Water Journal June 2003

JUNE 2003

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Volume 30 No 4 June 2003 Jou rnal of t he Aust ralian Water Association

Editorial Board F R B isho p, C hairman B N Anderson, W J Dulfer, G Finke, G Finlayson, GA Holder, B Labza, M Muntisov, P Nadebaum,J D Parker, F Roddick, G R yan, S Gray

•, Water is a refereed journal. This symbol

CONTENTS OPINION 2

indicates that a paper has been refereed.

Submissions Instructions fo r authors can be found on page 2 of this journal. Submissions accepted at:

www.awa.asn.au/ publications/

Sustainable Management; Aquaphemera; Make 2003 the Year of Action; My Point of View, Toward Effective Trade-Off, J Tilleard

ASSOCIATION ACTIVITIES 6

Including AIWA Report

Managing Editor

PROFESSIONAL DEVELOPMENT

P e ter Stirling

10 Details of courses, classes and other upcoming water events

News and Supervising Editor Brian M cRae AW A Technical Director Tel: (02) 9413 1288 Fax: (02) 9413 1047 Email: bmcrae@awa.asn .au

Technical Editor EA (B o b) Swinto n 4 Pleasant View Cres, Wheelers Hill Vic 3150 Tel/Fax (03) 9560 4752 Email: bswinton@bigpond.net.au

Water Production Hallma rk E ditions PO B ox 84, Hampton, Vic 3188 Level 1, 99 Bay Street, Brighton, Vic 3186 T el (03) 9530 8900 Fax (03) 9530 8911 Email: hallmark@halledit.com.au G raphic desig n : Mitzi Mann

Water Advertising

NEWS BYTES 12 Featuring selected highlights from the AWA email News

CROSSCURRENT 22 Wimmera Mollee Pipeline Project; AusAID, Water and Sanitation Goals; Sludge Drying Technology Could Save Millions, G Borton

CONFERENCE REPORTS 26 Ozwater 2003: The Workshops, D Lord, T Bridle 27 Young Professionals TECHNOtour S6 Efficient 2003 Conference, A Turner, D Cordell 29 WATERWORKS Articles contributed by the Water Operators Industry Association on water quality in the wake of the devastating bushfires; biosolids; and off tastes and distribution systems

Natio n al Sales Man ager: B ria n R ault Tel (03) 9530 8900 Fax (03) 9530 8911 Mobile 0411 354 050 Email: brault@halledit.com.au

BIOSOLIDS FEATURE

Water {ISSN 0310 • 0367)

S7 THE NATIONAL RESEARCH PROGRAM FOR BENEFICIAL REUSE OF BIOSOLIDS

is published eight times a year in the months of February, March, May, June, August, September, November and December.

Report by M J McLaughlin

BIOSOLIDS MANAGEMENT - A SIMPLE TECHNICAL SOLUTION

S9

Australian Water Association

Market survey, then process trials

PO Box 388, Artarmon, NSW 1570 Tel +61294131288 Fax: (02) 9413 1047

P Darvodelsky, J Huf, H Moritz

AWA

Email: info@awa.asn.au

ABN 78 096 035 773

Federal President

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EXPERIENCE WITH TWO CONTRASTING TECHNOLOGIES FOR SLUDGE STABILISATION

Horses for courses

Rod Lehma nn

N Read, M S.impson , P Foster, A Carvell

Executive Director

AUSTRALIAN WATER

C hris D avi s ASSOCIATION Australian Water Association (AW A) assumes no responsibility for opinions or statements of facts expressed by contributors or advertisers.

Editorials do not necessarily represent official AW A policy. Advertisements are included as an information service to readers and are reviewed before publication to ensure relevance to the water environment and objectives of AW A. All material in Water is copyright and should not be reproduced wholly or in part without the written permission of the Managing Editor.

Subscriptions Water is sent to all AWA members eight times a year. It is also available via subscription.

70 ::: SLUDGE DEWATERING PITFALLS

A pragmatic assessment A Hertle

WATER 74 :E SINGAPORE'S NEWater DEMONSTRATION PROJECT High grade industrial and indirect potable reuse H Seah, J Poon, G Leslie, I B Law

WASTEWATER 78 DESIGN OF A WASTEWATER TREATMENT PLANT FOR DAVIS BASE , ANTARCTICA

Some unusual constraints for a summer peakload facility K Heaton, C Paterson

Visit the Australian Water Association

HOM E PAGE

and access news, calendars, bookshop and over 100 pages of Information at

OUR COVER: Davis Base, Antarctica. In an ongoing attempt to minimise the impact of the research facility on the environment, the Australian Antarctic D ivision is looking at options for upgrading the existing wastewater treatment plant. See article on page 78.

Photo: Camille Boxall, Project Officer, AAD. WATER JUNE 2003

1

FROM

THE

PRESIDENT

SUSTAINABLE MANAGEMENT Irrigation One of my first official duties since assuming the role of President was to attend th e ln-igation Association's annual conference in Dubbo. It was a good opportunity to catch up with recen t developments in irrigation practice and farm management. I was impressed with improvements that have been ach ieved in water efficiency and also with the smart ways now available to monitor act ual water application . Apart from m easuring applied water with great subtlety in the fie ld , farmers can also generate p lots of the yield across each field - reflecting how well water has been distributed by their equipment. Since irrigation uses more water than any other acti vity, it is encouraging to see the attention that farmers are giving to water efficiency, and !AA is to be compl imented fo r showcasing the progress. Another encouraging aspect was the keenness of the lAA executive to get together and talk about issues which are common to both associations. In my view, the division between urban and rural water users is blurred and both parties should be talki ng together to better understand common issues.

Recycling Queensland Branch recently co nvened a sem inar on sustainable use of water, partic-

water

Contributions Wanted The Water journal welcomes the submission of papers equivalent to 3,000-4,000 words (allowing for graphics) relating to all areas of the water cycle and water business to be published in the journal. T opical scories of up to 2,000 words may also be accepted.

All su bmissions of papers intended for the main body of the journal should be e mailed to the Technical Editor, bswinton@bigpond. net.au, with a copy to the AW A website, www.awa.asn.au/publications. Sho rter news items should be emailed to news@awa.asn.au and also to the website. A submi t ted paper will be tabled at a monthly Journal Committee meeting where, if appropriate, it will be assigned to referees. Their co1nmencs will be passed back to the p rincipal author.

If accepted and after any co11rn1ents have been dealt with , t he fina l paper can be emailed with the text in MS Word but with high re.solution graphics (300 dpi tiff. jpg or eps files - Zip disks or C D-ROMs can be accepted) in separate fi les, or hard copy photos and graphics suitable for scanning by the publishe r can be maikd to 4 P leasant View Cres, Wheelers Hill, Vic 3150.

2

WATER JUNE 2003

Rod Lehmann

ularly the use of recycled water. A key message, not new, but reinforced , was that the major barrier to greater use is the water practitioners th em selves , and n ot the co mmunity. T h is suggests to me that we need a renewed push to educate our industry about recycling, whereas we were tending to see the community as the prim e target. This is not to say that we shou ld not continue our community education ini tiatives through the We All Use Water project, but that we sho uld ensure that ou r colJ eagu es are included as well. I hope our Water R ecycling Forum members will take up the cudgels and indoctrinate their colleagues who haven't seen th e light. It was also interesting to note that, at the same seminar, a politi cian pointed out that th ere was a need for politicians to become better informed on water issues. This is a challenge for all of us and one which we intend to focus on in future .

Sustainability Although sustainabl e managem ent of water is our mission, I see a blockage on the road, in that we have no good tools to measure sustainability. It's easy to bandy the word around , and that's done to death these days, but it is a great dea l harder to actually run a ruler across a scheme, or a system, and objectively measure the degree to wh ich it is sustainable. The triple bottom line is good for public relations, but isn't a scientific tool.

Straight economics do not fill the bill either, and the Natural Step, while an interesting concept, is ha rd to operationalise in practice. I would like to work on this through our national Policy Commi ttee, with a view to developing some overalJ tools for assessing the sustainability of projects.

Perhaps we will see some ideas brought forward at the Envir04 Convention next year.

Rod Lehmann

Aquaphemera Several ACT Governmen t agencies and ACTEW Corporation recently formed the ACT Water R esources Strategy Taskforce, to develop an agreed way forward with the com m un i ty for water management in the T erritory. T he goals of the strategy are to : 1) provide a long term reliable so urce of water for th e ACT and region; 2) to increase the effici ency of water usage; 3) to pro mote an integrated r eg i ona l approa ch to the ACT /NSW cross-border supply and managem ent of water; 4) to protect the water quality, enhance environmental values and protect the health of river users; 5) to incorporate Wate r Sensitive Urb an Design (WSUD) into urban develo p me n ts; and 6) to promote community involvemen t in the p rocess. Commu n it y for u ms com m ence in June and the citizens o f Ca nb e rra are welco m e to com m ent (contact : Gary .Cros to n@act.gov.au) . T h e draft Strategy will be available for public comment in October 2003.

T his strategy builds on the 20% reduction in water use achieved in Canberra in the mi d- 1990s and the innovative stormwater management systems developed in th e 1980s.

But what has been most gratifying in the process so far, is that m ost other capital cities have been or are going through, similar processes.

Sydney w ith Water Plan 2 1 (1997), S011/h Australia's State Water Plan (2000), Melbourne's Plan11ingfor the future of our 111ater resources (2002), and Perth's Securing our water f uture, A State Water Strategy for Western A11stralia (2003). Gratifying in that they all recognise the scarcity of water and are actively attempting to reduce consumption an d have set targets to be achieved by certain dates. R eduction in potable water consumption by arou nd 20% and increases in effluent re-use by around 20%, in the next 20 years, are conm1on aims. They are also readily achievable if there is a w illingness to do so.

T hese directions being pursued

by Govenm1ent and water businesses around Australia, augurs well for our fu ture, and parti cularly for th e health of ou r precious rivers.

- Ross Knee

BIOSOLIDS

THE NATIONAL RESEARCH PROGRAM FOR BENEFICIAL REUSE OF BIOSOLIDS Report by M J McLaughlin (CSIRO Land and Water) Collaborators M J McLaughl in and D P Stevens (CSIRO Land and Water, G Barry (Q ueensland Department of Natural Resources and M ines), M Bell (Queensland Department of Primary [ndustries) M Whatmu ff (NSW Agricultu re) M Warn e (NSW EPA), D Prichard (Curtin University, WA) N Pen ney (WA Water Corporation) an d J Stokes (Victorian Department of Primary Industries) .

Scientifically defensible guidelines for use of biosolids and other wastes In view of the importance of this project, natio n-wide, several major Figure 1 . Sites across Austra lia. research proj ects have combined to The Queensland component is princitake the first step in a national approach pally fund ed by Brisbane Water/ Brisbane to research into reuse ofbiosolids on soil C ity Council (BW / BCC) and South Ease and the ecotoxicological and food quality Queensland R egional Organisation of impacts of contami nants in these materials Councils (SEQROC). The research will (h ttp:/ / www.awa. be undertaken jointly by the Departments asn.au / NS IG/bio / index.asp). T he data of Natural R esources & Min es (NR&M) gathered w ill augment the information and Primary Industries (DP!) w ith the already available from biosolids re-use support of BW/ BCC and the R ecycled research p rograms in various agencies.

Organics Consortium (ROC ) at Laboratory and field experimentation have a common experimental design , allowing integra tion of the data and extrapolation to a wide range of soil and crop environments.

T he proj ect has the potential co provide the necessary data to underpin the production of scientifically defensible regulations at State and National levels for reuse of biosolids and other metalcontai11ing waste materials. Sites are currently established in Queensland , New South Wales, South Australia, Western Australia, and Victoria (Figure 1).

Biosollds to Land: International Regulations Part II - a survey of regulations for pathogens by H Reid, has been held over to the August Issue.

Uni versity of Q ueensland. The NSW component is fu nded by the NSW Environmental Trust (and Sydney Water) and the research undertaken by NSW Agricu ltu re, NSW EPA and CS IRO. T he WA componen t is funded by WA W ate r Co rpo ration and t h e research being done collaboratively wit h C urti n Unive rsity an d CS IRO Land and Water. The Victorian component is being und ertaken by the Victorian D epartment of Primary Industri es an d ha s b een funded by a consortium of 16 water authorities representing the metropolitan and regional urban water authorities (via Vic Water), the D epartment of Sustainabili ty & Environment and Victorian E PA . The South Australian component is being undertaken

by CS IRO Land and Water and funded principally by SA and U ni ted Water, and the Australian Centre for International Agriculwral Research wh ich has an international componen t involving sites in Thailand and Vietnam (Figure 2) To ensure the dissemination of results at State and National levels, the various

Tra ng

Figure 2 . Sites across South East Asia.

WATER JU NE 2003

57

BIOSOLIDS

Figure 3 . Sites establishment, SA, April 2002 .

projects are coo rdinated by State-based advisory panels with a yearly national workshop organised by CSIRO Land and Water involving State EPAs, water industries and researchers. The next workshop, which will include a session open to the public, will focus on emerging issues with regard to contaminants in biosolids "Land application of Biosolids - H ealth risks and con tam inants", 9:00 - 5 :00, Friday 1st August, 2 003, QDP I

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Figure 4 . Assessment of the effect of nutrients and organic matter from biosol ids on crop growth.

Conference Centre, 80 Ann St., Brisbane.

The workshop aims to identify any knowledge gaps and prioritise any future research required to ensure the sustainability of applying biosolids to land. For more details and registration see (http: //www.clw.csiro.au/ conferences/ biosolids/).

As part of the trials, benchmark metal dosing treatments have been established in the field, with initial work foc ussing

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WATER JUNE 2003

on Cd, Cu and Zn (Figure 3) .

Ecotoxicological endpoints b e ing measured are plant germination, growth, and m etal uptake, with soil mi crobial endpoints being substrate-induced nitrification and substrate-induced respiration.

These endpoints are being related to various measures of metal speciation and bioavaiJability in the soil. E cotoxicological responses in these metal control treatments will be related to those in soils treated with biosolids and waste materials containing metals.

As well as contaminants, the beneficial effect of nutrients and organic m atter in biosolids on crop growth is also be ing assessed, with various cropp ing systems around the nation being evaluated (Figure 4). It is well know that biosolids contain a variety of beneficial properties for crop growth, and the nutrient supply potential of a wide range of biosolids is being evaluated as part of the program.

Contact Dr Daryl Stevens and Dr Mike M claughlin, CSIRO Land and Water, Glen Osmond, SA 5064, Tel: 08 8303 8533 or 08 8303 8433, Ema i l: Dar y l.St evens@csi r o.a u or Mike .McLau ghlin@csiro .au

Land application of Biosolids - Health risks and contaminants 9:00 - 5:00, Friday 1st August, 2003, QDPI Conference Centre, 80 Ann St, Brisbane (http://www.clw.csiro.au/ confere nces/biosolids/ )

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BIOSOLIDS

BIOSOLIDS MANAGEMENT - A SIMPLE TECHNICAL SOLUTION P Darvodelsky, J Huf, H Moritz Summary This pape r covers th e steps, lea rning and initiatives taken by South West Water Autho rity (SWW A), Victoria, when developing its biosolids management plan fo r the Warrnambool Wastewater Treatment Plant. The project included a market survey of potentia l o utlets for biosolids products, a trial of a hi gh- rate d1ying bed and costs comparison with the existing belt press dewatering and a fin al step of air drying to stabilise the biosol ids using a proprietary mechanical aerati o n auger to aerate the biosolids to provide a simple, low cost technical solution to biosolids m anage ment.

