is used to demarcate micro-pollutant elimination processes such as activated carbon absorption or ozone oxidation from precipitation, flocculation and, if necessary, sand filtration, all of which are standard processes used in many sectors and already count as tertiary wastewater treatment.

In addition to the UV irradiation and chlorination disinfection processes, the

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more extensive wastewater purification processes also include ozone oxidation, which is used to eliminate trace substances, and it also has a high disinfection potential. As Rechenburg stated, ozone works by damaging the cells /6/. A reduction of 2 - 6 log 10 levels can be realised, but this depends on the dosage. However, thick-walled protozoans can survive this process. Researchers at the Karlsruhe Institute of Technology (KIT) and the University of Darmstadt studied the inflow and outflow from an ozonisation reactor as part of the BMBF TransRisk project, in which and after final purification, purified wastewater was treated in a municipal clarification plant. It proved that specific clinically-relevant ARGs and specific bacteria can survive ozone treatment /10/. In the surviving organisms, the frequency of the resistance genes to the imipenem and vancomycin antibiotics had also increased, whereas the frequency of other resistance genes remained the same or even decreased. Imipenem and vancomycin are not standard antibiotics.

Vancomycin is used in bacterial infections that are resistant to conventional antibiotics such as penicillin, cephalosporin or macrolide. Imipenem is a reserve antibiotic administered intravenously with cilastatin in life-threatening urinary, respiratory or abdominal infections (see: www.onmeda.de). Two pilot-scale parallel treatment processes installed behind the ozone reactor, a two-stage biofilter and a two-stage activated carbon filter with granular activated carbon, could not produce any improvements here.

Membrane processes are able to retain microbes, because an intact membrane with correspondingly small pore widths (MF / UF) acts as a virtually absolute barrier. This has also been expressed by the AK Mikroschadstoffe working group from the German Society for Membrane Technology. In Berlin Werner Ruppricht, the head of this working group and the representative from Microdyn-Nadir, a membrane and module manufacturer, showed the possible deployment sites for membrane systems in clarification plants (see Fig. 3). Even though membranes present a barrier to microbes, they are not a barrier to dissolved micro-pollutants, which include antibiotics that are currently being affected by the emergence of resistances. Therefore the favoured and fully effective solution for a so-called hybrid 4th cleaning stage process, such as the combination of a membrane bioreactor and adsorption on powdered activated carbon (PAC-MBR), is the use of membranes for sanitising after activated carbon adsorption and, if necessary, a sand filter for PAC separation or membrane filtration as pre-treatment for the final purification before ozone oxidation. References to PAC-MBR processes with immersed membrane modules exist and there is also a membrane plant with pressure-driven capillary modules (BASF Inge), which is installed after the PAC treatment process together with a subsequent sand filter in the Steinhäule clarification plant in Neu-Ulm (see Item 3 in Fig. 3).

The use of membranes does not make the disinfecting processes superfluous, as the retentate from membrane filtration or the separated sewage sludge in MBR plants contains the surviving organisms. Therefore technical measures implemented to prevent the spread of microbes should also take into consideration the treatment of concentrates, sewage sludge or sludge water.

systems. Wastewater systems need technical measures to stop the spread of resistant germs /2/. Membrane technology offers itself as such a technical measure.

Literature /1/ M. A. Cooper, D.Shlaes: Fix the antibiotics pipeline; Nature Vol 472, April 2011, S. 32 /2/ Dechema e.V. (Hrsg.): BMBF-Fördermaßnahme RiSKWa (Risikomanagement von neuen Schadstoffen und Krankheitserregern im Wasserkreislauf), Praxishandbuch 2016, ISBN: 978-3-89746-189-5 /3/ P. Antwi-Agyei: A Health risk assement of wastewater in Ghana, Abstracts World water week Stockholm 2017, s. www.worldwaterweek.org /4/ R.A. Blaustein, D.R.Shelton, J.A.S. Van Kessel, J.S. Karns, M. D. Stocker, Y. A. Pachepsky: Irrigation waters and pipe-based biofilms as sources for antibiotic resistance; Environ Monit Assess (2016) 188:56, DOI: 10.1007/s10661-015-5067-4 /5/ A. Christou, A. Agüera, J.M. Bayona, E. Cytryn, V. Fotopoulos, D. Lambropulou, C. M. Manaia, C. Michael, M. Revitt, P. Schröder, D. FattaKassinos: The potential implications of reclaimed wastewater reuse for irrigation on the agricultural environment: The knowns and unknowns of the fate of antibiotics and antibiotic resistant bacteria and resistance genes – A review; Water Research 123 (2017), S. 448-467 /6/ A. Rechenburg: Hygienisch-mikrobiologische Herausforderungen für die Verfahrenstechnik auf der Kläranlage, Vortrag 1. DWA-Hygienetag 25.10. 2016 Düsseldorf /7/ Eawag (hrsg.): Verbreitung von Antibiotikaresistenzen im Wasser, Factsheet Juli 2015, www.eawag.ch /8/ C. Schreiber: Einträge, Vorkommen, Verbreitung und gesundheitliche Bedeutung antibiotikaresistenter Bakterien in Abwasser und Gewässern, Dissertation Rheinische Friedrich-Wilhelms-Universität Bonn 2011 /9/ N. Czekalski, U. von Gunten, H. Bürgmann: Antibiotikaresistenzen im Wasserkreislauf, Aqua & Gas No. 9 2016, S. 72 – 80 /10/ J. Alexander, G. Knopp, A. Dötsch, A. Wieland, T. Schwartz: Ozone treatment of conditioned wastewater selects antibiotic resistance gens, opportunistic bacteria, and induce strong population shifts; Science of the Total Environment 559(2016), S. 103-112

6. Summary Municipal wastewater that has been purified using conventional processes still contains a certain percentage of microorganisms, which include harmful germs. Due to the worldwide increase in the occurrence of antibiotics-resistant bacterial strains, they are also found in municipal wastewater and wastewater from agriculture.

A plethora of worldwide research work is addressing the potential risks that can arise from discharging clarification plant wastewater into surface waters and the reuse of wastewater in irrigation

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Phosphor Recovery from Sludge and Other Waste Streams – Conditions and Processes H. Lyko* Phosphor is an element that is vital to everyone alive as nothing can replace it in the production of food. As 80% of the world’s phosphor reserves are found in just four countries, Germany and Europe are virtually completely dependent on imports. The development of processes for the recovery of this element as phosphate or phosphoric acid means that it should now be possible to cover approximately 50% of the phosphor demand in Germany, which is around 500,000 t/ pa, using recyclates. The amendment of the Sewage Sludge Ordinance, which came into force in October 2017, means that the Federal Government is also smoothing the way for the recovery of phosphor. A huge number of processes have been developed in recent years for the recovery of phosphor from wastewater and sewage sludge as well as from industrial wastewater, slurry or fermentation residues. The processes ascertained by various sources are summarised in the following, albeit without a guarantee of completeness.

1. Introduction Phosphor is an element that is vital to everyone alive on this planet and it has been classified as a “critical raw material” by the European Commission /1/.

Phosphor compounds are included in central structural areas and organ functioning and nothing can replace it regarding this function. Phosphor deposits on Earth are concentrated in just four countries: 80% of the usable deposits are found in China, Morocco, Russia and the USA. About 90% of the mined quantities are used in the production of fertiliser.

The limited availability of phosphor currently meets the increasing global demand, which can be traced back to the global population growth and its related food needs. As important as phosphor is as a plant nutrient, phosphates are undesirable in clarification plant process because they can contribute to the eutrophication of water. Effective biological and chemical/physical processes enable clarification plants to implement extensive phosphor elimination, with the result that large amounts of this valuable substance can now be found in sewage sludge or in sludge water. The amendment to the Sewage Sludge Ordinance restricts the use of sewage sludge for agricultural purposes, whereas the recovery of phosphor from wastewater or sewage sludge is stipulated for clarification plants of a specific size. A complete range of procedures have been developed and tested during recent years in anticipation of these new conditions. In a study conducted by the Institute for Energy and Environmental Research (IFEU) in Heidelberg, which was commissioned by the German Federal * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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Environmental Agency, the various processes were compared and evaluated and recommendations were made regarding the development of a phosphor strategy for Germany /2/. This article from 2015 provides a summary of the various technical processes as well as recent developments in certain projects. Further information relating to the details released in 2012 as well as substance flow processes that do not originate from clarification plants, is given in the dissertation by Kathrin Gethke-Albinus, which was prepared at RWTH Aachen /3/.

2. The state of phosphor recycling in Germany The amendment of the Sewage Sludge Ordinance was published in the Federal Law Gazette on October 2nd, 2017, and thus became effective on October 3rd,2017. According to the current state, some 1.8 million tonnes of sewage sludge (dry mass) are disposed of every year, of which around 60% is burnt without recovering the phosphor that it contains. Only around one-third of the sewage sludge is used for fertilisation in agriculture and landscaping. In the new version of the Sewage Sludge Ordinance, the requirements covering these sewage sludges, which can be used as fertilisers, increase in relation to their pollutant contents. This means that the majority of sewage sludge can no longer be used as fertiliser in the medium term, even though the pollutant content in municipal sewage sludge has declined by over 90% in recent years according to BMUB. The new version of the ordinance stipulates that phosphor must be recovered from sewage sludge, wastewater or sewage sludge incineration ash after a transitional period of 12 to 15 years. This applies for clarification plants of sizes > 50,000 PE.

The goal of the German Phosphor Platform (www.deutsche-phosphor-plattform.de), which was founded in 2015 and was able to be present at IFAT 2016 in Munich with their own stand as well as presenting a small lecture program, is the “establishment of sustainable and environmentally compatible phosphor management in Germany with the help of efficient use of phosphor as well as effective recycling and reprocessing”. Members of this platform are participants from the relevant industrial, public and private organisations as well as R&D facilities. The platform’s self-defined tasks also include the creation of an interdisciplinary understanding of the system and the development of guidelines and recommendations for decision-makers as well as the organisation of meetings, seminars and workshops. The 2nd congress, “Phosphor - a critical raw material with a future”, was held in Stuttgart in October 2016 under the patronage of the Baden-Württemberg Ministry of the Environment. More than 200 participants from locations throughout Germany and other European countries vouched for the high relevance of this topic. The majority of the lectures from this event are available for downloading from the platform’s website.

According to the platform’s CEO, Dr Daniel Frank, the potential for recovering phosphor compounds from sewage sludge and other biogenic waste streams for effective fertilising in Germany is about 250,000 t/h, which corresponds to around half of the annual consumption.

At IFAT, Dr Claus-Gerhard Bergs, from BMUB, stated that the phosphor contained in sewage sludge could theoretically cover about 60% of the demand for mineral phosphate fertiliser.

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3. Phosphor recycling processes considered during the IFEU study A total 11 processes were considered during the IFEU study /2/, in which either digested sludge, dried sewage sludge, sewage sludge ash or sludge water, i.e. the water recovered during the dewatering of sewage sludge or digested sludge, were used as the raw material. In which proportions and which chemical form the valuable raw material can be found in water or in dry masses depends on the type of phosphor elimination process used during wastewater treatment. Precipitants containing iron, aluminium or calcium ions are used in chemical phosphor elimination processes. The precipitated phosphates are present in the primary sludge or in the excess sludge still in the clarification plant process and remain predominantly in the solids after the sludge dewatering process, but this depends on where the dosed precipitation agent is introduced in the process. During biological phosphor elimination, some of the microorganisms effective in the clarification plant are induced to absorb more phosphor than is necessary for their own cell growth by the creation of a stress situation and to store them in the form of polyphosphates.

The stress situation arises from changing the phosphate-rich and phosphate-poor ambient condition. Reproduction of the polyphosphate-storing bacteria succeeds in a clarification plant when the living sludge is alternately exposed to aerobic and anaerobic conditions. An organism with a full polyphosphate reservoir releases phosphates into the aqueous phase under anaerobic conditions. The precise processes and the technical options for implementation in clarification plants can be found in /4/. The conclusion here is that after the digested sludge has been dewatered, the proportion of phosphate in the sludge water that can be recovered is higher if a biological phosphor elimination was previously made instead of or in addition to a chemical phosphor elimination.

Tab. 1: Processes for phosphor recycling from sewage sludge (abbreviations: MAP = Magnesium Ammonium Phosphates), CSH (Calcium Silicate Hydrate) as well as the reported recovery rates based on the quantity entered into the clarification plants from the IFEU study References > pilot scale /2/.

The processes considered during the study and the important parameters are all listed in Table 1 /2/. The presentation of flow charts and process details are not

shown here due to their large number, but they can be found in the original text /2/. During the process evaluations, other aspects such as costs, CO2 footprint,

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Fig. 1: Slurry treatment as per BioEcoSIM process

Fig. 2: Block diagram of the Stuttgart process supplemented with ultrafiltration (released as per /6/)

resource consumption and the proportion of recoverable phosphor in comparison to the quantity incorporated in the clarification plant and the usability / biological availability of the relevant phosphor compound also played a role. For example, the latter also includes the depletion of hazardous substances (heavy metals) in the phosphor-containing product. The potential for substituting fertilisers made from raw phosphates, including the necessary transporting of the raw material, was offset against the expenditure. In general it was determined that the expenditure as well as the yield relative to the amount of phosphor incorporated in the clarification plant increases, the further back the phosphor recovery process is implemented along the sewage sludge treatment processing chain. The increased expenditure is due to the fact that the phosphor, which is bonded to the dry substance in the sewage sludge or in the ash, has to be eluted again, which can be realised either by the use of thermal energy or chemicals (acid).

The processing of sewage sludge ash has

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the general advantage that, in addition to the high yield, such ash is easier to store and transport due to its lower volume and its chemical and thermal resistance, which means that greater temporal and spatial flexibility exists regarding the treatment.

However, mono-incineration of sewage sludge is always preferable under these circumstances.

4. Phosphor recovery from other waste streams Sewage sludge is not the only source of secondary phosphates and neither is it the major source. At IFAT, Dr Daniel Frank, from the German Phosphor Platform, estimated the potential of sewage sludge in Germany at 60,000 t/pa as well as a much larger quantity (173,000 t/pa) of liquid manure and fermentation residue.

One possible procedure for the preparation of manure into a solid phosphor product is fermentation into biogas and a subsequent solid / liquid separation of the digestate. If the fermentation stage is omitted, then further stages for diges-

tates from other biogas plants are also conceivable. The continuous solid / liquid separation (at least one decanter is used at the start) mostly involves ultrafiltration.

The phosphor is recovered either with the addition of the relevant precipitants (magnesium- or calcium chloride) as MAP from the filtrate formed during ultrafiltration or after ammonia stripping and further concentration through reverse osmosis in the form of liquid fertiliser containing P and K. Furthermore, the ammonium sulphate formed during the ammonia stripping process is also available as an effective fertilising substance. Gethke-Albinus also described three different processes, two of which also include an MBR stage for the degradation of dissolved organic constituents from the liquid fraction of the fermentation residue /3/. The other process that she described used pure urine as the raw material. However, these applications require the use of separation toilets, which have not been used to speak of.

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dinated by the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart, a process was developed and used as part of a demonstration plant, from which ammonium sulphate was produced as a nitrogen fertiliser and a type of biochar that could be used as a soil improver was also produced from liquid pig manure in addition to a phosphate fertiliser (mixture of MAP, calciumor magnesium-phosphate) (see Fig. 1).

The aqueous slurry is pre-treated with sulphuric acid in order to dissolve all of the phosphor contained in the aqueous phase. The dewatered solid phase is dried in a closed system after the solid / liquid separation stage and converted into a hygienised organic biochar through pyrolysis at 300°C. The phosphor contained in the liquid phase is precipitated as calciumor magnesium-phosphate or as MAP. The solids are separated during ultrafiltration and the ammonium is recovered as a sulphate from the liquid phase. Recently, IGB announced that Suez Deutschland GmbH will bring the BioEcoSIM process to market for treating manure.

The Parforce process, which was developed at the Mining Academy TU in Freiberg, is aimed at the treatment of precipitation product from the purification of

phosphate-containing industrial wastewater and the recovery of phosphor from ash formed from the incineration of offal, but it can also be applied to sewage sludge ash /5/. According to details provided by the Institute, waste from the food and pharmaceutical industries as well as the phosphor from used neon tubes can also be used for the recovery of high-quality phosphoric acid. In this process the solid is solubilised using hydrochloric acid, whereby not only the phosphor but also iron and aluminium ions from the precipitation products are partially dissolved. The latter are removed from the aqueous, phosphate-rich phase by liquid / liquid extraction using an organic solvent and recovered through backwashing using hydrochloric acid as the chloride. They can be fed back into the precipitation process and this helps to reduce the chemicals needed for wastewater treatment. The phosphate-rich aqueous phase also contains calcium chloride and unused degradation acids. This mixture is separated electrolytically and the resulting phosphoric acid is treated through extraction and concentrated through evaporation.

The process is currently being brought to market through the use of a demonstration facility as part of a publicly-funded business start-up procedure.

5. Recent processing developments Even though some of the processes listed in Table 1 have now come to the point of industrial application maturity, the search continues for economical and environmentally-friendly phosphor recovery processes from different raw materials.

Some of the processes mentioned in recent publications are briefly described below.

A modification is known for the Stuttgart process listed in Table 1, in which the solids separation process was supplemented by ultrafiltration after acid hydrolysis, whereas the process originally consisted of a chamber filter press and a slurry tank (see Fig. 2). Consequently, the recyclates obtained from the ultrafiltration filtrate have a lower heavy metal content and a better visual appearance (lighter powder).

The ePhos process, which was developed by Fraunhofer IGB, is based on electrochemical phosphate precipitation from sludge water. The processing occurs in an electrolysis cell, which consists of an inert cathode and a sacrificial magnesium anode. Water molecules are split by the cathodic reduction and the OH ions that are formed increase the solution’s pH-value.

The magnesium dissolves at the anode and

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the processes mentioned above are based on the solids fraction, it was accepted that other metals and heavy metals that are dissolved during the degradation will also be precipitated during phosphate precipitation. Exceptions here are the Parforce process, in which iron- or aluminium-salts are extracted separately or the Stuttgart process, which is supplemented by ultrafiltration, in which some of the heavy metals are apparently retained. In the studies described in Aachen, which were carried out at the University of Applied Sciences and Arts in North-West Switzerland, the sewage sludge was disintegrated using sulfuric acid and the solids fraction was separated afterwards by ultrafiltration. The UF permeate also contained sulphur, iron from the phosphor precipitation that formed as part of the wastewater treatment as well as dissolved heavy metals in addition to the phosphoric acid. Phosphor is present as phosphoric acid under acidic conditions and it can pass through a nanofiltration membrane whereas the iron and heavy metal ions are retained. The separation was carried out in the form of multi-stage diafiltration, in which a higher phosphor yield could be achieved as opposed to using pure single-stage nanofiltration. Phosphate was precipitated afterwards from the diafiltration permeate by using a sodium hydroxide solution to increase the pH-value to 8.5. This process appears to be quite complex with regard to the required acids and alkalis as well as the amount of water to be pumped in for diluting. The nanofiltration modules that have to be installed in several stages are also an additional cost factor.

6. Conclusion

Fig. 3: Pilot plant that uses the ePhos process for the recovery of phosphor from phosphate-rich wastewater (Image: Fraunhofer IGB, Stuttgart))

then reacts with the nitrogen and phosphor contained in the water to form struvite (MAP). The process has been successfully tested at a biological clarification plant using a biological phosphor elimination process, whereby an average of more than 80% of the phosphor contained in the sludge water could be recovered as struvite.

Under the biological phosphor elimination conditions in which the sludge water is fed back into the bioreactor, the process helps to prevent any operating problems that might be caused by phosphate precipitation in filtrate water pipes or the dewatering apparatus.

As magnesium electrodes are already provided as the consumable materials, this saves having to use chemicals for degradation and precipitation. A licensing agreement for the marketing of this technology in North America was concluded with OVIVO, a US clarification plant constructor, in 2016.

The AVA ‘cleanphos’ pilot plant, sponsored by the German Federal Foundation for the Environment (DBU), came online in Karlsruhe in 2016. The core of this process is a HydroThermal Carbonisation plant (HTC) for wet biomass (in this case sewage sludge), in which this biomass is converted into biochar under pressure and at a higher temperature (from 120° to around 200°C) and the biochar also contains the phosphor from the sewage sludge. This is recovered from the carbon through acid degradation and then precipitated by adding magnesium salt afterwards. The HTC is used here as a cost-effective process as compared to the more expensive mono-incineration of sewage sludge. The depleted carbon can be dewatered, dried and used as a fuel after the phosphor has been recovered.

