Water Journal June 1992

JUNE 1992

AUSTRALIAN WATER & WASTEWATER ASSOCIATION

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ISSN 0310-0367

Volume 19, No. 3, June 1992

Au stralian Water & Wastewater Association Incorporated ARBN 054 253066 FEDERAL SECRETARIAT Exec utive Director -

Chris Davis

Business Manager - Margaret Bates PO Box 388.

Artarmon 2064 Telephone (02) 413 1288 Facsimile (02) 413 1047

FEDERAL PRESIDENT Barry Sanders, Phone (09) 420 2453

CONTENTS 3

My Point of View Association News News from the Executive It Seems To Me News from the Branches

4 5

12 14

Features 16

FEDERAL SECRETARY Greg Cawston .

Phone (042) 29 0236

FEDERAL TREASURER John Molloy, Phone (03) 615 5991

24 26 30

BRANCH SECRETARIES Canberra. ACT Alan Wad e.

PO Box 306. Woden 2606 Phone (062) 513 368 Nw South Wales Nick Apos tolidis, GCEC. 39 Regent Street Railway Squ are 2000 Phone (02) 699 9922 Vi ctoria

John Park, Cl- Water Training Cen l re,

PO Box 409, Werri bee 3030 Phone (03) 741 5844

AWWA Position Papers IAWPRC News Industry News

32

Odour Minimisation at Werribee T. Gul ovse n, P. Hansen, D. Hutchison, J. Russell, P. Scott Update on Odour Control in Geelong's Wastewater System G. J. Sewards and D. S. Barkley Odour Problems from North Head STP M. Lagi nest ra Odour Control by Wet Scrubbers at North Head A. McDougall Odour Control Strategies at Bolivar STP M. F. Kennedy, P. M. Thomas and K. P. Yerrell

Technical Notes 36 38 40 42 43 44

Olfactory Studies Related to Odour Emissions Odour Control - Some Queensland Notes Effective Sulfide Deodorization Seminars, Courses Environmental Notes Conference Calendar

.,

Queensland Don Mackay.

PO Box 412, West End 4101 Phone (07) 840 4844 South Austral ia Neil Palmer, Ct- State Water Laboratories, E&WS Private Mail Bag, Salisbury 5108 Phone (08) 381 0268 Western Australi a

OUR COVER

erwater;

Bi ll Chapman, WAWA PO Box 100. Leederville 6007 Phone (09) 420 2462 Tasmania

Annette Ferguson , GPO Box 503E, Hobart 7001 Phone (002) 28 2757 Northern Terri tory

Lindsay Mon teith.

PO Box 351. Darwin 0801 Phone (089) 81 5922

ANOT HER POLLUTION SOLUTI ON Our cover pict ure shows the Wet Scrubber Towe rs and Activated Carbon cham ber at the en t ry of the Outfall Sewer into the North Head Treatment Plant of the Sydney Wate r Board. The system was designed and install ed under a very tight time schedu le by Process and Poll ution Contro l Pty. Ltd., and operated

by Thi ess Env ironment Di vision un der a BO.OT. co nt ract to The Water Board .

Pape rs desc ribin g thi s and other strateg ies for minimi sing odour at treatm ent works around Australia are cont ained in thi s iss ue.

EDITORIAL CORRESPONDENCE E.A. (Bob) Swinton , 4 Pl easan t View Crescent , Glen Waverley 3150 Office Phone-Fax (03) 560 4752 Home (03) 560 9306

ADVERTISING Ann Sykes-Smi th.

Appita, 191 Ro;al Parade. Parkv ille 3052 (03) 347 2377 Fax (03) 348 1206

PRODUCTION EDITOR John Grainger, Appita, 191 Ro;al Parade, Parkville 3052 (03) 347 2377 Fax (03) 348 1206

PU BLI CATI ON Wate r is bi-monthly. Nominal distribution times are the th ird weeks of February, April , ).me. August, October, December.

IMPOR TANT N OTICE The views expressed by the contributors are not necessarily erdorsed by the Australian Water and Wastewater Association . No reade r should act or fail to act on the bas is of any material contained herein. No responsibility Is accepted by the Association, lhe Editor or the conlrlbutors for the accuracy of inlormal lon conta ined in the !ext and advertisements.

The Austra lian Water and Wastewate r reserves the right to alter or to omit any article or advertisement slbmltted and requires Indemnity from advertisers and contributors agalns1 damages ¼hlch arise from material published.

All mat erial in Water Is copyright and should rot be reproduced wholly or In part without the written pe rmission of the ed itor.

WATER June 1992

1

TECHNOLOGY

Odour Minimisation at Werribee

by T. GUWVSEN, P. HANSEN, D. HUTCHISON, J. RUSSELL, P. SCOTT Part 1. -

Odour Survey.

Part 2. -

Design of Aerators, Installation, Operation.

Part 3. -

Anaerobic Pot Cover.

Part 4. -

Odour Reduction.

A ll the authors have been involved at various stages of the project for Melbourne Water.

1i·evor Gulovsen is Enginee,; Sewage Treatment Operations, and David Hutchison is Engineer, Research and Development at the Werribee T,·eatment Complex.

John Russell is Manager of Process Technology, Sewage Division, Peter Sco tt is Manager, En vironm ental Management

Division, at Corporate Headquarters.

Paul Hansen managed the Odour Survey in 1987, and is now working in the Water Technology Group of Gutteridge Haskin & Davey.

This paper was prepared by the Ediro,; based on official reports to Melbourne Wate1; and discussions with th e variou authors.

OVERALL SUMMARY Melbourne Water is developing a long-term strategy at the Werribee Treatment Complex to cope, on the one hand with increasing inflow of sewage, and on the other with increasing stringency of discharge parameters to the receiving waters of Port Phillip Bay. Another factor is the public perception and reaction to odour.

The cost study indicated that by far the most cost-effective optio n is to deve lop the lagoon systems, both in capacity and efficacy.

A prolonged and intensive odour survey was conducted, which indicated that the grass filtration areas (in winter), and the first ponds of the lagoons were the major sources of odour. Principally with regard to odour minimisation, but also with regard to other aspects of treatment efficacy, the decision was made to proceed with installation of surface aerators in the early ponds of the new

lagoon systems, as well as the isolation, and possible covering , of the 'anaerobic pot' at the entry of the raw sewage.

Design, testing and installation of the aerators in Lagoon 115E was completed by 1990. It has proved very sat isfactory, with almost complete elimination of odour from the aerated areas of pond No.I and pond No.2 together with a significant increase in treatment capacity.

A further contract to in stall aerators on the first pond of a new lagoon system, 55 E, has been nego tia ted and is currentl y in progress.

The installation of covers on the anaerobic zones is in progress, and the possibility of using th e sludge gas °for power generation is being explored .

Modifications to the grass filtration system are being trialled to minimise the odourous a naeropic zones.

Part 1. ODOUR SURVEY SUMMARY During 1985-7, Melbourne Water (then the Melbourne Board of Works) conducted a survey of odour in and around th e huge Werribee Treatment Complex.

The conclusions were that, contrary to the long-held belief that the primary sedimen tat ion tanks and digesters were responsible, the main sources of odour were the · anaerobic ponds of the lagoon treatment systems, and the anaerobic areas of the grass filtrat ion bays.

INTRODUCTION The Werribee Treatment Complex (or The Farm, as it is generally termed) is wellknown for its cost-effective treatment of the majority of the domestic and industrial wastewater from the city of Melbourne, and has operated for some 100 years (Dul fer & Swinton, 1991). It encompasses some II 000 ha of flat land abutting Port Phillip Bay, some 30 km south-west of the city. Currently it treats an average of 500 ML/d.

It utilises three treatment systems: • Land filtration: Raw or settled wastewater is flood irrigated onto pasture, which, after an interval, is grazed by livestock .

This system can only be operated in the growing season, November to April.