Background Warrnambool is a coastal town of 30,000 people which lies 265 kilo metres west of Melbourne. T he area is one of the main dairy farming regio ns of Australia.

Two major milk produ ct factories and an export abattoir provide nearly two-thi rds of the biological load to the treatm ent plant, i.e. 47,000 ep together w ith about 30,000 e.p. of domestic load. T he sewage fro m the townships of Allansford and Koroit is also processed at this treatment plant.

The treatment plant is an intermittently deca nted extended aeration plant with no further solids stabilisa tion process. Mixed liquor is wasted directly from the aeration

Figure 1.. Tria l High Rate Drying Bed .

Figure 2. Turning Biosolids with a Mechanical Aerator.

p hase to a gra vity drainage deck and belt filter press. The resulting dewatered biosolids has characteristics substantially determi ned by the load from the da iri es (ty pically an increased fat content) and varies seasonally between 10- 13% solids.

I nit iall y SWWA estab li she d a composting facility at th e local landfill where it co mpo sted the dewa te red biosolids for subsequent beneficial use .

The closure of the landfill required the compost facility to relocate. SWWA was unable to establish a new site due to the N IMBY (No t l n My Back Yard) phenomena. In 1999, with no other alternative in place , SWW A negotiated to transport biosolids to Melbourne Water's W estern Treatment Plant for storage fo r an interim period and called tenders for co nsulta nts to prepa re a biosolids manage ment strategy.

Understanding the Treatment Processes Available T hroughout the project SWW A made a sig nifi ca nt e ffo r t to increase its knowledge. Both th e officers and the Board of SWW A made a range of study tours to look at processes and biosolids management techniques in Australia, the USA and Europe. These tou rs included a one week to ur when Board members and key officers hired a bus and visited relevant biosolids operations between Warrnambool and Sydney to gain first hand experience of the p rocesses and techniques being evaluated in the strategy.

The stu dy tours had a ve1y positive influence o n the project as it allowed SWWA to gain a greater first hand understa nding and th erefo re make better in formed decisions as th e strategy was developed. T he benefit o f these study

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WATER JUNE 2003

59

BIOSOLIDS

tours to the outcomes of the proj ect cannot be over-estimated.

Phase 1 - The Market T he initial request for tenders from consultants focussed on the AT AD (a uto the rmal aerobic digestion) and lime stabilisation tec hn ologies. The selected consultant offered a different approach, which emphasised the impo rtance o f the bioso lids markets. The co nsu ltant proposed that treatment processes must pro du ce a product which is best suited to the local area and therefore could only be selected after the potential markets for bi oso lids we r e assessed l ocall y.

Accordingly the strategy process started with a detailed review of potential beneficial uses for biosolids in the surrou nding areas.

T he survey reviewed a range of potential biosolids markets including site rehabilitati on, forestry and a range of agricultural end uses. The outcome of the investigations was that agriculture was by far the best alternative. W ithin the agricultural area it was recommended that application to Victorian EPA Stabilisation Grade T3 (NSW EPA equivalent is Grade B) be adopted, which would al.low use on crops, such as wheat, oats and oth er food crops not in contact with the biosolids, and sheep grazing. Pasture application for dairy or edible animals was not reco mmended because it required high er stabilisation grades and due to withholding periods placed by the Victorian EPA draft biosolids guidelines on grazing after biosolids application.

T h e p roduct best sui ted to t he identified markets was dewatered biosolids of stabilisation Grade T 3 or better. In order to further redu ce potential and perceived risks associated w ith biosolids application it was decided to produce a dewatered biosolids product of Grade T l /2 (equivalent to NSW EPA Grade A).

It was believed that producing a product of greater quality than required reduced potential risks to SWWA.

WASTE

FIGHT LOOMS

of li fe cost estim ates indicated th at a co mbination of these technologies could provide a solu tion which was 30-50% cheaper than th e next best mechanical stabilisatio n option .

Since the wastewater treatment plant is on a confined site the preferred optio n was to d ewat er bi oso lids at th e Warrnambool WWTP site on high rate drying beds an d transport it to a second site for stabilisation by spread ing, further dewatering by air drying and stockpile storage.

Phase 3 - Acquiring a Site

Figure 3. Unwanted Public Attention.

Phase 2 • The Processes The initial strategy report reviewed nearly all the commonly used stabilisation processes and a few less conventional processes. Using the AT AD and lime stabilisation processes as a baseline for comparison, together with the preferred agricultural market, a broad whole of life cost evaluation was prepared.

The key outcome of the ini tial strategy review was that the overall cost of the strategy was strongly dependent o n the solids content of the fina l product; if this could be improved, the key cost components of transport, application and storage would reduce greatly. T he secondary key o utcome w as that a suitable site for processing and storage of biosolids w as needed.

The initial strategy identified two innovative processes which had the potential to reduce biosolids volumes by up to 5 times, use less energy and rely on much simpler technology. These two processes were a proprietary system of high rate drying beds (Figure 1) and further air drying of dewatered biosolids using spreading and m ec hanical aeration to speed drying times (Figure 2). Whole

Acqu iring a site for pro cessing was a m¡ajor issue. Before the start of the strategy SWW A had lost access to the former composting site at the Warrnambool la ndfill and lost the battle to re-establish the co mpost operation at the nearby town of Koro it due to commu nity concerns. As a result of this encounter w ith the communi ty, the issue ofbiosolids was not perceived well by the commun ity .

Attempts to canvass the possibility of locatin g the biosolids sto rage and further air dryin g facility at Mortlake, about 50 km north east ofW arrnambool, were m et w ith vigorous community opposition .

The proposal beca me a local political footba ll, made the local newspapers as seen in Figure 3, and any short term chance of establishing biosolids management operations at the M ortlake WWTP dri ed up .

Subseq uently and fortuitously the opportunity arose for SWWA to purchase a former 75 hectare dairy treatment plant site in Camperdown, about 70 kilometres from Warrnambool. This site had an EPA li cence, existing lagoons and good proximity to transport corridors and end markets, and was ideal for further air drying and storage op erations.

To ensure the success of "selling" the Camperdown site as the processing site, SWWA engaged a public relations consultant. This consultant developed strategies to allay community fea r and gain community acceptance of the site. T he strategy was then implem ented in-house by the C.E.O . ofSWWA.

Phase 4 • Pilot Trials

Figure 4 . Deskins Biosolids Harvester.

60

WATER JUNE 2003

Figure 5. Deskins Polymer Mixer.

T he high rate drying bed concept had not been proven in Australia, despite having some 200 plus installations in the USA. Also on investigation it was found that w hilst there were anecdotal accounts ofbiosolids air drying, there was very little rigorous information available on stabilisation or drying rates by spreading and turning which could be used for designing

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an operation. Both of these approaches depend on th e loca l weather conditions and it was the refore decided that th e potential cost savings warranted pilot trials.

A full scale high rate drying bed of 12.4 me tres wide and 20 me tres long was bui lt and th e proprietary syste m including d rying bed m edi a ce ll s (Fig ure 1), harvester (Figure 4), polymer dosi ng equipm ent (Figure 5) , design and support was purchased. T rials were designed to determine the optimum loading rate , polym e r dose rate, solids content and to c heck claim s abo ut genera l operations of the system.

Th e optimum polymer dosa ge was found to be about 3 kg/ tonne dry solids, compared to the 4 to 6 kg/tonne dry solids used on the belt press. At a loading rate of 380 kg/m2/year, the harvested cake averaged 20% dry solids, after 7 days on th e bed . W hilst th is compared ve ry fav ou rably w ith th e belt fi lter press cake o f 12% dry solids it was less than predi cted by the manufacturer, due to th e high content of dairy waste in th e sewage and relative ly cool, wet weather en c ount e r e d th a t s umm e r at W arrnambool. (E vans 2002) .

Air d1y ing trials at th e Camperdown site were designed to compare the rate of d1ying and degree of stabilisation. Turning the solids compared using a dozer with a propri etary bi osolids turnin g device, a Brown Bear m echanical aerator (Figure 2).

Turning regimes of once, twice and three times per day were cotnpared. In addition the biological indicators of salmonella, E. coli, enteric viruses and H elminths (the micro-organisms regulated in the Victotian EPA biosolids guidelines) were measured to determ ine the degree of stabilisa tion achieved through the process.

The a ir drying tria l s at th e Camperdown site proved very successful.

Initial spreading took the dewatered

cake from 12% up to 30 - 40% solids and regular turning on a daily basis after this achi eved nearly 80% solids in 3 weeks ove r th e sum mers of 2001 /02 and 2002 /03 . Stabilisation ac hieved by the process was also very effective. The microorganisms regulated in the Victorian EPA bioso li ds gui delines we re measured to decrease to stabilisa tion Grade Tl / T2 (NSW EPA Grade A) levels altho ugh furth er veri fi cati on is required to ascertain w heth e r G rade T1 can b e reliably ach ieved. T he drying response and levels of E. coli fo r one typi ca l trial are shown in Figure 6 .

Phase 5 - Finalisation of Strategy Th e final phase of the strategy was to incorporate the data gathered from th e high rate drying b ed and air dryin g trials and review the w hole of life costs of the suite of biosolids managemen t options previously evaluated including use of th e n ew Ca mperdown site. T his evaluation was carried out together w ith a series of internal workshops and revie ws w h ich ensured that all de partments within SWW A had the chan ce to maintain th eir inpu t into th e fi nal strategy.

T h e main outcom es o f th e pil ot trials had two main impacts; • Whilst the high rate drying beds performed significa ntly better than the ex isting belt press, the relatively poor dty ing climate at W arrnambool meant that the bed area required was larger than fi rst estimated. As a result the cost advantage o f the beds over the belt press was marginal. When this factor was combined with the pressure for space w hi ch exists on th e site, it was decided to retain and augmen t the ex isting belt press fac ility .

Th e cost compari son was influe n ced by a managem ent decisio n not to install a standby belt press but to rely on an active

Virotec's new breakthrough YiroSewage TM Technology provides 20-30% savings in sludge management operational costs where it matters most in haulage and chemicals costs.

Because YiroSewageTM Technology improves the sludge texture, the solids content of the bio-cake, on dewatering, increases by some 20%.

With 20% less water being transported, an STP spending $500,000 per annum on haulage would save approximately $ 100,000.

The amount of polymer used to prepare the sludge for dewatering is also reduced by up to 60%, offering additional savings .

To learn more about these and other benefits of ViroSewage TM Technology - including phosphorus removal, odour reduction and plant augmentation - phone Frank Gnanam now for more information on (07) 5530 80 14.

ViroSewoge Technology delivers on environmentally friendly, odour-free soil conditioner as on end product.

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WATER JUNE 2003

61

Aquatec-Maxcon is Australia's leading supplier of wastewater treatment equipment, with an impressive range of products for minimizing biosolids production.

These products include:-

Thermo-System is the world leader in solar drying technology for sewage and industrial sludges and is represented by Aquatec-Maxcon in Australia and New Zealand. By optimising local climatic conditions and utilising solar radiation, Thermo-System provides an economical , efficient and environmentally acceptable alternative to conventional thermal sludge drying methods.

This versatile technology is able to dry sludges from as little as 2% to in excess of 90% dry solids content with minimal energy input, producing a substantially reduced volume of biologically stable, reusable biosolids for land application or incineration.

Ultrasound Sludge Treatment: Award winning Ultrasound Technology that can greatly reduce the amount of sewage sludge produced is available from Aquatec-Maxcon .

The process involves mechanically treating a portion of digested sludge, resulting in improved dewaterability and increased biogas production. Ultrasound treatment produces microscopic bubbles within the sludge, which implode and collapse. This cavitation helps break down sludge particles by releasing and activating enzymes, which accelerate the digestion process. Gas production can be increased by up to 45% in anaerobic sludge digesters.

AN>RITL GUiN&.VU> Andrltz-Guinard is one of the world's leaders in the manufacture and supply of Centrifuge Decanters. For over 30 years Guinard has been dedicated to the production of dewatering equipment and currently enjoys sales in excess of 300 units per year. Guinard has an international reputation for producing a quality, energy efficient and robust, low maintenance product.

Aquatec-Maxcon through its heavy equipment division and technical support team is well equipped to meet all service and spare parts needs.

•

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Queensland

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BIOSOLIDS

preventative maintenance program including a greater spare parts in ventoty and purchase of a mobile dewatering unit, which could also be used elsewhere in the region .

• Air drying o f biosolids by Brown Bear or dozer to in excess of 65% solids was successful and reduced the w hole of life cost of biosolids management. It also indicated that stabilisation grade Tl was possible to achi eve and T2 likely to be achieved. It shou ld be noted that further verification work is required to confirm the stabilisation performance of the proposed process, as requ ired by the EPA. The preferred option is a very simple technical option which requires a minimum of energy input and does not require any sophisticated equ ipment. It is also about 30% cheaper than the least cost mechanical stabilisation option. The preferred optio n also best meets th e primary project aims of being sustainabl e, environmentally friendly, cost effective and soc ially acceptable.

Broadly the preferred strategy for Warrnambool was as follows: 1. Trade waste control to maintain and in1prove biosolids quality 2. Applying biosolids to crops, such as wheat, oats and other food crops not in contact with the bi osoljds, and sheep grazing in accordance with Victorian EPA biosolids gu idelin es a!Jowable uses for Stabilisation Grade T3 biosolids 3. Producing a dewatered and air dried biosolids product of around 65% dry solids and a very high visual and microbial quality, with a minimum Victorian EPA Stabilisation Grade T2 and preferably Tl 4. Wastewater screen ing to eliminate recognisables from the bi osolids 5. WAS pumping upgrade 6. Augmentation of the belt press facility by holiling a greater range of spare pares and purchasing a mobile dewatering unit 7. T ranspo rt of dewatered biosolids to the Camperdown site 8. Air drying and long term storage for stabilisation 9. Seasonal storage of product at Camperdown 10. Finding suitable farmers and farms for land application 11 . Transport and application of biosolids to farms 12 . Establishing a biosolids management plan 13 . Community consultation

Lessons Learned The biosolids strategy is now moving toward implementation.

Out of the strategy process a number of important lessons were learned. Some of these are set out below: • Getting a su itable site for pro cessing is hugely important. If biosolids cannot be processed and stored at the treatment plant site then there are significant transport, storage and acqu isition issues which can impact both on cost and the public.

• Th e solids content of dewatered biosolids is a major cost driver.

The drier the dewatered biosolids the lower the cost of biosolids m anagem ent.

• Communi ty acceptance is critical. It can affect nearly all aspects of a biosolids management programme, particularly siting, transport and end use sites. Dealing with the community takes time and effort; go slowly, allow plenty of time and gain and build credibility. Using a professional public relations consultant to prepare a PR strategy reduced the risk of community rage.

• Understand the needs of the biosolids end users. A biosolids management programme depends on accepta nce and use of the biosolids product, in our instance by farme rs. If the marketing of biosolids is not successful and the right product is not produced to satisfy the market, then the biosolids management programme will probably fail, regardless of how good a processing plant is built.

BIOSOLIDS

• Understand about perceptions of the co mm u n ity, end users, n e ig hbo u rs, community leaders, Board, other authorities, and ourselves. Science is not Ekely to be the limiting factor, but such issues as the perception of a professional operation w ill have a marked effect (clean looking trucks w hich do not spil.l any of their load , neat w indrow s and stockpil es of produ ct w ith labelling, a clean fiiable homogeneous product with no recognisables, no clay, no clods) as w ill an open and hon est approach to community concerns.