At the 11th Aachen water technology conference held in 2015, a process for using nanofiltration as part of a process for recovering phosphor from sewage sludge was presented /8/. As the majority of 36

The chemical options for recovering phosphates from sewage sludge, liquid manure, fermentation residues or other waste streams are well-known in principle. They have been and are being realised in different combinations and are also being combined with mechanical separation processes and thermal processes, whereas a few of them have already been implemented on a large scale. The optimum process certainly depends on the phosphate source (e.g. whether a chemical / physical or biological phosphor elimination occurs in a clarification plant) and on the quality of the resulting phosphor-containing product, i.e. the availability to plants of the phosphor from the recyclate that is produced.

Processes in which (in the best scenarios) all of the components in the raw materials that are used are converted to directly usable or storable and marketable products seem to be the most economical and the most promising.

Literature /1/ European Commission: On the review of the list of critical raw materials for the EU and the implementation of the Raw Materials Initiative, Brussels, 26.5.2014 COM (2014) 297 final /2/ D. Montag, W. Everding, S. Malms, J. Pinnekamp, J. Reinhardt, H. Fehrenbach, U. Arnold, M. Trimborn, E. Goldbach, W. Klett, T. Lammers: Bewertung konkreter Maßnahmen einer weitergehenden Phosphorrückgewinnung aus relevanten Stoffströmen sowie zum effizienten Phosphoreinsatz; Umweltbundesamt (Federal Environmental Agency), Text 98/2015 /3/ K. Gethke-Albinus: Verfahren zur Gewinnung von Sekundärphosphaten aus flüssigen Stoffströmen und deren Einfluss auf die deutsche Phosphorbilanz; Dissertation, RWTH Aachen, 2012 /4/ J. Pinnekamp, D. Montag, K. Gethke, S. Goebel, H. Herbst: Rückgewinnung eines schadstofffreien, mineralischen Kombinationsdüngers („Magensiumammoniumphosphat – MAP“) aus Abwasser und Klärschlamm, Umweltbundesamt (Federal Environmental Agency), Text 25/2007 /5/ P. Fröhlich, R. Lohmeier, G. Martin, J. Eschment: Die Gewinnung von Phosphorsäure aus Reststoffen, GIT-Laborportal für Anwender in Wissenschaft und Industrie, http://www. git-labor.de, 19-08-2016 /6/ D. Montag, D. Bastian, J. Pinnekamp (2016): Gutachten zur Umsetzung einer Phosphorrückgewinnung in Hessen aus dem Abwasser, dem Klärschlamm bzw. der Klärschlammasche. Gerichtet an das Hessische Landesamt für Naturschutz, Umwelt und Geologie, HAD reference number 4824/8 /7/ C. Glasner, G. Deerberg, H. Lyko: Hyrothermale Carbonisierung: Ein Überblick, Chemie Ingenieur Technik 2011, 83, No. 11, pp. 1932-1943 /8/ T. Krahnstöver, C.Niewersch, T. Wintgens, S.Yüce: Nanofiltration als Metallseparierungsverfahren für die Phosphorrückgewinnung aus Klärschlamm, in: M. Wessling, J. Pinnekamp (Hrsg.): Verfahren der Wasseraufbereitung und Abwasserbehandlung, Proceedings 11th Aachener Tagung Wassertechnologie, 27/28 Oktober 2015, pp. 179 – 186, ISBN 978-3-95886-056-8

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Water Technology for the Beverage and Food Industries Report from the 14th VDMA Water and Wastewater Conference H. Lyko* The VDMA Water and Wastewater Conference has now been held for nearly 25 years. With its changing thematic focus, it offers the member companys from the water and wastewater technology department of the German Mechanical Engineering Industry Association the opportunity to present their innovation and performance capabilities, exchange experiences and network with one another. Dr Marcus Höfgen, chairman of the department and chairman of the board of INVENT Umwelt- und Verfahrenstechnik AG in Erlangen, welcomed 55 participants to last year’s event, which was held at the end of April. Prof. Markus Engelhardt, head of the Department of Sewage Technology at IWAR at the TU Darmstadt, moderated the event.

Membrane technology used in the fruit juice industry Armin Eisenhofer, from Grünbeck Wasseraufbereitung GmbH, showed how the introduction of membrane technology can contribute to greater operational safety within the fruit juice industry.

A reverse osmosis plant was installed for the production of process water from well water in the first example that was presented. This process water, with an optimum hardness of around 5° dH, is needed in different plants with up to 5 filling lines. More specifically, these are tunnels, rinsers, CIP plants and belt lubrication systems.

The reverse osmosis plant replaced a decarbonisation plant in which the carbonate hardness of the well water was removed using hydrochloric acid and a weak-acid ion exchanger resin. This treatment technology was no longer adequate because it only removed the carbonate hardness and therefore it could only reduce the total hardness from 25° dH to approximately 14° dH. However, salt retention by the reverse osmosis process was so high that the permeate had to be blended with filtered well water in order to attain the required hardness of 5° dH. The blending device is controlled by measuring the conductivity. Eliminating the use of hydrochloric acid also negates the associated reduction in the water’s pH value.

The acid tank was superfluous and the risk of corrosion due to the escaping acid fumes now no longer exists. The space available for the RO plant also posed a challenge. This was solved by arranging the pressure pipes in the structural design into two parallel strands, one above the other (see Fig. 1).

In the subsequent discussion, the question arose as to whether nanofiltration could also be carried out or not with sufficient regard to the required residual hardness of the process water. Eisenhofer pointed out that the salt retention in the nanofiltration process depends on the composition of the raw water and possibly on other impurities in the raw water as well. This is why reverse osmosis was regarded as the safest variant. The described plant is operated at 10 bar and this results in a power consumption of approximately 0.3 - 0.4 kWh/m3.

The second example mentioned relates to the degassing of product water with the aim of reducing the oxygen content and this should increase the product’s shelf-life. In the operation under consideration, fruit juice concentrates are blended with well water that was previously filtered, UV-disinfected and degassed. The old vacuum degassing plant was able to reduce the oxygen content * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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from its original 9.5 to approximately 3 - 4 mg/l. According to user’s newest requirements, this value should be below 0.5 mg/l.

This is why the vacuum degassing plant was replaced by two membrane contactors (Liquicel Extraflow, 3M) which are operated using CO2 as the stripping gas. The contactor plant’s rating is 40 m3/h. A pressure surge tank was used so that up to 6 filling lines could be supplied simultaneously and to cover minimum or peak quantities. This was overlayed with nitrogen to stop any new oxygen from entering.

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Fig. 1: Reverse osmosis plant in the structural design for water treatment in the fruit juice industry (Image: Grünbeck Wasseraufbereitung GmbH)

Wastewater technology for Mexican breweries Mexico is the sixth largest beer producer in the world with an annual production of 90 million hectolitres of beer.

The beer market in Mexico is firmly in the hands of two brewery groups, InBEV and Heineken. Wastewater technology components from INVENT Umwelt- und Verfahrenstechnik AG have been installed in five of the eight breweries operated by Heineken. Dr Peter Huber described the special challenges presented by brewery wastewater and showed two agitating and aeration system application examples used in mixing and equalising tanks as well as in the aeration tank.

The brewery wastewater that was examined contained fine-grained kieselguhr, disinfectants from the CIP processes, alternating acidic and basic cleaning chemicals and a high BOD concentration that occurred at higher temperatures (> 35°C.). Equalisation tanks were used due to the fluctuating pH values and to dilute the high concentrations of disinfectants.

Hyperboloidal agitators from INVENT are used to counteract the formation of deposits, e.g. from kieselguhr. This also reduces the build-up of odour in such tanks. The agitator is positioned close to the bottom of the tank so that it can also agitate at the lowest filling level. Huber reported on 15 years of damage-free operation of these agitators in a brewery clarification plant.

The hyperboloidal agitator was used both with or without aeration. The combination of agitating and aeration leads to partial decomposition of the BOD in the equalisation basin, which also reduces the odour build-up. Aeration presents a major challenge in brewery plants as the

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oxygen transfer factor can be very low due to the high concentration of cleaning agents. The iCBA system has been introduced for installation in aeration tanks. It consists of wear-free, rectangular stainless steel elements with staggered opening diameters arranged in rows. The openings have been dimensioned so that the air is spread evenly throughout the entire tank. These aerators were installed as a replacement for the surface aerators in the Heineken Cuauhtémoc TECATE brewery.

It also showed that the mean annual energy consumption for the aeration could be reduced.

Water technology used in milk processing Dairy wastewater is mainly produced during plant cleaning and is highly organically contaminated due to the product residues that are rinsed out and the cleaning agents that were used. However, the contamination level is subject to severe fluctuations, which is why it is sensible to control the clarification plant’s inflow according to the COD load so that it does not become overloaded. Wastewater can also serve as an indication of problems in the production process or during the optimisation of biogas production in an anaerobic stage. The Berlin-based company LAR Process Analyzers AG specialises in online analysis of the cumulative TOC, COD, BOD, TP, TNb and toxicity parameters. Caesar Dombrowski described how the measuring technology is used at the inlet to the clarification plant at the Altentreptow site belonging to DMK Deutsches Milchkontor GmbH. More than 10 million t/pa of whey are processed at

this location. A total of 3,000 to 3,500 m3 of wastewater are cleaned and discharged into a river every day. As direct online determination of the chemical oxygen requirement using potassium dichromate is just not possible, the total carbon content (TC) is measured and converted into the COD by using a predetermined correlation factor. High concentrations of dairy products in wastewater samples and the need to collect suspended organic carbon (e.g. fat particles and clumps) without any filtration presents a challenge to the measuring technology and the sampling process. Two parallel sample flows without carryovers and cross-contamination will be recorded in Altentreptow, whereby their COD values can be between 5,000 and 40,000 mg/l. The quick analysers used here operate at 1,200°C and have a patented, intelligent sample feed into the furnace so that all sample components are included. Sampling is undertaken using the also patented FlowSampler sampling device, whereby the sample is extracted from the centre of the sample flow and against the main flow direction.

In the EU-FP7 SUSMILK (redesign of the dairy industry for sustainable milk processing) project a total of 21 partners from 9 countries were involved in different technology sectors in order to make industrial milk processing more sustainable. The Fraunhofer Institute for Environmental, Security and Energy Technology (Umsicht) in Oberhausen coordinated the project, which ran from November 2013 to October 2016. The lecture given by Dr Christoph Glasner focused on the part of the project in which the treatment of CIP solutions using membrane technology was studied. Chemicals and/or water should be recovered and the concentrates obtained should be used for the production of biogas or bioethanol or made available for the recovery of lactic acid. In a Serbian dairy, which operates CIP cleaning with sodium hydroxide as a so-called “lost cleaning process”, various membrane processes (NF with and without upstream UF as well as RO with upstream UF) were tested, whereby the retention of the total COD and the suspended matter as well as the loss of the cleaning agent caused by retention on the membrane was determined. Accordingly, a compromise has to be found between the achievable permeate quality and the tolerable loss of the cleaning agent. With the help of an online calculator developed within the project, the savings which depend on the quantities generated and the economic conditions, can be determined for single-stage and dual-stage membrane processes.

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Chemical

Environmental

Food

Fig. 2: MOL-LIK module with catalytically acting foils to accelerate the equilibrium between molecular water and bulk water (Image: MOL Katalysatortechnik GmbH)

Operating cost optimisations within operator projects Beverage and food manufacturers are compelled to operate an appropriate wastewater treatment plant, but many companies do not have their own expertise and personnel capacity to operate them continuously and optimally.

A solution to this problem is that the providers of water and wastewater treatment plants should also provide operational management and they should also assume the responsibility for process and cost optimisation whilst providing the services required by the client or the legislator. Operational management and contracting are also part of the range of services provided by EnviroChemie, who are based in Roßdorf. Claudia Müller reported on two operator projects running in the potato processing and dairy industries.

In potato processing, 1,300 m3/d of starch-containing wastewater has to be purified until it reaches the direct discharge quality. A preliminary analysis undertaken prior to assuming operational management showed that the operating costs could be significantly reduced by modifying the process technology, modernising the plant and making further adjustments during operation. The original clarification plant, consisting of mechanical pre-treatment and aerobic stages as well as secondary clarifiers, was fitted with a flotation system and an anaerobic stage. Optimisation of other operating parameters, reducing the operating times of energy-intensive aggregates and the optimisation of the biogas yield all resulted in the amount of sludge being reduced by 62% as well as energy consumption being reduced by 70%.

In the dairy industry, EnviroChemie has been running a process wastewater treatment plant since 2010. This example shows how the processing cost conditions are altered as a result of internal and external changes. The internal changes include a necessary capacity increase resulting from the increase in the production volume, whereby the wastewater loads that had to be removed increased disproportionately. This circumstance alone necessitated a performance update through multi-stage expansion. Despite the difficulties encountered in adapting the treatment capacity to match the increasing amount of wastewater in good time, the specific electricity consumption could be steadily reduced through the use of several optimisation measures. The external condition that changed during the operating time, is the price of the sludge that has to be disposed of. Production and social wastewater had

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already been separated during the start, which meant that the sludge to be treated could not be disposed of as slurry but as low-cost bio-sludge. The cost increase for the sludge disposal could be compensated for by the installation of screw presses in order to reduce the transport volume as well as the commissioning of a mixing and equalising tank so that a large part of the acid used for the pH regulation would be rendered superfluous.

Disinfecting water meters Dr Lothar Ophey, from Mainsite Technologies, described the risk of contaminating drinking water systems by using new water meters. Generally, these meters are tested by the manufacturer or in test institutes with water, packaged afterwards and then stored without being completely dried out beforehand. The meter housing’s humid interior forms an ideal breeding ground for pseudomonas aeruginosa microbes. This is a widespread bacteria that can survive chlorine concentrations > 1.0 mg/l of free chlorine. It can also cause infections that are dangerous to people with a weakened immune system and even be life threatening to infants. If a new water meter is installed in a drinking water distribution system (which is normally done every 6 years for household connections), the bacteria is distributed throughout the water system and it can then take several weeks until no more contamination is released from the meter. In a microbiological study of 2,700 water meters that was undertaken in 2014, this organism was established in around 23% of brand-new water meters, with the rate of positive findings and the level of contamination in meters with plastic housings significantly higher than that found in meters with metal-housings /1/. Disinfection of the meters after testing / calibrating or before installation can contain the risk. Mainsite Technologies has specifically developed “Desiree”, a disinfecting device that allows plumbers to disinfect water meters on the day of installation in just a few simple steps. The system’s effectiveness has been certified by an accredited test laboratory.

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Low-chemical inhibition of scaling and fouling Steam sterilisation is used to preserve food before packaging. The water used to generate the steam is circulated during the process and the condensate passes through temperatures ranging between 15° and 45°C. Scaling and biofouling, which are usually encountered during filtration, biocide dosing and chlorination, can be facilitated through temperature variations as mentioned above. The module presented by Dr Jürgen Koppe, from MOL Katalysatortechnik GmbH, addresses the equilibrium setting between the two boundary structures of liquid water. One part is present as so-called bulk water, i.e. the individual water molecules are connected to each other by hydrogen bonds and they are not available for hydration or hydrolysis; neither do they contribute to the dissolving of other substances. The other part is present as single molecules and they can dissolve substances as well as being capable of diffusing, e.g. through a membrane, and they can also participate in corrosion processes. The equilibrium between the two sections is pressure and temperature dependent, i.e. the higher the temperature, the greater the proportion of molecular water. If the water is subjected to the temperature changes that occur during the described condensation circulation, then the equilibrium will be disrupted.

After cooling, the proportion of molecular water is higher than the equilibrium proportion for a specific time and this is reversed after heating. An equilibrium shift towards more bulk water can facilitate scaling and fouling and the effect of biocides is reduced due to the lack of molecular water. The Mol-LIK module contains mineral/metal foils, which accelerate the equilibrium setting between bulk water and molecular water. The biocide effect is selectively controlled by this.

In the example shown where the module was installed in the condensation tank, the chlorination in the autoclave circuit could be adjusted and the use of ozone and UV light for disinfecting was minimised.

Nevertheless, a lower microbe count was realised than previously using chlorination

and stronger ozonisation as well as UV irradiation.

The state of German exports German companies in the general mechanical engineering sector as well as the providers of water technology are superbly positioned in the world markets. This was clearly illustrated by the latest import and export statistics, which was presented by Peter Gebhart, from the VDMA’s Department of Process Engineering, Machinery and Equipment.

German machinery exports in 2016 remained at roughly the same level of 155.9 billion euros as in the previous year.

Imports registered a slight 3.6% increase to 64.3 billion euros. The most important export regions for mechanical engineering are the 28 EU countries followed by East Asia, North America and other European countries. The absolutely highest growth in 2016 was attained in Egypt and the highest export decline was seen in the exports to China. Looking at the development of exports in the “equipment for filtering and purifying water, including that used by civil aviation” sector, the export figures remained stable at the previous year’s level, whereby the largest proportion of components and system were sold in Europe (56% in EU 28 + all other European countries). The Asian market proved to be the second largest market.

The Russian market for process equipment and machinery exhibited the greatest fluctuations of all the partner countries, but it still registered a significant increase over 2015.

Literature: /1/ B. Hambsch, M. Hügler, M. Schönthal, T. Kempf, M. Maier: Bestandsaufnahme der mikrobiellen Belastung in Wasserzählern. DVGW energie/wasser praxis 67, Nr.5, S. 84-91 (2016) /2/ TZW-Schriftenreihe Band 73: Pseudomonas aeruginosa in Trinkwassersystemen- 1. Wachstumsansprüche und Gegenmaßnahmen 2. Belastung von Wasserzählern (2016) ISSN 1434-5765, zu beziehen über TZW: DVGW - Technologiezentrum Wasser, www.tzw.de

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Membrane Technology Used in Waterworks: Experience gained from removing ingredients H. Lyko* Drinking water is an irreplaceable food. It should be colourless, clear, cool, odourless and tasteless as well as being low-germ and microbiologically harmless as stipulated in DIN 2000, the guideline for central drinking water supplies. The concentrations of any ingredients contained in the water must be so low in order to ensure that no damage to human health can be expected as a result of lifelong consumption and use. Nitrates and micro-pollutants were the main focus in the discussion about the quality of the raw water used for the recovery of drinking water and the measures to be taken for its preparation. The nitrate concentration is considered to be particularly problematic due to the fact that if the nitrate concentration in the raw water reservoir exceeds the 50 mgl/l limit value stipulated in the Drinking Water Ordinance (2001), then the reservoir cannot be used for drinking water recovery. As indicated in the most recent nitrate report from the Federal Ministries for the Environment, Nature Conservation, Building and Nuclear Safety as well the report from Food and Agriculture, nitrate concentration are above this limit in 28% of the measuring points in those catchment areas where agricultural usage predominates /1/. For more information on the continually increasing costs to the users regarding the nitrate concentrations, please refer to the recent study /2/ published by the Federal Environmental Agency and its conclusions /3/.

Membrane technology was also considered as a nitrate removal option in this study /2/. The technology for removing particles, micro-organisms, salts and other parasitical content has already been established in drinking water treatment plants in many locations.

Duisburg / Essen University, the Deutsche Gesellschaft für Membrantechnik (DGMT) and the Deutsche Meerwasser Entsalzung GmbH (DME) all held an initial joint seminar in Duisburg last June in order to provide an insight into the state of the art technology, current research activities, operated plants and the options for implementing the technologies and the legal framework conditions. Claus Mertes, the CEO of DME GmbH, moderated the event.

Jörg Matthes, a water manager and director of water management for the Düsseldorf district government, explained his critical view of membrane technology. According to him, it is used as a source of remote preparation and it is often installed at the point of maximum dilution. Believing in technical feasibility in water treatment promotes the readiness to take risks with regard to possible pollutants entering the waters. Classifying the drinking water supply as a municipal task means that the imposed costs are socialised, i.e. to the detriment of the general public, as the profits from plants where water pollutants can enter remain in the hands of contractors (private sector).

The benchmark for water management should be the provision and not the after-treatment. The main content-bearing pathways for pollutants entering the waters are agricultural use (use of manure, artificial fertilisers, clarification substrates, crop pesticides and their metabolites), clarification plant drainage (micro-pollutants) as well as abandoned polluted sites and damaged ones. Attempts have been made to reduce pollutant inputs through advising farmers and co-operating with the water recovery producers.

The options and limitations of membrane technology The current dilemma facing drinking water treatment became clear during the first two lectures given by a water management expert and a technology developer: Drinking water treatment plants are confronted with unwanted contaminants in their raw water reservoirs and these concentrations have either actually increased (such as the nitrate content in certain reservoirs due to inputs from agriculture) or where better analysis and more recent findings on their harmfulness now require action, as is now the case with micro-pollutants. If, in the context of preventive water protection, it ever became possible to ensure that these impurities never enter reservoirs used for drinking water recovery, then one would not have to install high-quality treatment technologies in waterworks. * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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Fig.1: Schematic layout of the monitoring equipment in the NF/RO plant monitoring concept (Image: IWW Zentrum Wasser Mühlheim)

Fig. 2: Measuring technology installed at Wasserwerk Löhnen (SW Dinslaken) (Image: IWW Zentrum Wasser, Mülheim)

Fig. 3: View of some of the 11 blocks with 15 pressure tubes each for two-stage low-pressure reverse osmosis installed at Wasserwerk Löhnen (Image: Stadtwerke Dinslaken)

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The 4th cleaning stage used in clarification plants should minimise the input of micro-pollutants during wastewater treatment.

