Wastewater Treatment and Technology

Innovation driving sustainable solutions to treat Yorkshire’s wastewater

Yorkshire Water and its partners Stantec and BarhaleDoosan JV are currently constructing an integrated wetland at Clifton wastewater treatment works to help reduce reliance on energy intensive treatment processes.

Here Yorkshire Water project lead Michael Housby explains the thinking behind the innovative project. Phosphorus removal from treated wastewater is a particular focus for Yorkshire Water and all water companies alike and we have looked at a variety of innovative ways of meeting our goals in this area. We are always looking for innovative/ alternative solutions. One element of our programme identified a number of our existing sites where the creation of wetlands integrated into the treatment process could have significant benefits in terms of energy saving, carbon reduction and long-term positive impacts for the environment and local biodiversity while achieve the regulated Phosphorus performance Integrated wetlands are considered to be low-cost, low-energy and low-maintenance in nature, compared with traditional chemicalbased solutions. They are particularly well suited to rural areas, so our innovation and strategic planning teams identified our wastewater treatment works at Clifton – a small site near Doncaster – as the number one site to begin this project. As a result, we are now building a wetland which will be planted with more than 20,000 plants to naturally remove phosphorus from treated wastewater before it is returned to the environment.

The £1.2m project is the first of its kind in Yorkshire and will remove phosphorus from millions of litres of treated water in a natural, sustainable and low-carbon process, while also achieving a biodiversity net gain. The project also removed the need for carbonintensive engineering solutions to upgrade the treatment works. The mechanically driven rotating biological contactor at Clifton required replacement and the new 4mg/l phosphorus permit would require the installation of a chemical dosing set up, new settlement tanks and regular deliveries of ferric sulphate to the small rural site.

By reducing reliance on building and grey infrastructure and removing the chemical dosing activity at Clifton, we will be enabling a 58% carbon efficiency in terms of the entirety of the scheme, with reduced operator intervention and next to no energy input, with the additional benefit of being a biodiversity net gain. Our approach instead uses the natural slope present at the treatment works with construction of a series of shallow natural clay cells, approximately the size of three Olympic swimming pools, planted with a diverse range of native water vegetation to mimic the natural processes that occur in wetlands to remove pollutants. These cells use a combination of sedimentation filtration via the action of plants, as well as aerobic and anaerobic breakdown of pollutants by microorganisms and insects, resulting in clean water for discharge to local watercourses. We worked hard with the Environment Agency throughout the planning stages and because of our collaboration this is one of the first projects to be delivered as part of an operating techniques agreement, which is designed to encourage innovation. The flexibility afforded by the agreement has enabled us to use natural clay in the wetland rather than an artificial pond liner, helping us to be much more integrated with nature and deliver real benefits.

material movements offsite, and to enhance local biodiversity, a material management plan has been approved under the CL:AIRE process to keep all excavated material on site, further reducing carbon emissions and potential disruption to local residents. The wetland has also created opportunities for engagement with the local community. We will be engaging with local schools to get pupils involved with the planting process and asking them to build bug hotels for the new biodiversity section of the works that will be completed once the wetlands is in operation. Not only does this let the next generation play a part in establishing the new ecosystem but also gives them a first-hand opportunity to see the process and the importance of treating sewage. To enable YW to learn from this project, we have accelerated the delivery of this project three years ahead of schedule and it really is just the start for Yorkshire Water when it comes to integrated wetlands and natural treatment solutions. Seven further sites have been identified where wetlands could be implemented and feasibility investigations are underway with our strategic planning partners Stantec. We hope to use Clifton as a potential template for future nature-based solutions to support our 2030 net zero carbon commitment and change the way in which we consider design and construction within the built environment.

Solution of the corrosion of sewage systems and the release of Hydrogen Sulfide problems

MagTreat-S® is a well-stabilized, non-foaming suspension of magnesium hydroxide which is used as an alkali in marine scrubbers. It is based on the natural mineral brucite and is made in various slurry make down plants which are strategically located near main ports.

The problem of the corrosion of sewage systems is especially severe in some areas. As usual, this is a result of a number of physical and chemical factors.