• In dea ling wi th biosolids th e worst sce nario needs a solution. Contingency plann ing needs to be o wn ed by th e Authori ty and expe ri ence over Australia has shown many ti mes that all risks cannot be transferred to a co ntractor. SWW A 's 01iginal strategy for the provision of a new com pose site was co in co rporate the co ntingency plannin g li ability in the contr ac to r 's compost te nd e r . Th e composter w as not able to esta blish a new s ite in time d u e to th e N IMBY ph eno mena. This was not a transfe rable risk and had a much grea ter impact on SWW A as a resul t.

AGAL Australlan Government Analytical Laboratories

• Understand the treatment processes.

T his assists grea tly in gainin g co nfidence in decisions and credibility w he n dealing w ith Board mem bers and the commu ni ty.

There is no learning substitute for seeing, smel.ling and fee ling a process in operation and the value of doing so cannot be overestimated.

• Y ou need co kno w w here the b iosolids regulations are goin g. SWW A's strategy was develo ped at th e sa me time as the EPA were developing the ir biosoli ds guid elin es. Th e gu ideli nes sec the goal poses fo r any strategy and it is the refore essential that any strategy has th e flexibili ty to acco mm oda te deve lopm e nts a nd changes in regu lation s.

• T rea tment of bi osolids is manageable , be encouraged 11 It comes with knowledge and acceptance by all involved. Someti mes it is too easy to fo cus o n all th e negative aspects and potential problems. B ene fi cia l use of biosolids is a relati vely low risk and va luabl e recycling ini ti ative.

• Persevere - th e answer is there - it may take a w hil e to find it - w hat w orks for one may no t wo rk fo r anothe r.

• H avi ng the right consultant o n board is ve1y important. D eal w ith som eo n e w ho has a pro ve n track reco rd as a spec ialis~ in dealing w ith bi osolids.

Acknowledgements T h e a ut h o r s would l ik e co ac kn o w ledge the efforts of och er partne rs in th is proj ec t; the Board and staff o f SWW A, PSD P ty L td , MWH Australi a Pty Ltd and LV R aw li nson and Associates Pty Ltd. Their contributions co the proj ect are grea tl y app rec iate d.

The Authors Paul Darvodelsky, is a prin ci pal o f PSD Pcy Led. John Huf is Direccor of Engin ee ring Services and Hank Moritz, C ontracts M anager o f So uth W est W ater Auth ority.

References Darvodelsky P, M o rris C, 2003. Guide co M anaging J3iosolids. W arer 30 , February Evans A, 2002. T rialling the Deskin Quick Dry Filter Bed .fo r Biosolids Red ucti on - 65th An n u al W ater Industry Eng ineers a nd O perators Con fe rence, Septe mber 2002, rep roduced in WnterWorks D ec 2002 .

EXPERIENCE WITH TWO CONTRASTING TECHNOLOGIES FOR SLUDGE STABILISATION N Read, M Simpson, P Foster, A Carvell Abstract Th is paper compares two relatively mature Grade A stabilisation technologies for biosolids and quotes case histori es of facilities commissioned early in 2002. Ac Malabar, Sydney, the Alkaline Stabilisation Unit (ASU ) utilises a combin ed lime and heat system to process up to 500 dry tonnes per week of dewatered, digested primary sludge . In W ellington, N ew Zealand, th e Seaview WWTP uses the Thermal Drying Facility (TDF) to process just over 100 dry tonnes per week o f dewatered primary and waste activated sludge.

Introduction Community and env iro nm e ntal pressures concerning biosolids disposal are creating drivers for meeting ' Grade A' stabilisation requirements. Owners and their engineers are faced today with more options for processing and disposing of biosolids than ever before and o ften the choice between these options can be difficult. E va lu ati on of the va ri ous technologies is complicated by a lack of track record, particularly lo cally, or by a lack of experience with operating fa cilities .

The aim of this paper is to provide som e details of recent and local experience with two ofche more mature proprietary technologies available. le is assumed that the reader is familiar with the fund amentals of alkaline stabilisat ion a nd t h e rmal drying. T h e information on delivery, operations and maintenance history to date is intended co provide some background on the pra ctical issues associated w ith each technology.

Facility Descriptions Malabar STP Alkaline Stabilisation Unit (Owner/Operator: Sydney Water Corporation) The Malabar Alkaline Stabilisation Unit (ASU) is loca ted at Sydney W ater Corporation's largest sewage treatment plant at M alabar. Anaerobically digested primary settled sludge is fed to the facility 64

WATER JUNE 2003

from three existing centri fu ges at an average ra te of 4.4 dry tonnes per hour and a dry soli ds conten t of between 23% and 32%. The facility can also process raw primary sludge. The duty train is a proprietary process developed and supplied by RDP T echnologies, which uses electric heating and quicklime addition co achieve Grade A stabilisation. The standby train consists of a sludge/lime mixer w hich produ ces Grade B biosolids and can process up to 6. 7 dry tonnes per hou r.

SWC Biosoli ds strategy required that all significant investment in biosolids processing have Grade A capability.

Stabilised biosolids produced at Malabar contribute co SWC's o verall beneficial reuse programme and are tru cked off site for la nd application. Alkaline stabilised biosolids are particularly suitable for application to acidic soils common in the disposal area.

The main drivers for this project were to use a proven and familiar technology to produ ce Grade A biosolids, and to provide 5 days on-site storage - thus elimi-

nating the need to keep semi-trailers on site continuously and permitting weekend storage on site. This ASU is the second of three similar facil ities installed at Sydney Water plants.

Ancilla ries supporting the pro cess include ven tilation and odou r co ntrol systems; roads, landscaping and drainage; lime sto rage and conveying; chemical storage and dosing; a biosolids conveying system; electric power supply; closed circu it television and a control system li nked co the existing distributed control system (D CS) . Odour co ntrol for ammonia and hy drogen su lphi de emissions comprises wet scrubbers with acid dosing followed by biofilters. The equipment buildings and odour treatment equipment take up 2 100 m 2 .

Seaview WWTP Thermal Drying Facility (Owner: Hutt City Council, Operator: Hutt Valley Water Services) T he Therm al Drying Facility (TDF) is loca ted at the Seaview WWTP in Lower Hutt, near W ellington in New Zealand.

BIOSOLIDS

.L__ =--¡-

ITOIUI TAIi

- - -===- - -===-- - -Som Figure 2. Seaview TDF faci lity and solids processing area layout.

Local manu fac ture r Flo- Dry E ngineerin g su p pli e d a nd in s tall e d the dr y in g equipment. Th e syste m comprises a dewatered sludge silo , a single train w ith rotary drum, direct fired convection dryer, produce cooling and recycle system , d1y ing air and conde nse r loop, and tw in product silos for storage of up to three days produ c ti o n. Th e fee d sludge is a dewatered blend of raw primary and w aste activated sludge from a high race co ntact stabilisation process. Three centrifuges feed 22% - 24% DS cake co the fac ility at an ave rage race of 1.1 d1y conn es per ho ur.

At design average feed rate, the utilisation at the fa cility is about 96 hours per w ee k.

In th e event chat the dryer is unavailable fo r a period exceeding upstrea m storage capa city, cake ca n be o ut- loaded directly fro m th e storage sil o fo r trucking off-site .

Dri ed product is discharged into tru cks directly fro m the produ ct storage silos. To dace , all product fro m Seaview has been disposed o f to landfill. H owe ver, th e operating consortium is ac ti vely co nsidering a number o f optio ns for marke ting th e produce for various forms of benefi cial re-use. Current environ me ntal strategies in N ew Z ea land acti vely disco urage disposal o f organic material co landfill.

Th ermal d1y ing represented the lowest w ho le o f life costs for sludge processing and disposal at Seaview, even allowing for landfilJ- tipping charges. Fu cure b eneficial re-use is exp ec ted to furth er imp rove the economi c performance of the fac ility .

Co mprehensive safety systems include a nitrogen blanket in the event that smouldering or high temperatures are detected ..

Strategically loca ted explosion vents are provided in th e ' hot end ' of the system.

Th e cooling w ater for the condenser and fire suppression system s is suppli ed fro m th e plant reclai m ed effluent syste m.

Condensate is returned co the hea d of the primary sedimentatio n tanks. AlJ process units and silos are maintained under negative pressure to facilitate odour control. A spiration air from th ese units is

directed to the plant bi o filters togethe r w ith excess air from th e drying ai r loop and fou l ai r from ot her areas o f th e plant.

Th e fac ility is housed in a steel fram ed build ing w hich also accommodates other solids processing equipment, the main plant elect1ical room , the plant control room and th e labo rato ,y . The foo tprint occupi ed by the d1y ing system and siJos is approximately 570 111 2 . The faci li ty contributes approximatel y on e third o f the total fo ul air load co the biofilte r, wh ich represents a further 800 1112 o f site area in total. (Thu s 270 111 2 can be attributed to odour control requireme nts for th e dryin g system.)

Delivery Both facilities w ere delive red under c omp e titi ve ly te nde red d es ign - bui ld contracts, and in th e case of th e Sea view

TDF, contract responsibility continues for a further eighteen years of operations. The partners in the design- build consortia w ere common co both projects - Bovis Le nd Lease and C H2M HILL for M alabar, Bovis Lend Lease and CH2M - Beca fo r Seaview. Th e Malabar ASU was a standalone proj ect, starti ng at the discharge from the existing dewatering centrifuges, w hereas th e Seaview TDF forms part o f th e n ew Seaview WWTP. Sydn ey W ater C orporation 's specifi catio n for the M alabar ASU contained b o th pres c r ip t i ve and pe r formanc e elem e nts, in compariso n to Hutt C ity C oun cil's DBO contract w hic h was based almost enti rely on pe rformance requirements and standards o f service .

The deli vety timefram e for the M alabar fac il ity, fro m J anu ary 2001 to Augu st 2002, was comfortably ach ievable Th e program fo r Sea view was subj ect co diffe re nt co nstraints. T he TDF had to be integrated w ith other proj ect works, and the liquid stream of the new plant had co b e comm iss io ned fi rst in order to produce sludge for pro cessing . This provide d more time for design, but increased th e coordinatio n pressures on site du ring installation and commissioning. D esign comme nced in D ecembe r 1999, and co mpletion , after th e twomonth proving peri od, was reached in Marc h 2002. In t he absence o f o th e r proj e ct constraints, it is estimated that th e overa ll programme for de live ry of t h e

Figure 3 . Malabar alkaline stabilisation unit. TOP: View of overall facility. Dewatering building left foreground, stabilisation building left background. Storage building right background and biofilter on right foreground. LOWER RIGHT: St orage building, odour ducts, fans and scrubbers. LOWER LEFT: Int erface with dewatering centrifuges.

WATER JUNE 2003

65

BIOSOLIDS

Figure 4. Seaview TDF - main dryer components Installed prior to building erection.

dtying facility could have been accelerated by nearly a year.

Design and Construction The Malabar ASU facility was installed in a vacant area within the boundary of Malabar STP which is overlooked by n eighbouring properties. Equipment of 'industrial' appearance such as fans, chemical scrubbers and du ctwork, was situated so that it was screened from view by the buildings . A 12-metre height restriction also impacted the layout, particubrly that of the product storage building.

The 1nain physical interface is at the discharge from the centrifu ges, and required modifications to and extension of the dewatered cake conveyors. Th e pre-existing lime stabilisation plant r e main e d op e r atio nal throughout construction. The existing lime silos re main ed in se rvice, thus a staged changeover was implemented to maintain ope rations during constru ction and comnu ss10nmg.

The Seaview TDF required numerous interfaces with the treatment plant, but the main logistics challenges were during construction. The dryer building houses a n umber of bulky components, notably the rotary drum, cyclones and the recycle silo. This required a staged approach to construction - the building foundation and parts of the frame were constructed first, and then construction paused to p ermit installation of the bulky items. With suitable physical protection, the building works continu ed, which then provided a weatherproof enclosure for the M&E installation work.

At Seaview, it was possible to integrate the TDF layout with upstream sludge processing equipment, the main electrical room and the main p lant control room.

This avoided duplication of site services and provided easy access for operators.

lin e odour limitations are stringent. At Malabar, the design contends with both ammo nia ge neration and hydrogen su lphide , w hich re quires chemical scrubb in g followed by a 'polishing' biofilter. At Seaview, elevated temperatures, high process airflow ra tes and (odourous) dust generation compounded the odour problems.

Control Systems

At Malabar, the ASU facility was interfaced with the existing DCS . This necessitated a single source supply, and the ASU suppliers developed comprehensive funct iona l specifications t o e nabl e programming of the DCS. The control system for the Seaview TDF is integral with a PLC based site control system for the entire plant. Programming of the proprietary elements of the system was carried out by the supplier and downloaded into the main plant PLCs.

Commissioning At M alabar, interfa ce issues that presented challenges during installation proved to be useful during process commissioning - allowing easy diversion of feed between the existing and new systems. Thus the new facility could be started and stopped relatively easily .

Stable operation was demonstrated during the functional verification trial period com p rising two 10 da y periods.(one for the duty train and the second for th e standby train). The ASU

and odour control systems operated well from the start although minor optimisation of the process continu ed as more experience in continuous operation was gained. The commissioning team guided 'on the job' operator training during th e trial period. Following the functional verifi cation trial, a 12-week processproving period co mmenced, when the Sydney Water staff operated the plant with day to day supervision by the contractor.

At Sea View the 'dry run' tests were carried out using imported dried sludge from another TDF on the North Island.

Back mixing of dewatered sludge with recycled material is an essential part of the process, and the imported material was also used to 'seed' the system when process commissioning co mmenced. System testing involved extensive use of a process simulator to prove that the control logic was consistent and had addressed all the control issues identified in the HAZOPs. This was an arduous procedure, but was useful in enabling problems to be rectified early, befo re ' live' commissioning. The team was keen to commission the TDF on the optimum blend of p1ima1y to waste activated sludge as thermal drying plants are sensitive to variations in sludge feed quality. Temporary arrangements were mad e for disposal of dewatered primary sludge, which was produced as soon as the WWTP was put on line, until such time as the biological process generated sufficient WAS to produce the desired blend.

The temporary arrangements were costly and increased the risk of offensive odours during commissioning - it was key to the success of the project that process comm.issioning of the TDF went smoothly.

While commissioning of both facilities did proceed relatively smoothly, it would be rare to commission any process plant without some teething problems. At Malabar, a previously undetected wiring anomaly in equipment supplied from the US resulted in some heating coils burning out during system testing, causing a short delay while new coils were sourced.

Odour Control

Odour control was a major influence in the design of both facilities, as fence

66

WATER JUNE 2003

Figure 5. Seaview TDF - interior and exterior views of completed facility.

BIOSOLIDS

D uring process commissioning, a procedural error with ma nual li me addition resulted in a temperature rise exceeding sp ecifi cation , whi ch damaged conveyor linings. The most significant problem faced during commissioning was the control of am moni a levels in th e storage building during out-loading. Distu rbance of the stockpiles by the front-end loader ca used brief, localised, high concentration emissions. M odifications to the ventilation system and installation of airflow bailles effectively addressed the issu e, and now the ammonia concentrations remain well below OS H standards.

At Seaview, the control system relies on numerous fie ld instruments. A fau lty instrument can resul t in shu t down of conveying systems, fo llowed by a shut down of th e burn er, and ultimately a shut down of the entire syste m . A full emergency shutdown w hil e the system is full of partially processed sludge is to be avoided , as the system needs to be cleared and made safe before a re-start. In addition, starting the system from co ld can take up to an hour before oxygen levels with in the drum are low enough to allow processing to comm ence.