Raw water treatment is necessary in the case of abandoned polluted sites and acutely damaged sites, but this should be undertaken as close as possible to the natural environment. Matthes sees sensible applications for membrane technology, especially with regard to the cleaning-up of abandoned polluted or damaged sites as well as in cases where extraction from waters is efficient enough to absorb the concentrates from membrane treatment or the concentrates are not problematic for the waters.

The widely practiced partial-flow treatment using nanofiltration or reverse osmosis followed by the intermixing of the fully demineralised permeate with raw water (pre-filtered) is hardly acceptable in Matthes’ opinion because of the trace substances that were not fully removed.

Being an expert on drinking water treatment, Prof. Stefan Panglisch, from Duisburg / Essen University, said that it also plays a key role in preventive water protection, but in many places it is already “five minutes after twelve”, i.e. the burdens on drinking water reservoirs are now so high that they need to be treated. He described the fundamentals of the membrane technology used in waterworks that focus on nanofiltration and reverse osmosis processes. There are around 60 NF or RO drinking water plants currently installed in Germany. The most frequently used membrane modules are Low-Pressure Reverse Osmosis elements (LPRO). A total of approximately 45 million m3/year of water is treated in these plants, with 90 % of the plants having a capacity of less than 300 m3/h. The pure water yield is 70 - 83 % and the average permeate flow is 24 l (/m2/h) and the operating pressures lie between 4 and 13 bar.

The primary treatment objective of the majority of plants is water softening and about half of all the systems are used for partial-flow treatment. One of the advantages of the membrane systems highlighted by Panglisch is their ability to replace several other treatment stages. At least 50% of the small non-polar molecules are usually retained.

The disadvantages of these membrane processes are the comparatively high specific costs, the need for excellent pre-treatment and the dosing of chemicals to prevent scaling and corrosion as well as the need for after-treatment. The latter is necessary because the membranes retain ions together with carbonates but not dissolved gases such as CO2. The result is a permeate that is not in the lime/carbonic

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acid balance and this has to be de-acidified somehow.

One of the most important problems that arises through the use of membrane technology in the waterworks is that about 20% of the raw water that is used ends up as concentrates. These contain the retained pollutants, which include the antiscalants used in high concentrations.

On-site treatment of these concentrates in the waterworks presents a problem with regard to the water protection zone. One proposal is to introduce it in clarification plants, which is rather more positive with regard to the carbonate content as well as the nitrates.

Monitoring membrane plants After the DVWG’s W 236 “Nanofiltration and low-pressure reverse osmosis used in central drinking water treatment plants” draft worksheet was published in 2014, it became clear during the objection period that there are still gaps in the knowledge associated with monitoring the integrity of NF and RO membranes.

Normal monitoring of the permeate quality via its conductivity is unsuitable for indicating localised membrane defects in multi-stage and/or multi-line membrane plants. A theoretical concept was devel-

oped at the IWW Zentrum Wasser in Mülheim in 2015 that covered how this monitoring can be carried out in order to close these gaps. Conversion of the theoretical concept into an effective and practical concept for online monitoring in waterworks is to be implemented in a current DVWG research project, which was launched earlier in 2017. Co-ordination lies with the IWW, whose representative, Oliver Dördelmann, described the objectives of this project and the initial activities. The water supply companies in the cities of Dinslaken, Osnabrück and Sondershausen are also involved in this project as well as a fittings manufacturer and four measuring instrument manufacturers.

The monitoring concept provides for conductivity measurement in the permeate using individual pressure tubes rather than solely in the collecting line as well as online parameter measuring which reacts much more sensitively to local membrane defects than conductivity does, such as the sulphate content or the hardness (see Figs. 1 & 2).

Measurements are also taken in the test plant at the IWW test facility whereby membrane elements can be specifically manipulated and trace substances can also

be dosed-in, in addition to the measuring equipment being installed in the waterworks. The results will then be integrated into the W 236 worksheet.

No results about the effects of membrane damage were available at the time when the event was held. However, it has already shown that the permeate quality can vary between the individual pressure tubes without a defect being present.

The chemistry of reverse osmosis membranes The separation effect of dense membranes depends on the selective solubility or diffusivity of substances in the membrane matrix as well as on the charging effects. With more open membranes, such as nanofiltration membranes, surface charge also plays a significant role regarding the retention of polar molecules or ions. The membrane retention capability changes accordingly with the water matrix. In order to counteract this, Lanxess has highly crosslinked its reverse osmosis membranes, so that they now have a low charging density on the surface.

Dr Jens Lipnizki compared the results obtained using this membrane with those from retention studies using membranes from their competitors. These compara-

Fig. 4: Water treatment processing technology used at Löhnen waterworks (legends translated, original picture kindly supplied by Stadtwerke Dinslaken)

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tive studies are described in detail in /4/.

Clearly improved nitrate retention was seen in Duisburg when compared to a competitor’s membrane, as well as very low dependence on the pH value of the raw water. The fouling tendency in the feed channel was also reduced through the use of newly developed spacers in the spiral wound modules (see /5/). Ion exchangers are also very well suited to removing nitrates from the water in addition to the reverse osmosis membranes.

Specific water constituents can be selectively removed from the water through the use of resins for ion exchangers, whilst other needed ingredients still remain in the water. In addition to the substances to be separated, the possibility of disposing of the regenerate from of the ion exchanger or the RO concentrate is an important criterion when choosing between reverse osmosis and ion exchangers or else a combination of the two methods.

Operating experiences in waterworks The Wasserwerk Löhnen (Dinslaken) draws its raw water from several wells near the banks of the Rhine. Water from the Rhine can enter the aquifer as a result of mining damage. After a worstcase scenario was calculated and after the micro-pollutants contained in the water from the Rhine reached a relevant concentration in the raw water supplied to the waterworks, a reverse osmosis plant was built parallel to the existing conventional treatment plant operation. Marco Binder, from Stadtwerke Dinslaken, described the plant’s features, as it was designed for full-flow treatment (1,100 m3/h). This is realised using 11 lines, each capable of 110 m3/h and with one line held in reserve.

It has a feed pump installed in each line, two pre-filters (5 and 1 μm) connected in series and a two-stage low-pressure reverse osmosis block which has a membrane surface of 3,600 m2 (see Figs. 3 & 4). As the worst-case scenario has not yet occurred, the plant is initially operating with just a partial load. In order to be prepared in case of emergency, the installation of the plant was started with monitoring of micro-pollutants in the runup to extracting the water. When full-flow operation starts it will be orientated to the development of pollutant concentrations, but the actual conversion will take about six months.

The production costs, along with all the planning services, were slightly less than 14 million euros. The major proportion

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of the costs, which was around one third, were accounted for by the electrical engineering costs, as an overland power supply line had to be upgraded in order to cover the reverse osmosis energy requirement.

The concentrate is currently supplied with the rainwater from the polder water pipeline belonging to the Lippverband.

Frank Hörnschemeyeer, from Stadtwerke Osnabrück, described the experiences gained from using membrane filtration at Wasserwerk Düstrop. In this waterworks, which has existed since 1908, more than 1 million m3/year of spring water and deep-well water have been treated to become drinking water. The safe removal of microbiological impurities was stated as being the motivation for the installation of a nanofiltration plant in 2005. The raw water also contains hardness forming agents (lime) such as nitrate, sulphate and chloride. The nanofiltration system consists of 4 blocks, each handling 110 m3/h of pre-filtered raw water, which is carried outwards in two stages using a total of 96 membrane elements from Hydranautics fitted in 16 pressure pipes (11 in the first and 5 in the second stage).

The plant’s permeate yield is 80%. The total salt content as well as the nitrate content should be halved in addition to ensuring microbiological harmlessness. These requirements were clearly exceeded when the plant was accepted, but a reduction of the retention of 5.5% for divalent ions and 4% for hydrogen carbonate and more than 17% for nitrate was determined during the 2005 - 2011 operating period. The permeate was microbiologically safe throughout the entire operating period, i.e. the UV disinfection system that was installed for safety purposes was kept in standby mode and has not yet been used. The plant’s membrane elements have been replaced in the meantime and the 5 μm cartridge filters were exchanged for 1 μm filters in the pre-filtration system. This waterworks also participates in the membrane integrity monitoring project described by Oliver Dördelmann.

The RO concentrate is fed into the drainage channel. The current authorisation runs until 2018.

Concentrate feeding: legal aspects The fact that approximately 20% of the raw water ends up as concentrates in the treatment of drinking water when using nanofiltration or reverse osmosis was addressed in several lectures. The questions as to whether this is waste to

be treated in accordance with the Waste Recycling Management Act or as wastewater or if the concentrates should even be treated in the protected zone in which the waterworks is located, and, in particular, under which conditions concentrates are introduced into surface waters, play an important role when planning membrane systems.

Stefan Wiesendahl, from Kümmerlein lawyers and notaries in Essen, showed the legal basis for the case of feeding-in the concentrate resulting from the processing of raw water into drinking water, into surface water. The plant operator must obtain a permit (see § 8 Para. 1 of the Water Resources Act (WRA)), which is generally time-limited, for the bringing or feeding-in of substances into waters.

In accordance with § 12, Para. 1 of the WRA, the issuing of a permit is subject to the discretion of the authority responsible (planning assessment). This WRA paragraph only determines when the authority may not grant permission. However, the applicant does not have a legal right to be granted a permit, even if all of the WRA conditions are met.

The most important requirements of the WRA are also given in § 27, in which the prohibition of deterioration or order of improvement is formulated, and in § 57, in which it is required that the water treatment to be used must correspond to state-of-the-art technology. This is made more specific in turn, by the corresponding legal regulations (e.g. the wastewater ordinance).

The following assessments were made regarding the question of the demarcation between waste and wastewater: If the treatment of a concentrate results in a liquid capable of being fed in, then it is wastewater treatment. Conversely, solids produced in plants with ZLD (Zero Liquid Discharge) are classified as waste.

Literature: /1/ BMUB, BMEL (Hrsg.): Nitratbericht 2016, Stand Januar 2017 /2/ Umweltbundeamt (UBA, Hrsg.): M.Oelmann, C. Czichy, U. Scheele, S. Zaun, O. Dördelmann, E. Harms, M. Penning, M. Kaupe, A. Bergmann, C. Steenpaß: Quantifizierung der landwirtschaftlich verursachten Kosten zur Sicherung der Trinkwasserbereitstellung, Endbericht 2017, UBA-Text 43/2017 /3/UBA: Factsheet: Wieviel zahlen Trinkwasserkunden für die Überdüngung? 6. Juni 2017, s. www.uba.de /4/ J. Lipnizki: Die Chemie macht den Unterschied, F&S Filtrieren und Separieren 29 (2015) Nr. 1, S. 49-52 /5/ J. Kidwell, S. Tielen, B. Paesen, J. Ogier, S. Lehmann, C. Schellenberg: Innovative FeedspacerTechnologie bewirkt eine verbesserte Leistung von Umkehrosmosemodulen, F&S Filtrieren und Separieren 29 (2015) Nr. 5, S. 323-326

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Biological Treatment of VOC contaminated Extracted Air or Wastewater by Using an Activated Carbon-Doped PU Carrier A report from centrotherm clean solutions GmbH & Co. KG* Solvents are used in many industrial sectors, such as the production and processing of paints and lacquers, which often enter the environment as Volatile Organic Compounds (VOCs) together with processed exhaust air flows. However, many companies are putting extracted air purification measures far behind other investments, as they rarely contribute to direct value creation. However, increased governmental requirements regarding environmental protection as well as residents’ complaints about unpleasant odours have increased the pressure on companies to make more provisions for reducing VOC emissions or to improve existing treatment concepts.

This is why Centrotherm clean solutions GmbH & Co. KG has expanded its product portfolio to include plants for biological treatment of VOC containing extracted air or wastewater flows.

The basic CT Eco method eliminates pollutants by taking advantage of the fact that most organic compounds are biodegradable if special microorganisms are used. A modular plant concept makes it possible to customise the process to the specific application.

Both the investment costs and the need to comply with legal emission limits play important roles when selecting a suitable extracted air purification concept. Factors such as operating and maintenance costs, energy and other operating costs as well as the flexibility of the process to adapt to different processing conditions must also be taken into consideration. Whereas the biological decomposition of organic pollutants is a long-established process, e.g. the treatment of municipal wastewater in clarification plants, biological processes for extracted air and wastewater purification have still to become established in industry. The reasons for this *centrotherm clean solutions GmbH & Co. KG Johannes-Schmid-Strasse 3 89143 Blaubeuren, Germany Tel: +49 (0)7344 92494-0 Fax: +49 (0)7344 92494-199 Email: info@centrotherm-cs.de Internet: www.centrotherm-cs.de

are, amongst others, the large space requirement for conventional biofilters as well as the, at times, poor long-term stability of the degradation process. Biological processes are also often difficult to adapt to fluctuating operating conditions such as fluctuating pollutant concentrations and compositions.

Therefore extracted air flows that contain VOCs are usually treated in the processing industry through the use of thermal processes, such as Thermal Post-Combustion (TPC). As the largest volume of the extracted air flows that contain VOCs has a comparatively low pollutant load, this can become an extremely high energy and operating cost-intensive process under certain circumstances.

By using a solution from centrotherm clean solutions, it is possible to ensure comprehensive biological decomposition of organic pollutants from waste gases and wastewater in a multitude of applications, whilst also taking into consideration the different system requirements. Examples of the possible applications

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Clean gas

Clean gas

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Rinsing water (circulating)

Filter bed with biofilm

Filter bed with biofilm

Nutrient salts

Raw gas

Rinsing water (circulating)

Raw gas Nutrient salts

Fig. 2: Biological waste air purification using a bioscrubber, in which pollutants absorbed in water are biodegraded in a separate module

Fig. 3: Biological extracted air purification using a biotrickling filter, in which both absorption and the biological degradation of the pollutants are realised within a single module.

are the treatment of VOC contaminated extracted air flows from paint shops or the semiconductor or chemical industries as well as the reduction of the Chemical Oxygen Demand (COD) of organic wastewater from the food or cellulose industries. The CT Eco process can also be used for the removal of odour-intensive substances during ground or process water treatment. As most of the organic substances are biodegradable when special microorganisms are used, this process is used mainly without the need of chemicals and is distinguished by a broad range of applications as well as low operating costs.

The CT Eco process uses a carrier material made from highly-porous polyurethane foam bodies and it is additionally doped with active carbon to further enlarge the surface (Fig. 1). It also has a film of bacteria that is able to absorb the pollutants and to metabolise carbon dioxide and water. The microorganisms use the pollutants as a food source. Other nutrients essential for bacterial growth are dosed in as required. During operation, a bacterial culture adapted to the relevant conditions is formed, by which a large number of organic pollutants can be degraded. The active carbon coating on the PU carrier material provides optimal living conditions for the bacteria to fully develop their biological activities.

High degradation rates in a small space are made possible by this.

The activated carbon also has a sort of buffer function: Pollutant peaks are first adsorbed on the activated carbon surface and they are then degraded by the microorganisms in situ over an extended period of time. At the same time, this buffer also causes the bacteria to survive without external pollutants over a long period of time. The CT-Eco method solves previous biological plant problems as it works with microorganisms suspended in a solution or immobilised on non-porous carrier materials. Decisive advantages are the high space/time yield and the resulting compact design of

the plants as well as the plant’s huge tolerance against process fluctuations and downtimes.

The plant’s modular design also makes it possible to customise the process to the specific application. By combining different modules, the plant can be designed both as a bioscrubber for extracted air purification as well as a biofilter for treating organically polluted wastewater. Biological extracted air purification is realised using a bioscrubber, in which pollutants are absorbed in water and subsequently biodegraded in a separate module (Fig. 2).

A biotrickling filter can also be installed, in which both absorption and the biological degradation of the pollutants are realised within a single module (Fig. 3).

By using the most extensive circulation possible, the media consumption of the plants is restricted to small amounts of fresh water, which are needed to compensate for evaporation losses as well as electricity for driving the air extraction fans or wastewater pumps. A nutrient solution for the bacteria normally has to be added in order to bridge longer downtimes. The customer also needs a requirements assessment as part of the project, whereby a material balance will be prepared and through additional analysis if necessary, and the application as well as the local conditions will be discussed. Only then can the project planning and design of the plant, the selection of the appropriate bacterial culture as well as the planning and definition of the structural measures be undertaken. Finally, a demand report will be drawn up and a mobile test plant with all previously clarified conditions will be put into operation for a few weeks in order to ensure that the planned implementation meets the requirements and the required wastewater and extracted air purification will also be realised under real processing conditions. The trial operation can simultaneously be used to adapt the design and operating parameters for the later construction of the large plant in a process-specific and customer-specific manner.

Once this has been satisfactorily completed, the detailed planning and construction of the coordinated CT Eco plant at the customer’s site can start. Centrotherm clean solutions has a worldwide network of highly-trained service staff and process specialists for commissioning as well as any maintenance or repair work that might be needed.

A high degree of automation as well as intelligent communications between the plants with customers’ on-site process or factory control systems have already been implemented as standard components. This ensures that the plants always work at their optimum operating points and that the operating and maintenance effort is minimised. Further improvements regarding energy efficiency, e.g. through energy recovery measures as well as processes for recovering valuable components from extracted gases and wastewater flows, are the focus of future developments. A CT Eco plant for wastewater purification is shown in Fig. 4.

Fig. 4: CT Eco plant for biological wastewater treatment

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Development, Production and Testing of Nonwovens for Filtration Use Report from the 2017 Filtrex conference H. Lyko* For the first time, the Filtrex conference was held in Geneva at the same time as the Index exhibition. The European nonwovens association “Edana” was the organiser of both the trade fair and the lecture event. Some of the conference and accompanying “table-top” exhibition participants appreciated the proximity to the Index exhibition as being an upgrade of filtration topics within Index, in which filtration is just one amongst many nonwoven applications. Pierre Wiertz, the managing director of Edana, welcomed 136 conference participants to a programme that included a total of 23 presentations covering air pollution and health, fibre and filter media, equipment, filter media testing and quality assurance. For the first time the winner of the Filtrex innovation award was chosen and awarded the prize as a special conference highlight.

1. Introduction Nonwovens are used both for gas and air filtration as well as liquid filtration.

Innovations in this sector are often the result of the changing requirements placed on specific applications. One of the most important drivers of filter and filter innovations is the air pollution found in many regions of the world and the resulting negative effects on human health. A keynote speech as well as an entire series of lectures were dedicated to this topic at this year’s Filtrex conference. The energy efficiencies of various filter media were another important aspect. Other sessions focused on various fibre production options, material web quality checks run during production as well as the subsequent checks on the filter medium or filter element as well as application-oriented filter media development. An analysis of the global filter market as well as a detailed look at the initial experiences gained from the new ISO 16890 standard for air filter testing completed the programme.

summary of the interrelationships between air pollutants and a variety of health impairments is given in the publication by Thurston et al. /1/. A distinct cyclic relationship exists between the air pollutants that people are exposed to, the effects on the health and mortality of individuals, the impact on public health (mortality and economic consequences) and the policy conclusions to be drawn from it. Adopting regulations for the control and reduction of emissions will directly affect the quality of the air that the population is exposed to.

Air pollution is caused by an orchestra of particles of different sizes and chemical or biological activities, gases and volatile hydrocarbons. As we do not have a specific type of air pollution, neither do we have a single, all-embracing solution to the problem. For places where there are public air measuring stations, the current PM10 and gaseous air pollution values can be found at: www.aqicn.org. The African continent can be recognised as

a predominantly white spot on the map, with extreme air pollution problems as shown by the separate studies from Accra (Ghana) as well as Teheran (Iran). The fact that more stringent statutory regulations have actually resulted in improved air quality was explained using various examples. Künzli described the argument that air pollution is the price to be paid for economic development as nonsense, pointing to the latest World Bank study covering air pollution costs /2/.

The measurement of mass particle concentrations as shown in Fig. 1 is the standard. However, in his lecture Dr Andreas Mayer, a director of the Swiss company TTM, described the current state as metric chaos, because the various official metrological definitions are, on one hand not comparable or even interrelated and on the other hand, air quality cannot be described in relation to ultrafine particles from vehicle emissions. On the basis of various comparative measurements between the

2. Effects on health caused by air pollution Prof. Nino Künzli, director of the Swiss School of Public Health (SSPH+) and head of the Epidemiology and Public Health department at the Swiss Tropical and Public Health Institute (TPH), gave the keynote address about the connections between air pollution and health and showed that airborne pollutants affect not only the airways but the pulmonary functions as well. Numerous studies have deduced a 1 - 2% increase in the number of deaths caused by air pollution with each increase of the PM10 value by 10 μg/m3.