16

WATER June 1992

• Grass filtration: operated du ring the winter; sett led sewage is run across a paddock through a growing stand of coarse grass. A biofilm develops on the stems, and this serves in effect as a horizontal trickling filter.

• Lagoons, consisting of a number of ponds in series, (typically 10), ranging from anaerobic, through facu ltat ive to aerobic. The shift of a particular pond from one mode to th e next varies with temperature. While so me of the older lagoons receive settled sewage, the newer lagoons receive raw sewage.

• Primary sedimentation of a proportion of the incom ing sewage is conducted in a number of deep tanks, excavated in the earth, and desludged weekly.

• Sludge digestion is conducted in two open lagoons, 180 m by 550m, with continuous feed and discharge of supernatant. They are desludged every two-three years.

For the first 30-40 years of operation, the land and grass filtrat ion systems were adequate but as population and load increased , winter flows, especially peak flows, were treated in lagoo ns (Bremner & C hiffings, 1991). Odours had long been recognised as a nuisance, but the complex was surrounded on one side by sea, and on

the other sides by" la rge areas of agricultural and horticultural la nd , where the odours were tolerated by the rural population as being quite normal.

As the years progressed, however, various factors came into play: • despite the diversion in 1975 of 400Jo of the city's sewage to the South Eastern Purification Plant, the increasing vo lume to be treated, and the proportion of indust ri al wastewaters, led to increasing reliance on the lagoo ns.

• the development of the nearby township of Werribee into a population centre led to encroachment of housing into the agricu ltura l buffer zone, and the proximity of the digesters to the main Geelong Highway was a concern.

The Board had also to consider the longterm options for the treatment of the projected inflows. By far the most costeffective option was the further development of the lagoo n system, and works approva l was so u g ht for ex te nsio n s. In it s deliberations th e Board included th e aspect of odour minimi sat ion , even thou gh there had been relatively few formal complaints, to eit her the Board or the Victorian EPA, by the Board's geographic neighbours .

PHILLIP

PORT

BA Y

Seve n snap sho t samplin g da ys were conducted over a 12 month period . On each day several hundred grab samples from all processes on the Farm were analysed for sulfide.

Emission rate estimates.

A floating odour hood was developed , roughly 0.07 m2 base (Figure 2) enablin g a continuous air sampl e to be abstracted directly from the surface of a pond, into a metered flow of fres h air for a period of 15 minut es. Th e res ultant sampl es were assessed by the Boa rd 's odour pqnel, using the dynami c olfac tometer. At the same time gra b samples of liquid beneat h th e hood we re collected for analys is of sulfide, VFAs and pH .

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Comnunlty obser•,.Hion po1n •.s

•

c l aces Meteorolog 1cal sr.at1ons

•

Seaweed survey sites

1nclud1n9 hone and work

Fi g. I -

Map of the area surrounding the Werribee Treatm e nt Co mpl ex, with odour s urvey sites

GEOGRAPHY OF THE AREA Figure I is a map of the area sur ro unding 'Th e Farm ', as it is generall y termed.

Apart from the growing tow nship o f Werrib ee, the clo ses t la rge ce nt res o f population are Altona , in th e wes tern suburbs of Melbourne, some 12 km away, and Corio to the north west o f Geelong, a si milar di stance away. Both th ese areas are the base for petroleum refin eri es, petrochemica l plants and noxious indu stries.

10 km ac ross a large arm of Port Philli p Bay li es the Bellarine Peninsula, along the shore of which lie a number of fis hing and holiday villages.

PREVIOUS SURVEYS In 1983, the Victorian EPA conducted an odour survey in th e industrial area o f Corio.

Th e Werribee Farm was not found to be a major source. In 1984, the EPA co ndu cted a Community Odour Survey in the Shire o f Werribee, but the res ults were inconclusive.

However, on its own ini tiative, in March 1985 the Board appointed an independent Consultati ve Panel (Laing et al, 1985) which reco mmended that the Board co nduct a detailed sur vey.

OBJ ECTIVES The Werribee Farm Odour Sur vey had two obj ecti ves: • To defin e the nature, extent and source o f th e existing nui sance.

• To establish the meteorological conditions which would result in odours in spec ifi c communi ty locations.

METHODS Six methods we re used: • Community Survey • Ambient air sampling • Chemical survey • Odour emission rate measurements • Meteoro logical da ta and di spersion modelling • Seaweed sur vey Th e map in Figure I is annotated with with reference to the following description:

Co mmunity Survey.

The communit y survey aimed to defin e the frequency and nature of odours detected by the community. Th e re ult s provide a base line for assess ment ofodour redu ctio n wo rk s.

For thi s very wide survey, ex tending over so me 1500 km2 , the invo lvement o f the publi c was necessa ry. Appeals to loca l Service Clubs, bac ked up by advertisements in th e local papers, rec ruited over 100 volunteers. Testin g for sensitivity to odour and abil ity to defin e it reduced the panel to 43. The geographi cal distributi on o f the panel is noted in figure I. Each observer was issued with a diary fro m whi ch data co uld be transcribed into a compu te r data base.

Each observer was as ked to note: • time and duration o f the odo ur • descripti on (rotten eggs , amm onia, fishy, petrol -like, ac rylic paint , burnt rubber, pun gent, earthy, o ff-meat, sewage) • acce pta bili ty (ve ry pl easa nt to ve ry unpleasant , on a scale o f + 2 to - 2) • odour strengt h (none to very strong, on a sca le o f O to 5) • wind directi on.

Regul ar co ntac t with the observers was necessary to keep them mo tivated over the 15 months o f the sur vey.

A mbient air sampling.

Several attempts we re made to collect air sa mples around the Fa rm boundari es and meas ure the odour strengt h by dynami c olfac tometry. Howeve r, the results we re inconclusive, mainl y due to the in sensitivit y o f the test to low levels of odour.

Chemical sampling.

Two ap proaches to chemi ca l sampling of process liquids we re used: ro utine sampling to provide in fo rmat ion on seasonal trends: sna pshot sampling to identi fy those areas o f the Farm likely to generate significant odours.

Ro utin e sampl ing was conducted fo rtnightl y from June 1986 to June 1987 by ta king gra b samples fro m 40 locations and analys ing each fo r sul fide, sul fa te, vo latil e fa tt y acids (VFAs) and pH .

Fig. 2 -

Odour emiss ion measurement : Th e floatin g hood

.,

Meteorological Daw. To obtain more detailed data on relevant wind directions and strength , three stations we re establi shed on th e Farm , and one at Clifton Springs, south of the Farm on th e Bellarine Peninsula. More data was obtained fro m Government station s at Poi nt Cook a nd Lave rton . A tea m from Mo nas h Uni ve rsit y was co mmi ss io ned to model dispersion pat tern s.

Sea weed survey.

Od ours from ro tting seaweed we re a possible fac tor, so measurements were made o f th e amo unts o f seaweed at te n point s along the Fam1 's beach, and around Co rio Bay, as shown in Figure I.

RESULTS Community survey.

Du ring the fiftee n month s o f the sur vey 36- 39 observers we re acti ve at any one time, and 2154 observati ons were recorded . On average each observe r recorded one odour eve ry eight days. (All areas show a pea k in the first month of operat ion , pro bab ly due to ea rl y enthu sias m) .

Figure 3 summari ses the frequency of observat ions in each o f th e main areas: Bellarine, Corio/ Litt le River, Werribee/ Hoppers Crossing, Werribee South .

Th e greatest frequency was deri ved from th e predomin a nt ly ma rk et ga rd en community at Werribee South particul arl y during summer.

WATER June 1992

17

li quid. S" coll'ld va ry by 100% between sa mples taken 300 mm apart.

• The lack of precision of the dynamic o lfactometer system, due to th e va ri ation in huma n response.

The seasona l variat ion seen in lagoon S" did not correlate with measured odour em ission rates.