The first factor has a hydrodynamic nature: as a rule, it is water streams that flow at a high speed or fall fr om a high height that sometimes reaches up to 60 meters. It has been optimized by proper configuration of the sewage system and flows. The second factor is usually a complex biochemical process. When the initial effluent has an acidic reaction and carries sulfurcontaining compounds, for example, sulfates, hydrogen sulfide (H2S) is released from water into the gas phase with the appearance of a strong unpleasant smell. The released gas is adsorbed on the concrete walls of the sewage and is gradually oxidized by thiobacteria to sulfuric acid (H2 SO 4), which begins to corrode the concrete, as evidenced by a drop in its pH. If this process is uncontrolled, then the result is the destruction of the sewage. The speed of this process depends on the concentration of hydrogen sulfide, the grade of concrete and the presence/absence of protective layer. Schematically, this process can be represented as follows:

One of the most effective solutions to this problem is to adjust the pH of waste water from acidic to basic area. As a result, the equilibrium of the reaction below shifts to the left, contributing to the formation of aqueous S2- and not gaseous H2 S. S2- + 2H+ = H+ + HS- = H 2 S Aqueous phase | Gas phase Above you can find a phase diagram showing the concentration of all substances depending on pH: As can be seen at the pH of 8.5, the release of gaseous H2S drops almost to zero. If there is no release of hydrogen sulfide into the gas phase, then there is no biochemical corrosion of the sewage system. The MagTreat® - S reagent by Brucite+ produced on the basis of natural magnesium hydroxide is the most effective and at the same time safe alkali, giving much more hydroxide ions than caustic soda (NaOH) as example. The reagent also provides a very high buffering capacity of wastewater, which prevents the loss of alkalinity with time resulting in pH decrease (acidification) after the dosing of reagent into the system. So how does it work? Typically, the reagent is introduced into sewage system where the wastewaters are collected and start its way to municipal wastewater treatment plant. In this case, wastewater does not emit H2S along its entire way and coming with already optimum pH of 8-8.5 for biological treatment. Magnesium hydroxide is classified as sparingly soluble in water. Inside wastewaters with an acidic reaction MagTreat® begins to dissolve gradually releasing magnesium cations and hydroxide anions that neutralize the acids. Due to the limited solubility MagTreat® is consumed gradually, providing the system with a “buffer effect”. Divalent Mg2+ cations are involved in the processes of coagulation, compaction of sewage sludge, and are also micronutrients for activated sludge bacteria. Due to the formation of insoluble or poorly soluble salts with various anions, MagTreat® is used to precipitate phosphates, magnesium-ammonium phosphates, fluorides, regulates the content of sulfides, reduction of odor in the wastewater treatment plant. Hydroxide anions promote the precipitation of heavy metals in the form of insoluble hydroxides. Magnesium hydroxide forms insoluble magnesium-ammonium phosphate with phosphate and ammonium ions, decreasing N and P load in wastewaters. Moreover, MagTreat®-S is a safe and ecofriendly product. Recently Carbon Footprint Ltd. has provided a life cycle assessment of MagTreat®-S that have been acknowledged as a CO 2e accessed product. The assessment was dedicated to the greenhouse gas emissions associated with 1kg of the product. This analysis focused on the embodied raw material emissions, the transport of these materials, the manufacture, processing and limited distribution of the product. Following the assessment it was concluded that the carbon footprint of MagTreat®-S is fairly low. According to the assessment the emissions caused by extraction of the brucite ore (a raw material for MagTreat®-S) are close to zero accounting for 9 gCO2e per 1 kg which indicates that the ore has very low carbon footprint and it is close to be a carbon neutral raw material.

Use the unique properties of natural magnesium hydroxide to meet your environmental challenges. www.europiren.com info@europiren.com +31 (0) 10 350 6206

Healthy dosing

Good maintenance of chemical dosing systems is essential to meeting increased water quality compliance challenges. Graham Ward of WES has some money-saving and environmentally sound advice on this subject for water companies and contractors

The water industry’s current Asset Management Period, AMP7, has seen a tightening of legislation on removal of phosphorus from wastewater. It aims to reduce eutrophication - nutrient over-enrichment of lakes, rivers and other surface waters, which generates algal blooms. Chemical dosing is a critical element of the necessary treatment. With stricter, lower limits on phosphorus levels, dosing systems are now being introduced at many smaller treatment works which previously had no such requirement. Each needs to be properly maintained if its operation is to remain compliant and cost-effective.