The most up-to-date and comprehensive * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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Fig. 2: New micronAir blue automobile interior air filter with four differen media layers for separating fine dust, allegens, fungal spores and odours (Image: Freudenberg Filtration Technologies)

number concentrations and PM2.5 mass concentrations, it was found that no conclusions could be drawn between PM2.5 mass concentration and number concentrations of the same size class. The particle size distribution in exhaust gases (both diesel and petrol engines) have maxima of around 100 nm. As a result of the steady improvements in diesel engines (from Euro I to Euro VI), the particle mass concentrations in the exhaust gases have drastically decreased, but not the number of particles. More severe limit values require a shift to number concentrations anyway, so one does not have to set limit values that lie below the measuring threshold for mass concentrations. Mayer also pointed out that it is not just number concentrations but also the chemistry of the particles that are decisive with regard to the harmfulness.

Welding processes are well-known in industrial workplaces as being sources of ultrafine particles. Welders and people in surrounding workplaces are exposed to a mixture of particles with different chemical compositions and they include copper and zinc. The effects on health caused by these emissions are the research topic of Thomas Kraus, Professor of Occupational Medicine at RWTH Aachen. In order to study the effects of specific welding methods on human health without using a background aerosol, laboratory tests were carried out on subjects who volunteered to be exposed to welding fumes of 2.5 mg/m3 over a period of 6 hours. Blood, urine, nasal mucosa and sputum, etc., from the subjects were all examined afterwards and the lung functions were also tested.

Accordingly, the inhalation of zinc and copper lead to an inflammatory reaction after 24 hours and which of the two metals was the main cause of this reaction was studied through systematic selection of the welding processes. Both metals showed inflammatory potential, but copper was

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the highest. Considerable attention has been paid to the results as exposure measurements taken after pure NO2 was used in filtered air did not shown any reactions in the subjects. As NO2 is the diesel exhaust gas component currently being targeted, the question of its harmfulness was taken up again in the subsequent discussion.

Kraus speculates that NO2 is only a marker substance for another harmful exhaust gas component. Prof. Künzli also expressed the assumption that this gas increases the harmful effect of particles due to its oxidative effect.

Dr Kirsten Sucker from the Institute for Prevention and Occupational Medicine of the German Statutory Accident Insurance also spoke about their research into odours in interior spaces during this session. The details can be found in Article /3/.

3. An insight into the global filter market The filter industry is a customer for technical fabrics and nonwovens. Some manufacturers of integrated filter elements also have their own production capacities for nonwovens and / or are involved with partners in R&D with regard to new filter media. Being a well-versed expert in this industrial sector, analyst and specialist author Adrian Wilson gave interesting insights into the structuring of the filter industry in the second keynote speech and also named the nonwovens industry’s most important customers. This information was partially included in the whitepaper published for Index as well /4/. The filter market took an approx.

11% share of the nonwovens market and this came to more than 900,000 tonnes in 2015. The megatrends within the global filter industry are the demands for pure air and clean water - which are also driven by stricter legal requirements - as well as the increasing requirements regarding the separation of ultrafine particles from liquids

in the processing industry, hot gas and diesel exhaust filtration as well as energy efficiencies covering filtration processes in general. The market for nonwovens and filter elements is subject to constant transitions resulting from various company mergers or acquisitions and this has led to production capacities and market shares becoming highly concentrated. According to Wilson the global filter industry is extremely fragmented as about 40% (> $ 20 billion) of the total turnover is generated by ten corporations. He said that the current 10 global market leaders for filter products are (in descending order) Mann + Hummel, Cummins Filtration, Pall Corp./Danaher, Parker Hannifin/Clarcor, Donaldson, Mahle (whose industrial filtration division has been part of the Filtration Group since August 2016), 3M, Pentair Flow and Filtration, The Filtration Group and Camfil.

4. Filtrex innovation award For the first time the Filtrex Innovation Award was awarded for a new development in the filter media and filter media production sector. A total of eight companies applied for this award in advance. The five nominated candidates were given the opportunity to present their innovations in a ten-minute presentation. The award winner was then determined through a secret vote taken by the conference participants.

The nominated products were the Statguard filter medium from Ahlstrom, the Nanofics plasma coating process from Europlasma, the micronAir blue cabinet air filter medium from Freudenberg, the three-layer hybrid filter medium from Johns Manville and the sawascreen enAIRsave bag filter medium from Sandler.

The Statguard conductive filter medium, presented by Jan Kaukopaasi, reduces the risk of fire and explosion during industrial dust removal. The setting up of the specific properties of the cellulose-based medium was realised through the use of a wetlaid process. This process permits various properties such as the flame retardant finish, nanocoatings and high conductivity to be combined as opposed to dry nonwoven fabric production. The filter medium can also be folded on a rotary folding machine without having to use adhesives and this results in a self-supporting folding structure.

The micronAir blue interior automobile air filter medium from Freudenberg consists of four layers and it also retains allergens and microspores from fungi mould in addition to fine dust and odours.

Alexander Oelsner took over the brief product presentation in the nominees group and Uwe Häfner also had the opportunity to describe the history of this medi-

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um and the experimental details in a later lecture. As Häfner explained, the new VDI 6032-1 guideline recommends that allergic persons should have their car’s interior cabin air filter replaced twice a year. This shows the need for these filters to be upgraded to attain improved allergen separation. This requirement also exists with regard to ventilation system filters. A special challenge that arose when selecting suitable filter media was to produce a suitable test dust with dry, free-flowing and non-clotting particles that also had a high allergy potential. The test dusts also had to have reproducible particle and allergen distribution. Generally accepted A2 or A4 test dust was chosen as the carrier dust to be used for the air filter test.

After tests were carried out using a series of test substances recommended by physicians, freeze-dried epithelial cells for cats were also chosen as the suitable allergen particles. Further tests were carried out using cladosporium cladosporoides fungus spores, which are widely distributed throughout nature. The retention capacity of the tested filter materials against the allergens was determined using the ELISA (Enzyme-Linked ImmunoSorbent Assay) process. The retention capacities of the filter media that were tested against the allergens were not always the same as those for the mineral test dust. A higher retention of allergens was measured for one of the tested media than that of mineral dust.

Extensive preclinical studies were carried out on media samples in the laboratory as well as on a prefabricated filter element used in an air conditioning system after the suitable media was chosen. Clinical trials were carried out afterwards on subjects allergic to asthma or colds. The subjects were placed in a closed mobile test chamber that was aerated by a ventilation system in which the filter was installed. The test was successful as none of the subjects showed an allergic reaction.

The Nanofics plasma coating process from Europlasma had already been awarded various prizes before this nomination.

Peter Martens gave the brief process presentation. In this process all kinds of textiles, including filter media or prefabricated filters, can be treated to be hydrophilic or hydrophobic. The particular advantages are that in contrast to immersion or coating processes, no water is used as a solvent and the consumption of the chemicals, which cause the functionalisation of a surface, is less by a factor of 4 or more. Auxiliary chemicals such as cross-linking agents are not required either. Eva Rogge, the R&D manager at Europlasma, showed in a later lecture which plant portfolio is already available for low-pressure plasma coating and the product groups that they are used in. PlasmaGuard and Nanofics

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Fig. 3: Marines Lagemaat (centre), director of Technology and Research at Edana, presents the first Filtrex Innovation Award to Alexander Oelsner (left) and Uwe G. Häfner (right) from Freudenberg (Image: Freudenberg Filtration Technologies

110, which are used for the hydrophobic treatment of sports and outdoor clothing or in the electronics, medicine and filtration sectors, enable processes with water-repellent functionalisation to be used without having to use any controversial chemicals such as PFOA (PerFluoroOctanoic Acid) or PFOS (PerFluoroOctaneSulfonic acid).

Roger Eckrich, from Johns Manville, presented the nominated three-layer hybrid filter medium made from micro glass-fibres and synthetic fibres. This development means that the stability of a synthetic medium could be combined with the high separation efficiency of glass fibre media.

The fragile glass fibre medium made from non-biopersistent glass is coated with a synthetic fibre medium on both sides here (see Fig. 4). The synthetic fibre backing is also used for pre-filtration and as a droplet separator, which means that the medium can also be used in moist ambient conditions. The upper layer on the other side is a high-loft medium that increases the dust intake capacity overall without appreciably increasing the pressure drop.

As compared to a pure synthetic filter, the hybrid medium exhibits a pressure drop that is stabilised at a lower level as well as a higher dust absorption capacity of 75%. The development was carried out together with Camfil, the Swedish filter manufacturer, whose chief designer, Richard Ringström together with Roger Eckrich, presented details of the medium’s production and properties during a later presentation. The hybrid filter medium was designed as a pocket filter. According to ISO 16890, its separation efficiency is characterised by ISO ePM1 60% (this corresponds to Filter class F7 as per EN 779).

The sawascreen enAIRsave bag filter medium from Sandler is a purely synthetic medium that has been developed with a special focus on improved energy efficiency. The inflow into this multi-layered filter medium, which has graduated fibre thicknesses, is from the coarser side. The finest fibres are less than 500 nm thick and form the last layer on the discharge side. This design enables high separation efficiency to be realised against PM1 and

Fig. 4: Cross-section of a three-layer hybrid filter medium (Image: Johns Manville)

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Fig. 5: Arrangement of light sources and cameras in the EasyInspect system for the online inspection of flat media (Image: Dr. Schenk GmbH Industriemesstechnik)

PM2.5 particle fractions, which can both be measured using a glass-fibre medium.

The fact that all of the medium’s layers are available for storing dust particles results in a reduction in the filter surface needed for a specific quantity of dust. This means that over time the finest layer absorbs the last dust particles, yet the dust accumulation in the coarser layers does not seem to have a serious effect on the pressure drop and the pressure drop increase during the dusting is less than that in conventional media made from synthetic fibres or micro glass-fibres. This was documented using the energy indicators determined in compliance with ISO 16890. Further development work details can be found in /5/.

The conference participants chose the micronAir blue filter media from Freudenberg as the winner of the first Filtrex Innovation Award (see Fig. 3).

5. State of the new ISO 16890 test standard The change from EN 779 to ISO 16890 allows a filter’s efficiency to be directly specified against the PM1, PM2.5 or PM10 fractions during the testing of air filter media. This makes direct selection of filter media possible based on the concentrations of these particle fractions present in the outside air and the required interior air quality (see /6/ as well). Thomas Caesar, from Freudenberg, is one of the fathers of this new standard and he gave an insight into the test chart and the calculation of the mean fraction separation efficiencies, which also include typical particle size distributions for both urban and country air. The preceding EN 779

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Fig. 6: Online web quality control using the EasyInspect optical inspection system (Image: Dr. Schenk GmbH Industriemesstechnik)

standard will finally be withdrawn in all European countries in July 2018.

Chris Ecob, technical director at Camfil, emphasised the benefit of ISO 16890 as an international standard that is that it facilitates global trade. With the explicit consideration of the PM1 fraction in this standard, it becomes possible to select filters with which the air in interior spaces will be improved, especially with regard to ultrafine particles. With the new standard it will not just be the separation efficiency of filters that will be classified according to new criteria. The classification into energy classes, which is based on filter classes according to EN779, is also omitted and the Key Energy Performance (KEP) number is introduced instead and this does not specify an energy class, but is actually an individual measurement for each air filter.

6. Filter testing and quality analysis during the production of nonwovens In classical filter testing a filter medium or a prefabricated filter element sample is inserted in a test system. The test procedures are implemented either according to the standards applicable to the corresponding filter element or according to a user’s special requirements. Palas GmbH, located in Karlsruhe, specialises in the production of components and systems for air filter testing. Sven Schütz presented the range of test systems and listed the test conditions needed for specific air filter applications. Specific test systems and task details can be found in /7/.

Dr. Schenk GmbH supplies automatic optical inspection systems for various flat media such as glass, plastics, paper, screens and touch panels, fabrics and nonwovens. Hans Örley described the design and functionality of the camera-based EasyInspect and EasyMeasure systems designed for on-line quality control. EasyInspect detects defects such as foreign body inclusions or macroscopic defects (cuts or cracks) in a material web or a coating. As it is difficult to image a defect against the surrounding medium using simple high-contrast fluoroscopy systems, the medium is illuminated from above and below so that a transmission and reflection combination results in a sharp camera image. The backlighting adapts to the material (ABI = Adaptive Background Illumination). Another technology that is used in conjunction with ABI is “virtual X-ray” technology that uses visible light. LEDs with extremely high light intensity are used to illuminate the material. These different methods are combined with a camera (or series of cameras) through MIDA (Multiple Image Defect Analysis) technology. Fig. 5 shows a component arrangement diagram and the technical production implementation is shown in Fig. 6.

The EasyMeasure system is used to determine material parameters such as surface weight, material homogeneity and layer thicknesses or the variations in layer thicknesses (cloudiness). It is possible to derive the surface weight from the light transmission up to a value of about 300 g/m2 directly using a high-resolution grey-scale.

Online pressure drop monitoring also provides filter media manufacturers with

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the option to optimise their production.

Vesa Kukkamo, vice president of the Finnish company ACA Systems presented such a system for online pressure drop monitoring. It is based on the Permi system, which was also developed by ACA and has been proven in many permeability measuring applications (see Figs. 7 & 8).

The measuring head, the area and the pressure at the inflow side are adjusted (these adjustments depend on the medium that has to be measured), so that a stable measurement is realised. The pressure drop for the measured volumetric air flow is calculated using the values given for the pre-pressure and the measuring area.

The correlation of the pressure drop value measured online together with data from the laboratory measurements showed good conformity (R2 = 0.9797 in the example shown here). The system can be installed either in a permanent position or be moved across the width of the medium (for scanning). It can measure pressure drops ranging from 1 - 2,500 Pa at temperatures up to 150°C. 7. Application-oriented filter development In addition to the hybrid filter medium from Johns Manville, other product

Fig. 7: Air permeability measurement principle, where the time-dependent pressure drop is calculated from the volumetric air flow (Image: ACA Systems)

developments were presented that were specifically designed to meet the increasing requirements placed on specific applications. Bastian Keil, director of global distribution at Hollingsworth and Vose, addressed the 2015 guideline published by the WHO, whereby the annual average for the internal concentration of the PM2.5 fraction should be 10 μg/m3 and a 24 hour average of 35 μg/m3 should never be exceeded. The simultaneous requirement is that new buildings should also be CO2 neutral from 2020 onwards. These two

requirements are realised through using filter elements with increased surface densities with media with lower pressure drops, whereby no trade-offs are wanted with regard to the separation efficiency and pre-filtration is not to be dispensed with either. Keil presented the next generation of this pocket filter medium using the NanoWave LM medium, which has a different support structure as compared to the previous generation. This backing has a 14% reduced pressure drop and this increases the filter medium’s service life.

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Fig. 8: Online pressure drop measuring of the material web during continuous production (Image: ACA Systems)

Thomas Heininger, responsible for the development of automobile interior filters at Mann + Hummel, emphasised that cabin air filtration is dominated by electret media, but they lose their electret effect through the effects of moisture. This leads to a dramatic drop in the media’s performance over a typical service interval of 2,000 km. The solution to the problem is nanofibre media as the nanofibres do not cause an extreme increase in the pressure drop. The dust absorption capacity must also increase with the separation efficiency if the service interval is not to be shortened. The filter was installed in a test vehicle so that the long-term behaviour of this new type of cabin interior filter could be studied. This filter was removed and tested in the laboratory after a specific time had elapsed. It could be shown that the separation efficiency for 100 nm-size NaCl particles decreases far less quickly over this mileage than with electret filters.

Improved activated carbons were used to improve the gas elimination process. A new filter medium can contain up to three layers of different selectively activated carbons. The laboratory measurements taken when using different test gases were successful whereas the field measurements still had to be made at the time the lecture was given.

Filtration at gas turbine inlets plays an important role with regard to the operability and the service life of the turbines as well as the overall energy efficiency.

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Ahlstrom provides usable media for this, which range from cellulose/polyester blends, synthetic media, glass-fibre media, nanofiber media up to membranes. Jan Kaukopaasi described the requirements whereby turbine air filters must retain droplets, salts and any organic material to prevent abrasion, corrosion and biofouling, but this also depends on the ambient conditions. The trend is towards synthetic media because they are less swellable and more stable.

With filter media development, they revert to using their own filter test stand in Finland, where a large number of realistic filter loads can be simulated. The usual test dusts proved to be much too course for testing turbine air filters, so soot had to be used. Kaukopaasi also presented the three-layered Trinitex medium, which is a new development and it is a medium produced using a wetlaid process with tiered pore sizes within the three layers.

The results obtained from the filter testing were produced after several cycles at 80% humidity with subsequent soot loading.

The filter medium proved to be particularly water-repellent and exhibited a lower pressure drop increase than other synthetic media when combined with moisture and soot. The aged filter media had the highest quality factor amongst all of the media that were used.

8. Innovative media, ultra-fine fibres Welspun India is a globally-operating Indian nonwovens manufacturer with 26,000 employees and agents in 50 countries. Their representative, Lalit Joshi, gave an insight into the production of water-jet-bonded nonwovens manufactured using the Spunlace process, which produces air and liquid filter media for motor vehicles. Up to four different fibre types can be produced simultaneously also with up to four layers and with tiered porosity in the company’s own production facility. The achievable surface weights lie between 15 and 550 g/m2. Air filter media for two-wheelers, hydraulic and motor oil filters are produced using this process.

JX Nippon ANCI, a French company that is part of the JX Nippon Group, specialises in the production of very thin, porous polymer layers. Marc Levillain, the CEO, described the CLAF process that was invented at the end of the 1970s, in which a polymer film is stretched and fibrillated and onto which a second layer is added, stretched in the orthogonal direction and the fibrillated layer is then laminated. Two mutually orthogonal and stretched fibre layers are superimposed on one another and thermally bonded in the new Milife medium. One finds

oneself somewhere between meltblowns and nanofibres with regard to the fibre fineness. In a next development stage 200 - 500 nm fibres will be produced using laser-assisted supersonic stretching, i.e. multifilament yarn enters a vacuum chamber, is melted using a CO2 laser and is then divided up by an airflow with a supersonic velocity. This results in an ultra-fine fibre distribution as compared to meltblowns.

The particle separation efficiency is higher than that of meltblowns of the same surface weight and can still be improved with heat treatment. It can be assumed that this medium can replace an air filter membrane if a suitable fibre density and heat treatment are used.

Tobias Thiem, from Norafin, reported on the production of sintered metallic nonwovens. A polymer-fibre nonwoven is used here and it is loaded with metal powder. The metal particles are deposited on the polymer-fibres. The metal particles bond together and the polymer fraction is burned away during the subsequent sintering process and the nonwoven’s original spatial structure is largely retained.

Loading of the polymer nonwoven with metal particles can be carried out using either dry or wet processes. The latter enables a higher particle intake through the nonwoven, which results in a denser filter medium. The sintered metal nonwovens show a much lower weight and a much higher air permeability than that of a sintered metal filter produced directly from powder with comparable particle separation efficiency.

Fibres form the basis for filter nonwovens, especially fibres with submicron diameters, and nanofibres have also gained in importance in recent years. Adrian Slater, from Lenzing, described the fibrillating of their company-produced Tencel cellulose fibres as an option for producing submicron fibres. Fibrillation occurs in a type of modified pump, whereby the proportion of the fibrils and their diameter distribution can be adjusted over several cycles. The process creates a structure of oriented nanofibrils and crystalline regions. Using microfibrillated cellulose as a blending material in nonwovens or as a fibre support means that higher separation efficiencies can be realised. This also provides an option for producing glass-fibre free HEPA filters.

Borealis is the second largest polyolefin producing company in Europe and it also actively optimises its own products for the production of meltblowns. Gustaf Tobieson and Henk van Pariedon reported on experiments carried out at the meltblown pilot plant at the R & D headquarters in Linz, Austria, with the aim of producing PP fibres that are finer than those currently available. The typical nozzle

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diameter for the polymer melt is 0.4 mm. The fineness of the fibres can also be influenced by the processing speed, the air velocity and the melt temperature (melt viscosity). However, these options are limited to the extent that a reduction in the production speed can be uneconomical, an increase in the air velocity will hinder the positioning of the fibres on the substrate and a severe reduction in the viscosity due to a temperature increase also increases the risk of shots forming in the nonwovens. The solution to these problems is a new polymer formula (not mentioned) in which the tendency to form shots is reduced. This allows the polymer to be processed at an elevated temperatures of 15° - 20°C which creates finer fibres.