0 B

s V N

s I

Table I - Odour Emission Rates (ODU m3/ m2.s)

0 B

Process

s

Raw Sewage Anaerobic lagoon Facu ltative lagoon Grass f iltrati on Land filtration Seaweed

E. R V E R

otes

JUN

MAR86

AUG

OCT

DEC

FEB

APR87

MONTH Fig. 3 -

Seaso nal wriation of odour observations

The observers recorded 'sewage smell' 60% of the time, but not all such record ings cou ld definitely be assigned to th e Farm .

'Seaweed' was noted only 8% of the time.

The peak time for recordings was 6- 10 am, wit h a smaller peak at 4- 10 pm. These are t he times when the observers were most likely to be at hom e and less distracted by work duties. Atmospheric invers ions mainly occur at ni ght, wh ich co uld co ntribute to the peaks, though stro ng invers io ns were rare.

Chem ical survey.

Raw sewage In this case, snap samples were taken on seven days during I986/7 from the point of entry of the Main Carrier into the Farm.

Hourl y profiles of S" ranged from 0.5 to 2 m g / L with no evident periodicity.

Oxidised su lfur in raw sewage is typica ll y a round 200 mg/ L. Carriers.

So me 850 km of chann el distribute the sewage over the Farm area . In the main Western Carrier wh ich travels 18 km, S " levels rose to 4 to 5 mg/ L due to the anaerob ic cond itions.

Primary Sedimentation.

Samp les were take n routine ly every two weeks. For S" the median va lue at the inlet was 2.5 mg/ L and rose by about 20%.

The median level of VFAs was ca. 100 mg/ L, with occas ional exc ursions to 400 mg/ L. The S" and VFA content of the sludge was a n order of magnit ud e higher than that of th e superna ta nt liquid , a nd varied with sludge age, but this did not seem to affect the supern atant liquor, nor, by in ference, the odour levels.

Digesters.

The inflow resu lts reflect the high but very va riabl e va lu es in the sl ud ge in the sedimentation tanks, but interestingly, the S" fell to low levels at the li quor outflow.

Since the SO,1 levels remained low, th e sulfu r compounds must either be captured in the solids, or re leased to atmosp here.

Lagoons.

Sulfide levels in the lagoo ns show a marked seasonal trend, with hi gher levels in

18

Soluble sutridc

WATER June 1992

the winter. The transition zone from 0.2 mg/ L to lower va lues is typicall y at the end of the first pond in summer, but extends as far as the fourth pond in winte r. S" levels as high as JO mg / L were somet imes reco rd ed. VFA levels did not show the same seasonal trend, typicall y being around 60- 100 mg/ Lin the first pond and less than 30 mg / L in subseq uent ponds.

Grass filt ration.

The genera l flow is typically abo ut 20 mm deep. Samp les had to be taken from occasion al small pools, whic h may have affected the res ults. S" could rise to as high as 14 mg/ L during travel over the first 30% of the bay, but wou ld then fa ll to practicall y zero at the end. Interestingly, the SO 4 levels in the first 10% of the bay fe ll from 200 to less than 10 mg/ L. VFAs show roughl y a n expo nential decay down the bay, and levels a bove 10 mg/ L were found only in the first 15 % of the bay.

Land Filtration.

The bays operate on a 20 day cycle, being irrigated for two days, dried for two days, a nd then grazed for 16 days. At a ny one time, only about 10% of the 3900 ha is under irrigation. Levels of S" in poo ls during the irrigation a nd drying period were found to be low, with a mean of I.I mg/ L, and a median of 0.5 mg/ L. The levels of VFAs averaged 120 mg/ L, similar to those in the raw sewage.

ODOUR EMISSION RATES T he floating hood was utilised on a number of locations, with some difficulty.

Typical odour emission rates are summarised in Table I for each process, co upled with the relevant S" concentrations in the liquid. There were large variations in the measured odour emission rates. Possible reasons for th ese variations include: • The small area of the floating hood compared to the huge areas of the lagoons a nd filtration bays, so that, for example, in bubb ling areas of the lagoons it may not have captured a particular so urce of odour.

• Large spatial variations in liquid concentrations in the relatively slow-moving

IO

rn g/ l.

Odour Emi ssion rate

1.0-2.5 0. 1-24 0.05- 1.5 0.2-5.0 0.1 -2 .5 0.03

0. 7- 14* 0.05 -7.Jt 0.01- 0.2 0.05-3 .5 0.02-0.05 0.01

Table I:

• For raw sewage the low em i sion rate corresponds to a st ill liquid, the high to a turbule nt zone. t Th e seasonal va ri at ion in lagoon was not seen in the measured odour cmi sliion rates

s·

An attempt was made to correlate the a nal ys is of the liquid with the emission rates measured using the floatin g hood. S" and pH should give the concenration of H 2S in the liquid , which, with temperature, should give the partial pressure of H , S in the 'headspace'. H 2S was measured 'in the air stream leaving the hood , and ranged from 0.01 to 200 ppm (v/ v). There was some corre lation with t he di ss olved H 2S concentrat ion , with a regression coefficient of 0.75 .

However, there was such a large scatter between H 2S in the air stream and the ODUs assessed that it was as useful to correlate H 2S in' the liquid with the odour emission rate. Generally, high S" and / or hi gh VFAs gave hig h odour emission rates, but with considerable scatter in the results.

Some o;servations of interest were: • t he odo ur emissio n rate from a recent ly co mi ss io n ed anaerobic lagoon was typically double that from older lagoons .

• the concentrat ion of S" was a better indicator than the concentration of VFAs. • emission rates from the lagoon rose sharply at a liquid redox potential lower than -250 mv (based on li mited data) .

GROSS FLUX The gross odour flux from each area of the system was estimated from the measured S" levels, the correlations for each process disc ussed above, and the exposed surface areas. (Since the completion of the survey, more odour emiss ion rate measurements have been made, and the average of this data is now used instead of the calc ul at io ns based on the levels of S " ).

The results are summarised in Table 2 and de mon st rate that because of the areas involved, grass filt ration and lagoo ns are the major odour sources.

Ta ble 2 -

Estimates of Relative Odour Flux

Process

percentage of to tal odour emission summer

Sedim entation Di gesters Land filtration Grass rilt ra ti on Lagoo ns

0.4 1.2 1.3 97.1

winier

0.2 0.4 51. 7 47.7

Since grass filtration is replaced by the relatively innocuo us land filtration in the summer, this analysis indicates that there

should be a large decrease in emissions from winter to summer. The comm unit y sur vey did show this relationship in the Bellarine Peninsula, but not in other areas . The predom in ance of north / north wester ly wind s in winter may be the ca use.

DISPERSION ANALYSES Mo n as h Un ivers it y Department of Geog rap hy (Tapper & Sudb ury, I987) used two methods for a nalys ing the survey results to identify odour sources in the western Port Philip Bay region. The first, christen ed PONG2, combined the meteorological data with the observer reports to determine th e li ke ly sou rce of odour in the reg io n. The second used an atmosp heric di spersion model to link the odour emi ssion rates meas ured by the floatin g hood and the meteorological data to determine whet her each o bservati on co uld have been ca used by the Farm . T he PONG2 ana lysis, which is indepe ndent of emission rate estim a tes, showed th e Farm to be a significant od o ur so urce, wit h the g rass fi lt ration areas identifi ed in winter and lagoons in summer.

The dispersion modelling estimated that a minimum of 27% of the com munit y observers' resul ts could have been caused by the Farm in sum er, a nd 54% in win ter. The dispersion model used was a simple fixed refe rence point ga ussian plume model.lt ass um es odours from different sources are ad diti ve, takes no account of terra in effects a nd ass um es wind direction , speed remain constant over t he a rea modelled .

A lthough all th ese assu mp tions are not necessarily valid, th ey allow a relat ively easy a na lys is of the data .