T he emergency provisions provided in the design (some as a result of HAZOPs), plus the exhaustive system tests carried out beforehand proved their worth and a full , un-sch eduled shu tdown was avoided during comntissioning. The fi rst few days of start-up proved to be lab our intensive as th e system was contin ually monitored and adj usted to cope with the nature of the feed, and address unforeseen minor probl em s before they could invoke a full sh utdown co ndition. Some PID loops were particularly sensitive and could only be properly tuned during operation.

Malfunction or fouling of field instruments (particularly flow and limit switches) caused a number of spurious alarms before they were replaced or modified. An unexpected nitrogen release into the recycle silo occurred shortly after conu11issioning when an instrument suffered water damage.

The TDF ac hieved stable operation within a week of start-up , allowing the overall treatment plant to enter into the 60-day proving period required under the contract. "On-the-j ob" operator training continued throughout the proving period, and the permanent operators gradually took over from the commissioning team.

During the proving period, a succession of 24-hour performance tests were undertaken under differing feed conditions to verify performance.

Table 1. Operations history Operations

Malabar ASU July - Oct 2002

Seaview TDF Jan - Oct 2002

2 5 30

259 4

10100 440 10 0 %

2820 217 96. 5%

Dry tonnes processed Product tonnes Product truck movements Overal l Availability (of time when needed for processing)

Note: Trucks used at each facility are different. At Malabar a mixture of semis, truck and dog trailer and B doubles is used, with load capacities between 22 - 32 tonnes per truck.

At Seaview, covered trailer units have an effective capacity of about 1 4 tonnes.

Operations Th e TDF has been operational since the beginn ing of 2002, and full-scale operations commenced at Malabar in July.

Th e operations h istory followi ng start u p is su m marised in Table 1.

One of the main operational issu es com mon to both fa cilities is managing fl uctuations in the q uality of the feed sl udge. At Ma labar, th is relates to the water conten t of the cake, which impacts both th e electric heati ng requirement and the rate of lime addition. At Seaview, both cake water co ntent and the ratio of primary to waste activated sludge ca n affect operations. A wetter ca ke will req uire adjustm ents to the recycle stream to control the quality of th e mixed feed to th e dryer. If th e raw blend has a high primary sludge content, this tends to result in a mo re friab le produ ct, which may in tu rn prod u ce m ore du st and affect produ ct qu ality. The Seaview TDF also reacts to vario us other internal and external influen ces, including airflow rates, produ ct consistency, ambient conditions, recycle product size and dryness.

Safety system s are checked prior to eac h start up as part of standard operating procedures.

At M alaba r the lon g conveying distances of the stabilised biosolids via shaftless conveyors produce a sli ghtly clayey material. This has been noted at other SWC plants and longer conveyin g distances m ay need belt conveyors in lieu of screw conveyors.

Both facilities incorporate automatic control systems, w hich can cop e with ntinor hour to hour variations in feed sludge, but in both cases operator input is required to adjust the base parameters should the cake vary by more than 2% water content. If the base parameters are not adjusted, this can result in excessive lime dosing at M alabar, and operation at elevated or depressed burner temperatures at Seaview. At both facilities, cake water content is measured on a regular basis, and both have m ean s of visual observation of

the feed. (A CCT V system at Malabar, and transparent observat ion panels, plus sampling ports at Seaview.)

Maintenance At Malaba r, the ASU maintenance in terva ls for major equ ip ment are m e a s ured in terms of mon t h s .

Maintenance schedu ling is facili tated by th e d uty/standby tra in arrangem e n t, which all ows the process to continue to operate if major maintenance activities take place.

M ain tenance issues include the gas detectors (ammo ni a an d h ydrogen sulphide) in the biosolids storage building and the odou r du ctwork prior to the li me sc ru bber. T he gas detectors are linked to the access door con trols to th e biosolids storage b u ilding and p reve nt access if the gas co nce ntrations are high. These are important sa fety devices and require strict manual ent1-y procedures to be implemented if faulty. Th ese m eters are sensitive and requi re specialist servi ces to maintain. T he odour ductwork prior to the li me dust scrubber builds up lime dust over time and is manually cleaned by flushing to low points.

At Seaview it had been expected that dust m igh t acc umu late wi t hin th e building. [n operation , this has not proven to be a problem, but regular housekeeping is still impo rtant, particularly during scheduled maintenance. Th e dust from th e TDF is also inhere n tly abrasive. M ost components from the prima1-y mixer through to the product handling system co mbine hard surfaci ng an d wear strips to cope with attrition.

Wear components need regular checking to ensure that tolerances are not exceeded, and a regular replacem ent program is in place. Experience over the past year has enabled the operators to refine their spares invento1-y and spares ordering procedures.

Each fac ility has specifi c maintenance activiti es and issues, but the TDF is more maintenance intensive than the ASU. The operating regime fo r the TDF requires at least one day a week reserved for prevenWATER JUNE 2003

67

BIOSOLIDS

tati ve maintenance tasks. T h ese typi cally include cleaning of air extraction lines, greasing bearings and drum run surfaces, cl eaning and inspectio n o f instrumentation , a ch emi cal clean- in-pl ace of cooling water lines and co ndenser, and general insp ection o f fans, screens and o ther equipment. R egular cleaning o f th e internals of the drying air loop and condenser system is necessa ry to prevent partial blockages and instrument fouling.

Table 2 . Comparison of facility design and operating parameters.

Parameter

Units

Processing rate (design average)

Ma labar ASU

Seaview TDF

OT/wk

500

98

Processing rate (maximum)

OT/ h

4.4 (Grade A) 6. 7 (Grade B)

1.15

Feed dry solids content

%OS

23 to 32

20 - 22

Product dry solids content

%OS

35

92

h m2/m3

120

72

680/ 8 ,160

500/ 5,000 70/ 700

Product storage capacity Process bu ilding footprint/ enve lope (average throughput)

Facility Comparisons

Product storage footprint/envelope

m2/m3

1,420/ 14,200

Direc t comparisons between so lids processing faciliti es are problemati c, as many points of compariso n are site or sludge specific. This case is no exception, in fact th e two facilities bear li ttle in common other than they w ere delivered under similar m echanisms, and at roughly the sam e time. Non etheless, a comparison o f design and operating param eters is considered a useful exercise, in th at it h ighlights the principal practical differences be tween the two tec hnologies.

N o te that the informatio n provided in T able 2 takes no acco unt o f th e di ffe ren ces in facility size or nature of the feed sludge between the two facilities.

Based o n the d esign and op erating param eters for eac h facility, these data have be en n orm.alised in an attempt to provide comparative figures based o n processing requi rem ents per dry tonne (Table 3) . As the feed sludge solids co ntent at each fac ility differs, the figures for Sea view have been adjusted for a feed o f dry solids comparable to M alaba r - ie. approximately 1. 57 d ry tonnes per ho u r at 30% dry solids. O ther principal p oints of difference, w hich m ay ske w the co mparison, are discussed below.

Th ere are many differences between the two facilities that are not represented by this comparison. T he M alabar facility processes ana erobicaUy di gested primary sludge, w hereas the Seaview facility p rocesses a blend of raw p rimary and waste ac tivated sludge . Fu rther, the processing capacity at Malabar is five times that at Seaview . Malabar also has a standby p rocessing tr ain, w hi c h t e nd s to exagge rate the process foo tprint fo r M alabar in the comparison.

The main difference is the quantity and natu re of the produ ct. For every to nne of dry solids processed at M alabar, four tonnes of spad eable product results, w hereas at Seaview, the ratio of dry to produ ct tonnes is close to un ity and the p rodu ct is granular with a lower bulk density. The impact on the facilities is seen in the storage fo otprint requirem ents, air flows fo r odour treatment, and in tru ck

Utilisation (average production)

h/ wk

112

96

Total connected load

kW m3/h

986

350

57,000

12,000

68

WATER JUNE 2003

Foul air ventilation rate (to odour control)

m o vem ents. For roughly the same throu ghput, number of truck m ovements at Malabar, including lim e delivery trucks, is fi ve tim es greater than at Seaview. Produ ct o u t-loading, handlin g and di sposal req uirem e n ts are also ma rkedly different.

The co mparators given in T able 3, eve n no rma lised , hav e site sp ecific attributes. (One example is th e h eight restrictio n on structures at M alabar).

Similar facilities co nstru cted at di ffe rent sites w ould be unlikely to compare in exactly the sam e manner.

This discussion has deliberately stopped short of comparing capital and processing costs for the two facilities, for a number of reasons: • A true co mparison of processin g costs sh o uld incl u de upstream pro cesses, inclu ding thi ckening , di gestio n and

dewatering, and their influ en ce o n operatio n of th e Grad e A stabilisatio n system s. For exa mpl e, drying p la nts retro- fit ted at plants with an aerobic digestio n are often integrated into the overall heat and energy cycle, fi red by digester gas and recycling waste heat to the digesters. At Malabar however, where co-gen eratio n systems are already in place to utilise d igester gas, integration in this mann er would be m ore compli cated.

• Th e two fac ilities are loca ted in di ffe rent co untries. Also, Malabar uses tech nology and equipme nt impo rted from the US, w hereas the d ryer at Sea view is of lo cal manu fac ture . Th ese factors would inevitably skew a cap ital cost compariso n, even though the two fac ilities were delivered in a similar fashio n.

• Although operating consumables ha ve been verified by perform.ance trials, th ere

Table 3. Normalised facility design and operating parameters (per dry tonne processed at 30% OS feed sludge).

Parameter

Units

Malabar ASU

Seaview TDF

Process bu ilding footprint

m2/0T.h

306

318

Product storage footprint *

7.96

0 .57

Odour treatment footprint

m2/0T.h m2/ 0T.h

470

180

Total facility footprint (excluding roads)

m2/ 0T.h

784

459

Foul air venti lation rate (to odour control )

m3 / 0T.h

12,768

7,637 223

Total connected load

kW/OT.h

221

Electrical power consumption

kWh/ OT

184

Gas power consumption

kWh/ OT

Total power consumption

kWh/OT

184

Quicklime consumption

kg/OT

224

Water consumption (plant effluent wate·r)

m3/0T

Other Chem icals:

* Based on 5 -day product storage capacity.

156 2059 2215 102

H2S04 for ammon ia scrubber (1.2L/d)

NaOH for CIP systems.

Nitrogen gas for safety system

BIOSOLIDS

i¡s still scope for optimisation at both facili ties. Maintenance and replacement costs w ill also be a sign ificant factor, and it w ill be some time before these costs can be properly established at either fac ility. • Product disposal costs w ill have a significa nt impact, but do not necessarily reflect the inherent value of the product. As a soil am endment and source of nutrients, the Malabar product has a value in terms of beneficial re-use that can be difficult to quantify in dollar terms. At Seaview, beneficial re-use has yet to be full y in vestigated, and it is possible that the product may gen erate a revenue stream.

Conclusion The discussion has highlighted similarities and differences between two technologies, rather than draw definiti ve conclusions. Both tech nologies are now relatively mature, w ith numerous install atio ns arou nd the world. Each has specifi c benefits and drawbacks depending on the biosolids management strategy adopted .

In terms of delivery, the two facili ties were very similar.

Competitive procurement against a performance specification remains an effective m eans of procuring these techn ologies, although the number of suppliers is limited. Properly delivered, either technology will provide an effective, workable and reliable installation. Other means of delivery such as Alliances cou ld yield si milar or better resu lts.

Management of interfaces and coordination issues were the key factors in the successful delivery of both projects, assisted by recognition of the importance of early award of sub-contracts for the proprietary and long lead equipment.

Commissioning and operati ons issues are quite different. The th ermal drying facili ty has many more co mponents and systems than the alkalin e stab ilisation unit. The majority of th e systems are critical to the operation of the d1yer, and a failu re in any one of them can lead to an un-schedul ed shutdown. Although both faci lities are fully automated and can be run with mi ni mal operator input when properly set up, it must be recognised that there is greater poten tial for service interruption with the dryer than with the ASU. Although both technologi es are sensitive to variations in feed sludge quality, adj ustments to the drying system are possibly more involved and complex than those requ ired for th e ASU. H ence comprehensive operator training is essential.

T he differences carry over to maintenance, although there is insufficient experience with either facility as yet to draw fi rm conclusions. Nonetheless, the indications are that preventative maintena nce and wear replacement requirements for the d1yer are more time consuming and onerous than for the ASU. Energy consumption is far higher for the d1ying plant than the ASU, but this needs to be balanced against the most significant¡ differe nce between th e two technologies, w hich is the quantum and nature of the product, and the potential that the produ ct holds. The alkaline stabilised product is intended for land application and has little potential for other forms of beneficial reuse. The dried product is lower in volume and has potential for various forms of reuse - as fertiliser, direct use as a fuel, or conversion via other processes to other forms of fuel or energy.

Services; Mr Peter Flynn, Bovis Lendlease; Mr Paddy Atkinson, C H2M Beca.

References New Zealand Waste Strategy - Towards zero waste and a sustainable New Zealand, Ministry for the Environment and Local Government New Zealand (March 2002).

The Authors Nicholas Read and Murray Simpson are Senior Project Man agers at CH2M HILL Australia Pty Ltd. nread@ch2m.com.au, msimpson@ch2m.com.au. Peter Foster is a Senior Project Mechanical Engineer at C H2M HILL Australia Pty Ltd. pfoster1 @ch2m.com.au. Andrew Carvell is the Operatio ns Supervisor for th e Sea':'iew WWTP at Hutt Va lley Water Services, acarvell@hvws.co .nz

Acknowledgements The authors would like to acknowledge the following for contributions and permission to publish this paper: Mr Barry Windschuctel, Sydney Water Corporation; Mr Alan Bannatyne, Hutt City Council; Mr Mark Christison , Hutt Valley Water WATER JU NE 2003

69

~~!]it~~

OS OLI DS

SLUDGE DEWATERING PITFALLS A Hertle Abstract A large proportion of the costs for benefi cial reuse of bi osolids, or for the d isposal of non-reusable sludges, is transport. Reducing the water content (dewatering) ofbiosolids and sludges is a key cost saving exercise at water and wastewater treatment plants.

Th e two dominant mechanica l dewatering technologies are belt fi lter presses and solid bowl centrifuges. These are both estab lished tec hnologi es .

However, a significant number of installations do not operate to the satisfaction of the end-user. The purpose of this paper is to raise awareness of typical operationa l issu es chat can reduce the performance of mechanical dewatering equipment, and co provide a basis for co nstru ctive dial og between suppliers, designers and users.

Background Sludge is a by-produ ce of almost all water and wastewater treatment processes.

Due to the quantity and / or putrescible nature of sludge, it usually undergoes further processing on site before reuse (e.g. as " bi osolids"), disposal o r furth er processing off site (e.g. composting). A typical on site processing step is the reduction of the water content (dewacering), which may be carried out by various means ranging from sludge d rying beds to thermal dryin g . M edium and large size installations often employ mechanical dewatering to reduce trucking costs or as a prerequisite fo r further processing.

M any mechanical sludge dewacering techno logies are ava ilable. The two dominant technologies in today's market are belt filter presses and solid bowl centrifuges. Boch are long established technologies that have been developed over tim e t o meet increasing user demands. D espite that, sludge dewatering installations, in particular fo r wastewater sludge, seem to attract an over- proportional quantum of negative assessmen t from their users. M ost reported problems are related to: • m echanical issues, such as corrosion, vibration or leakage • electrical or control problems • performance problems.