Elmarco provides equipment for coating media with nanofibres using a nozzle-free electrospinning process. Lukas Plistil reported on the study into the effects of the discharge process stipulated in the new ISO 16890 standard that uses isopropanol on this type of nanofibre media. This standard stipulates that a special chamber must be used for the discharging of a medium or a filter element using IPA vapour. The question here is whether this method could affect the bond between the nanofibre coating and the carrier medium or a finished folding structure made from such a nanofibre medium. It should also be shown that nanofibres do not lose their filtering effect during discharging as compared to electret media. The experiments using PA6 nanofibres on PET substrates were carried out in the Blue Heaven Technologies’ laboratories in Philadelphia. It was found that the discharge hardly reduced the fraction separation efficiency and the high dust absorption capacity remained.

Nanoval, a company from Berlin, originally specialised in the production of metallic nanoparticles and is a newcomer in the filter industry. Christian Gerking described how the nanoparticle production process that is based on injecting molten metal from a Laval nozzle has been successfully applied to polymer melts and spinning solutions. Starting from a spinning nozzle, which has a much larger diameter compared to the meltblown process, the polymer-liquid enters the Laval nozzle together with a faster enveloping airflow. The thread emerging from the spinning nozzle is split up by the relatively higher air velocity and fluid dynamics in the Laval nozzle. The result is fibres ranging in size from 1 - 20 μm. The production capacity is therefore about 15 times greater than that of a meltblown process. Meanwhile, nonwovens with low surface weight fluctuation margins can be produced using this method. The process is also suitable for embedding metallic nanoparticles in polymer-fibres, i.e. in order to produce magnetisable or permanently charged media. The company is looking for a competent partner from the industry in order to optimally use fibre production for filter media production. The company also has its own process for spinning cellulose from lyocell solutions. A pilot plant for 300 mm width webs exists at the Thuringian Institute for Textile and Plastics Research (TITK) for this purpose. This makes it possible to process cellulose from recycled waste paper.

Literature: /1/ G. D. Thurston, H. Kipen et al. (in total 24 authors): A joint ERS/ATS policy statement: what constitutes an adverse health effect of air pollution?

An analytical framework; European Respiratory Journal 2017, 49:1600419, doi. org/10.1183/13993003.00419-2016 /2/ Int. Bank for reconstruction and Development/ The World Bank: The Cost of Air Pollution – Strengthening the Economic Case for Action, 2016, s. www.documents.worldbank.org /3/ H. Lyko: Air and Gas Filtration R&D, F&S International Edition 2018 (this issue) pp. 54-57 /4/ A. Wilson: Nonwoven filter media – Getting to know the customers; Whitepaper at Index 2017, 4-7. April, Genf, Schweiz, index17.org /5/ L. Summa: Energieeffizienz im Fokus von Markt und Prüfnormen – Weiterentwicklung synthetischen Filtermedien im Hinblick auf veränderte Leistungsanforderungen, F&S Filtrieren und Separieren 30(2016) Nr. 5, S. 286 - 290 /6/ H. Lyko, T. Stoffel: Testing of air filters in compliance with the new ISO 16890; F&SGlobal Guide of the Filtration and Separation Industry 2016-2018, pp. 215-220, ISBN9783-00-052832-3 /7/ H. Lyko: New developments and results in the field of air quality monitoring, filter testing and nanoparticle measuring technology – Report from the 30th Palas aerosol technology seminar, F&S International Edition 2017 pp.58-65.

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Air and Gas Filtration R&D Report from the 8th IUTA filtration day H. Lyko * Filters used in ventilation systems, room air cleaners and compressed air filters are all the focus of current research projects at IUTA. In detail, the 8th filtration day, which was held in November 2016 at the institute’s premises, covered the combined separation of particles and noxious gases, the identification of the causes of indoor air pollution and last but not least, the energy efficiency of filters and the digitization of filtration solutions within the framework of the Internet of Things. The high level of interest shown by the trade visitors was also reflected in the number of exhibitors, which was higher than that of the previous year. Prof Dieter Bathen, chairman of the institute, welcomed a total of more than 130 external participants, all of whom were comprehensively informed not only by the lectures, but also by the accompanying exhibition of cooperation partners from the industry.

Indoor air quality Indoor air quality is influenced by the quality of the air supplied from the outside and, to a large extent, by the indoor activities as well. Protection against possible hazardous substances in the working world is controlled by workplace limits and regulations with regard to appropriate active and passive protective equipment, but there are no mandatory limit values for air pollution from odours. Dr Kirsten Sucker, from the Institute for Prevention and Occupational Medicine of the German Statutory Accident Insurance at Ruhr University in Bochum, is concerned about odours in interior workplaces. She used various substances to show that perceptual threshold and workplace exposure limits (MAK values) can be quite different and that it is necessary to evaluate the boundary between the mere perception of an odour and an actual irritant. Two concentration guidelines, RW I and RW II, currently exist for indoor areas. RW I is a precautionary benchmark below which no adverse health effects can be expected from a substance, even with lifetime exposure to it. RW II is an effect-related value and if it is exceeded, then a health hazard has to be assumed and there is an immediate need for action for health safety reasons. Hygienically undesirable loads that exceed the normal level can occur in the range between both values and these should be reduced for precautionary reasons. RW I and RW II values were determined by the Interior Guidelines Committee for a great number of substances and they can be called up from the Federal Environment Agency’s website at: www.umweltbundesamt.de. The values were determined by animal experiments in which rats were used and the assumption is that humans and rats react with the same * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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sensitivity. There also exists a draft of the definition of odour conductance values and these were determined by means of olfactory measurements taken with the help of test persons /1/, whereby so-called trained “average noses” are selected as the test persons. The provisional vGLW odor control values were defined for this purpose and they were calculated as being the multiple odour threshold ODT50 (Odour Detection Threshold = an odour concentration that triggers odour perception in 50% of the test subjects): vGLW I corresponds to the six times the odour threshold and is defined as an “odour-conspicuous” concentration, whereas with 48 × ODT50 a concentration is produced that is perceived as being “odorous and considerably irritating”. In the current “Effects and evaluation of odours in indoor workplaces” research project, the air quality in office workplaces will be examined more closely through interviews and evaluations of complaints and health impairments.

With regard to the fine dust load in indoor areas, causes such as externally

introduced particles, dust on and from clothing, hair or skin flakes, dust brought in by pets and last but not least, dust produced by open fireplaces are all generally plausible causes. The extent to which certain indoor activities can have an influence on the type and level of particle pollution and the health of humans has been examined by IUTA as part of the EPIA study (Effects of Particles from Indoor Activities). Bryan Hellack described the test and exposure chamber, in which activities such as burning candles, toasting, frying and baking (ready-made pizza), operating a stove, a hot air radiator, an alcohol burner and a gas burner as well as grinding paint containing nanoparticles were carried out. The influence of these activities on the mass, the number concentrations, surface area and the chemistry of particles was measured. The toxicities of collected particles were also determined in vitro and blood pressure and lung function measurements as well as blood analyses and nasal fluids were conducted in test subjects who were exposed to the activities for 2 hours

Fig. 1: Full rows: over 130 external visitors followed the 8th IUTA filtration day lectures [Photo: IUTA e. V. (Photographer: Sabine Kreckel)]

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in order to detect any possible health impairments. With the help of the mass particle concentrations it was shown that the vacuum cleaner, the stove, the burners and the radiator as well as the oven emit rather low amounts of particles, whilst the burning of candles, roasting and toasting lead to high mass concentrations. There were partial differences due to the measurements being carried out with or without a running climate control system and not every candle emits the same amount of particles. The differences could clearly be seen here with the number concentrations.

The high-emitting toasting, roasting and candles sources are particularly relevant with regard to ultra-fine particles <100 nm and organic particles were also present, albeit hardly any soot. The test subjects’ measured health effects were very weak, but present. More specifically, toasting caused an increase in systolic blood pressure, which did not appear with candles or roasting, but the latter activities did show slight pulmonary function effects.

Dr Christof Asbach and his team have been investigating mobile room air cleaners for some time now, in which a combination of particle and adsorption filters separates both fine dust and gaseous pollutants. As room air cleaners are used throughout China, IUTA implemented the measuring in compliance with the Chinese test standard as well. The cleaning performance of these devices for formaldehyde was also determined in the current measurements, as provided for in the latest version of the test standard. It was also determined that different devices with the same particle performance capability showed significant gas elimination differences. The separation performance of the room air cleaners is measured as the Clean Air Delivery Rate (CADR) that is delivered per unit of time. The finer the filter, the quicker the present particulate contamination of the air is eliminated, but the energy consumption increases very clearly with the degree of fine filtration used. In one example it was shown that the change from filter class E10 to H14 (according to EN 779) resulted in time savings of 15% up to the realization of a specific air quality at the expense of an 150% increase in energy consumption.

Due to its charging, an electret filter is able to separate more particles with the same pressure loss. However, the electret effect decreases with increasing filter loading and the mechanical separation capacity increases simultaneously. The effect of these two opposing tendencies on the CADR value of a room air filter was examined during a recent AIF project. The initial results have shown that the contri-

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bution made by the electret effect and the filter aging effect have a greater effect on larger particles because the charge probability decreases with very small particles.

Another question that had to be answered in this project was the transferability of the CADR values determined in the test chamber to real areas. A typical furnished office space was used for this purpose, in which an open window encouraged outside air effects, and the room was equipped with several room air cleaners of the same type and particle measuring devices were positioned in different places. The particle measuring devices determined the Lung Deposited Surface Area Concentration (LDSAC). The room air cleaners were fitted with a new filter as well as an isopropanol discharged filter for the tests carried out in this room.

Transferability of the standard tests to the real areas appears to be possible according to these initial studies.

Industrial Internet of Things (IIoT) The Institute for Industrial Management (FIR) at RWTH Aachen University is researching industrial management in the company organization and company development sectors and is also keeping an eye on technologies for Industry 4.0. Dr Gerhard Gudergan pointed out that these technologies, which have to process huge amounts of data in a short time, are now available. Every relevant component in a process is fitted with measuring sensors whose data must be recorded, analysed and consolidated. The machines have to be networked because people are virtually unable to process this amount of information and to make prompt decisions derived from the data analysis. For the first time ever, more ‘things’ than people were connected up to each other in 2012. The next step after this machine network, which is called the Internet of Things (IoT), is Artificial Intelligence (AI), i.e. machine systems that are capable of making conclusions that up to now have been made by people based on data analyses. This also includes the possibility that machines “learn” their work plans themselves, i.e. they learn to “see” where specific assembly components can be found. Consideration was given to capturing and analysing indoor data for a ventilation system in real time as part of a specific transfer to a filtration topic. This also included filter elements also being fitted with sensors. The IIoT has so far been realized in three projects at Parker, a filter manufacturer, one of which concerns the operation of filters. Dr Jürgen Timmler not only showed how the technical implementation works with the help

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Tab. 1: Comparison of the air filter test standards (released after the presentation by F. Spehl, Vokes Air @ Mann + Hummel)

of a so-called smart filter for compressed air and the company-owned Parker Cloud, but also presented this kind of networking as an opportunity to develop new business areas for customer service (aftersales service). According to its definition, IIoT consists of the incorporation of machines and systems into a network of sensors and evaluation programs. In more detail, the pressure, temperature and volume flow are measured at each filter installed in the compressed air network and the data is then transferred to the cloud via suitable interfaces (gateways) from where it can be analysed either in real-time or offline. As the individual sensors are no longer fitted with displays, the data from the specific measuring points can be read out using smartphones at the gateways whenever necessary. Very small, battery-powered, robust and low-energy sensors (SensoNODE) are used for collecting the data and they are controlled by a microprocessor. The results from the data analysis are used for maintaining and servicing the system at the times and the extent necessary. A question about Parker Cloud’s data security was asked during the subsequent discussion. Several proprietary specifications covering the security of data sources and transmission components were pointed out for this reason and all devices and protocols were certified by the

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company and the network is not publicly available.

Combined gas and particle filtration Frank Spehl, from Vokes Air GmbH, which belongs to Mann + Hummel, reported on the experience gained within his company with the filter qualification according to ISO 16890. He welcomed the possibility, in contrast to the preceding EN 779, to design a filter for a room ventilation system in a realistic manner after considering the external air conditions, because the same reference particle sizes as used in meteorology and medicine are used to classify the filters. However, he also pointed out that the new standard meant a paradigm shift and that the transition from EN 779 might not be so easy with a translation table. The new standard’s test conditions compared to EN 779 can also be found in /2/. The most important aspects of ISO 16890 compared to the preceding standard were presented

by Spehl in the form of Table 1.

Based on a practical example for an office building in Shanghai, it was calculated how to obtain the required degree of separation for this PM class from the known outdoor air quality for a PM class (using data provided by the WHO) and the

required indoor air quality (with an extra surcharge that takes the interior activities into consideration). The corresponding filter can then be directly selected.

Dr Uta Sager, from IUTA, was concerned with the implementation of DIN EN ISO 10121 (2015) covering the qualification of adsorption filters for ventilation systems. The standard describes both the testing of filter media as well as pre-assembled filter elements. The pressure loss, the cleaning capacity and performance are determined for both, and the residual loading after using the test substance and after desorption is measured. In particular, the testing of filter elements is a major challenge, mainly because different filter designs and sizes have to be taken into consideration and due to the filter’s high volumetric flow rates (test volumetric flow = filter’s nominal volumetric flow) and high required test gas concentrations high amounts of test substances must also be provided for the test stand. In addition to the costs and the effort involved, safety aspects such as the protection of the environment from toxic test gases and the protection of the test equipment also play a role, for example, in the case of corrosion caused by measurements made using acidic gases in moist air. This raises a question about under which conditions can the test results from the filter media test systems be transferred to the properties of the readymade filter. The existing filter test rig at IUTA was modified to comply with EN 779 for measuring with gaseous test substances, i.e. breakthrough curves were measured for different test gases using panel and V-filter elements. After comparing the results from this test stand against the breakthrough curves from the media test stand, it was concluded that, among other things, the comparability of the inflow velocity at the filter must also be given. The matching of the incoming flow velocities on the test stand to the values obtained on the real filter produced, for example, congruent breakthrough curves for the toluene and n-butane test gases, but this transferability was not possible when using SO2. This substance dependency will be studied using other substances and other filter shapes will also be included.

Keynote speeches Some of the institute’s other research topics were presented in the keynote speeches. Dr Wolfgang Mölter-Siemens reported on the effect of the re-entrainment phenomena on the qualification of compressed air filters. The experiments and important results have already been described in /3/. The studies into the catalytic low-temperature denitrification

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Ambient air

Noxious gases

Adsorption filter

Humidity and temperature measuring

Dispersal section

Water cascade

Test filter

Pure gas measuring position Mixing chamber

HEPA filter

Differential pressure measuring

Absolute filter

Pressure reducer Blowing column

Particle disperser

Particle

Differential pressure measuring

Dust bunker Compressed air reservoir

Pump

Adsorption filter

Condensation drain Heat exchanger

Volumetric flow measuring

Pump

Filter Condensation tank Pressure reducer

Compressed air network

Condensation drain Exhaust air

Chilling water

Air (no particles) Aerosol Aerosol + water Water Condensation Particle

Fig. 2: Block diagram of the complete plant for studying the catalytic low-temperature denitrification in a surface filter (Fig. IUTA)

using new types of particle-shaped catalyst materials made from manganese and copper oxides on ceramic carriers has also been described in /3/. The heart of the studies is the MMTC 200H filter test stand made by Palas, in which the temperature can be adjusted to 250°C and the relative humidity to 80% (at 90°C). This test stand is integrated into large peripherals (see Fig. 2) that also include the monitoring of all of the gases involved. Dr Margot Bittig was able to present new results that allowed conclusions to be made about the temperature dependence of the catalyst activity, the effect of the filter operation, including cleaning, on the concentration of the nitrogen-containing gases and the effect of the forming of a filter cake.

The timed dependent NOx-concentrations obtained by using catalyst particles as the only particle fraction as well as with the added or dosed test dust were measured.

Therefore an essential criterion for the operability of the process is the formation of a complete filter cake so that no gas can flow through the filter medium without contact to the catalyst. The addition of inert dust can increase the effectiveness here. The filter cake formation also depends on the filter medium.

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Thomas Klamp, from Trox GmbH, concluded the lecture series by considering the energy efficiency of indoor air filters (see /4/ as well). He showed how the energy class is determined according to EN 779 and how the new ISO 16890 determines the KEP factor as a new energy efficiency measurement. The filter class must first be determined according to ISO 16890, as the dust load relevant to the pressure loss measurement depends on the AC Fine test dust for the calculation using Equation 1. According to the lecture, it is proposed to load ISOePM1 filters with 300g, ISOePM2.5 filters with 400g and ISOe PM10 filters with 700 g of test dust (Classification into classes ISOePMx, see /2/).

The KEP value is calculated using the relevant degree of separation ePMx, the mean pressure loss during the dust loading — Δp and a factor C for the effect of the filter geometry: (Gl. 1) The filter medium is responsible for a significant share of a filter’s energy costs and this was proven by comparing the two media. The energy efficiency of a convection filter can also be increased not

only by optimizing the throughflow and the geometry, but also by increasing the area. When selecting a filter, the number of filter stages and the filter medium’s dust storage capacity also play a role in addition to the dust load. With the energy classification according to Eurovent and as in the case of the KEP determination, it is assumed that the entire test dust spectrum is present at the test device, but this is not the case if a pre-filtration stage is installed.

Literature: /1/ Bekanntmachung des Umweltbundesamtes: Gesundheitlich-hygienische Beurteilung von Geruchsstoffen in der Innenraumluft mithilfe von Geruchsleitwerten Entwurf der Ad-hoc-Arbeitsgruppe Innenraumrichtwerte der Kommission Innenraumlufthygiene und der Obersten Landesgesundheitsbehörden zur öffentlichen Diskussion bis Ende Dezember 2015; Bundesgesundheitsblatt 2014 · 57:148 –153 DOI 10.1007/s00103-013-1882-3 © Springer-Verlag Berlin Heidelberg 2013 /2/ H. Lyko, T. Stoffel: Testing of air filters in compliance with the new ISO 16890, F&S Global Guide of the Filtration and Separation Industry 2016 – 2018; VDL-Verlag GmbH, Rödermark, 2016, pp. 215 – 220, ISBN 978-3-00052832-3 /3/ H. Lyko: New developments and results in the fields of air quality monitoring, filter testing and nanoparticle measuring technology; F&S International Edition No. 17 (2017), pp. 58-65 /4/ T. Klamp: Energieeffizienz bei Filtern für raumlufttechnische Anlagen, F&S Filtrieren und Separieren 30 (2016) Nr. 3, S. 151 – 153

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Efficiency and Pressure Drop of Air Filters used in General Ventilation Systems F. Schmidt ¹, T. Engelke ², A. Breidenbach ³, E. Däuber 4 The following article reports on laboratory tests in which air filters aged in real applications or loaded with ASHRAE or A2 test dusts were compared.

1. Introduction The new DIN EN ISO 16890 ”Air filters for general ventilation” test standard replaces EN 779: 2012 [1], which itself will become invalid in Europe not later than July 2018. The most important changes are explained for example in [2].

Even if the test methods are modified once again and the classification system is totally different, the measurements are merely for the qualification and characterisation of air filters under comparable, i.e. reproducible, conditions [3].

Performance data of air filters evaluated in the laboratory in compliance with EN779 are not comparable to the real-time efficiency and pressure drops [4 & 5] as the test aerosols that were used differ considerably from the actual air pollutants with regard to particle shape, particle material and charge state. The extent to which the modified test methods and the assessment of the air filter elements using PM1, PM2.5 and PM10 fine dust classes result in better compliance between the laboratory results and those found in practice, will be studied in a new research project.

The effects of the test dusts that were used were also studied in a research project that addressed the laboratory tests and the results from existing ventilation systems [6]. Whether the test results should be based on ASHRAE test dust (a mixture of cotton fibres, A2 test dust as per ISO 12103 and soot, which is defined in the ASHRAE 52.2 standard regarding composition, grain size and fibre length distribution) or if A2 test dust solely should be used was studied with regard to whether the separation efficiency and the pressure

¹ Prof. Dr.-Ing. Frank Schmidt Nanoparticle Process Technology at the University of Duisburg-Essen Institute for Combustion and Gasdynamics Lotharstr. 1, MF 148 47057 Duisburg, Germany Tel/Fax: +49 (0)203 -379 2780/4453 ² Dipl.- Ing. Thomas Engelke IUTA e.V.; Duisburg ³ Dipl.- Ing. Achim Breidenbach EMW filtertechnik GmbH, Diez 4 Dipl.-Ing. Eckhard Däuber IUTA e.V.; Duisburg

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drop of filter elements during real-time operation can be adequately depicted over the filter’s service life.