After the odo ur survey was completed further modelling was done usin g the AUSPLUME model, with updated emission rate d a ta. This model makes sim il ar ass umpti ons to PO G2. The resu lts are compared wit h t he average results for some o f the co mmunit y observers in Table 3. The output has been exp ressed in term s of frequency of odours greater than 4 OD Us (approximately t he recog nition limi t for a n average pe rso n) as t he sim p li fy in g ass umptions will not allow th e model to accurately predict ma xi mum odour concentratio ns at a give n time.

Table 3 Frequenc)

or Odours, 0 •o or lime

Noted b) Obser\'e rs O bse n ¡er Group

All

Sewage

Werribee Sou1h Wer ribee Lillie Ri ver Lara Leopo ld Clif1on Springs Por1 arling1on

2.1 0.9 0.3 0.2 0.7 0.6 0.4

1.5 0.2 0.2 0.04 0.4 0.4 0.2

OICS 10

Model Predi ctio n

4 0. 7 1.2 0.6 0.4 I.I

2.5

Table 3:

0.I O'o of time is 8. hours pe r yea r.

Sc"age 1ypc odo ur i\ 1ha1 desc ribed by the obse rver.

T he f rcqucncies recorded are fo r 1987. befo re I he wo rk s described lau:r were ope ratin g.

The average communit y responses we re rath er different from those of indi vidua ls li ving close to one a nother, which highlights the problem of the 'sensitive individual'. In a ll a reas exce pt Leopold the model overpredi cted observations . This may partly be du e to th e model incl udin g odo urs at times when th e observers would not be awake.

Leopold is 18 km dista nt from the Farm , and

mi ght have beeq affected by other odour sources, such as the high accumu lation of seaweed on their beach.

SEAWEED SURVEY The largest acc umul atio ns of rott ing seaweed occured a long the Farm coast line a nd a t Leopo ld . Anal ysis of the communit y observations and modelling of the odour emissions suggest that seaweed odours o nly cause prob lems with in I km of the beach.

DISCUSSION AND CONCLUSIONS Despite odours from the ot her so urces, s u c h as c hem ica l pl a nts, agr ic ul t ure, fe rtili sers (both organic and in o rga ni c) abattoirs and rott ing seaweed, the res ults clearly identified the Farm as mak ing a sig nifica nt contr ibu tion to odour. The maj or sources were the grass filtration a reas in late winter a nd spring, and th e lagoo ns in both winter a nd summer. This was contrar y to the previously accepted belief that the primary sedim entatio n tanks and di geste rs we re the main sources.

The proposals for replacement of the simple sedim entation tanks by a mecha nical primary treatment system a nd enclosed di ges ters were therefore inappropriate.

Since th e proposed development of the Werribee Treatm ent Complex was to build more a nd bigge r lagoons it was judged esse nti al to desig n th em to emit minima l odo ur, a nd also to modi fy th e g rass filtrat ion system to minimise a nae robi c a reas.

Part 2. THE AERATORS SUMMA RY Principall y to reduce odour, but also with rega rd to other aspects of treatment effi cacy, th e decisio n was m ade to proceed with insta llati o n of surface aerators in t he early ponds of th e new lagoon systems, as we ll as the isolation , a nd possible covering, of th e 'anaerobic pot ' at the entry of the raw sewage.

Design , test in g and installation a nd co mmi ss ioning of th e ae rators in Lagoo n I 15E was completed by September 1989 . It has proved very sati sfa ctory, with a lmost complete elimina tion of odour from pond I a nd pond 2, except for th e initial anaerobic zo ne.

A further contract to ins tall aerators o n th e appropriate areas of a new lagoon system , 55 E, has been negotiated a nd is currentl y in progress.

deep, th e remai nin g ponds 2 m deep. T he operating ca pacit y of the system is 60 ML/d of raw sewage, with ave rage co ntent of

450-500 mg/ L BOD (due to the relativel y hig h input of trade was tes into the Western system) .

INTRODUCTIO N A large new la goon , I l 5E, wa s commi ssioned in 1986. It co mpri ses 11 po nds in series, lying in a SW direction a long the coast. Figure 4 is a photogra ph of th e lagoons with the aerators in operation. The first pond is 1000 m long, and 150 m wide; the succeeding ponds a re the same wid th , but progressively longe r, as show n in the photograp h. The first two ponds are 3m

20

WATER June 1992

fig. 4 -

Ae ri a l view of Lagoo n l lSE with aerators a nd anaerobic pot, prior to in stallation of the cover (note test tank in foreground)

The new lagoon is in close proxim it y to the developing comm unit y of Werribee South. Once the lagoo n was commission\!d, there was a reaction from this com munit y, to which Melbourne Water responded, since good relations with the local com munities are of prime importance. The decision was made to proceed as fast as possible on the basis of theoretical design combined with pragmatic decisions. The overall co ncept was modular, so that it could be modified after comm issioni n g without undue financ ia l penalty.

DESIGN Trials of a floating aerator were conducted on the first pond of a n exist ing lagoon, from which it was concluded that if a positive dissolved oxygen conten t (DO) of approximately 2 mg / L cou ld be maintained on the surface, odour wo uld be substantiall y reduced.

At t he same time, it was judged that the facu ltative act ion of these ponds wou ld be maintained if the positive DO did not extend for th e full depth of the liquid layer.

In this old 3 m deep pond, it was found that there was a si lt layer whic h reduced the depth in some regions to 1. 5 m. The cone of suction under a floating aerator was found to sco ur this o ut.

The first step in the upgrading of Lagoo n l 15E was to form the 'anaerobic pot' at the point of entry of raw sewage. This was ac hi eved by means of a boom a nd curtain , (described in Part 3), isolating the first 220 m of the lagoon.

Data on the BOD load profile leaving th e a naerob ic pot were acc umula ted. This zo ne has been found to reduce BOD from ca. 500 to ca. 180 mg/L. An est imate was made of the oxygen transfer required using stand ard methods.

Oxygenation provided by the normal act ion of wind and waves over the lagoon surface was factored into the estimate. .A specification was drawn up for th e surface aerators. The comparative shallowness of the oxygenated zone was a factor. Power costs were estimated to override th e costs of capital, so an oxygenatio n

efficiency of 1.60 kg 0 2 transfer per kWh was assumed in determining the number of aerators required . .

This specificat ion was below the norma l range of operation of sur face aerators, a nd the specification included the requirement to test a prototype unit. The Board gave advance warn in g to Austra li a n manufacturers to enable them to deve lop both the gea rbox and the und erwa ter cables required.

A water tank was constructed in which a contractor's rig cou ld be tested to ASCE cond iti o ns. The tank was excavated to conta in 5.5 ML, a t a depth of 3 m , with banks of 2: 1 batter a nd lined with HOPE .

The wate r was dosed with sodium sulfi te to achieve zero DO, a nd the oxyge na tion metered hy DO probes.

(Since these first tests, the tank has been made avai lab le to ot her A u stra li a n contractors on a basis of shared cost, and this has enabled development of the des ign, to th e stage where future tenders can be presented with less risk, a nd in fact, future tende rs wi ll include a bonus cla use for hi gher effi ciency. The equ ipment ca n now be offered for ex po rt. T he impact on th e qu otat ions for imported eq uipment was significant).

The design of the grid pattern followed, with provision for shutting off mac hines to fo llow oxygen demand, on a rostered basis to equa li se maintenance requirements.

INSTALLATION The contract for th e aerators for Lagoon I ISE was won by Warman International Ltd. Six ty-t hree units were deli ve red on th e first contract during 1989 (see Fig ure 5). T he 37 on pond No.I are powered by 30 kW motors, and t he 26 on pond No.2 by 15 kW motors, all supp lied by Pope Pty Ltd . The power cab les, supported by fl oats, were suppli ed

by Olex Cabl es Pty Ltd.

OPERATION Pond No. I is now co ntrolled by a DO probe in the transfer chan nel to pond No.2.