70

WATER JUNE 2003

Centrifuge

This paper foc uses on performance problems. Common causes for these problem s are discussed based on the author's experience.

Performance Problems Most problems are recogni sed or perceived du e to non-compl iance with performance expectations or performance guarantees. The underlying cause of a performance problem can usua lly be attributed to : 1. unrealistic performance guarantees or expectations 2. duty other than specified 3 . shortcomings in the dewatering un it or its ancillaries 4. impacts from processes outside sludge dewacering 5. unsuitable indicato rs to measure th e performance.

Unrealistic performance guarantees and duties other than specified should be a matter of the past given the networks (such as the AW A) available these days to share experiences.

Unfortunately, for various reasons knowledge sharing is not as good as it could be and professionals should exercise p ersonal judgement and experience when considering performance guarantees.

Shortcomings in the dewatering uni t, external process factors impacting on sludge dewatering an d suitable performance indicators are discussed in the following sections.

Shortcomings in the dewatering unit Belt filter presses Belt filter presses are ofte n chosen fo r their simplicity as they are compara tively easy co sec up and optimise compared to cen trifuges. In practice however, significant experi ence is required to achieve satisfactory performance. A belt filter press that is known to perform we ll in one industry may not necessari ly offer the best solution for a different appl ication. For exa1nple a press designed for paper sludge will possess significantly diffe rent features fron, a machi ne designed fo r juice pressing or sewage sludge dewatering.

Fu rther, a comparison between various sewage sludge presses will yield differences in design features as the suppliers seek to address the demands of particular markets, e .g. small plants, hi gh cake dryness, corrosive atmosphere, low budget etc.

Typical differences include: • fram e shape, weight, material and functi onality • drive system • bearing selection • belt selection • number, size and design of rollers • length and design of gravity drainage section • length and design of wedge section • length o f pressing section and number, size and type of rollers therein (S-bend rollers or line pressure ro llers ("pressnips")).

BIOSOLIDS

Each of these pa rameters affects cost as well as machine perfo rman ce.

From a general perspective, the variety of belt fi lter press types available is desirable as it allows selection of the most suitable produce fo r a certain applica tion.

H owever, th e drawback is that a thorough u nde rstanding o f the tech nology is required to make a well-informed decision w hen selecting a belt fil ter press. Exam ples are :

Centrifuges

• A long drai nage section ma y not provide an advantage w hen the feed sludge is already fairly thi ck.

• When maxim um cake dryness is the goa l, drainage and wedge zone belt supports are important as well as the length o f these zones and various features in the press zone.

• Th e type and design li fe of bearin gs needs to be cons idered. Fo r a long and tro uble-free bearing life, the bearing seal syste m is a criti cal design fea tu re.

• Fram e material se lection mu st not only cake into considera tion corrosion but also possible differences in the mechanical strength of the frame. A low price sta inless steel fra me may provide benefits in terms of corrosion con tro l but may also have a pe nalty i n regard to maximum belt te nsion etc.

• T he type and quality of the belts is often overlooked. Diffe rences between products can be significa nt .

The principle chat it is against eco nomics to obtain a better product for a lower price (apart from the price fluctuations due to com petitio n) ce rtain ly applies for belt filter presses. With the large range of machine types and brands that are available, a cost co mpari son muse therefore include a tho ro ugh tech n ical assessm ent of eac h offered ma ch in e design.

Common causes for non-performance of a belt filter press include: • Wear: Blinded belts; W o rn belt supports/sagging belts; D rive ro llers slipping.

• Design : Utilisation of gravity drainage and wedge zone areas; Belt supports in the gravity drainage and wedge zones; Fi rst press rolle r perforated or not; Number, size and arrangement of further press rollers; Filtra te trays overflowing onto roll ers below.

• Operation : Belt speed too high (insu ffi cient residence time in the press); B elt speed too low (sludge layer too thick); H ydraulic and / or solids load fluctuat ing; Wrong polymer; P olymer dosing (details discussed below); Impacts fro m upstream or downstream install ations (see below).

Hi gh er ca ke dryness is the main reason for an apparent tre nd towards m ode rn high speed / hi gh performance centrifuges in some parts of Europe. M any E uropean sludges are readily dewacered by high performance centrifuges, and the costs associated with increased polymer and/or power consumption are generally offset by reduced disposal costs, w hich are generall y on a very high leve l. These economics are however not necessarily the sa me for an application in Austra lia.

As with belt filter presses, centrifu ge design has an impact on performance and price : • high performa nce (high speed) decanter or standard d ecan ter

Ce ntrifu ges offe r several advantages over belt filter presses such as small footprint, odour and aerosol control, and possibly a higher cake dryness (depending o n sludge characteristics). In regard to the latter, it is noted chat so me modern belt filter presses ac hi eve cake dryn ess of t he sam e order of magnitude as ce ntrifu ges, bu t they may impose a greater footp rint and may inc ur higher capital costs .

• scro ll (sc rew conveyor) dri ve system • main dri ve system • bowl mate rial • cou nter- or co-current feed • start up options, such as flu id co uplings or VFD • control system to maintain constant scro ll torque • wea r/ab ras ion protection system • noise level.

Apart from these points, the solids co n vey ing an d cen t rate syste m s o f ce ntrifuges are sometimes found co reduce their potential performance.

W hilst each of the parameters above influen ces the performance and/or price, the key parameter is w h e th e r t h e centrifuge is high performance or standard.

Alth ough the autho r is not aware of a fo rmal definition, in water treatm e nt and sewage sludge applications the terms " high performance" cennifuge and " high speed" are most com monly applied to centrifuges that produce a centrifugal acceleration G of ~3,000 times the earth 's gravitational acceleration (g) at th e bow l wal l.

Centrifugal acceleration C, angular speed Q and bowl radius r are linked via the fo rmula G = Q 2 r. Centrifugal acceleration is most common ly quoted in mu ltiples of g, the centrifuge's speed is expressed in revolutions per minute II and bowl size is expressed as diameter d. With d measured in metres, C is expressed as

7t2 112 d 112 d G = 30 2 -2 9.81 g = 1800 g

(l)

Ic is clear from Equatio n (1) that t he bowl speed requ ired to achieve ?'.3,000 g is dependen t on the bowl diam eter. For example, a centrifuge with 550 111111 bowl d iameter wo uld require a min imum o f 3 130 rpm to mee t this criterion , whi lst a sma ller mach ine with 350 111111 bowl diameter would requ ire almost 4 000 rpm.

Another impo rtant difference between centrifuges is the type of scroll drive system. Som e manufacturers offer syste ms w here the differential speed between scroll and bowl is fixed (pul ley sec). H owever it is more common fo r centrifuges these days to be deli vered w ith automaticall y co ntrolle d scroll dri ve systems where the differential speed is variable and con trolled su c h that a preset scro ll to rq u e is mainta ined . Various mechanica l/electrical scroll torque control syste ms have been developed with different levels o f sop histication. M.ost modern systems all ow user-defined setting of operating torque and can alter differential speed over a relatively wide range. T he differences between these modern scrolJ drive systems are considered rat her philosophica l in the sense that performance problem s are rarely due to li mitations of the control system (alth o ugh less soph isticated systems may lead to a slightl y lower performa nce).

Notwithstanding that, a decision between chose (variable) scroll drive systems should be made considering all th e ir respective features.

In genera l, the torque setting is one of the most impo rtant parameters affecting ca ke dryness. It sho uld the refore be se t reaso nably close to the scroll d rive un it's maximum opera tional torque. For a give n sludge the torqu e increases w it h cake dryness and feed solids load. B oth parameters therefore have to be balanced and the scroll dri ve unit has to be designed such t hat it does not pose a limitation.

Another important centrifuge setting influen cing the key performance param eters of solids capture race and cake dtyness is the pond dept h or wei r diamete r. In co ntras t co thi cke n in g centrifuges, dewacering centrifu ges can be operated w ith a weir diameter that is less than the sol ids discharge diameter because the outlet via the cake discharge is blocked fo r the centrate by the cake accumulated in the conical section of the mach ine. A small er we ir dia m eter increases t he centrate retention time in the centrifuge and can thus increase the capture rate . At sma ll weir diameters the pressure of the water column in the centtifugal field assists WATER JUNE 2003

71

BIOSOLIDS

the scroll in conveying the cake out of the centrifuge. Both effects thus contribute to higher throughput.

Potential operational reasons for poor performance, apart from unsuitable torque setting and pond depth, are similar to those of belt filter presses.

T he centrifuge feed arrangemen t 111ay be counter-current or co-current. This is rarely a distinguishing factor these days as all 111odern high performance centrifuges are designed with counter-c urrent feed.

Historically counter-current feed arrangements were rarely favoured du e to co ncerns that solids which settled in the cylindrical pare of the centrifuge have to be con veyed past the feed point. It was thought chat the turbulence at the feed point would disturb the sediment and thus be detrimental to the captu re race.

H owever, experience has shown that this is not the case, and counter-current feed arrangements are now favo u red.

A final issue that will be discussed here is the main drive system. Historically fluid couplings were preferred as they reduce the start up currents of the main drive motors by reducing the load on the shaft.

Howeve r , fluid coup lings caused frustration because they may lim it the number of start-u ps as the oil has to cool down between start- ups. Whilst this is not so much a performance problem, it is an operational and troubleshooting impediment, in particular at times when the n1.achine is experiencing other problems and therefore sh u tti ng down more freque ntly. W hen overheating protection was provided by plugs, cleaning up of oil spills was a further problem. Fortunately most modern centrifuges are equipped with electronic solutions, most commonly fre quency inverter start up.

Ancillary and upstream Installations The impacts that the ancillary installations at a dewatering plant have on its performance are sometimes overlooked or under-estimated . Shortcomings in the polymer system (make up or dosing) must be one of the most frequent causes for u nsatisfactory performance.

Polymer system The addition of organic polyelectrolyte (polymer) is vital for the satisfactory operation of belt fil ter p resses and dewatering centrifu ges. Although the latter could theoretically work without dosing, the solids capture rate would typically be below industry standard. A significant portion of the operating cost of dewatering equipment can be attributed to polym e r consumptio n , w hich is

72

WATER JUNE 2003

Belt filter press

therefore often chosen as performance indicator (see below).

The design of the pol ymer system unfortunately is often somewhat neglected or subj ected to budget constraints.

H owever, it must be rememb ered that a constrained polymer system will limit th e performance of the dewatering plant.

Typical errors may occur in any part of the polymer system, for example: • unsuitable polymer • insufficient polymer ageing time • incorrect polymer concentration • dos ing pump capacity is li mi ting dewatering machine throughp ut • po lymer dosing control strategy unsui table • polymer dosing point(s) not optimal (mostly belt filte r presses) • insufficient (or too much) turbulence at the point of polymer injection • insufficient floe maturation time (belt filte r presses only) .

When designing a polymer system it should be kept in mind that no sludges are exactly equal. H ence there is no universal polymer or dosing regime that provides optimum floe and cake stability, and good clarification at high throughputs and acceptable costs. Rather, this must be determined fo r each plant individually.

It is good practice to undertake lab scale and/ or pilot testing upfront, and then design the polymer system. However, sludge properties are liable to change due to operational alterations upstream of the dewatering process or for no obvious reason at all. While if this happens fu rther tests may be undertaken to determine a suitable alternative polymer, it is likely that for some time the existing polymer would have to be used at a significantly increased dose rate. It is therefore advisable to design the polymer system with consideration of

the high end of the dose rates suggested by th e supplier or reported from similar installations.

The poly111er dosing control strategy also has to be carefully considered. Small installations often operate with fixed speed sludge pu111ps and the polymer flow rate is adjusted 111anuall y to suit the sludge feed. More sophisticated installations feature flow-paced polymer dosing where the polymer flow au tomati cally fo llows the sludge flow according to a pre-set ratio. This system works well so long as the feed sludge concentration and polymer concentration are reliably constant. If the latter is not the case, the polym er syste111 has to be modified to reliably ac hieve constant polymer concentration . If the feed sludge concentration is not constant (e .g. feed from a thickener), solids loadpaced polymer dosing is required unless the upstream process can be modified such that a u niform feed sludge can be provided. If the dewatering feed is from various sources th e potentially different dosing requirements have also to be taken into account.

Impacts from upstream processes Upstream processes can influence sludge properties and quantities, therefore impacting on the performance of a dewatering plant . Given the variable nature of water and wastewater treatment plants only the key impacts are given as examples: • varying slud ge concentration if w ithdrawal is fro m a tank where consolidation can take place • seaso n ally varying algae conte n t (quantity and species) • change to a different coagulant or a different coagulant dose rate for algae, solids or o rganics removal • introduction of new process steps/plant upgrades

BIOSOLIDS

• increased volatile solids (VS) content in digested sludge due to greater sludge quantities or shorter hydraulic retention time (HR T) in the digesters • change in sludge composition due to different sludge species in a sludge mixture.

Most of these causes are self-explanatory, however, they should not be overlooked when assessing reasons for poor performance.

From a design perspective it is important to conservatively consider all impacts of the likely upstream process variations.

Preferably they should be explained to the supplier so that they are included in the equipment selection process.

Upstream processes can also impact on the operational side ofdewatering. For example, if the treatment process is modified to achieve enhanced biological phosphorus removal, crystallisation of struvite is possible. Whilst such problems are not always the case, they do occur and may require installation of a standby dewatering unit to cover unplanned downtime (struvite blockage) or planned downtime (struvite removal).

Suitability of performance indicators The performance of dewatering installations is typically measured and assessed by one or a combination of the following parameters: throughput cake dryness polymer consumption solids capture rate energy consumption.

On closer examination, however, these parameters are not fully suited as performance indicators without further qualifications or explanations. For example polymer consumption is mainly a function of how well the polymer suits the particular sludge. A high consumption may therefore only indicate that the polymer is unsuitable and that an alternative type should be investigated. Thorough polymer testing is therefore a key element in commissioning of dewatering machines and ongoing endeavour to optimise the polymer dose rate and to find a more efficient product should be part of the operating routine (in particular if a performance drop has occurred). It is noted that whilst jar tests typically identify a well-suited product for belt filter presses, in the author's experience the same is not always true for centrifuges.

Another parameter that may misrepresent poor performance is energy consumption. For belt filter presses the largest proportion of the total power uptake is by the belt spray water pump. However, since a clean belt is vital for good permeability and thus dewatering performance, the spray water pump power requirements are an inevitable expenditure. The actual power draw is determined by belt type and belt width, and can only be safely reduced by choosing a more efficient pump.

For centrifuges, the power uptake is mainly determined by the acceleration of the feed and work at the scroll. The total power uptake is thus a function of bowl speed and scroll torque.

Under the same operating conditions and operating goals, all centrifuges would have similar power uptakes. Although the various scroll drive systems do have different characteristics in regard to how the differential speed affects the total power uptake of the centrifuge, it is questionable whether these differences are significant enough at typical operating differential speeds to justify a decision in favour of a particular system. At the same time, a power uptake that is significantly beyond the range suggested by the supplier indicates a setting that probably requires optimisation.

Lastly, the reader is reminded chat particularly for centrifuges, performance indicators and operational settings are often linked.

For example, polymer consumption and solids capture rate are interrelated. The latter is also dependent on throughput and scroll (differential) speed and thus not independent from cake d1yness and so forth.