2. Testing procedure Testing of fine dust filters in compliance with the standard DIN EN 779 was performed at IUTA’s filter test rig (Fig. 1): - Measuring the initial pressure drop as a function of the volumetric flow rate; - Measuring the DEHS initial fractional efficiency (DEHS = Di-Ethyl-HexylSebacate);

- Measuring the DEHS fractional efficiency at different loading stages using ASHRAE dust (30 g, etc.) up to the final test pressure drop of 450 Pa and calculating the average efficiency for ASHRAE loading for 0.4 μm DEHS particles as a classification criterion; - Measuring the minimum efficiency for 0.4 μm DEHS particles as an additional classification criterion for F7 to F9 filter classes (tested on media samples after isopropanol treatment) as per DIN EN 779: 2012.

Tab. 1: Classification of air filters as per DIN EN 779: 2012

Group

Filter class

Final test pressure difference

Average separation efficiency (Am) of the synthetic test dust %

Average efficiency (Em) with 0.4 μm particles %

Minimum efficiency with 0.4 μm particles %

Course

Fine

Fig.1: Standard rig stand at IUTA (manufacturer: Topas GmbH, Dresden)

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This testing of air filters made from synthetic and glass-fibre media was repeated using A2 test dust as loading dust.

In addition some filters were installed in ventilation systems at the University of Duisburg-Essen and were periodically removed, tested and reinstalled. After aging in real-life conditions, these air filters were installed in the test rig mentioned above to measure their DEHS efficiency.

The filter pressure drops and efficiencies from real-life operating conditions were determined and compared against the standard-conforming filter tests or testing using A2.

In Fig. 2 the fractional efficiency (retention) is depicted at different dust loading stages using ASHRAE dust for three different types of fine filters (two F7 bag filters and one F9 compact filter, cassette).

The initial efficiency of the filter elements was also the lowest efficiency measured during the loading process.

In order to complete the stipulated test procedure, it also had to be verified that the 0.4 μm efficiencies of the isopropanol-treated media samples comply with the classification criterion. The media samples were dipped in isopropanol (isopropyl alcohol, IPA) and dried in order to discharge them. The media samples from the F7 filter made from synthetic material showed a clear reduction in their fractional efficiency after this treatment. The F7 failed the minimum efficiency of 35% and the F9 filters passed the minimum efficiency of 70%.

In Fig. 3 the fractional efficiency of the same type of filters is plotted at different dust loading stages using A2 dust (instead of ASHRAE). Comparable dust loadings were realised. The comparison of the fractional efficiencies using the two different test dusts clearly demonstrates that the ASHRAE dust resulted in a significantly greater increase of separation efficiency in all of the studied cases. The pressure drop after the last loading step using A2 was significantly less than the final pressure drop so that the average efficiency could not be rated as being conforming to standard.

Fig. 4 shows the pressure drop increase for the three filter types plotted versus the separated particle mass divided by the filter area. ASHRAE dust and the A2 dust loading were compared. For example, the F7 synthetic filter was loaded with ASHRAE dust in several loading steps up to the final pressure drop of 471 Pa. The second F7 filter of the same type was loaded with A2 dust, whereby the same dust mass increments as in the loading with ASHRAE dust were realised in each

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Fig. 2: Classification criteria: average efficiency and minimum efficiency, Top left: F7 bag filter (synthetic fibre with electret properties), Top right: F7 bag filter (glass-fibre), Bottom: F9 Compact filter (glass-fibre)

Fig. 3: Efficiency when loaded with A2 test dust, Top left: F7 (synthetic fibre with electret properties), Top right: F7 (glass-fibre), Bottom: F9 Compact filter (glass-fibre)

Fig. 4: Pressure drop developments when loading with ASHRAE or A2

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Fig. 5: DEHS fraction separation efficiencies of a F7 bag filter (synthetic-fibre with electret properties) after ASHRAE, A2, real-time and soot loading compared to a new filter and to IPA treated media samples

Fig. 6: DEHS-efficiencies as a function of particle mass divided by filter surface (F7 bag filter / synthetic)

Fig. 7: Pressure drop increase as a function of particle mass divided by filter surface (F7 bag filter - synthetic)

of the loading steps. The pressure drop at 3,400 m³/h had increased by 379 Pa at the end of the last loading step when ASHRAE dust was used and only by 29 Pa with A2 dust loading as compared to the initial state.

This difference was somewhat less pronounced when glass-fibre filters were used.

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In Figs. 5 to 14, the fractional efficiencies, the 0.4 μm DEHS efficiencies and the pressure drops when loaded with ASHRAE or A2 dust are compared against those that were obtained after aging in real-life conditions [6] for usage periods from 3 up to 21 months. The separation efficiencies

of the new filters and the minimum efficiencies determined on media samples are included as references in the comparisons.

Furthermore, the effect of loading the filters with soot particles was also taken into consideration in the comparative evaluation. In all cases, choosing ASHRAE dust for the loading resulted in significantly greater pressure drops and clearly higher fractional efficiencies than for the filters from the real-life operations.

The results for the F7 bag filter made from synthetic fibres with electret effect are shown in Figs. 5 to 7. The two upper diagrams in Fig. 5 show the DEHS fractional efficiencies for loads of approx. 20 g/m² or approx. 40 g/m². Loading with ASHRAE dust (light blue curve) resulted in a significant increase in efficiency when compared to the new state (black curve).

Loading with A2 dust (dark blue curve) also resulted in an increase in efficiency, whereas loading the filters in the ventilation system resulted in a continuous reduction (green curve) that approached minimum efficiency (red curve). In the lower diagram one can see that loading with approx. 4 g/m² of soot also resulted in an efficiency close to the minimum efficiency level.

The 0.4 μm DEHS efficiency as a function of the related particle mass separated on the filter surface for the different loading cases is depicted in Fig. 6. The three filters, after usage periods of 3.5 months (turquoise dots), 8 months (dark-green dots) and 18 months (light-green dots) in the ventilation system, showed retention values of between 0.27 and 0.38 as compared to the new state. The filters’ electret effect was largely lost during the first 3 months of use. The minimum efficiency for F7 filters was sometimes less than 0.35 (magenta line). The retention value which was determined as the minimum efficiency on the IPA-treated samples (red broken line) is only about 0.23. The ASHRAE (red curve) and the A2 (yellow curve) dust load curves result in unrealistic high values when compared to real-life operation.

Soot loading (black data points) resulted in retention at the minimum efficiency level of approx. 4 g/m², i.e. a discharge comparable to IPA bath discharging is possible just with soot loading. When a loading with A2 dust (orange curve) is carried out after soot loading, then the curve progression is obtained similar to that of A2 loading on the filter in the new state (yellow curve), only moved downwards in parallel, starting from the minimum efficiency level.

Fig. 7 represents the pressure drop of the F7 synthetic filter as a function of the

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particle mass related to the filter surface area for the different cases. Again loading with ASHRAE dust resulted in significant over-prognosis when compared to real-life operation with regard to the pressure drop.

The A2 loading only resulted in a very small increase in the pressure drop, which is similar to that what were shown for filters from real-life operation.

The comparison of the fractional efficiencies for the F7 glass-fibre bag filter are shown in Fig. 8. In the two upper diagrams it can be seen that loading with ASHRAE dust (light-blue curve) resulted in an over-prognosis of the separation efficiency as compared to the real-time load (green curve) of approx. 5 g/m². With A2 loading (dark-blue curve), the efficiency is still roughly equal to the efficiency of the filter in its new state (black curve). A slight improvement in the efficiency of the filters from the real-time operation has been realised in the approximately 40 g/m² loading stage. The efficiencies for both A2 and especially ASHRAE loading are overestimated here. It can be seen in the lower diagram that soot loading (magenta curve) up to approx. 2.7 g/m² resulted in no change when compared to the initial state.

Fig. 9 shows the change in the 0.4 μm DEHS efficiency with increasing loads for the different variants (analogous to Fig. 6). The retention of the four real-life operation filters considered here after 3 and 9 months of use, is around 0.6 as in the initial state. There were slight improvements after 16 and 21 months. The ASHRAE and A2 load retention values are consistently higher, whereby the ASHRAE loading also leads to a pronounced over-evaluation for this type of filter. There was no change when compared to the initial state to be seen with soot loading. The differences lie within the measuring inaccuracy range.

As with the previously considered F7 synthetic fibre filter with electret effect, loading the F7 glass-fibre filter with ASHRAE dust also resulted in significant over-prognosis regarding the pressure drop as compared to real-life operation (Fig. 10). The pressure loss caused by loading with A2 dust corresponds well with that of the filters from the ventilation systems.

The fractional efficiencies for the F9 cartridge filters made from glass-fibres are compared in Fig. 11. The DEHS fractional efficiency curve did not change significantly during real-life loading as compared to the initial state in both loading stages at approx. 2 g/m² and approx. 14 g/m².

Differences between the initial state efficiency, the minimum efficiency determined on the medium and the efficiency of

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Fig. 9: DEHS-efficiencies as a function of particle mass divided by filter surface (F7 pocket filter / synthetic)

Fig. 10: Pressure drop increase as a function of particle mass divided by filter surface (F7 bag filter / glass-fibre)

Fig. 8: Efficiencies of new and loaded filters compared to those of IPA treated media samples (F7 bag filter / synthetic-fibre with electret properties)

the real-time operation filters lie within the scatter range. Error bars have been omitted for the sake of clarity. The retention curve after A2 load is also at a comparable level in the first of the two loading stages; the

ASHRAE load curve is somewhat higher.

In the second loading stage, both the fractional efficiency for the A2 loading and especially that for the ASHRAE loading are at a higher level than is the case with

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Fig. 11: DEHS fraction separation efficiencies of a F9 compact filter (glass- fibre) after ASHRAE, A2, real-time and soot loading compared to a new filter and to IPA treated media samples

real-time operation. Soot loading (lower diagram) shows a gradual improvement when compared to the initial state.

The change in the 0.4 μm DEHS efficiency with increased loading (Fig. 12) for this type of filter shows the over-evaluation for ASHRAE and A2 loading when compared to real-time operation. In the case of soot loading the slope corresponds to that of the ASHRAE loading curve.

Loading with A2 dust (orange curve) after soot loading resulted in a parallel upward shifting curve as compared to the filter’s A2 loading curve in the new state (yellow curve). The pressure drop change (Fig. 13) for the real-time operation filter is well represented by the A2 load. The

ASHRAE loading and especially the soot loading resulted in clearly steeper curve progression. The pressure drop curve for A2 loading after soot loading is shifted upwards in parallel to the curve produced without prior soot loading.

In addition to the described sequential loading of the filters with soot and A2 dust, the simultaneous addition of soot and A2 was studied as a further neutralisation and loading method. This study was only carried out using the F7 bag filter made from synthetic fibre material with electret properties, as this filter exhibited the most significant changes to the filtration properties during the loading. In Fig. 14 the 0.4 μm DEHS efficiency is shown in the

Fig. 12: DEHS-efficiencies as a function of particle mass divided by filter surface (F9 compact filter / glass-fibre)

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left-hand diagram and the pressure drop as a function of the particle mass in relation to the filter area in the right-hand diagram.

The results from simultaneous addition of soot and A2 into the test channel were compared against those from sequential addition. Furthermore, the results from comparing against exclusive A2 dosing are also shown.

In the left-hand diagram of Fig. 14 it can be seen that a reduction in the retention from 0.5 to about 0.4 can also be seen initially with simultaneous dosing (magenta curve). With soot loading (black dots) the retention is reduced to about 0.25. The curve for the simultaneous addition of soot and A2 has a parallel upward shift similar to that for A2 after soot (orange curve) for larger particle masses. It lies below the curve for the exclusive A2 loading (yellow curve) whereby no decrease in retention occurred at the beginning. The curve progression in the case simultaneous dosing is determined by the mixing ratio of soot and A2. With the mass concentrations of about 2 mg/m³ carbon black and about 7 mg/m³ A2 chosen for the experiment, there is not a complete loss of the electret effect before the increased loading again resulted in an improvement in separation efficiency. With a particle mass of about 25 g/m² relative to the filter area, the 0.4 μm DEHS efficiency is once again at the initial state level.

The pressure drop increase (right diagram) with simultaneous dosing is somewhat higher than that shown by the other two loading variants that were considered.

Only very moderate pressure drop increases were seen at the electret filters from real-time operation, even after an 18-month operating period (see Fig. 7).

The separation efficiency did not improve to the initial state level over the entire operating period (see Fig. 6). With the mixing ratio chosen here for the simultaneous dosing of soot and A2 the results from the real-time operation are shown as being less than those for the sequential addition.

Fig. 13: Pressure drop increase as a function of particle mass divided by filter surface (F9 compact filter / glass-fibre)

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Fig. 14: DEHS-efficiencies as a function of particle mass divided by filter surface (F7 bag filter / glass-fibre)

Even with other mixing ratios one would not be able to depict the progression as is the case with real-time operation.

3. Conclusion Loading air filters with ASHRAE test dust led to significant higher pressure drops (see Figs. 7, 10 & 13) compared to filters aged in real-life operation. Therefore the calculated average efficiencies were significantly higher than in practice.

When A2 (fine) test dust were used for loading, the resultant pressure drops were similar to real-application. As a result the dust storage capacity were greater with A2 and these values were more realistic by far.

4. Outlook Determining the average efficiency (with a dust load) is no longer requested in ISO 16890. However, a comparison of the initial separation efficiencies of the filter elements and the media samples after being discharged in an IPA bath against the measured values of the filters aged in the real-life operation suggests that the new testing methods will significantly improve the meaningfulness of the laboratory measurements. This is precisely what is to be studied in a new project [7].

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The previous practice of discharging media samples in an IPA bath has always been critically discussed. ISO 16890 now states that filter elements are to be discharged in a test chamber. The air inside the chamber is saturated with IPA vapour so that the filter element is uniformly loaded with IPA after a period of 24 hours. The modification to the test procedure entails high safety-related expenditure, since larger amounts of saturated isopropanol vapour could escape into the laboratory when the chamber is opened (to remove the filter elements). Statements covering the reproducibility of this test and the comparison against the previous testing of the media samples have not yet been published and are expected to be included in the above-mentioned research project.

Funding information The IGF project 17659 N of the research association Institute of Energy and Environmental Technology (IUTA) was funded by the Federal Ministry of Economics and Energy through the AiF as part of the promotion of the joint industrial research programme, which is based on a decision taken by the German Bundestag.

Editor: Prof. Dr.-Ing. Siegfried Ripperger Birkenstraße 1a 67724 Gonbach / Germany Phone: +49 (0) 6302 57 07 Fax: +49 (0) 6302 57 08 e-mail: SRipperger@t-online.de

The IGF project 19095 N of the research association Institute of Air and Drying Technology (FLT) was funded by the Federal Ministry of Economics and Energy through the AiF as part of the promotion of the joint industrial research programme, which is based on a decision taken by the German Bundestag.

Literature: [1] EN 779:2012 Particulate air filters for general filtration – Determination of the filtration performance [2] Lyko, H.; Stoffel, T.: Testing of air filters in compliance with the new ISO 16890; F & S International Edition 16 (2016), pp 71 – 75 [3] Ripperger, S.: Sinn und Zweck der Normung und Standardisierung auf dem Gebiet der Separationstechnik, F & S Filtrieren und Separieren 25 (2011) No. 2, pp. 90 – 92 [4] Mayers, D.L.; Arnold, B. D.: Electret and filtration: Lab testing and field performance head to head; Filtration and Separation, 42 (2005) No. 7, pp. 44 – 49 [5] Raynor, P.C.; Chae, S. J.: The long term performance of electrically charged filters in a ventilation system; Journ. of Occupational and Environmental Hygiene, (2004) No. 1, pp. 463 – 471 [6] Experimentelle Untersuchung der Effizienz von RLT-Filtern als Grundlage für praxisorientierte Prüfmethoden sowie für die Weiterentwicklung der Filter durch Modellierung des Filtrationsverhaltens, IGF-Forschungsvorhabennummer 17659 N; www.iuta.de [7] Untersuchung der Wirksamkeit von Filtern der allgemeinen Raumlufttechnik zur Reduzierung von Feinstaubkonzentrationen, insbesondere PM1, PM2,5 und PM10, IGF-Forschungsvorhabennummer 19095 N; www.iuta.de

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New Aspects Regarding the Testing of Air Filters Report from the Palas Air Filtration seminar H. Lyko* Palas continued their aerosol technology series of seminars, which they have held for the last 30 years, with a modified concept in 2017. The focus was solely on the testing of filter media and filter elements at this year’s air filtration seminar. Prof. Eberhard Schmidt, from Wuppertal University, moderated the event. The event now addresses an expanded auditorium having changed the conference language into English.

The initial seminar of this kind proved to be very successful with over 80 participants, of which 40% were foreign listeners. The event was supplemented by a workshop held on the following day, during which the performance capabilities of the measuring devices and filter test stands produced at the Palas GmbH facility could be directly related to the relevant object. The lecture topics relate to adapting the filter testing systems and procedures to ISO 16890, new findings in the compressed air filter testing sector, studies into the aging behaviour of filters and the further development of filter test stands.

Filter testing and classification as per ISO16890 The ISO 16890 test standard for air filters used in general ventilation technology came into force in January 2017 (see www.iso16890.de). The transitional period for the preceding EN 779 standard will run until mid-2018, when it will then expire and become invalid. The significant changes made to the filter testing procedure and the determining of the filter classifications based on the measured separation efficiencies have already been reported several times (e.g. /1/, /2/). In summary, it should be noted that with regard to the classification of particulate matter filters, the fraction separation efficiencies over the complete particle size range of 0.3 to 10 μm must be used here and the separation efficiencies for the three PM1, PM2.5 and PM10 particle classes can be given with 5% accuracy. The standard consists of four parts: The first part stipulates the filter classification criteria, the second part defines the procedure for determining the flow resistance and fraction separation efficiencies, the third part defines the determining of the separation efficiency and the flow resistance when test dust is applied and part 4 describes the conditioning methods for determining the minimum fraction separation efficiencies.

Achim Breidenbach, from EMW FilterTechnik, gave a lecture on the IGF project being conducted by the Institute for Nanoparticle Process Technology at the University of Duisburg-Essen and the Duisburg Institute for Environmental and Energy Technology IUTA, the

* Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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“Investigation into the effectiveness of filters used in general ventilation technology for reducing fine dust concentrations, in particular PM1, PM2.5 and PM10” (Project-No. 19095 N). This project investigates the problems that arise with filter testing in compliance with the new standard and whether the test procedures and the classification system better reflect the behaviour of the air filters in real use as opposed to testing in accordance with EN 779. One of the implementation difficulties regarding the test procedure is that the stipulated 45% relative humidity can be significantly exceeded during the summer months. This resulted in problems with the KCl particles test aerosol, which was needed for detecting larger particles, as the particles partially dissolve.

A special feature used during determining the efficiency values is the weighting of the fraction separation efficiencies measured in the laboratory with a particle size distribution that is assumed for the outside air. It is based on bimodal distributions for urban and rural ambient air.

Both have maxima of 0.3 and 10 μm, but differ in that the fine proportion predominates in the urban air, whilst particles in the order of 10 μm dominate in the rural air. According to these differences, the ePM1 and ePM2.5 separation efficiencies were weighted with the urban distribution and the ePM10 value was weighted with the rural distribution. Standardised distributions were used so that the filters could be compared regardless of their test locations. This project has shown how the calculated efficiencies of a filter can change when they are based on the real outdoor air distributions at the test site.

The distributions at the IUTA and the University of Duisburg-Essen locations,

which showed clear deviations from the standardised distributions, were measured using the Palas Promo system. Calculation of the real distributions of the weighted efficiencies for the specific particle classes appears sensible in order to predict a filter’s efficiency during real operation at a particular location. The efficiencies determined using the real distribution were higher in this example.

The Saxon Textile Research Institute in Chemnitz (STFI), represented by Marian Hierhammer, has an urgent problem with the implementation of Part 4 of the new standard in that it requires the discharge of the test specimen into isopropanol (IPA) vapour inside a sealed chamber. To date, only one chamber is available on the market for this type of conditioning and its size was adapted to ready-to-install filter elements. Whereas EN 779 requires the media sample to be discharged through immersion in liquid IPA. The institute develops filter media or manufactures nonwovens on behalf of customers, for which a procedure is needed for the rapid estimation of the filter’s expected efficiency. Filter media were previously tested in a test setup in which the parameters corresponded to those stipulated in EN 779. In order to realise a procedure based on the new filter media standard, one needs, among other things, a simpler and more compact option for the conditioning using IPA vapour. This should also reduce the effort required to maintain the safety technology used to deal with the risk of explosion arising from using IPA vapour.