T hi s is maintained at ca. 4 mg/ L, whi ch guarantees that at least 2 mg/ Lis achieved in th e in let area. Pond No.2 is also controlled

by a DO probe in th e_-.o utlet , but the targe t is for no more than I mg/ L. Aerators are turned o n/ off manually to ac hi eve these levels. On Pond o. l , durin g winter, approximately 23 aerators are in operation, a nd 17 in summer.

The increase in oxygenation has ena bled the average capacit y of the Lagoon to be increased by up to 50%.

FURTHER DEVELOPMENTS A new lagoon, SSE, is b ei n g commissioned. Pond No. I is 220 m wide, by 1500 m long, including an 'anaerobic pot' 400 m long and 6 m deep.

The co ntrac t for the aerators has been awarded to Aquatech-Maxco n Pty Ltd , a nd 89 units, dri ve n by 30 kW TECO motors, are being supplied for operation in Pond o.l.

A more so phi sti cated system of control is being installed . The pond is divided into 4 ce lls by floating booms. Eac h cell has a DO probe, which feeds data to a PLC which switches aerators on / off to maintain the set point of 2 mg/ L. The PLC rosters the unit s and logs hours of operation. An energy management fac ilit y is a lso incorpo rated.

The average week ly flowrate is fed to the PLC, a nd si nce the ave rage res idence time of sewage in the pond is 6 days, th ere is scope for taking ad va ntage of the significant saving in off-pea k power rates without ris kin g deve lopment of odours.

Part 3. THE ANAEROBIC POT COVER SUMMA RY In order to capture odour em issions, improve a naerobic efficiency a nd a ll ow capture of methane gas for energy, a floating cover has been installed over Lagoon I !SE, one of the major lagoons, and is the first o f a series planned at Werribee to transform a n odour problem into an energy-prod uci ng asset.

The cover is 3.3 ha in area, the first such cover in Ausrali a, a nd th e largest of its type in the wo rld . A lthough this tec hnique has often been app lied for anaerobic treatment of hi gh strengt h industrial wastes, this is the first app li ca ti o n to muni ci pal wastewater.

INTRODUCTION

l•ig. S -

Surface aerator (Warman type)

In the co urse of the stra tegy to reduce odo ur emi ss ions, the sur vey iden tifi ed th e a naero bic zo ne in th e lagoo n systems as a major contributor.

Lagoon II SE is fed with raw sewage. Its first pond is 150 m wide, and has a total lengt h of 1000 m . a nd is 3 m deep. In the first 200-300 m of this pond a consid erable amount of anaerobic decomposition occurred. In certain seasons a th ick crust of sludge form ed on th e sur face. W heth er WATER June 1992

21

liquid or semisolid, the surface was continually erupting methane, admixed with H 2 S a nd other odours.

ISOLATION In view of the installation of the surface aerators in the succeeding area on pond No.I, it was essent ial to separate the oxygenated zone from this active anaerobic zone.

Two hundred and thirty metres out from the inlet a floating boom was installed, from which was suspended a curtain of HDPE sheets, separated by sli ts through which the liquor flows into the next stage.

Once this curtain was established, it was found that the anaerobic zo ne was reducing the incoming BOD of ca. 450-500 to ca.

150-180 mg/ L. It was also found that the turbulence caused by the generation of methane in the sludge was automatically desludging the bottom of the pond. Conseq uently, the installation of a cover cou ld be considered, since desludging wou ld rarely, if ever, be necessary.

used a temporary barge floating on the sludge. which supports the cover as it is welded in panels, prior to moving the barge forward to the next position. This method a llowed effective anchoring of the cover aga inst wind uplift as the work proceeded.

Gundle hot wedge and extruding welders were used. An extract ion fan ran cont inuously to exhaust the sludge gas whic h accumulated under the partly installed cover. (Figure 6)

GAS PRODUCTION Prior to the insta llation of the cover, the floating hood test unit (ref Part I) was mounted over this anaerobic zone, and the gas collected and analysed. Table 4 summarises the data.

It is estimated that some 10 000 m 3 of gas will be generated from the 18 000 kg of BOD decomposed per day in Lagoon ll5E .

Table 4 -

Anae111>bic gas composition VIV% Werribee

cf. conventional closed digesters

CO2

12

CH4

80

N2

8

H2S

0.5

35 65

CONCLUSIONS The cover at the time of writing has just been completed, and the reduction in odour is very noticeable. Gas production is being monitored, in preparation for installation of a power generation unit, which is planned to deliver power back into the State grid . It is estimated that the power so generated will be of the order of all the power required for th e surface aerators.

The contract for the much larger cover (9 h a) of the new 55E lagoon is und er discussion.

DESIGN OF THE COVER The proposal for the cover was advertised widely, and a numb er of Australian companies, in consortium with overseas associates, developed designs and tendered their registration of interest in the project.

The contract was awarded to Polyfelt and Geosynthetics Pty Ltd applying technology developed by Gundle, Houston, Texas.

The HDPE sheet, 2.5mm thick, is the polymer used for black polyethylene pipe, and is known to provide long term performance in an exposed situation .

The design includes a system of floats and ballast-filled HDPE pipes which control the shape of the cover and allow storm water and wind loadings to be managed. The weighted pipe system a lso directs accum ulated gas to a peripheral collector pipe system, which varies from 315 to 500 mm diameter.

Three edges of the sheet are buried into perimeter trenches. T he leading edge of the cover is reinforced by a stainless steel cable and fitted with a weighted skirt of HDPE which hangs down some 1.5 m into the liquid layer just short of the separating curtain, to prevent escape of gas or entry of air.

T he cover is designed to operate with a small internal vacuum maintained by external gas fans, and a lthoug h so me inflation for storage is possible, a fully deflated co ndition must be maintained during periods of high winds.

, Fig. 6 -

Part 4. ODOUR REDUCTION. Measurements of odour production on the first pond of the ll5E lagoon were taken before and after installation of the aerators, using the floating hood. These values of ODU were used to calculate the Odour Emission Rates.

Trials were conducted on the grass filtration system, which had a lso been identified as a significant source of odour in winter. Instead of being fed with primary settled sewage, with a BOD of 400-500 mg/ L, and suspended solids of 150 mg/ L, the trial bays were fed with sewage which was drawn from the first pond of an aerated lagoon, with a BOD of ca. 50 mg/ L. Odour production was compared with that from conventiona l grass filtration areas.

INSTALLATION The HDPE sheet was delivered in rolls, 7 m wide, and 70 m long. The contractor

22

WATER June 1992

generally less than 250. A power outage occurred in June 1990, and the odour level immediately reverted to previous levels, falling again as soon as aeration was recommenced. The anaerobic zo ne was unchanged.

Along with the reduction in odour was a change in its nature from the objectionable hydrogen sulfide/ fatty acid odour to a hydrocarbon type odour.

Odour emission from the anaerobic pot will cease once the cover is installed.

Grass filtration:

Lagoons:

Recent trials have shown that 800Jo of the odour from the anaerobic wnes of these bays can be eliminated by pretreatment of the incoming sewage, as shown in Figure 8.

The odour assessment panellists did not report offensive hydroge n sulfide odours when ODU levels were less than 300.

Sampling points in the ll 5E lagoon were set up 100 m, 400 m and 900 m from the raw sewage inlet of pond No.I. Note that the curtain to isolate the anaerobic zone was at the 250 m mark.

Results of the ODU measurements are shown in Figure 7, covering the period June 1989 to June 1990. As soon as aeration was commenced on September 25. The ODU levels in that zone dropped from ca .1800 to

The decision has been made to deploy all incoming sewage through covered anaerobic pots, so that not only will grass filtration be fed with partially treated sewage, but also the land filtration bays. Thus odour production will be reduced all round, combined with maximum production of sludge gas for energy.

GAS HANDLING Fans collect the gas from the HDPE and stainless steel perimeter pipe and pass it through condensate traps and filters prior to evaluation for energy production. For the time being it will be fl ared off. The gas handling system has been sub-contracted to Fluid Waste Treatment Pty Ltd.