Beware of false economy

Cutting corners on maintenance makes breakdowns, unplanned downtime and extra repair bills more likely. A poorly serviced system may also run inefficiently and measure inaccurately, leading to higher energy consumption and wastefully large chemical doses. In addition, any deterioration which allows chemicals to leak can result in costly damage or injury. While these defects increase operating expenditure, poor maintenance also puts pressure on capital expenditure budgets by shortening the equipment’s lifespan. The same malfunctions threaten the environment too. Underdosing may leave wastewater insufficiently treated, while overdosing can make discharges chemically toxic. Serious faults in the equipment could lead to significant chemical leakage, or discharge of untreated wastewater, directly into natural habitats. Its impacts might include large fines, enforcement undertakings, remedial works and damaged reputations.

Dosing systems should have at least an annual maintenance and calibration visit Proper maintenance of dosing equipment is critical

The value of maintenance and audits

Dosing systems need at least an annual scheduled maintenance visit. This should cover planned servicing of pumps and other components, as well as checks on calibration, condition and functioning. Further preventative maintenance measures may include additional ‘health check’ visits during the year, in which components are cleaned and tested to ensure they are in good order and performing optimally. A good provider will carry out an initial site survey to determine the equipment’s maintenance needs, which vary greatly according to site conditions, applications and set-ups. The operator will then be offered an appropriate choice of service packages, such as one of WES’ Gold, Silver or Bronze schemes.

In addition, dosing equipment should be audited regularly to ensure its specification still meets the application’s requirements. There may have been changes in, for example, the volume or content of the wastewater being treated, or the chemicals used. Altering the system’s configuration to suit the new conditions can increase its effectiveness, economy and longevity. If a system has not been reviewed for some time, an audit should be requested to assess its fitness. This will identify any work needed to rectify damage and deterioration. It should also identify aspects which no longer meet current asset standards. Systems can often be brought up to date by upgrading key components.

Solutions for tricky sites

When choosing dosing equipment for one of the smaller sites which now require dosing equipment, it makes sense to consider the costs of installation and ongoing maintenance. These sites tend to be unmanned, remote from specialist engineering staff, hard to access, with little space or scope for positioning of equipment, and without buildings to protect equipment from the weather. Today there are compact packaged dosing systems which overcome these difficulties. Their low weight, small footprint and preassembled, pre-tested configuration makes installation easy and expands location choice. They come with inbuilt weather protection and are designed to operate with minimal maintenance intervention, save for scheduled maintenance.

For further information on phosphorus removal and dosing system maintenance, detailed white papers can be found under Resources/Downloads at www.wes.ltd.uk

Graham Ward is Business Development Director at dosing system specialist WES Ltd.

Inefficient wastewater level measurement system

In a wastewater level measurement system that was originally set up with float switches, the first switch initiates the filling of the tank when the level drops to a minimum. A second switch stops filling the tank when it reaches the maximum level, while switch number three acts as an alarm that also prevents the tank from being refilled.

There is a simpler method, however, which involves using KELLER 26 Y level transmitters instead of several floats. This electronic measurement technology offers clear advantages in sewage applications. For one thing, the piezoresistive level sensors do not detect foam as a level of liquid (as is the case with ultrasonic sensors), which ensures accurate level values. Because the system does not have mechanical components that can get jammed or blocked, it’s also less likely to break down. In addition, measurements are taken continuously and current level values can be read off a display at any time. All in all, it’s a highly reliable and simple solution.