The energy consumption during the filter’s service life is also decisive with regard to the purchase decision in addition to the separation efficiency. Thorsten Stoffel, from DencoHappel, who is also

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Fig. 1: Ageing methods for indoor air purifiers; left: IUTA method (simultaneous burning down of 12 cigarettes in a 25 m3 chamber, hourly repetition is also possible), right: Ageing chamber as per Chinese standard GB/T18801-2015 (50 cigarettes simultaneously in 3 m3-chamber, repeated until the room air concentration ≤ 35 μg/m3). (Photos: IUTA e.V.)

a member of the standardisation group, described how the new energy classification should take place and what work still needs to be done. The Eurovent governing body will award energy labels ranging from A+ (lowest energy consumption) to E (high energy consumption), which are similar to those for filter testing under EN 779. As part of EN 779, discrete efficiency classes also entail discrete energy classes, i.e. certain value ranges for the energy consumption during the dusting were defined for a specific efficiency class using a pre-defined amount of test dust and then assigned energy classes. According to the EU energy classification regulations, the classification of all considered efficiency class species into energy classes must be subject to normal distribution. Energy performance indicators are calculated for each PM fraction as per ISO 16890 (kep = key energy performance). Both the filter efficiency as well as the pressure difference measured during the dusting using a defined amount of dust flow are included in the calculation. Which kep values are assigned to which energy classes can only be known if one already knows the distribution of these values for a correspondingly large number of filter products. This is why Eurovent required all companies whose filter elements are classified as per EN 779 and according to their energy consumption to submit the kep values for at least 50% of these products by the end of January 2018. These filter products had to be chosen as being representative of the portfolio, i.e. both the products from different energy classes according to old classification method or different efficiency classes or even different types of assembly must be taken into account in compliance with this 50% rule. Recently developed filter elements that have not yet been given an EN 779 energy indicator cannot be classified until this data collection process is complete and the normal distributions are listed.

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Testing of compressed air filters The compressed air quality is classified into three categories, i.e. particle content, dew point (water content) and total oil content according to ISO 8573-1: 2010.

The VDMA has summarised the quality levels recommended for specific applications in the food and pharmaceutical industry in a specification sheet /3/. No limit values are specified in the standard but are defined by the user himself for certain high-purity applications (Quality class 0). The total oil content in compressed air comes from oil-lubricated compressors, and where it is not possible to use oilfree compressors, coalescence filters are used for separating the oil aerosols. Dr Wolfgang Mölter-Siemens, from IUTA, who has been testing compressed air filters according to the ISO 12500 test standard as well as by using parameters beyond this standard, for some years now, gave an overview of the compressed air technology and state-of-the-art compressed air filtration now being used. Two recent work packages are the development of a concept for an energy label for compressed air filters and the clarification of the factors that affect the re-entrainment of oil particles from the filter’s clean gas side into the clean gas flow. The measurement of the fraction separation efficiencies of oil aerosol filters is an important step for both tasks. A classification of the filters into energy classes must be made according to their separation efficiency. The data from a variety of tested filters for such energy classifications and a concept for subdivision into 4 energy classes is available, but there is still no application available.

Re-entrainment of oil droplets on the clean gas side occurs when the filter medium is saturated. This is also the state in which the test must be carried out.

The difference between oil droplets that pass through the filter medium as primary particles and those that are carried along

by the air flow (re-entrainment) from the clean gas side is determined by the particle size. The droplets carried along from the drainage layer and, probably, the oil reservoir are larger than those that pass through the filter medium. The result of measuring the fraction separation efficiencies at different temperatures (corresponding to different oil viscosities) and by using two different oils was that the oil concentration increases approximately linearly with the fluidity (= 1/viscosity) due to re-entrainment on the clean gas side and the first droplets were carried along at a fluidity of about 5 m2/Ns. How steep the increase in concentration becomes with increasing fluidity depends on the filter’s separation efficiency.

Parts 2 - 9 of ISO 8573 describe the procedures for determining the compressed air quality at the point of extraction and there are partial similarities to the ISO12500 filter testing methods. The oil aerosol concentration is given as a mass concentration in both cases. Stephen Smith, from the English company Filter Integrity Ltd., is a convener of the TC118 ISO technical committee, which develops or revises the relevant standards for compressed air technology. He reported on efforts to change the method used for measuring the mass concentration of oil aerosols that is stipulated in both standards. Oil aerosols are currently collected on an absolute filter, then extracted using a solvent and then analysed using infrared spectroscopy. Apart from the huge amount of time required for this procedure, EU Regulation 291/2011 covering the use of ozone-depleting substances, which also includes solvents used for analysing oils and greases, provides for a ban on such substances if other analytical methods are available.

The determination of the concentration of oil aerosols using the Welas aerosol spectrometer made by Palas meets the requirements of such an alternative

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Fig. 2: Prototype of the KCI generator recently developed by Palas

method in many aspects, especially with regard to the possibilities of automatically measuring concentrations with high temporal resolution. Other aspects, such as calibrating at test pressure, are still difficult. The biggest problem that Smith encountered when using sample evaluations arose through converting from a measured particle number concentration to a mass concentration using the pre-set refractive index for the calibration. The correction of the refractive index using a downstream gravimetric mass determination on an absolute filter provided a good correlation between the mass concentrations measured using the Promo system and the filter. The compressed-air filter test was carried out on a separate measuring stand using the corrected refractive index and the measured values exhibited high stability during continuous operation.

Ageing effects of filter media Air filter ageing is caused by the increasing dust load during the filter’s service life. In general, increased particle loading is accompanied by a rise in the pressure drop together with a simultaneous increase in separation efficiency. The cause of both is the increasing blocking of the pores by the particles. Dr Christof Asbach reported on two different filter ageing projects. The effect of ageing on nanoparticle deposition was investigated in the former and the ageing effect on electret filters was investigated in the latter. If the nanoparticle separation during ageing was considered separately, it appeared to be based on the examination

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of the nanoparticles moving through cylindrical tubes. The penetration through such tubes (or filter pores) does not depend on the diameter of the free cross-section, but on the flow velocity, which increases at a constant volumetric flow rate and increased pore narrowing. Whether this is the case was tested on an air filter test stand in which salt nanoparticles were produced using a flame generator and they were then drawn into the test stand under reduced pressure. Contrary to the theory outlined above, ageing with ASHRAE dust also increased the separation efficiency in the nanoparticle range. The charge on the filter surface causes improved particle separation at a constant pressure drop with electret filters. Ageing results in the loss of the electret effect. Electret filters are popular in indoor air purifiers because they allow the Clean Air Delivery Rate (CADR) to increase per unit time whilst maintaining the same fan output. As China is the largest market for these devices, indoor air purifiers are tested at IUTA in accordance with the Chinese test standard.

This provides for aging from cigarette smoke and this point was changed two years ago by significantly increasing the number of research cigarettes to be burned down per volume, thereby accelerating the ageing process. Fig. 1 shows the two ageing methods that were used. Ageing by 400 cigarettes resulted in a CADR reduction of 20% of the initial value without a pressure increase. Discharging with IPA produces the same ageing effect, but it does not provide any evidence about the filter’s service life.

Filter media testing under broader conditions Filter testing standards are used to make filters comparable, but they do not fully reflect the reality of filter operation. With air filters this affects both the composition of the aerosol that has to be separated as well as the relative humidity and temperature. Martin Schmidt, from Palas, showed the MFP 3000 HF filter media test stand, which was also built for testing under conditions way beyond the applicable standards and it is also flexible as it can be adapted to the meet the needs of the user when its components are assembled. The relative humidity can be set between 20% and 80%, the air temperature between -10° and +50°C and the conditioned air can be circulated for measuring volumetric flows above 200 l/min. DEHS, salts (NaCl, KCl) and A2 fine test dust can all be used as the test aerosols. They ensure that particle sizes of around 20 nm to 40 μm can be

produced. A special development is the KCl generator, which must generate at least 500 particles in the upper size class (7 - 10 μm) in the adjustable volumetric flow range (see Fig. 2). The KCl generator used in the filter element test stands as per ISO 16890 has been designed for a correspondingly higher volumetric flow (3400 m3/h).

Testing of particulate matter filters On one hand, determining the number of airborne nanoparticle concentrations needs the particles to be classified according to their electromobility and, secondly, the counting of each specific size class using aerosol spectrometry, after the particles have grown to a size suitable for the aerosol spectrometer through the condensation of a liquid. Palas provides the MFP Nano Plus filter test bench for this measuring task as part of the filter test according to EN 1822. Classification after electromobility occurs in an electric field and the subsequent aerosol discharge prevents the charge effects from the electro-classifier from affecting the filter’s separation efficiency during filter testing.

Mara Pfeffinger, from Palas, used the EN 1822 particulate matter filter test to show how the fraction separation efficiencies of such filters change when the aerosol is not discharged or is discharged using a radioactive neutraliser or alternatively by using soft X-rays (<5 KV). The tested filter generally exhibited a slightly reduced separation efficiency for discharged aerosols.

The test standard for particulate matter filters does not provide for the discharging of the filter medium as opposed to the particulate matter filter test according to EN 779 or ISO 16890. It could be seen that the fraction separation efficiencies realised using both discharge methods were very close to each other. Therefore discharging using a non-radioactive neutraliser is a suitable alternative to radioactive discharging.

Literature: H. Lyko, T. Stoffel: Testing of air filters in compliance with the new ISO 16890 F&S Global Guide of the Filtration and Separation Industry 2016-2018 (2016) pp. 215-220, ISBN 978-3-00-052832-3 /2/ H. Lyko: Development, Production and Testing of Nonwovens for Filtration Use-Report from the 2017 Filtrex conference , see this issue, pp. 47-53 /3/ VDMA-Einheitsblatt 15390-2 (Draft Dec. 2016): Druckluftreinheit-Teil 2: Typische anwendungsspezifische Reinheitsklassen gemäß ISO 8573-1:2010 und Anleitung zur Erzeugung und Überprüfung von entsprechenden Druckluftreinheiten für Anwendungen in der Lebensmittelund Pharmaindustrie

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Separation Processes Used in the Treatment of Bulk Solids and Recycling Technologies H. Lyko* 500 exhibitors and around 6,800 visitors created a new record for the dual Bulk Solids (Schüttgut) trade fair and the Recycling Technology trade fair, which was held in Dortmund for the fourth time in May. It was also the eighth event for participants in the Bulk Solids trade fair. The trade fair organiser attributed the success of both events to the extensive lecture program at both topic complexes as well as other matters.

Mechanical separation processes are used in both bulk solids treatment and recycling technology. Even if the classic dust extraction process is mainly attributable to the bulk solid treatment topic, dust extraction plants are an essential component of many recycling plants, especially for mineral and fibrous materials. Sieving, sifting and sorting technologies formed part of both trade fairs. The recycling of construction materials, a topic that has been intensively discussed against the background of the Federal Government’s draft Covering Ordinance, was included as mechanical separation processes are one of its core technologies.

Dust extraction The separation efficiency and the filtration efficiency as well as the optical aspects also play a role in dust filtration in addition to the suitability of specific materials and the operating conditions. The Filtration Group GmbH with its Ti 2011 material currently offers the only white filter medium in order to meet the wishes of the pharmaceutical industry with regard to optical “purity”. The filter medium has been developed for particularly fine, electrically charged and ignitable dust. It consists of an electrically conductive material (polyester / bico-fibre fleece), which has a PTFE membrane laminated onto it.

Electrically charged particles, which are retained on the filter’s surface, transfer their charge to the underlying medium.

The filter medium is also characterised by its high tear strength and chemical resistance.

Herding participated as an exhibitor at the exhibition for the third time and evaluated this fair as a veritable counterpart based in the West of Germany to Powtech in Nuremberg. The characteristics and function of the sinter-plate filter made by Herding were presented by the example of an exhibited system of the Flex series.

These filter plants are fitted with vertically installed sinter plate filters, whereby all types of sintering media offered by the company can be used depending on the requirements profile. The volumetric flows range from 500 m3/h up to several 100,000 m3/h in modular designs. The Flex system is used for dust extraction during the production of pharmaceutical solids, electrostatic enamelling, steel * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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pipe production or the separation of toner dust. The same sintered plate filters are also installed in the large Herding Maxx filter plants, which are used to solve dust extraction tasks in steel production and the recovery and treatment of sand or ore in recycling technology.

A Herding filter was also part of the experimental set-up installed in the open air, in which REMBE GmbH and IND EX e.V. carried out exhibition detonations as part of the third German Fire and Explosion Protection Congress to point out the importance of protective measures (see Fig. 1).

Cartridge filters such as the Infa-Jetron AJB from Infastaub are used for the dustfree pneumatic filling of bulk material silos (see Fig. 2). A dust cloud is created inside the silo during the filling and it is forced out of the silo by the feed pressure.

The silo top filter allows the air being forced out to escape and this ensures

pressure equalisation together with simultaneous dust retention so that the maximum permissible residual dust content is reliably complied with. The quantity of air to be cleaned by each silo top filter is a max. of 900 m3/h during extraction and 2,700 m3/h during the final surge. The pressure switches integrated in the filter helps with quick filling. The first pressure switch activates the filter cleaning in the event of overpressure in the silo caused by the filling process. The second pressure switch helps to reduce and keep the final surge at a level that does not open the overpressure flaps on the silos. The final surge limit is realised by the pinch valves installed in the filling line, which are activated by the second pressure switch.

Sieving and sifting Sifting out of foreign objects is imperative when unloading silos or big bags.

Foreign bodies can lead to considerable

Fig. 1: Exhibition detonation in the open air at the Bulk Materials trade fair (Image: easy fairs)

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Fig. 2: Infa-Jetron AJB cartridge filter used for dust-free silo filling (Image: Infastaub GmbH)

complications, particularly in the food and pharmaceutical industries. Haver & Boecker have developed a compact round sieve, the Haver R class, especially for automatic sifting in known big-bag and silo plants. It can be easily retrofitted at various interfaces thanks to its small dimensions. The round sieve is available in different diameters and mesh widths and provides feed rates of up to 1,000 kg/h.

Linear screens are used for protection, control or as classifying sieves for dry and free-flowing bulk solids. The horizontal sieve movement causes the finegrained portion to move directly above the sieve’s mesh, which leads to a very high separation effect. This sieve process is especially suitable for sieving sensitive products. J. Engelsmann AG recommends their JEL Phoenix linear sieve for use in the chemicals and plastics industries. A modular sieve cartridge system in which up to 4 sieve decks are stacked up forms the core of the system (see Fig. 3). The machine is capable of processing granular, powdery, fine powdery, fat-containing and granular-shaped bulk goods. Even difficult products can be sifted efficiently and with optimum use of the sieve mesh thanks to the lifting and tilt adjustment.

Sieves made by Spaleck are more often used for coarse application materials in minerals processing and recycling technology. The centrepiece of several plants is the patent-pending flip-flow cartridge that can be used both in the material sieve in combination with 3D machines and in conveyor feeders. The sieve material used here is a rubber-elastic sieve tray

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Fig. 3: JEL Phoenix linear sieve (Image: J. Engelsmann AG)

which, when the dynamic frame moves relative to the base frame, is severely deformed through stretching and bending and is therefore self-cleaning. The flipflow screen enables difficult to sieve, sticky and moist materials to be classified with separation cuts ranging from 0.2 to 120 mm. During waste preparation the feed material first meets this type of sieve, which is characterized by a hole width that is smaller than the target grain size.

The residue of this primary sieve meets the material sieve. The efficiency of the material sieving process is increased by the preceding separation of fine materials, because the openings of the material sieve can no longer be blocked by fine, sticky particles. The company was also delighted to receive the recycling technology award for their ActiveCLEAN self-cleaning conveying channel (see Fig. 4). It ensures considerable time savings during the conveying of sticky or caking bulk materials such as slag.

ISS Schüttguttechnik recommends sifting as a simpler way of processing bulk material. The possibility of clogging / blocking the sieves is eliminated due to the absence of sieve coverings and the lack of moving parts makes a sifter wear-resistant and the separation limit can be adjusted both individually and linearly. The most important separation criterion is not the size but the sedimentation velocity of the substances that have to be separated.

Material separation functions as soon as the fractions that have to be separated have different sinking rates. The product is fluidised in the sifter by the air flowing in

from below, which prevents the build-up of deposits in the plant. The bulk material’s dwell time in the sifter is decisive with regard to the separation result. The inclination angle is flexible and it can be adjusted to match the process or the product.

Recycling of construction materials The building materials recycling topic was discussed in 2016 with particular regard to the draft German Covering Ordinance for Substitute Construction Materials and Soil Protection /1/, which was adopted by the Federal Cabinet shortly before the exhibition (for further information about this draft, please contact the German Federal Ministry for the Environment, Nature Conservation, Construction and Reactor Safety at: www. bmub.de). The core of this regulatory plan is the introduction of a Substitute Construction materials Ordinance and the new version of the Federal Soil Protection and Contaminated Sites Ordinance. For the first the Substitute Construction Materials Ordinance should establish the requirements for the production and implementation of mineral substitute construction materials. Such substitute construction materials are recycled construction materials obtained from construction or demolition waste, slag from metal production and ashes from thermal processes. They are used in civil engineering, e.g. for roads, railways, fortified areas, cable trenches, noise and visual protection walls. Up to

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now, the production and use of recycled materials has been regulated at level of the federal states (see example given in /2/). The Covering Ordinance stipulates limit values for specific pollutants used in substitute construction materials and also defines installation instructions that have been adapted to these limit values in order to prevent or limit the input of pollutants into the ground or ground water through seepage water. Under this Covering Ordinance, which still has to be adopted by the Federal Council, there will be a total of 232 million tonnes of mineral waste per year, which is the largest waste stream in the country according to information released by the BDE. Critical opinions about this cover ordinance were also given within the framework program as well as during the run-up to the trade fair. Primarily, a change in the assessment of recyclable materials is expected, which leads to the fact that the proportion of construction waste that ends up in landfills will not become less but even more. The Duisburg FEhS Institute for Construction Materials Research published the concerns of its chairman, Dr Rolf Höffken, in that the planned substitute construction materials ordinance counteracts resource conservation.

This relates to the assessment of the recycling capability of steelwork’s slag.

According to the new ordinance, some 40% (about 2 million tonnes) of slag could no longer be used as a construction material and it would have to be disposed of.

The typical procedure for centralised construction material recycling consists of presifting the construction rubble that has already been crushed and possibly freed from its reinforcing iron, the picking-out of foreign substances such as wood, plastics, light materials or iron, reduction in an impact crusher and subsequent (multistage) screening, if necessary in conjunction with a magnetic separator that will remove any residual metals /4/. Presieving should free-up the impact crusher. The material sifted during this processing stage will be treated separately, e.g. in order to remove light materials.

Mogensen, a subsidiary of the Allgaier Group, also specialises in machines for the processing of mineral construction waste /4/. Mogensen offers bar sizers for coarse separation in the range from 60 to 400 mm, which are driveless, sturdy screening plants, in which the separation cut is adjusted via bar diameter and clearance. It is also possible to arrange for it to have several bar decks. Such bar screening machines are also available in designs fitted with vibration motors. Decks with bars and those combined with sieve meshes in

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Fig. 4: Spaleck’s trade fair team celebrate their recycling technology award for their ActiveCLEAN self-cleaning conveying channel (Image: easy fairs)

a single machine are available as another machine specification. If the grain size or the grain weight is not sufficient to use as a distinguishing feature for the correctly sorted separation, then optical processes or other sensors will be required, and these can be used to separate according to shape, colour or even chemistry. The MSort sorting system was conceived for such applications and it has been available on the market in its original form for more than 15 years and is available both as a stationary device and as a mobile system.

The feed material is isolated by a vibrating conveyor in the sorting system and is then fed into a chute from which it drops vertically downwards. It is recorded by one or more high-resolution colour line cameras mounted in the drop zone. The camera images are evaluated by a computer that precisely controls up to 512 fast and robust compressed air valves. Compressed air transports specific parts out of the main stream according to their colour, shape or size. The detection can be improved by using double-sided camera monitoring and a combination of inductive material detection (metal detection) and camera systems is also possible.

Fine fractions with particle sizes of 2 mm and below produced from the sieving and sorting of fractions derived from construction rubble are currently not being used anywhere, they are just being deposited.

The BauCycle research project that is being undertaken by four Fraunhofer institutes (IBP Building Physics, IML Material Flow and Logistics, IOSB Optronics, System Technologies and Image Exploitation as well as UMSICHT Environmental, Safety and Energy Technology), aims to develop new and attractive utilisation options for the fractions that are still not usable. As

Jan-Philip Kopka, from Fraunhofer IML, indicated in his lecture on this project, waste is nothing else but a raw material in the wrong place. The motivation to look at this fine fraction arose from the high demand from the construction industry for sand and gravel for producing concrete. The project is intended to address three challenges: product development, the development of a cost-effective sorting technology and the development of a market platform for recycling fine fractions (see Fig. 5).