Installing the HOPE cover on llSE lagoo n

RESULTS

CONCLUSIONS

5

3000

Q.

2500

June '89 to June '90 - --- - - - --· - - - , - - - - - -

0

•

...-----.

.!!!

"i:

.2 :i i5

...::::, 0

,.

Sampling Point in Zone Without Aeration

Aeration Commenced

2000

::)

C:

--]

1500

· Aeralors Off

e,4

"

(Short Period)

1000

500

"C

ltt. 'I-•

0

23,0ec-88

02,Apr,89

11·JuI·89

19-0ct,89

• •. •• 27,Jan-90

••

07, May-90

• 15-Aug-90

23-Nov-90

Date 100m From Inlet (now under cover) ._

•

400m From lnlel (now aera ted zone)

900m From Inlet (now aeral ed zone)

Fig. 7 -

Odour reduction on I ISE lagoo n

-------- - - - - - - - - - - - - -~

3000

5 0

Q.

.!!!

"i:

2500

2000

::) C:

1500

2 Q

1000

.2

:S

~

i•

~L

300 oou

-100 - - - ~ -200 ---- ----300 Distance From Inlet (m)

0

•

Reduced BOO Bav (800 =50mg/l)

~

Typical Opera1ion Bay (B00 = 400mgll)

Fig. 8 -

400

Belt Presses

Odour profil es in grass filtration bays

OVERALL CONCLUSIONS The odo ur survey condu cted in 1986 identified the major sources of odour in the Weribee Treatment Co mplex, a nd preve nted the unecessa ry expenditure of capital on the primary · trea tm ent and di gester systems, which had previously been thou ght to be the m ajor so urce.

Adoption of mechanical aeration on the first ponds of the large lagoo ns has no t only solved the problem of odo ur, but increased their operating capacity. Flexible cove rs on the anaerob ic zo nes of th ese lagoo ns will remove th e major source of the odour. Usi ng th ese a naerobi c pots to give primary treatment to a ll sewage enterin g the Werribee Treatment Complex will ensure minimal odours from th e grass and land filtration systems, a nd a lso give the potential for ge nerating the maximum amo unt of power from th e sludge gas.

Fo ll owed by the natural biologica l action of th e success ive aerobic pond s of the hu ge lagoons, this will co ntinue to provide a cos t- effec tive method for trea tm ent of the major portion of th e was tewater from the city of Melbourne for long into the fore seeable future without nuisa:-- - - LO the neighbouring comm uniti es.

"THAT BELT PRESS WITH THE UNPRONOUNCABLE NAME" Supaflo Technologies are now offering the Sernagiotto range of Belt Presses. Sernagiotto (pronounced "Serna-Jotto") un its were previously marketed in Australia and the US under the Andritz name. Today, after more than twenty years of development, the Sernagiotto name stands proudly in its own right.

These days when the heat is turned on to environmental and process issues, the Sernagiotto units offer the most critical factor - reliability.

At present there are in excess of 40 Sernagiotto units in operation throughout Australia in a number of different dewatering applications ranging from mineral processing to municipal sewage . Coupled with the international experience of more than 1000 installations worldwide Supaflo can offer you the technology that best suits your process.

Call Ian Bane in Sydney on (02) 949 3011 to discuss your requirements.

ACKNOWLEDGEMENTS Th e au th ors acknowledge the numerous people involved in this long in vesti ga ti o n, but particularly the community observers, a nd the field and laboratory staff a t the Farm .

SUPAFLO TECHNOLOGIES PTY. LTD.

REFERENCFS

1/14 Roseberry Street, Balgowlah , N.S.W. 2093 Ph. (02) 949 3011 Fax (02) 905 5856

Bremner, A . J.: C hiffings, A W: (199 1) 'The Werribee Treatment Complex: A n E nvironmental Perspecti ve'. Water, June 1991.

Du l fer, W. J .• Swint o n, E. A . (199 1) 'The Reli ef o f Smell bo urne' Water, June 199 1.

La ing, D. , Sanders, B. S. , Ta pper, N., 198 5, Report to Board .

Ta pper, N., Sudbury, A ., 1988 , Report to Board .

PERTH : Ph. (09) 316 1966 Fax (09) 316 1952 MELBOURNE : Ph . (03) 526 3628 Fax (03) 526 3652

• THICKENERS • PRESSUREFILTERS

•

AERATORS

•

FLOATCELLS

•

EFFLUENTTREATMENT

TECHNOLOGY

UPDATE ON ODOUR CONTROL IN GEEWNG'S WASTEWATER SYSTEM

by G. J. SEWARDS and D. S. BARKLEY ABSTRACT Odour ge neration in the Geelong a nd District Water Board's (Victoria) sewer system is compounded by the multiplicity of pump stations and long runs of flat risi ng m ains, so that up to 30 mg/ L of sulfides can be generated.

A number of options were evaluated in 1988 a nd a preferred stra tegy developed .

The paper presents an update of the current situation . The basic technique is injection of oxygen or air where appropriate, but in addition, ultraviolet radiation to generate ozone and some odo ur supression chemicals are being deployed at particular points.

INTRODUCTION The Geelong and District Water Board (GDWB) operates and maintains a sewerage system for the City of Geelong as well as several other smaller sewerage systems on the Bellarine Peninsula in Victoria (Figure 1). Domestic sewage and industrial wastewaters from Geelong proper and from the surrounding townships of Torquay, Jan Jue, Barwon Heads, Ocean Grove, Point Lonsdale, Queenscliff, Clifton Springs and Drysdale are discharged to th e ocean at Black Rock.

The wastewaters are treated by milli screening (0 .5 mm apert ures) and grit removal prior to entering th e 1. 2 km offshore o ut fa ll .

Separate collection, treatment and disposal systems are operated for the towns of Anglesea and Portarlington .

Gordon Sewards is a Chem ical Engineer with 20 years experience in wastewater engineering. After working with Caldwell Connell Engineers for 9 years and Binnie & Parlnersfor 6 years, Gordon now operates his own consultancy, Envirocon, working out of his home in Melbourne. One of his major clients is the Geelong & District Water Board for whom he acts as a wastewater process consultant.

David Barkely has been with the Geelong and District Board for 18 years. He was responsible for the development of the original odour and corrosion contro l strategy in 1988. David has recently been appointed to the position ofManager Urban Maintenance in the Board, and will be in charge of implementing further measures to eliminate odour and corrosion problems in the wastewater collection system.

In addition, ultraviolet radiation was also considered as a measure for oxidising sulfides released at turbulent manholes or in pumping station wet wells.

The major recommendations of the strategy have been implemented progressively. Some qf the recommendations made in 1987 have been abandoned, for example the use of biocides to control sulfide production in small rising mains, because of the toxic nature of these chemicals.

This paper presents an update of the current situation at Geelong.

T he cornerstone of the strategy remains th e addition of oxygen to the sewer system either by direct oxygen inj ection using dissolvers or by direct air addition to rising mains. In addition, ul travio let rad iation is being trialled as well as some odour suppression chemicals.

PURE OXYGEN ADDITION

The Geelong w.istewater collection system

The systems cover large geographical areas and consequentl y th e sewage remains in th e sewers for lo ng periods of time during which significant concentrations of sulfide can build up. Also, there are approximately 90 pumping stations under GDWB control. Some of the rising mains from these stations are several kilometres lo ng and can generate 20 to 30 mg/ L of sulfides.

In 1987, the GDWB carried out studies with the objective of identifying a preferred strategy for the control of odours and corrosion in its sewerage systems. T he strategy was described in a pa per presented at the AWWA 13th Federal Convention held in Canberra (Sewards & Carpenter 1989) . A wide range of techniques was evaluated including addition of the following substances and chemicals: • bacterial suspensions • pure oxygen • nitrates • air • potassium permanganate • hydrogen peroxide • ferric chloride • biocides • ferr ic sulfate • chlorine • alkali • chlo rine dioxide

24

WATER June 1992

The GDWB now operates four U-tube dissolvers on rising mains in the main sewage collection system.