Piezoresistive level transmitters

Series 26 Y pressure transmitters are used in level measurement applications that are price-sensitive but also require a high degree of accuracy. These transmitters have a very low temperature error due to digital compensation of what is a purely analogue signal path. Here, amplification and the zero point can be influenced by digital-analogue converters. The accuracy of the end product depends in large part on the sensitivity and linearity of the measuring cell and the compensation of disruptive influences. The silicon measuring cell in the 26 Y series is reliably protected from the measured medium by a stainless steel membrane. The latter, in turn, is protected against mechanical stress by a plastic cap, while its large diameter of 17 mm makes it especially accurate and stable. keller-druck.com

Wastewater Level Monitoring

The notorious Genoa low, also known as “the V(5)-track cyclone”, repeatedly brings catastrophic rainfall in its wake. The low pressure system extends across the Mediterranean region near the Gulf of Genoa. As it moves above the Mediterranean, it fills up with humid air and then strengthens as it heads in a northwesterly direction around the Eastern Alps. Depending on the path it takes, the front can cause extensive and long-lasting steady rain in eastern and southeastern Germany, Poland and the Czech Republic. Nearly all of the major flooding disasters in recent years on the Oder, Elbe and Danube rivers can be attributed to the Genoa low. In 2010, for example, the Oder catchment area experienced the second-worst flooding disaster since the end of the 1940s. Between 15 May and 20 May 2017, a huge amount of rain fell in the Oder catchment area, with rainfall accumulation as high as 180mm/m2 . The second-highest rate of rainfall since weather services began recording such data – 2,100 cubic metres per second – was registered at the Czech-Polish border. Poland, which has been among the hardest-hit countries in terms of flooding, has invested a substantial amount of money in flood protection measures over the last few years. Unfortunately, Poland still faces major challenges, as instances of heavy rainfall continue to increase due to climate change. The expansion and monitoring of sewer systems is crucial here – and since 2007, more than 5,000 KELLER Series 46 X transmitters have been installed for sewage applications in Poland. The transmitters are mostly used in newly built or upgraded lift stations, which pump wastewater in so-called backflow loops to a level higher than the downstream manholes in the sewer system. In heavy rainfall, a situation is thus prevented in which wastewater is pushed back into buildings and ends up flooding basements. The pressure transmitters for level measuring serve as the main sensors for wastewater level monitoring, whereas the floating switches are used as a secondary control element. The main advantage of the 46 X is a chemically resistant AL2O3 membrane with a gold layer, which is also more resistant to mechanical damage than a steel membrane. Modern digital electronic systems enable free scaling of the 4-20-mA output, as well as the incorporation of the unit into a MODBUS communication network. In addition, the 46 X displays outstanding reliability in this extremely tough application.

A new approach for implementing vacuum degassing of digested sludge

Common operational problems with AAD plants are high loading and partly overloading of digesters - with the high dry solids concentration and high viscosity resulting in gas entrapment. This contributes to direct emissions being the major share of a WwTP’s carbon footprint, with methane emissions higher than the total indirect emissions from a WwTP.

Dwr Cymru Welsh Water and ELIQUO HYDROK partnered to test a new approach for addressing operational problems with AAD by the installation of an EloVac®-P Pilot Plant at Five Fords WwTW near Wrexham. The EloVac pilot scale trial ran for around 12 weeks over April-June. The main driver for the trial was to mitigate the excess foaming present in the digesters of the advanced digestion plant. Problems caused by foam generation meant that the pilot trial had to take place under variable operating conditions. Despite the inconsistency of the digestate density, the sludge discharged from the EloVac® was consistent in quality and of high density with virtually no foam present. The EloVac®-P Pilot Plant has a capacity of up to 20 m3/hour of digested sludge and by removing entrapped gas bubbles and dissolved gas, increases digestate density, avoids or reduces the use of expensive anti-foam chemicals, increases digester capacity and improves digester mixing efficiency. Dwr Cymru Welsh Water are a forwardlooking water utility and keen to explore and capitalise on innovative new technologies which improve their service delivery to their customers. The results of the pilot EloVac®-P trial are being assessed by Dwr Cymru Welsh Water for suitability of incorporation into their process at Five Fords and other AAD sites which they operate. For further information on EloVac®-P and any of the other Biosolids technologies offered by ELIQUO HYDROK, visit the website: www.eliquohydrok.co.uk or contact Neil Willoughby, neil.willoughby@ eliquohydrok.co.uk

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