Conclusions Although belt filter presses and centrifuges have long been used in the water industry, consumer satisfaction appears to be lacking more often than in other process areas.

A suite of common causes for non-performance of dewatering equipment has been outlined, covering aspects of design, operation and maintenance, its ancillaries and upstream processes. This discussion intentionally has been brief; and it is acknowledged that not all problems and/ or causes have been discussed.

It is noted that in some cases poor performance may be only perceived if the expected performance level is unrealistic or performance is measured with unsuitable parameters.

Conservatism, judgement and experience must be applied in the design of dewatering systems. Ongoing monitoring of the key operating parameters is required to ensure optimum performance.

The Author Arnim Hertle is a Chemical Engineer and Senior Process Engineer with GHD Pty Ltd, Perth. Telephone: +61 8 9429 6926; e-mail: ahertle@ghd.com.au.

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WATER JUNE 2003

73

B

WATER

SINGAPORE'S NEWater DEMONSTRATION PROJECT Another Milestone In Indirect Potable Reuse H Seah, J Poon, G Leslie, I B Law Executive Summary The R e pub lic o f Singa pore ha s conducted a compre hensive study to evalu ate th e feasibility of using dualme mbrane technology to reliably produce reclaimed water from municipal efflu ent.

Th e study was co nducted at a purpose built 10 ML/ d de mon stration facil ity at th e Bedok Water R.ecla matio n Pl ant (WRP). The objective of the study was to show that reclaimed water co ul d meet both th e US-EPA and WHO guidelin es for drinking water and could be used for either high grade industrial or indi rec t potable reuse appl ications. The fo llowing is a desc ription of th e operational perfo rman ce of th e demonstration plant since its initial commissio ning in May 2000 and hi ghlights the lessons that have been in corporated into the design of the subseque nt high grade reclamation facilities .

Introduction Th e island republ ic of Singa po re obtains approxi ma tely 50% of its water suppl y from outside its national borders.

In 1999, the Singapore Gove rnment launched a strategic initiative to discover alternative and renewable sources of water, in an effort to ensure reliability of supp ly and consistency of quality. This initiative, known as th e "Four Tap Strategy" co nsists of Imp orted Water, Seawater D esalination , Collection and Treatment of local surface run-off and W ater R euse. Water re use was always an importan t component of Singapore's wa ter suppl y, beginn ing w ith the Jurong Indu strial Water Works proj ec t in the early 1970s , w hich supplied tertiary quality efflu ent to industries in the so uth west of the island. Since 1999, however, the Singapore Gove rnment, through th e Public Utiliti es Board, bas aggressively developed advance water reclamation facilities, known as NEWater Factories, to supply the high tech semi-conductor manufacturi ng secto r - effectively, substituting traditional water supplies with h ig h-quality rec laimed water - and augme nting th e potable water storage reservoirs loca ted on the Island. The firs t 74

WATER JUNE 2003

Figure 1. Treatment process flow diagram.

stage of this programme was the decision in 1999 to develop a NEWate r de mon stration proj ect. The success of this project gave th e PUB the confid e nce to proc eed w it h th e p rogramme and introdu ce NEWater to the surface water reservoirs on February 2 I , 2003. Th e following pap er c hroni cles recent milestones in the d evelopment of the Islands reclaimed water resources and presen ts some data from the de mon stration project that was used in the design of the NEWater Fac tories .

The NEWater Demonstration Study NEWater is the term coined by the PUB to describe th e product fro m water reclamation using adva nced treatm ent processes of mic roporou s membrane fil trati on, reverse osmosis and ultravio let disinfe c tio n. Th e Singapore Wa t er R eclamation Stud y (" NEWater Study") was fi rst co nceptualised in 1998 as a joint initiative between Public Utilities Board (PUB) and Ministry of the Environment (ENV). The primary obj ective of the joint initiative was to determin e the suitability of using NEWater as a source ofraw water to supplement Singapore's water supply .

The centrepiece of the strategic initiative is th e operation of a 10 ML/d dualm embrane water reclamation plant called the "NEWater Factory". The NEWater Factory is a me mbran e based advanced

water reclamation plant co nsisting of mi crofiltration (MF), reverse os mosis (RO) and ultra violet (UV) disi nfection (Figure ¡1) . The plant is located on a compact site downstream of the Bedok Sewage Treatment Plant, recently re nam ed the Bedok Wate r R eclamation Plant (W R.P).

The design of th e NEWate r Factory dual-m embrane and UV tec hnology process trains are in lin e with the recom mendations of the United States National R esearc h Cou ncil (1998) in its report on the use of reclaim ed water to supplem ent wate r supplies. T he fi rst design te net was to ensure rigorous source control of the raw sewage . Th e Bedok W a ter R eclamation Plant (WRP) was selected as th e site o f the demonstration plant b ecause it receives more than 95% of its wastewater from dom estic sources. The sec ond des ign ten et was th e use of multiple physica l barriers for the removal of mi crobial pathogens and che mi cal con taminants (Figure 2) .

Source (fee dwa ter) water to the demonstration plant is a clarified seconda1y effiuent from an activated sludge treatment process, that typically co ntains: 10 mg/L BOD, 15 mg/ L TSS, 6.4 mg/ L ammonianitrogen and 400-1600 mg/ L total dissolved solids (TDS) including 12 mg/ L of total organi c carbon (TOC) . The

WATER

secondary eillu ent is fi rst mi croscreened (0.3 mm), followed by MF co re move suspe nded solids, prior co dem.ineralisation w ith RO. The MF process consisted of fi ve self contained un its operating in parallel. The MF un its were fi tted with po lypropylene hollo w fine fibre m embranes with a nominal pore size of 0 .2 micro ns. The membranes operated in single pass with a design process water recovery of 90%.

Two paralJel 5 ML/ d reverse osmosis trains are provided , each fitted with chin film aromatic po lyamide co mposite m e n,bran es configured fo r 80-85% recovery in a three stage array, As a last step , the RO permeate is disin fected by three UV units in series equipped with broad spectrum medium pressure lamps at a minimum design dose of 60 mj /cm 2 .

The NEWater demonstration study was designed to ge nerate in format ion in the areas that were deemed to be criti cal in an y decisions on the expand ed use of reclaimed water in Singapo re's ove rall water supply programme. Elements of the NEW ate r d e m o n s trati o n stu d y co mm e n ced w ith an assess m e nt of tec hnical feasibility and process rel iability.

The m e mbran e and UV technology was tested ove r a two ye ar p er iod for robustn ess and reliability to co nsiste ntly produce high qual.icy NEWacer. NEWacer qua lity and treatme nt reli abil ity was assessed by a Samplin g and M onitoring Programme (SAMP), w here a suite of physi cal, chem ical and microbiolo gical parameters was systematically m easured across th e process train to de term ine the suitability ofNE W ater as a source of raw water for potable use (T able I ). The water sampl es were anal ysed for all drinking water parameters listed in th e current USEPA N ational Primary and Secondary Dri n king Water Standards and W H O Guidelines fo r Drinkin g Water Quality.

Other parame ters of potential concern , but not listed in th ese standards/gu idelin es, were added to the list of an alytes based on the input of an indep endent advisory study panel. In total, som e 190 physical, chem ical and m.icrobiologi cal param eters were monicored and as of April 2002, over 22;000 physica l, c he mi cal and microbiologi cal tests had been performed fo r the NEWate r Study.

Th is co mpreh e n sive monitoring program was considered to be adequate to assess the sa fety of the NEWate r and th e reliability of the NEWate r process.

However, a two year H ealth Effects Tes ting Pr ogramme (HETP ) was developed co comple ment the SAMP, and address the potential health impact of unid e ntified co ntaminants in th e NEWater. T h e HETP involved a compar-

Table 1. Total number of parameters measured versus sampling location.

Sample Location MF Plant Feedwater Filtrate

Water Quality Parameter

UV NEWater RO Permeate Effluent

PUB Raw Water

PUB Drinking Water

Physical

9

3

3

2

8

8

7

Inorganic Disinfection By-products

6

1

2

1

6

6

6

Inorganic Other

39

2

32

39

38

39

Organic Disinfection By-products

22

22

22

22

22

Other Compounds

42

41

41

37

Pesticides/ Herbicides

50

50

50

50

Radionuclides

6

6

6

6

Wastewater Signature Compounds

4

4

4

4

Synthetic & Natural Hormones

3

3

3

3

3

3

10

9

7

10

9

3

69

189

187

177

Microbiologica l

191

Totals

18

3

Table 2. Health Effects Studies using Live Animals.

Project

Toxicological Assessment

References

Denver Potable Water Reuse Demonstration Project, Colorado, U.S .

Two-year chronic (carcinogenicity) mice and rats study. Reproductive study in rats.

Lauer et al., 1990

Tampa Water Resources Recovery Project, Florida , U.S.

90-day subchronic assay on mice and rats. Reproductive and developmental study on mice and rats.

CH2M HILL, 1993; Pereira et al., undated

Total Resources Recovery Project, City of San Diego , California, U.S.

Biomonitoring (28-day bioaccumulation and swimming tests) study.

Western Consortium for Public Health, 1996

Table 3 . Comparison of Design and Actual Operating Parameters (August 2000) .

Parameter

Specified Design

Actual

TOC Removal (%)

>97

>99

Ammonia Removal (%)

>90

96

TDS Remova l (%)

>97

96

MF Filtrate Turbidity (NTU )

S0.1

<0.1

Plant Feedwater (m3/ d) MF Filtrate (m 3/ d)1

13,300

13,850

11,800 (90%)

12,166 (88%)

10,000 (85%)

10,136 (83%)

Product Water

(m3/d) 1

ative tox.icological assessment ofNEWacer with existing raw potabl e water sourced from Bedok Reservo ir. Compared with previo us studies, th e NEWater demonstration is th e first programm e to in clude ch ronic testing of fish, in parallel w ith a chron.ic m.ice study. Previous studies in the U.S. were condu cted using one animal eith er in a chroni c (long-term) o r subchroni c (short-term) test (Table 2).

NEWater Demonstration Plant Performance NEWater Factory was first commissioned in May 2000 and to date plant performance has tracked closely with design requirem ents (Table 3). Analytical results from 9 May to 2 J an uary 2002 indi ca te that NEWater is of consiste ntly higher quality than those specified under U S-EPA 1998 and W H O 1993 dri nking WAT ER JUNE 2003

75

WATER

water regulations and guidelines (Table 4).

Impact of Plant Feedwater Quality on MF Performance

Perhaps the one of the most important observation from the demonstration study is that the perfo rmance of the membranes is closely linked to th e quality of the in coming secondary effluent (plant feed water) . In the case of the microporous membranes variations in feed turbidity or suspended so lids influ enced process recovery and cleaning intervals, w hile in the case of reverse osmosis membranes, variations in dissolved solids impacted on operating pressure and product water quality.

The MF process provided excell ent pre-treatment for th e R O system , resulting in stable and robust RO system performance. H owever, the performance of the MF was affected by the level of suspended solids in the plant feedwater.

An increase in the suspended solids in creases the solids loading on the MF membranes, which can necessitate more frequent backwash and clean-in-place (CIP) operations, which can vary from 10 to 15 days interval. To accommodate potential variations in feed turbidity, the full scale N EWater plants designed after the NEWater dem.onstration plant include an additional 20% membrane area, so that that membrane loading rate could be reduced dudng periods of elevate d suspended solids.

Similarly the RO process achieved the design requirements of a 97% reduction of TDS and a 99% redu ction in TOC (T able 3) . However, RO performance was influenced by variations in the dissolved solids in the plant feedwater. The TDS of the plant feed could vary from 270 to 2,270 mg/L depending on the extent of seawater ingress into the sewers tributary to the Bedok W RP , with the highest levels observed during the Spring tides (high water is higher and low water is lower than usual). Under these conditions the RO feed pressure increased (caused by the higher feed osmotic pressure resulting from the additional dissolved solids) leading to a decrease in the normalised plant product flow (Figure 3). In addition to the decrease in normalised flow, variations in feed water TDS also lead to variable product water ·TDS. Consequently, the conductivity of the NEWater ranged from 39.6 (~1S/cm) at perio ds of low tide to 71 .1 µSiem under high tide conditions (Table 4). In order to ensure that the NEWater plants produce a consistent quality, including consistent levels ofTDS, a recycle step was

76

WATER JUNE 2003

Figure 2. Multiple barrier approach for microbial and chemical contaminant removal.

included into the RO design for the NEWater plants that have been developed to supply industry. In these larger NEWater plants it is possible to blend the output from the MF process with some R O permeate to lower the TDS of the RO feed. By using this recycle step it is

possible to minimise the variations in the level of dissolved solids in the NEWater.

Conclusions and Project Milestones

The NEWater demonstration study has generated important data to guide the PUB in the development and expansion

Table 4. Water quality for NEWater Factory product water. All results in mg/L, unless indicated.

Water Quality Parameter

Colour (Hazen Units) PH Conductivity (µS/ cm) Alkalinity (as CaC0 3 )

NEWater Factory 1

<5

15

5.2 to 6.2

6.5-8.5

39.6 to 71.1

8

Total Dissolved Solids

22 to 41.3

Hardness (as CaC0 3 )

<5

Fluoride Nitrite (as N)

US-EPA/WH02

500

0 .18 to 0.22

1.5

0.38

0.91

Nitrate (as N)

0.49 to 1.65

10

Ammonia

0.35 to 0.57

Chloride

3 .6 to 10.9

0.16 to 0.54

1.5 250 5 0 .2 0.3 0.05 250

<0.004

3

Turbidity (NTU) Aluminium Iron Manganese Sulphate (as S0 4 ) Zinc Silica (as Si02 ) Phosphate (as P) Sodium TOC (µg/l)

<0.1 0.09 <0.003 <0.003

0.21 to 0.32 0.011 to 0 .044 5 .1 to 9 .6

200

60 to 90

Total Coliform (counts/100 ml)

<1

Not Detectable

Fecal Coliform (counts/100 ml)

<1

Not Detectable

Clostridium Perfringens (cfu/100 ml)

<1

Notes: 1. Taken from analytical results for the months of June and July 2000.

2. Lowest limit of either the US-EPA 1998 Surface Water Regulations or WHO 1993 Guidelines for Drinking Water.

WATER

of the use of reclaim ed w ater in the Island's overa ll water management strategy. T hese milestones in th e use of N E W acer are chronicled in cable 5. In ea rly-2003 the fi rst full- production N E Wacer plants went o n line ac Bedok W R P and Kranji WRP w ith a com bined initial capacity of72,000 111 3/d . These planes have che provisio n co expand co 168,000 m 3/ d in the future. The new Bedok and Kranji NEWate r plan ts w ill provide water to the microelectronics industry, there by saving existing drinking w ater fo r dom estic use. (T he microelectro nics industries are far m o re sensitive co water quality than dom estic users). In additio n co the industrial use of NEWater, In la ce-June 2002, a panel of local and overseas experts charged w ith reviewing che NEWater Stud y recommended che Singap o re Gove rnment adopt indirect potable reuse ofNEWate r w ith a po rtion of che production fro m the B edok and Kranji NEWacer plants b eing used to augm ent levels in the surface w ater reservoirs. On July 11, 2002, the concept of indirect potable reuse of NEWater was forma lly lau nch ed to the public. PUB's go al is to re use 20% o f the used water fo r industrial and potable use by the end of the decade. NEWater debut at the August 9 , 2002, N ation al D ay celebrations with some 60, 000 bottles o f NEWater being given away o n the parade day alo ne. Since then , more than a million bottles of NEWater have b e en distribut ed t o demonstrate che safety o f the water for potable consu mp tion to t h e public.