The conditions for the creation of quality-assured and certified products such as cement raw materials or as granulates for the use in acoustically active components such as noise barriers will be produced using the sorting technology. The substances can be sorted according to their colour and their chemical composition by using an opto-pneumatic process, which uses a line camera. Especially important here is the distinction between siliceous, sulphate or calcite components.

The possible correctly sorted recovery of this material is interesting with regard to the recycling of old concrete as a recycled aggregate. This will mean widespread and separate collection of demolition concrete and demolition waste that contains gypsum. Gypsum, chemical calcium-sulphate dihydrate, is produced in the form of plaster and floor screed as well as gypsum plasterboard panels. This sulphate in the old concrete fraction is less desirable because it can lead to changes in the structure of the recycled concrete (RC concrete) or can be washed out when the ground is filled (see /4/). However, gypsum is also a valuable building material, a binder that, in contrast to cement and lime, can be produced at moderate temperatures (180°C).

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Fig. 5: BauCycle project process diagram for utilising the fine fraction from construction rubble (Image: Fraunhofer-Institut für Bauphysik IBP)

Gypsum plaster and boards promote fire protection in buildings because of their water content. According to the Federal Gypsum Industry Association, gypsum is the only natural material that can be restored to its original state after treatment and used as a building material through recycling. As Dr Hans-Jörg Kersten, from the Federal Association, described during a trade fair lecture, the gypsum industry is currently purchasing about 65% of its raw materials from flue gas purification at power plants and the expected exit from coal-fired power generation will cause these sources to dry up. This is why the Federal Gypsum Industry Association has developed a concept for the recovery of recycled plaster for its member companies. Cut waste from construction sites and correctly sorted demolition materials are in great demand. Recovery and recycling concepts, mainly for gypsum plasterboards, also exist in other countries.

A current overview of these activities is given in a study recently published by the Environmental Agency /5/. Accordingly, the plant technologies currently used in Europe are similar to those used for the preparation of gypsum plasterboards. Only mechanical processing stages are used in stationary or mobile plants. They are intended to separate extraneous substances and impurities, especially the cardboard or paper portions. According to the details from the UBA study, two stationary recycling plants for gypsum plasterboards are presently being operated in Germany, one in Saxony and one in Baden-Württemberg.

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Both plants have a capacity of 50,000 t per annum. They are not suitable for the processing of impregnated gypsum board boards because they cannot separate the silicone adhesions. Processing the gypsum fibre boards is also problematic because the TOC content of the fibres in the RC gypsum is too high.

A key demand of the Federal Gypsum Industry Association with regard to the recycling concept, is the ending of the legal classification of recycled gypsum as waste.

Material recovery through transport reactions Rare metals and semimetals, which include certain critical elements whose availability is limited, are components in many electronic devices. However, they are difficult to recover from these devices using classical recycling processes such as metallurgical or wet-chemical processes.

With regard to metallurgical processes which are extremely energy-intensive, metals that are only present in small quantities are frequently lost, whereas wet-chemical processes that use water as the solvent often produce wastewater with toxic or highly corrosive ingredients and high costs are involved in its subsequent treatment. The Fraunhofer IWKS project group in Alzenau for recyclable materials and resource strategy has developed processes with so-called chemical transport reactions as a process for selectively separating specific metals from solid mixtures or mixtures.

The metal that has to be separated is selectively transferred to a gaseous compound using suitable, gaseous reaction partners and this makes it easy to separate.

The target component is finally recovered through separation or condensation at the reactor. The reaction conditions can be predicted according to the material that has to be separated as they are based on thermodynamic data and are optimised in laboratory tests. The gas that is needed can be returned to the process. Application examples for such a process are the recovery of indium from displays, the separation of cadmium from battery waste as well as metal recovery from slag.

Literature: /1/ Verordnung zur Einführung einer Ersatzbaustoffverordnung, zur Neufassung der BundesBodenschutz- und Altlastenverordnung und zur Änderung der Deponieverordnung und der Gewerbeabfallverordnung (Entwurf), Mai 2017 /2/ vero-Fachgruppe Recyling-Baustoffe NRW, Bundesvereinigung Recycling-Baustoffe e.V., Bundesgütegemeinschaft Recycling-Baustoffe e.V., Straßen- und Tiefbau-Verband (Hrsg.): Produktion und Verwendung von güteüberwachten Recycling-Baustoffen im Straßen- und Erdbau in Nordrhein-Westfalen – Leitfaden für öffentliche Verwaltungen, RC-Baustoff-Produzenten und Bauherren, Stand Dezember 2015 /3/ J. Matyschik: Rückbau- und Aufbereitungsverfahren von Bauschutt – eine ökobilanzielle Betrachtung, Präsentation Ökobilanzwerkstatt, TU Darmstadt 2010 /4/ Mogensen GmbH & Co.KG (Hreg.): Vom Schutt zum Baustoff, Aufsatz 04.2016, www.mogensen.de /5/ M. Buchert, J. Sutter, H. Alwast, N. Schütz, K. Weimann: Ökobilanzielle Betrachtung des Recyclings von Gipskartonplatten, Umweltbundesamt (Hrsg.) Texte 33/2017

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Powtech 2017: The Marketplace for Industrial Gas and Air Cleaning Systems H. Lyko* Air purification, occupational safety and/or the recovery of powdered products, which might be valuable food, metallic or non-metallic substances, pharmaceuticals, microorganisms, nanoparticles or even environmental toxins: the variety of industrial applications is reflected once again in the range of materials, designs and operating modes of dust filter elements and systems. Dust extraction technology is one of the core technologies used in bulk solids technology and once again it took a very large share of the products and services presented at Powtech 2017 trade fair that was held in Nuremberg.

Filter bag, cartridge or compact filter?

Many different criteria plan a role in selecting an optimum filter system: - the gas / volumetric air flow to be treated, the concentration and particle size distribution of the dust that has to be separated - the dust’s physical and chemical properties - the chemical composition and the relative humidity of the dust-bringing gases - the operating temperature - the required clean gas concentration - operational and economic requirements and conditions.

Intensivfilter Himenviro GmbH has been making bag filters for almost 90 years and they have compared the application fields for filtering separators against those of centrifugal separators, wet separators and electric separators in their online dust extraction dictionary (see www.intensiv-filter.com, /1/). Filtering separators are generally used for dust concentrations in raw gas up to 200 g/m3.

They have the highest separation efficiency over the entire particle size range (>> 99%) and have a unique feature in the < 0.5 μm size range. Electrical separators also have a noteworthy effect in the size range up to 0.1 μm, but with lower separation efficiencies of between approx. 95% and 98% /1/.

Filtering separators are designed as bag filters, cartridge filters (using pleated filter media) or compact filters with tube or lamellar filters as well as pocket filters. Cleanable filters can be used with high dust concentrations and especially in cases where the dust represents a valuable product that shall be recovered.

As compared to bag filters, cartridge or compact filters have the advantage that the required filter area is contained in a much smaller space, so that plants can be made much more compact.

The advantage of bag filters lies in the mobility of the filter surface during cleaning. This is triggered by the compressed air pulse inside the bag and as the bag inflates even sticky or very adhesive dusts drop off. A company called ts-filter also provides a support body in the form of an oscillating spring fitted inside the bag as an alternative to the widely-used support baskets that are used with bag filters. This element was developed for applications that handle particularly sticky dusts. In principle, pleated filter media, such as those found in filter cartridges, can be more easily clogged by adhesive dusts, which is why they are often recommended only for use with dry dusts.

Compact filter elements are made with self-supporting, rigid filter media and are designed either as lamellas or tubes. Their advantage, in addition to the compactness of the filter systems, lies in the * Dr.-Ing. Hildegard Lyko Dortmund, Germany, mlyko@t-online.de

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relatively high mechanical stability of the filter bodies. A unique feature of bag filters when compared to compact filters is that filter bags are available with temperature resistances of up to approx.

260°C. This feature is particularly needed in large dust extraction systems used in power plants, cement plants and waste incineration plants. Compact filters can only be used at significantly lower temperatures due to the lower resistance of the base material (such as in PP sintered filters with a PTFE membrane) or the casting compounds. As could be seen on Deichmann Filter Technik’s stand, bag filters reach their limits when dust concentrations of 1 mg/m3 or less in the clean gas are required. This property can only be realised in pure surface filters as used in compact filter elements.

The development of cartridge filter systems Donaldson, the company that invented the “cartridge dust extraction system” (according to their own data), showed, by comparing the current Downflo Evolution system against preceding systems (see Fig. 1), how the filter surface density within a system can be increased just by modifying the filter cartridge and it can also be increased through the filter system’s design and flow control. Starting from the first cartridge filter system launched in the market in 1970 to the most recent system model available since 2014, the filter surface per volume has been increased by a factor

Fig. 1 Downflo Evolution cartridge filter system made by Donaldson (Image: Donaldson Filtration Deutschland GmbH)

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Fig. 2: Quad Pulse Package 2 cartridge filter system (Image: Camfil APC)

of 3.5 - 4, which has reduced the number of filter cartridges installed. Development progressed from vertical to horizontal filter cartridge arrangements and the clean gas inlet was changed several times, starting from the horizontal inflow below the vertical filter elements and the cross-flow over the top of the horizontal cartridges up to the current lateral air inflow from above that enters via a pre-separator that removes heavy dust particles. Installing a doubly-diverging shaped pulse nozzle at the cartridge inlet ensures that the compressed air pulse is better utilised for cleaning. This ‘MaxPulse’ protected cleaning system also reduces compressed air consumption. The filter cartridge has a triagonal cross-section instead of a round one and it is positioned in the device with one of its three flat sides pointing downward. This also makes the cleaning process more effective. The unique feature of the filter cartridges is that when fitted with a nanofibre medium it is then possible to retain submicron particles. Typical applications are found in the metal processing sector (welding, cutting, blasting, etc.).

“Built like a safe” is an advertising slogan for Camfil APC’s Farr Gold Series of dust extractors and it definitely applies to the device’s external appearance. The housing is mainly found in the American market and the modular filter apparatus consists of thick-walled, dark-green powder-coated steel. The dust extractor, which mainly provides clean air in the workplace, uses vertically arranged cartridges that use so-called ‘HemiPleat’ technology.

Separators fitted inside these cartridges keep the filter folds open during filtration and cleaning. This results in a reduced pressure drop and therefore longer intervals inbetween subsequent cleanings. If

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Fig. 3: Power Core SVU silo top filter (Image: Donaldson Filtration Deutschland GmbH)

so-called gold cone filters are used then the filter surface density and the filtration efficiency per converted area are increased as compared to simple cartridges. These elements consist of an outer cylindrically-designed pleated filter medium and an inner conical filter core that is open at the bottom and closed at the top by the gold-coloured cone. The raw gas enters through the outer parts of the cylinder or enters the conical core from below during filtration. The clean gas from both parts collects in the space inbetween the cylinder and the core and exits at the top.

The conical cone at the top of the inner element also supports even distribution of the compressed air during cleaning.

A new size with 2 filter cartridges will be available for the Quad Pulse Package (QPP) filter series, which has been especially developed for the pharmaceutical industry and other hygiene-sensitive environments, as from March 2018 and the prototype was already on display at the trade fair (see Fig. 2). The system’s name refers to the primary filter whereby the filter cartridge is subdivided into four segments and one segment can be cleaned separately without interrupting the filter operation. This process makes it possible to keep the system extremely compact using one or, in the future, two filter cartridges. The segmentation of the relatively large filter cartridge ensures that the cross section through which the compressed air flows is quartered, so that the cleaning process becomes more efficient. The QPP system can clean 800 - 1,500 m3/h of air using a single cartridge for the cleaning and with two cartridges it can filter up to 3,500 m3/h. A HEPA filter connected downstream from the primary filter separates the fine dust particles and it is also

a tested flame and contamination barrier. The housing has a pressure-resistant design. This ensures that the system can be set up flexibly and close to production without the need for any extra explosion protection equipment.

Cartridge filters are often used in silo top filters. For this purpose, Donaldson demonstrated the PowerCore SVU filter (Fig. 3), which is shorter than conventional silo filters with an absolute height of 532 mm in its closed state and 1.08 m in its open state. The weatherproof filter, which is designed for pneumatically filled silos with air flow rates of up to 2,000 m3/h is fitted with two flat, rounded Power Core filter packages. They are especially efficient due to their use of an ultra-fine nanofibre medium and the honeycomb air duct structure that makes them easy to handle due to their low height.

Hot gas filtration Bag filter media are available in the market for continuous operation in service temperatures of up to approx. 260°C, i.e. typical flue gas has to be cooled down to this temperature on its way to the filter housing. Therefore all of the pipelines and plant parts such as heat exchangers must be designed to withstand a hot gas flow that might be laden with potentially abrasive particles. Hot gas metallic or ceramic material-based filter media are available as alternatives and they are stable at temperatures up to 1,100°C. The advantages of hot gas dust extraction are also described in the VDI 3677 Guideline for Hot Gas Filters /2/: - the possibility of recovering thermal energy after dust extraction - the exhaust gas does not have to be reheated

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Highlights 2017

- downstream plant parts are protected against abrasive particles - condensation and desublimation with consequential caking are prevented - hot gas filters can separate sparks or smouldering particles - the overall plant efficiency can be increased.

The disadvantage of filtration at extremely high temperatures results from the increased viscosity of the gases from which the dust has to be extracted and the dependence on the permeability of the filter medium, which can lead to a higher pressure drop than when using bag filters.

Rath Filtration GmbH, from Vienna, provides candle filters made from aluminium silicate wool and calcium / magnesium silicate wool for dust extraction up to 1,000°C. The elements, which are available in 60 or 150 mm diameters and lengths of 1 - 3 m, have a porosity of almost 90% and can handle flow rate speeds of 3 m3/min.

The pressure drop at this speed is given as about 450 mbar and the typical emission values are seen at around < 1mg/m3.

Applications for these filter elements can be found in waste incineration plants, power plant processes and combustion plants, in pyrolysis and gasification processes, high-temperature processes for the production / recovery of powdery substances and in the production of plastics.

Several flue gas purification stages can be combined in one unit by using Filtrath Cat catalytic filter elements. These filter elements can be used at temperatures of 250° to 400°C and they simultaneously remove particles, nitrogen oxides and gaseous organic compounds.

the removal of part of the filter dust, apart from the vaporous components that leave the system via the exhaust gas. Scheuch, an Austrian company, together with W & P Zement GmbH from Wietersdorf, Austria, and ATEC, a company, that specialises in exhaust gas technology, have jointly developed a process that removes mercury from the process. The ‘xmercury’ process is shown schematically in Fig. 4. The filter dust, which is at a relatively low temperature, is brought into contact with a part of the still very hot furnace combustion gas that is split off from the main cyclone heat exchanger in a second cyclone heat exchanger, so that any mercury present in the dust evaporates. The hot, mainly mercury-free dust is then separated using high-performance cyclones and a hot gas filter with ceramic filter cartridges that was especially developed by Scheuch, and is fed back into the process. The gas is rapidly cooled by water injection and it then comes into contact with activated carbon, which absorbs mercury and mer-

cury compounds. A downstream bag filter retains the activated carbon. It is returned to the sorption part of the plant until the maximum load is reached.

The hot gas filter developed for the xmercury process will also be marketed for other applications.

Filter regeneration solutions The efficiency and availability of filter systems and the service life of filter elements are also determined by the effectiveness of the cleaning and the energy consumption needed for the cleaning.

Deichmann presented a band top filter used with the newly developed and patented DELA cleaning system (DELA stands for: Decentralised, Energy efficient, Lowpressure, ATEX compliant). The filter is fitted with Deicolon compact filter elements, which consists of individual filter tubes. These elements are comparatively easy to clean because of their PTFE membrane coating. During the measuring it was found that a cleaning air pressure level of

Special mercury removal processes used during cement production The special problem that arises whilst extracting dust from exhaust gases during the production of cement clinker is mercury emissions. This pollutant can be added to the process either via the raw material or the fuel used to fire the kiln.

During cement production, the particulate raw material and the exhaust gas from the rotary kiln are fed into a preheated furnace consisting of several cyclone stages as a counter-current, so that the raw material entering the kiln is already at a temperature of around 800°C and the furnace gas has cooled to below 300°C at the other end. The dust separated in the filter is returned to the clinker process. The mercury in this system is either vaporous or solid or bound to the substance, but this depends on the temperature. The temperature control between the dust filter and clinker kiln creates a mercury loop. Up to now this loop has only been relieved by

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Fig. 4: Functional diagram of the xmercury process for extracting mercury during cement clinker manufacturing (Image: Scheuch GmbH)

Fig. 5: Band top filter with the DELA cleaning system (Image: Deichmann Filter Technik)

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Fig. 7: Remote monitoring of dust extraction systems (Image: Esta Apparatebau GmbH & Co. KG)

process that can save up to 40% of the compressed air energy. The band top filter is the first place that this cleaning system is being used in (see Fig. 5) and others should follow.

To provide compressed air optimally to any part of the filter medium for cleaning and not to consume more compressed air than is necessary is a possible motivation for the further development of cleaning strategies. Another is to run a filter as continuously as possible in its optimum efficiency range (optimum as used here means in terms of both the separation efficiency and the energy consumption) in order to maximise its service life. The optimal efficiency range is determined by the dust type and the concentration as well as the filter medium being used. The Slovenian filter manufacturer TRM Filter has developed the Rotatronic self-learning filter control for cartridge filters, which iteratively approximates the optimum cleaning parameters for the relevant filtration task. The start values are defined at the start of operation as switching points for starting the cleaning, i.e. for the upper differential pressure range tolerance value and for the residual pressure drop (the lower value up to when the cleaning starts). The pressure drop’s time increase is recorded and evaluated during the following cycles, from which new switching points can be determined as necessary. This will prevent the filter from being over-loaded for a long period and it will also safeguard against the cleaning cycles being too short.

The Rotatronic concept also includes a mechanical component: the cleaning air is distributed within the horizontal filter cartridge through a rotating nozzle yoke (see Fig. 6). This reaches the entire surface of a filter element so that it is fully available again for the next filtration cycle and extends the filtration times. The Rotatronic principle is not only used in filters with horizontal cartridges, but also in modified form in the company’s high-containment filter systems, which are available for pharmaceutical processes up to the OEB 5 protection category.

Internet-based services for dust filter systems The networking of plant components and their remote monitoring and, where needed, maintenance via the internet is becoming more and more prevalent in industrial dust extraction processes.

After receiving the “100 locations for Industry 4.0 in BadenWürttemberg” award for the Filterturm 4.0 in May 2017, Esta also integrated this networking option into the Dustomat and Mobex dust extraction series and the Dustmac system series. Information such as operating status, current air flow rate, operating hours or filter status can be retrieved at anytime and anywhere using a mobile device. They are simultaneously logged on an SD card in a comprehensible time and content way.

Nordic Air Filtration used Powtech to launch their myNordic online platform. This platform, which is currently only available to registered customers, can be described as a mixture of an online shop and a CRM system. It is possible to search within the complete product list for the required element, even customise it (size, filter material, etc.) and to request a quote to create and manage filter lists for your own projects, to place orders and to manage the processing and related invoices statuses.

Fig. 6: Mechanical elements of the Rotatronic cleaning system: rotating nozzle yokes (Image: TRM Filter d.o.o.)

about 3.5 bar is sufficient for effectively cleaning these elements.

The cleaning is now carried out through membrane valves integrated in the compressed air tanks and they are opened and closed via additional 2/3 directional control valves. This prevents the pressure in the cleaning line from dropping and that compressed air with a pressure of less than 3 bar, which is ineffective for cleaning, is “blown” through the filter tubes at the end of the cleaning process.

The decentralised compressed air can be generated via an oil-free compressor, such as a membrane pump. This results in a cleaning

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Literature: /1/ Intensiv-Filter (Hrsg): Know How: Das große Intensiv-Filter-Lexikon der Entstaubung, Rev0 (Stand etwa 2006) /2/ VDI 3677: Filternde Abscheider, Blatt 3: Heißgasfiltration, November 2012 /4/ Interview: Reduzierung der Quecksilberemissionen im Zementwerk Wietersdorf, in: ZKG-Handbuch Zementanlagenbau 2016/2917, Leitfaden für Einsteiger in die Zementindustrie, S. 116-119, 1. Auflage, Bauverlag 2016, Gütersloh, ISBN 978-3-7625-3678-9 /4/ Breaking the mercury cycle for emission abatement with the „ExMercury-Splitted Preheater System“ in: ZKG-Handbuch Zementanlagenbau 2016/2917, Leitfaden für Einsteiger in die Zementindustrie, S. 120 – 129, 1. Auflage, Bauverlag 2016, Gütersloh, ISBN 978-3-7625-3678-9

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