The Saltworks dissolver was the first unit installed by the GDWB. Extensive tests were carried out, and it was concluded that the unit could achieve 750Jo saturation at the governing operating pressure with close to lOOOJo oxygen utilisation, i.e. there was little undissolved oxygen at the pipe end .

Prior to oxygen injection, sulfide concentrations in this 450 mm diameter, 1550 m long pipeline were usua lly aro und 25 mg/ L and the di scharge created a severe odour problem at a local technical school. This problem has now been eliminated by addition of sufficient oxygen to oxidise su lfides formed in the pipeline and to provide a residual dissolved oxygen concentration of close to 10 mg/ L. The second dissolver installed by the GDWB was a sidestream dissolver on the 450 mm diameter Cowies Creek rising main. This rising main contributes about 400Jo of the flow to the upper reaches of the outfall sewer, and by saturating the flow, aerobic conditions have been established where previously they bordered on septi c conditions.

The Cowies Creek sidestream unit consists of a 200 mm diameter dissolver taking approximately 60Jo of the flow to which is added sufficient oxygen to result in a dissolved oxygen concentration of 10 mg/ L in the combined flow at the end of the rising main.

• For the Bowlers rising main. This is a substootial pumping station which receives domestic and industrial wastewaters, including the discharges from a wool scouring plant. The rising main from this pumping station contains on average 6 mg/ L of sul fides.

Oxygen addition is unquestionably the most cost effective sulfi de reduction technique for the rising main applications listed above which involve daily flow rates of several ML/d a nd potential endof-pipe sulfide concentrations of more than JO mg/ L. The unit costs of treatment, excludi ng capital recovery costs, vary between about $18/ ML and $40/ ML.

DIRECT AIR ADDITION

Side stream dissolver at Cowies Creek

In the early part of 1992, two oxygen dissolvers were installed on the Queenscliff rising main. This is a 375 mm diameter, 8400 m long pipeline capable of producing 30 mg / L of sulfide. The dissolvers replaced a hydrogen peroxide addition station which had not been successful in elim inating severe odour problems at the discharge point.

Two dissolvers were required for the Queenscliff main because of the low operating pressures within the pipeline and consequent low saturation disso lved oxygen concentrations that could be obtained. The first dissolver adds sufficient oxygen to oxidise most of the sulfides to ensure that the sulfide concentration arriving at the second dissolver is low. The second dissolver then adds suffic ient oxygen to oxidise the remaining su lfides and to produce a positive residual at the pipe discharge.

Due to the proximity of res idences to the pumping stations, the Queenscli ff main dissolvers have been partially buried to minimise their visual impact, and in one of the installations the oxygen storage tank has been hidden within a brick enclosure. The entire installation is hard ly visible from the roadway.

Dissolver piping: Queenscliff rising main

Oxygen add it ion is now being considered at other locations as follows : • For the Leopold rising main, 450 mm diameter, 6700 m long. This is anot her notorious rising main whi ch can produce more t han 20 mg/ L su lfide and contributes to objectionab le odours at its discharge point.

• At the Black Rock treatment plant, where it will be used to oxidise sulfides present in two long rising mains from Torquay (9600 m long) and Ocean Grove (II 400 m long), and to oxygenate a recircu lati ng flow which will be added back to the main sewer flow upstream from the plant to reduce sulfides in the flow arriving at Black Rock to zero. Anyone who has visited the Black Rock treatment plant will welcome this news!

• At the new pump-boosted syphon recent ly provided to replace the ageing aqueduct over the Barwon River. By saturating this flow, aerobic conditions could be imparted to approx imately one third of the en tire Geelong flow as it commences its long journey from Geelong proper down to Black Rock.

• For the Corio West rising main, which carries a significant load of partially treated abbatoir effl uent which has an object ionable odour.

A ir is being added to 12 small rising mains in the Geelong area.

The purpose is to reduce sul fide concentrations in sewage flows entering the collection system and simultaneously introduce oxygen at several locations. The mains a re all continuously rising pipelines which cannot become a ir bound. Direct air add ition can result in zero end-of-pipe sulfide concentrations and dissolved oxygen levels of 2 to 3 mg/ L where previously there had been none. Approximately 3 Lis per 100 mm pipe diameter is being added at a cost of $4-18/ ML.

ULTRAVIOLET RADIATION Ultraviolet rad iation is being trialled at two pumping stations in Geelong about which odour comp laints have been received. It is noted, however, that UV radiation is regarded by the GDWB as a belt-and-braces measure to combat the odour problem. Emphas is will be placed where possible on eliminating the cause of the odours, e.g. sulfide oxidation or prevention of sulfide generation .

One of the pumping stations is in the Cli fton Springs area. It serves a domestic catchment with no industrial contributions. The catchment is relatively small and the sewage arriving at the station is fresh. Sulfide concentrations measured in wet well samples have all been essentially zero. However, the pumping station is located in a depression at the end of a cul-de-sac and its vent is close to and at about the same level as an adjoining residence. Under certain wind conditions, the resident can detect odours of sewage origin .

The second is the Corio West pumping station which as indicated previously receives partially treated abattoir effluent. Despite closure of the sewer vents immediately upstream from the wet well , objectionable odours do escape at times.

Trial UV installations have been set up at both these locations.

Preliminary data at the time of writing'indicates that the units are successful in eliminating hydrogen sulfide and objectionable odours from the vent discharges. Meas urements of hydrogen sulfide and ozone concentrations as well as of wet and dry bulb temperatures for calculation of relative humidity will be undertaken as part of the assess ment of UV radiation for odour control.

The UV units installed at these pumping stations comprise a fan a nd an array of tubes installed in a stainless steel enclosure. The fan reci rculates air over the UV tubes. The capacity of the fan is . equivalent to fo ur wet well volume changes per hour. The UV units are screened from direct view for eye protection by the enclosure.

Additional safeguards include prohibition of entry to the wet well for 15 minutes after the UV units have been turned off and a ve ntilatio n fan turned on to clear the wet well atmosp here of a ny residual ozone.

The units have been removed temporarily pending repair and modification to ensure they do not create hazardous conditions inside the wet wells.

MASKING AGENTS, DEODORISERS AND OTHER ADDITIVES T he GDWB has trialled, is currentl y trialling or is proposing to trial several compounds which are either added as a solution to wet wells in pumping stations or atom ised into the wet well atmosp here or into sewer vent pipes.

The range of wastewater add itives includes biocides. As indicated a.bove, the use of biocides was considered by the GDWB in 1987 but subsequently rejected because of the toxic nat ure of the chemicals available. A new range of 'non-toxic' products is now being marketed which it is claimed can prevent sul fide generation in risi ng mains by stripping slimes off pipeline walls or preventing them from establishing. The GDWB has trialled some of these with limited success.

Conrinued on page 29

WATER June 1992

25

TECHNOLOGY

ODOUR PROBLEMS FROM NORTH HEAD STP

by M. LAGINESTRA ABSTRACT North H ead STP serves over I millio n people in Sydney's north , and h as a ca tchment area of 47 000 hectares. Since the commissioning of additional sedimentation tanks and the deep ocean outfall , odour complaints have significantly increased. The buffer zo ne (a lthough quite large) does not appear to attenuate odours.

Oxygen dosing of raw sewage, under pressure, has proven success ful in reducing odour generation and complaints.

Mitchell Laginestra, BE (Sydney) is a chemical engineer with the Water Board at North Head Sewage Treatment Plant. He has just completed a dissertation for a Masters of Environmental Studies at Macquarie University and has over 9 years experience in operation and investigation of sewage treatment processes.

INTRODUCTION North Head STP North Head Sewage Treatment Plant (STP) is a primary treatment pla nt servi ng an equivalent population of I 100 000. (The industri~l component is relatively low). The average dry weather flo w 1s approximately 310 ML/day.