NEWater began flo wing to the Bedok and Kranji surfa ce w ater reservoirs o n February 21 , 2003.

Acknowledgements C H 2M HILL is very gratefu l for the o pportunity to ace as a co nsultant co che Singapore Public U tilities Board on the NEWa te r Pro gramm e. T h e authors would also l ike to ackno wledge th e valuable co ntributio n of P aul G aughan, Tom M arshall , Upali Mahayliana and Shamuddin Sulaiman from C H 2M H ILL w ho w ere e ngaged in the design and deliv e1y of the NEWater plants as w ell as the d edicated staff fro m che PUB Water R epl e nishment Department.

RO Perm eate Production 3 ,200

''"

3 ,000

'50

2.800 2 ,800

•oo

2 ,4 00 350

i

~

£•

2 ,200

2,000

300 1,800

200

..

..

,., ...

;

- .·

100 Augu•t·00

the Water R eclam ation Department in the Singapore P ublic Utilities B oard.

H A RRY _SE A H @ p u b.gov.sg . Greg Leslie is th e water reuse te chnology manager fo r C H 2M H ill in the A sia Pacific R egion. gleslie@ch2m .com .au.

John Poon , a senior civil engineer w ith C H 2M H ILL, w as the study m anager fo r

',

.

1,600

.......

,·

'

Sopt•mbar·00

...

OelObet·00

No~ember·00

... ...

:

Dec , mber-OO

.....

.... '

J1nu1ry·DI

'

1,-100

..

1,200

1.000

,oo

'"

Dttt

Figure 3 . RO permeate prod uction, RO fe edwater cond uctivity a nd RO CIP events.

the tw o NEWater Facto1y Demonstration proj ects. Jpoon@c h2m.co m . Ian Law is now the Managing D irector of IBL solutions. Ian was C H 2M H ill's project m anager for the NEWater Demonstratio n project and prog ramm e manager fo r the delivery of che NEWater plants at Bedo k and K ranj i an d the NEWater visito rs cen tre . lblaw@ bigp o nd. com

References Natio nal R esearch Co uncil (USA) 1998. Issu es in P otable re-use: T h e viability of augmen ti ng drinking w ater supplies w ith reclaimed w ater.

Major Suppliers M F units - U S Filter M em co r; RO Units - H ydranaucics; UV units - H annovia.

Table 5. Water Reclamation Milest ones.

Year

MIiestone

1998

Water Re clamation Study initiative conceived by PUB and t he Ministry of the Environment CH2 M HILL commissioned fo r the engineering des ign, project delivery and st udy management of the Singapore Water Reclamation Study Bedok NEWater Factory De monstration Plant constructed and commissioned within a seve n month period . Design capacity of 10 ,000 m3 / day Commence ment of the most comprehensive and s oph isticated study into water reclamation: • Sampl ing and monito ring programme for s ome 190 wate r quality parameters • Toxicologica l assessment us ing bot h mice and fish for t he first time PU B announces its goal to recycle 20% of secondary treated used water for ind ustrial use CH2M HI LL awarded the engineering design and construction s upervision for full-scale Bedok and Kranji NEWater Plants , as we ll as interactive visitor/ publ ic education centre at Bedo k. Ultimate design ca pacity of 168,000 m3 / day Expert Panel recommends t he adoption of Indirect Potable Reuse of NEWater to supplement Singapore existing water supply sources NEWater debuts to wide public acceptance at the National Day Parade and celebrations. Up to 60,000 bottles of NEWate r give n away at t he on parade day.

Bedok and Kranj l NEWater Plants with an initia l capacity of 72,000 m3/ day The potable and non-potable use of NEWate r is offic ially launched by the Prime Ministe r of Singapore at a gala event. At the same time a visitor and public education centre was opened to the public. The unique centre is fully integrated with the Bedok NEWate r Plant and includes an e levated wal k-t hrough of t he process area, and a multimedia interactive exhibition/ education area with a 120-seat digital a udio/ video auditorium. The very latest in multimedia interactive learning tools a re used extensively t hroughout the centre.

February 1999 May 2000

October 2000

January 2001 Ju ly 2001

July 2002 August 2002

The Authors Harry Seah is the depu ty director of

..

250

January 2003 February 2003

WATER JUN E 2003

77

WASTEWATER

DESIGN OF A WASTEWATER TREATMENT PLANT FOR DAVIS BASE, ANTARCTICA K Heaton, C Paterson Abstract

Conseq u en tl y th e p lant w as protected from the elements by Th e summ er populations at the several small, insulating containers Au stralian Antarctic Base, Davis, with minimal hea ting (Figure 2). have climbed from 30 to almost 100.

Access requires a cra ne to remove Th e current wastewater treatment th e roof from the containers, which facility is overloaded, and an upgrade has proved im.possibl e over winter .Hurd is required. In addition, there is a ~, months, preventin g essential weekly desire for disinfection of the eilluent OO'W operational and maintenance activto prevent potential transmission of ities. ln addition , poor ventilation viruses and bacteria from humans to often results in the treatment process wildlife. being anaerobic.

A number of wastewat e r Over time, th e Au stra lia n treatment technologies for replacing Antarctic Progra m has expanded and the existing wastewater treatment summ er populations at Davis ha ve plant (WWTP) were recently assessed ?.ul1nd cl imbed from 30 to almost 100. The and a concep t design h as been current wastewater treatment facility ~ developed . llO" is overloaded, and an upgrade 1s Piojtct,)n Pollr $"1u'logrlfllllo '""'""~ Aunnlt.ln lrw Snlt1t71-S Srâ&#x20AC;˘ion Introduction required.

Figure 1. Location of Mawson, Davis and Casey B etween 1999 and 2002, a Th ere are approximately 5000 Bases, Antarctica (AAD, 2000). nu mber of wastewater treatme nt people from 29 nations working at technologi es were assessed and a 40 research stations in Antarctica. concept design was developed fo r a Davis WWTP consisted of a flow T he Australia operates three Antarctic Stations repl aceme nt WWTP at Da vis. T he equalisation tank, primary sedimentation year round - C asey, Da vis and Mawson proposed plan t inco rporates disinfecti on tank, an RBC tank w ith six disc banks (Figure 1). The rocky terrain of D avis of the eill uent to prevent potential transin series, a clarifier and an efflu ent Base is exposed for the brief "summer" mission of vi ruses and bacteria from retention tank.

Budget constraints at the (Figure 2). humans to wildlife. Nutrient removal was time prevented it being constructed in its In 1991, the Madrid Protocol for not considered a high priority given that own bui lding as p er Casey and Mawson.

Environm.ental Protection of Antarctica was established to m inimise the impact of Stations on the Antarctic enviro nm ent.

The Protocol's main requirement fo r sewage treatment was all permanent bases in Antarctica must macerate their sewage, and dispose o f it to the ocean in a place w here it will be rapidly diluted and dispersed.

Australia was the first country to go beyond this and install R otating Biological Contactors (RBCs) to treat wastewater to a seconda ry level. The plants were designed to cater for approximately 30 exp editioners and were commissioned at M awson (1 985), Casey (1989) and Da vis (1991) .

I'

..

....

"'" ll

8

T his is an edited version of the JY.lper which won the Michael Flynn Award for the best Poster Paper at the 20th AWA Convention in Perth .

78

WATER JUNE 2003

.

Davis Base, Antarct ica, with white wastewate r t reatment plant contai ners

WASTEWATER

th e nutri ent impact of hu m an wastes is negligibl e in com pariso n to wha t is disc harged into th e e nvironment by the large popu latio n o f Antarc tic animals. It was consid ere d that introd uced bacteria an d viruses (eg. A 11ia11 para111 yxo11irus, Paster11ella 1111dtocida, and Salmon ella e tc) pose the greatest th rea t to th e Antarcti c ecosyste m.

Concept Design Performance Criteria Th e two dri ving fo rces behi nd the treatm ent of wastes in Antarctica are: • Th e protection o f the Antarctic w ildli fe fro m introdu ced diseases; and • T he m inim isation o f po llution in Antarctica's pristine enviro nme nt .

E fflu ent from the WWT P will need to m ee t a m inimum effi ue nt quality o f: • Biochem ical O xygen Demand (BOD 5) - 20 mg/ L • Su spended Solids (SS) - 30 mg/ L With effiuent filtration , it is e xpected th e plant w ill achie ve lower efflu ent 13OD 5 and SS conce ntrati o ns of lO rn g/ L and 15 mg/ L, respecti ve ly .

Design Criteria T he fo ll ow ing criteria are di c tate d by the uniq ue Antarctic enviro nment: • Extre111e 111eat/,er co11dirio11s. T his included a te mperatu re range o f +5°C to - 40°C, m ax imum w ind gusts o f over 200 km / hr, and annual snowfa ll of 78 mm/y r. T he WWT P m ust the refo re be ho used in a suitably engi nee red building.

• H is li stret1Jttli a11d septicity ~f i11co111i11g 111aste111atcr. The w astewater gen erated at the Antarctic stations is classifi ed as me di u m to strong w hen compare d to no rmal do m es tic sewage in A ustralia.

T h ere are t h ree reason s for the high er stre n gth: (1) less dilution of o rga nic w astes due to lo w er water usage (J 60 Li pp/ day) and no sto rm wa ter or ground wate r in fi ltration inro th e above-gro und sewe r pip es.

(2) expeditioners are we ll fed w ith t hree meals per day and the fo od consu m ed has a high calorific valu e as w ell as bein g hi gh in grease and fa ts; (3) there is a h ighe r percentage o f m en co m pared tO wom en at the stati o ns than in th e averag e populatio n . Men produce stro nger w aste than wome n (M aven ic, 199 9) ; T h e long deten t ion time i n the sew e rage syste m results in highl y septic wastew ater in flo ws .

• R e111 ole location. Sh ip tran sp o rt is cu rre ntl y th e only m ethod uti lised by the AAD to access the Stations. T h is access is li mit e d tO th e sum m e r p e r io d

Figure 3. Insulated water tanks, heat-t raced pipes and effluent pipeline .

(N ove mber to Marc h) w he n th e sea ice retreats.

• Seasonal pop11la tio11 j/11ct11atio11s. T he WWTP design must cater fo r a min imum w inte r po pu lation of 20 for 7 months of the yea r, and a maximum su mm e r popu latio n of 150 fo r th e rema inde r;

• Se11siti11e recei11i11J/ e1111iro11111e111 . D ue to iso lati o n , A ntarc tic wild li fe m ay be vulnerable to com mon viruses and bacteria in th e wastew ater;

• Li111ited operator atte11tio11 and tmi11i11g . The two Station plu m bers have th e role o f wastewater treatm e nt pl an t ope rato r togeth er with w ate r t rea tm ent p lant op erator and norma l plu m b ing du ties .

Most ha ve n o p rio r exp eri e nce in operating w astewater treatm ent plants, and are given a two-day WWT P process cou rse prior to de partin g Aust ralia;

• Lo11111iai11re11a11ce req11ire111e11ts. This is due to the rem ote lo cation (spares m ust be stored in case o f breakdo wns, especially during w inte r isol atio n), and the limited tim e and skills available to th e pl umbers to m aintain the plant.

• Li111ited power availability. low energy consumptio n and conservation is required .

Station power (2 40 vo lt) is supplied by fo ur 125 kW diesel generators. E ne rgy costs are very high because all d iesel fu el m ust be transported to Antarctica by ship and stored in heated bulk ranks. E xcess heat produ ced by th e diesel e ngines h eats water that is piped around th e station to warm b uild ings. W astew ater infl uent te mperatu re arriving at the exiscing plant throu gh he at- t raced pip ework varies between 18°C and 25°C in su m mer, do w n to 15°C in w inter (Figure 3) . At these tem peratures all secondary treatment processes can operate sa tisfactori ly .

• Li111ited space for plant footpri111. Smaller footprin ts are desirable fro m a bu ildin g cost and e nviron me ntal pe rspec tive (to m in im ise im pac t o n th e Antarct ic landscape) .

• Tra11sporlatio11 ef pla111 co111po11e111s in seacontainers for pre fabricated, bolt- together constructio n. All mate rial must be able to b e transpo rted by ship and barge to the constru ctio n locati on ; • Li111ited co11str11ctio11 period o f 8 weeks per yea r d u ri ng su mm er w he n weathe r co nd itions allow outdoor w ork; • Disi1,Jectio11 of ef/111c11t. T his m ust be ac hieved w ithout im pact to the receiving environment to comply with the Antarctic T reaty (M adrid P roto col); • Cost ~f ret11mi11g sludge to A11stralia. All sludge must be transpo rte d bac k to Australia fo r disposa l, the refo re it is d es ir a b le to minimi se th e slud ge produ ction .

Features T he fi nal proposed concept design for t he Davis WWTP is illustrated sche matically in Figu re 4.

Primary Treatment

Preli111i11ary Trea1111e11t (eg. m aceration , screening) w as not considere d n ecessa ry b ecause th e sewage is macerated by the pumps in the station bu ild ings' holding tanks. Sim ila rly, there is no requ irem ent to rem ove grit and sand e tc b ecause this material do es not infi ltrate t he abovegro und sewe rage system.

A F/0111 Eq11alisatio11 Tank (FET) w as included in the concept design to balance out the in coming sewer £lows so that w ascewater ca n be deli vered to th e secondary treatm e nt sta ge at a cont rolled loa ding rate . It can also serve to partially dilute a shock load to the WWT P should toxic material inadvertently be discharged WATER JUNE 2003

79

WASTEWATER

co the sewerage system. An aerator is included in the FET design to " freshen " the incoming wastewater. It also serves to m ix the tank's contents to ensure a ho mogeneous mixture is fed to the secondary stage of the WWTP. The w ater level in the FET will be controlled by high and low level switches, chat will activate a pu mp chat discharges co the secondary treatment stage. An emergency high-water gravity take-off pipe is provided to prevent overflows. A bypass valve before the FET has b een included in the design to allow fo r complete bypass of the WWTP when plant maintenance or shutdow n is required.

Influent

''' ''' I' I

--- --

-- ---- -- -- ------ -- ---- --

Flowmeter

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I I

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,

I I

Blivct RBC System Stage 2 Footprint

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I I

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ti ___________

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ci . .

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0

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I

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Turbidity Meter

I I I

Field Waste Disposal Facility

A fac ility fo r disposal of field waste (urine and washing up water brought back by expeditioners in sealed co ntainers) has been incorporated into the design of th e new WWTP. This facility includes a small bunded storage area fo r th awing and diluting the waste 1:1 with wa ter at the point of entry. The liqu id waste w ill pass through a macerator and a grease crap before entering th e FET.

Sink for disposal Offield greywater

Plant Bypass

Sup~rnatant R~tum

Wet well

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It

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To 1500 L sludge storage bins

] Bypass

'' 'II ~ ------ Fi lter I ;----- F ilter 2 • -: l ~ilter _______ _.,:__ J i.........,._.., Backwash ..- ---------- - - -- ---j

_l?ili.est~r ..

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Bypass

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Water

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I

Secondary Treatme nt System

Several different o ptions for secondary trea tment were co nsidered based on the design criteria discussed previously. T hese were: • O ption 1 - interm ittently decanted extended aeration (IDEA); • Optio n 2 - activa ted sludge/R E C combination (Bl.ivet system or equivalent); • O ption 3 - conventional extended aeration with diffused air fo llowed by clarifiers; • Option 4 - extended aera tion with m embran e bioreacto rs; • Optio n 5 - rota ting bi o l ogi cal contactors (R.BC's) fol1o wed by clarifiers; and • Option 6 - sequ encing batch reactor (SBR) processes.

Optio n 3, co n ventional extend ed aeration using diffused air follo wed by clarifiers, was rej ected beca use of the high p rocess o pe rati o n and ma inte nan ce requirements.

Option 4 w as unattractive b ecause of the highly complex maintenance requirem ents o f membranes includin g chemicals for cleaning, the en ergy intensiven ess of the pro cess, and a potential for scaleformacion.

Option 5, the rotating biolo gica l co ntacto rs foll owed by clarifi ers, was rejected o n th e gro unds th at th e Blivet system incorporated all the operational and m ainte nance ad va ntages o f R.B C ' s w ithout th e need for clarifi er tanks.

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'

.......lJ.Y ...

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Bypass

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To Effluent Outfall

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~ontrol Room _j& Laboratory Not to Scale

Figure 4. Schematic of proposed design fo r th e new WWTP at Davis Bas e, Antarct ica.

Option 6, sequencing batch reactors, was considered unsuitable as it required either an additional SBR tank and was more energy intensive than the Blivet System.

Both th e IDEA (O ptio n 1) and Blivec System (Option 2) satisfi ed all the design criteria. B oth are proven processes, have the ability co cope with large flow flu ctu ations between th e winter and summ.er seasons, perform well with lo ng sludge ages, p roduce minimal slu dge, and have m inimal equipment main tenance and operational requirements if adequ ate operator training and support is provided.

After considering th e advantages and disa dva ntages of each system , th e Blivet RBC system (Optio n 2) was recom-

mended. T he Blivet system. was fo und to ha ve n umero us advan tages and few di sa dvanta ges co m p are d t o ot h e r secondary treatment options .

Advantages

• lower labour, energy and capital costs.

• less equipm ent maintenance required.

• smaller plant fo o tp rin t.

• smaller aerobic digester required for sludge storage and treatment.

• aerobic digester only required during the summer months compared w ith all year round fo r the IDEA treatment system.

• simpler operatio n - able to b e operated by a plumb er w ith lim ited wastewater treatment process kno wledge.

WASTEWATER

• adaptable to changes in popu lation loading within a few days, and better recovery for m shock toxic loads • prefabricated in Austra lia and easily transportable to Antarctica in a 40 ft (12.2 m) seaconcainer.

• easily installed.

Disadvantages • eillu ent can have hi gher turbidity than IDEA plane w ithout filtration.

• more sludge to be disposed of (14 x 1500 L sludge containers requ ired ve rsus 8 fo r the IDEA plant).

Overall it was considered th at th e Blive t REC system was easier to operate and m aintai n than other options and w as less likely co have process operational problems if operator attention and training was l imited. lt was considered that the reliability of th e operation al performan ce of the Blivec plane far outweighed the lowe r perform ance of the B livet in term s of eill uent quaEty and sludge production.

Briefl y described , the Blivec system is a co mbin ation of both fixed film treatment, using a rotating bi o logical contaccor design, and aeration of th e wastewater co p rodu ce some activated sludge. It incorporates three treatment zones in one modu lar unit: The primary treatment zone runs with upward flow through lamella parallel plates.

T he aerob ic/ fi xed film treatment zone consists of a mod ified ve rsion of a R o tating Biological Co ntactor plant.

Cylindrica l drums (term ed Aerators) fill ed w ith spiral media are 50% submerged . As the drums rotate corrugations on the outer drum entrain air into the wastewater, aerating the contents of the tank and the biomass, encouraging the growth of activa ted sludge . The rotation of the Aerator also ensu res th at excess biomass on th e media is sloughed off, maintaining an even growth across the m edia .

The rate of recircu lation can be adjusted to cater fo r winter and summer flows by adjusting weirs in the fina l co mpartm ent splitter box. Gravity rec irculation auto mati cally increases ac times of increased flow. This allows the plant co adapt to large changes in flow in a few days .

From the Aerator zone, wastewater flows into th e final sludge settlement zone.

The design is similar to th e prim ary trea t ment zo ne, with upward flow through parallel plates.

Solid particles settle out, leavi ng the fin al effluent to flow over a natched weir

into a wet well. Effluent is pumped from there co eillu en t fil ters.

Sludge recycling of 100% is required in winter to m aintain the biological population, and 50% in summer to reintroduce bacteria co the head of the plane, thereby speeding up decomposition of the raw wastewater. Sludge that settles in the bottom of the fina l solids settlement tank is pumped to the primary settlement tank using a tim ed submersible 0.75 kW pump.

T he plane suitable fo r Davis Base can treat an average inflow of up to 34.5 m 3 /day, and a BOD 5 lo ad of 9 .35 kg/ day at ·t 5°C. An ad diti onal we e well and an expand ed sludge compartment o n the sta ndard B livet design is required fo r the Davis appli cation .

Ove rall the Blivet plant w ill be approx imately 8 .2 m lon g, 2.27 111 wide, and a total of 2.9 m hi gh including the moveable tank covers. T he tank footprint is approx imately 19m 2 . T he plant tank will be m ad e of steel and glass reinforced p olyester (G RP) ens uring it is both durable and lightweight.

The d es ign h as addressed the m echani cal problems that have typ icall y plagued RB C plants in the past. Makin g the concactors from b uoyant material has eliminated th e potential for shaft brea kages. The contactor d es ign, consisting of cylindrical drums fi lled with spiral m edia , al so prevents eccentric biomass growth during power stoppages, again preventing shaft breakages. Th e m echan ical components of the system , including the shaft and gearbox, are protected from the con-osive environment of the WWTP building with an epoxy coating. Spare parts are minimal. In the concept plane design , a footprint area has been left for a duplicate m odular tank unit should D avis Base expand beyond 150 people in the future.

A turbidity m eter was located between the filters and the UV unit to enable r em o t e monitorin g o f the pl ant 's operation and eilluenc quality.

Filters are not required if a SARAN (screen) fil ter is fitted, assuming the plant meets th e B li vet effluent specification s of 10mg/ L BOD 5 and 15 mg/ L SS.

Effluent Filtration Eilluenc fil tration is requ ired co assist the ultraviolet (UV) disinfection process.

Effluent Disposal Outfall Th e c urre nt meth od o f efflu ent di sposal at D avis, through a h eat-traced gravity p ipeli ne of approximately 150 m in length discharging at the sea edge, will co ntinue .

Seve ral filtration op t io ns were considered , and mu ltimedia pressure filters with automatically timed backwash function were chosen due co th eir simplicity to operate and their lower capital cost. Filter backwash water will be directed to the FET after passing throu gh the fil ters.

The concept design shows c,vo filters operating in parallel as duty/standby. A filter bypass line has also been installed for maintenance purposes.

Effluent Disinfection E ffluent Disin fect ion is required to kill viruses and bacteria in the effl u ent before it is disc harged to the environment. UV radiation was the preferred m ethod of disinfection for Antarctica, as unlike chlorinati on , it leaves no residu al that is toxic to aquatic o rganisms. There is no danger of overdose, it is a relatively simple and in expensive sys tem to o pe rate (compa red to ozo nation), and it ca uses high bacterial inactivation within seconds.

A ·system with medium-stre ngth UV lamps or stronger is required for Antarctica because UV is affected by co ld temperatures at low-stre ngth UV lamp range. A UV uhit w hich all ows the effl uent to pass th rough multiple (3 or more) times was recommended.

Effluent Storage From th e UV unit, the eill uent flows to the efflu ent storage tank, wh ich stores the final efflu ent befo re it is pumped in slug doses to the effluent outfall. Pumping in this mann er reduces th e ab ility of the efflu ent to freeze and block the outfall pipe. Effiuenc is currently discharged from the existing plant at Davis at a temperature of approximately 13°C in winter and 19°C in summer. In summer, it is proposed that this heat be tra nsferred from the efflu ent through heat exchangers and used for heating the building, or utilised in the sludge dewatering process.

A flowm eter on the discharge li ne will record the volume o f effluent being disc ha rged to the environment. T he efflu ent tank can be bypassed for cleaning and ma intenance.

Sludge Handling & Stabilisation S ludg e removal frequency 1s constrained to tvvice per year at Davis Base by infrequent ship schedules, and the limited ability to store sludge o n site.

Th erefore it is envisaged th at sludge rem oval from th e wastewater treatment plan t will be done at the beginning and end of the summer period ie. in early WATER JUNE 2003

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Nove mber and in M arch (with th e last ship of the season). Sludge p roduction is highest in the su mmer period, thus governi ng the design of sludge storage and treatm ent facilities.

The B livet tank with exte nded sludge storage compartment ca n store 21 111 3 of sludge, w hich is more than adequate fo r the w inter (April to O c tober) slu dge production of 9 1113. Du ring the sum m er, excess sludge w ill be pumped to an 12 n'13 aerobic sludge d igester for fur ther stabilisation and to reduce pathoge ns, odou rs and the volume of sludge requ iring transpo rt back to Austra lia. Ae robic dige stion wa s reco m m e nded ab o ve c he mical stabilisa ti on, beca use of its simp le operation , 50% reduction in sludge volume, mini ma l odo u rs and sm alle r o pe rating costs . M eso p h ilic anae robic digestio n was rejected as an option because it requires an airtight ta nk and continual heating to ma intain an inte rnal temperature of 34°C to 36°C and is se nsitive to any toxic c hem icals.

Sludge Dewatering C u rrentl y it is proposed to ship no ndewatered slu dge (at 4% solids content) bac k to Australia each year in 14 x 1500 L contai n ers . D ewatering options are still being e valuated by th e AAD. T h e Am ericans (M artel, 2000) have opted for filter belt presses in the design of their new WWT P at McM urdo Base. H owever the filter belt press was not recomm ended for Davis because of the extra op erational, mai ntenance and chemica l requireme nts.

The AAD's p referred alte rnative to m echanical dewatering is slu dge freez ethaw dewateri ng beds, wh ich m ake use of the fr eeze/thaw pe riod in colde r climates to thicken and dewater sludges .

T hese h ave been used effec tively in Alaska, no rth ern U SA, and C anada since 1990. Advantages include (M artel, 1999) : • less energy consumption because nature does the freezing and thawing; • no conditioni ng c hemical requirem ent; • m inimal odours because o f the cold temperature;

• simple to o pe rate and main tain; • higher final soli ds content than a fil ter belt press ie. between 20% & 30% solids co nte nt.

A small scale test of th is me thod in J anuary 2003 at Casey Station on wate r treatm ent plant sludge dosed w ith ferri c chloride was successful , dewatering fr om 2.5% to 46% solids by w eight . Sludge is typically froze n in the b ed during the winter m onths and thaw ed during the spring and summer, making use of the natura l freeze-thaw cycles of ice crystals

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WATER JUNE 2003

w hich exclude most impurities as they are growing. W hen the ice c1ystals m elt, clean wate r is prod u ce d, w hi c h drai ns downward through the bed. T his wate r is pu mped bac k to the head of th e treatment plant, leaving the concentrated impurities attached to the now dewate red sludge (M artel, 1998). T h e qua li ty of the m eltwate r from the bed is roughly equivalent to that of raw waste water.

Achieving the requ ired depth of frozen sludge is easily obtainable in Antarctica.

H owever , ove r the eight week summe r at the Austra li an Antarc tic bases the ave rage monthly te mperatu re rem ai ns below freezing. Therefore thawi ng the sludge may need additional heat eith er fr om waste hea t from th e e ffl ue nt disc harged fro m the treatment plants or from a passive solar sys tem achieved by building the sludge freezing bed with a transpare nt roof and insulated sides.

A small scale pilot trial of a sludge freeze thaw dewatering bed w ill be co ndu cted fr om J un e to D ecember 2003 to test the thawing process. ff sludge dewa te ring can be accomp lished by th is method w itho ut supplementary en e rgy , then a sludge freeze-thaw dewatering bed w ill be inco rp o ra ted into the final WWTP design. Fo r an estimated sludge production of 21 111 3 per year, a bed of area 12.5 111 2 wou ld be requi red .

All sludge disposal options conside red involve transport bac k to Austral ia eith er for fu rther treatme nt i n a WWTP in H obart, i n cine ratio n, o r disposa l to landfill. Sludge disposal into th e sea was not conside red due to the pote ntial of introducing contam.inants and diseases in to the Antarctic e nviron ment.

Control Room & Laboratory

A control ro om & laborato ry withi n th e W W TP building w ill h ou se a Supervisory Control and D ata Acquisition (SCAD A) system o r equivalent to operate and monito r the plant, and allow simple wastewater analysis to be underta ke n .

Conclusion Th e ex isting WWTP at D avis, Anta rctica, is to be u pgraded to cater for 2020 population proj ectio ns ie. 20 people in winter, 150 people in summer. T here are many special design considerations fo r t h e o p era t ion , m a in t e na n ce a nd constru ction of a WWTP in the u nique Antarctic environment. After considering many process options, it is proposed that the new WWTP consist of the following major components: • Flow equalisatio n tank with aerator to freshen the raw wastewater; • Fi eld w aste disposal facility;

• R o t at in g Bi o l og ica l C o nta c t or / Activated Sludge syste m for seco ndary treatme nt; • Effiu ent Filte rs to polish the efflu ent; • U ltraviolet Radiation fo r disinfection of the effiu ent to kill viruses and bacteria.

• Fin al E ffluent Storage Tank fo r co ntrolled pumping to o utfa ll ; • Efflue nt O u tfa ll pipe for disposal of treated effiu en t to the sea; • Aerobic digester for sludge stabilisa tio n and sludge volume reduc tion; • Storage C o ntaine rs for transport bac k to Australia; and • Control room and laboratory for plant m on itoring, effl uent testing and ana lys is.

T he ne w WWTP w ill be commissioned in the 2004/ 5 summ er season .

P reli minary estimates indicate that this proj ect will cost approximately $2.4 m i ll ion t o c o m pl e t e, in c l udi n g co nstru c tion of a new building in An tarctica to house the W WTP. T his hi gh cost reflects the c hallenges in transporting the material to A ntarcti ca and the diffi c ult construction cond itio ns.

Acknowledgements This paper was develop ed from proj ect work sponsored by the Queens T rust fo r You ng Australians, the Water Corporation of Western Au stralia, the Au stra lian An tarctic Di vision, and th e University of British Columbia. Special thanks to D r Jim Martel fo r hi s des ign advice on sludge freeze-thaw ing beds, M KM C onsul tin g E ngineering and G eoff Kenda ll fro m the Wate r C orporation.

The Authors Kathryn Heaton is Senior Asse t Manage me nt E ngineer at the Wa te r C orporation, Karratha, W estern Australia.

Kathryn .H eaton@ watercorporation.com. au. Chris Paterson is C hief Engineer at th e A u stral ian A nta rc t ic Division , Kingston , T asman ia. Chris.P aterson@ aad.gov .au

References AAD (2000). Australian Antarctic Division Data Centre, D epartment o f Environment and He ritage, published by C om mo nwealth of Australia, J uly 2000.

M artel C .J. (1999) . Environmental Engineer in the Geochemical Sciences Division at the U S Army C orps o f Engineers C old R egions R esearch and Engineering Laboratory in H anover, N ew H ampshire, U SA. Personal Commun icatio n, via email , Martel (2000).

Ditto.

Mavenic D . (1999) . Professor o f Environmental Engineering. U niversity of Btitish Columbia, Wastewater T reatm ent C ivil 569 Lecture, March 1999.