The catchment area of the plant is the largest in Sydney. It covers some 47 000 hectares, and extends along the northern harbour foreshores to Hornsby and Narrabeen in the north, out to Blacktown in the west.

The plant is on a headland at the ent ry to Sydney Harbour, and is landscaped to a low profile, apart from the stacks. It is surrounded

by National Park and army land. The nearest neigh bours to the STP are the Nationa l Parks office, army barracks and housing, Manly Hospital, St Paul's School and St. Patrick's Seminary. Residential areas are over 500 metres from the plant boundary. (Figure 1).

North Head Process In considering odour problems from North Head, it is important to be familiar with the process.

A schematic diagram of the No rth Head processes is shown in Figure 2.

Sewage is screened by drum screens of 12mm a nd 5mm aperture, prior to pumping to the above gro und plant. Each of the four pumps has a capacity of 4000 LIS. Usually only one pump is required,

although during diurnal peaks a second pump will come on line.

Three pumps may be used to ha ndle wet weat her flow.

The above gro und plant consists of two grit removal tanks, fo llowed by four high rate primary sedimentation tanks (25 minu_tes retention time). Each of the sedimenta tio n tanks has a travelling bridge scraper to collect scum and sludge. '.fhe sludge is discharged to gravity thickeners which consolidate the solids from 1. 5-2% TSR to about 5.5% TSR. Thickened sludge is dewatered by centrifuge, with the sludge cake at present tra nsferred to a chemical stabi lisation process (N-viro soil , where lime and cement kiln dust are mi xed with the sludge).

Prior to January 1992, all solids byproducts (screenings, grit and sl ud ge) were incinerated on site. However, _co ncerns by th e. local communit y regarding the incinerator erruss1ons have prec1p1tated cessation of sludge incineration , pending a health study in the area.

C hem ical stabilisation for grit and screenings is currently bei ng commissioned. ' E fflu ent used to be discharged at the base of the cli ff into the Pacific Ocean, but with the Commissioning of the deep ocean outfall it is now discharged four kilometres o ut to sea, at a depth of 60 metres.

A80Vl C RO~O WOO Kt

..... c,.

Scum

1

tn c iMf"IIIOu 1

I

: lludQII St.abHuitlon

(81o~ycl•)

.........

NSOOS

....,,

4 - - tnjectton

OMp

o .....

NORTH HEAD

Fig. I -

26

Location of No rth Head S"IP

WATER June 1992

COW'IPHllno

Fig. 2 -

Ou1'11II OIK,._O,.

Nort h Head STP - Schematic Diagram

THE BIG STINK orth Head has been the subject of numerous odour complaints.

In the summer of 1990- 91, comp laints reached 'plague' proportions.

The previo us summers had regi stered o nl y a few complaints .

Certainly a slight increase may have been expected with the growing public awareness of the plant. However, the size of the difference is signifi ca nt and also the timing.

The sharp ri se actua ll y coincided with the commission ing of the ocean outfall in December 1990. Prior to this it had been conc luded that the majority of the odour complaints had been due to sludge and grit stockpilin g and trucking activities. However, these had dimini shed in frequency dur ing the ensuing period and were definitely not the cause.

In addition, there was an e no rmous disparity between the summer of 1989/ 90, when a total of about 20 complaints were made to the plant and summer, 1990/ 91, when over 20 were received in one day, not inc lud ing t hose mad e to the State Po ll ut io n Contro l Commission.

Continuous monitoring of the vent stack of the incoming sewer (NSOOS orthern Suburbs Ocean Outfall Sewer) started in August 1990. Previou s odour complaint s had init iated a low key e'ffort in determinin g the major so urces of odours. It was hoped that so me correlation cou ld be found between peak s in H 2S emissions (used as the indicator for odours) and the occurrence of compla ints.

Monitoring of th e vent stack was by a Drager Polytron senso r and indicator, coupled with a chart recorder. This monitor was found to be reliable, although there were some problems with moi st ure in the air stream.

Complaints were recorded on a standard form at the plant, which is shown in Table 1.

Table I -

North Head STP Odour Incident Reporting Form.

Da te ...... ........... ......... .

Odour co mplaint by ..

or.

Co mpl a in t was lodged via D phone and noted by ...

.. .................. . ........... (name) .......... (address) D other .... (specify) (yo ur nam e)

TIME OF ODO R OCCURRE E from ............. to ..................... .. (i.e. approx. tim e that sme ll was fir st noticed to the time it stopped) WEAT H ER O fin e/clear O part ly c loud y D rai n/ dri zz le D cloud cover TE 1PERAT RE (Ambient) at time of occurrence...

H MlD lTY W I, D SPEED

.. ............. C

D low D medium D high D sti ll condit ions D slight breeze D strong bn,e,e D wind y

W I, D DIRECTION from

............. .

D co ntinu ous D intermittent AND ODOURS were D fai nt D moderate D strong.

Th e TYPE OF SMELL was D earth y D rotten egg gas (su lfide) D burning D rancid D c hemical smell, e.g., kerosene D other ..... (specify) COM 1E TS/ REMARKS: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

S HIFT

IA NAGER'S COMMENT O

STATUS OF PLANT: _ _ _ _ __

Monitoring of the vent stack showed little change in the period from co mmissioning to March 1991.

So, what was the ca use of the extensive increase in comp la ints?

The differences may be attributed to several factors: • the hi gh temperatures of the summer of 1990/ 91, and the large size of the catchment area of North Head . This would undo ubtedly increase the potential for hi gher generation of sulfides in the incoming sewer. However, this is probably not a major factor give n that monitoring in the NSOOS stack showed no major increases; • the re-ro uting of the sludge thi ckener overflow back to the head of the plant (prior to the outfall coming on-line th is was discharged

straight to the effluent). This has provided the ideal situation for the ge neration of sulfid es within the plant processes, because of the frequently high solids content of this flow stream (Sludge thickener overflow is recirculated, since the p lant does not have the capacity to di spose of or in cinerate all the solids that are produced); • the commi ssioning of the deep water ocean outfall. Although this ca nnot be attributed directly as the cause of the odours, the requirement of a deaeration chamber at the beginning of the ocean outfall tunnel, to prevent air entrainment, has caused dispersion of sulfides and other odorous gases to atmosphere.

It is plausible that the recycling of the thickener overflow, in conjunction with the presence of the turbulent sites, has allowed increased generation of s1,;lfides a nd other odorous sewage gases.

This was the major factor in the increased incidence of comp laints.

Turbulent sites include the deaeration cham ber (since this immediately follows the 50 m drop shaft that the primary effluent trave ls), the channel immediately after the primary effluent measuring flume which drops some 10 m (known as the 'sk i jump'), the above ground inlet works (where the pumped screened sewage is re leased into a channel) and the grit removal and distribution channels, which are aerated.

The ventilation of the plant provides for collection of foul air from each of the above processes and venting to the atmosphere via the Ml (multipl e hearth incinerator building) stack.

MEDIA ATTENTION The ve nting of foul air in a stack adjacent to the incinerator exha ust stack led to much confusion both in the media and the public. Odour ge neration and operation of th e incinerators became sy nonomous. Local residents started to campaign to stop the incinerators operating, with many supporters believing that the new odour problem cou ld also sto p. (The incinerators operate at over 800° C.) Previously the main focus of the Sewage Treatment Plants had been on meeting licence conditions on effluent quality, rather than dea ling with odour nuisance. The public spotlight has now focussed on both iss ues. The Water Board has adopted a policy of integration with the comm unity, a nd that includes a clean air environment.

In March, 1991 the SPCC sent a letter to the Water Board requiring the investigation of odour control meafares at North Head STP with a time frame of only two months.

MONITORING AND MEASUREMENT OF ODOURS AROUND THE PLANT In monitoring of odours, perhaps the best form is measurement of ODU's (Odour Dilution Units).This is, after all, the 'bottom line' involving detection and perception of smells. However, this is not practical to carry out on a regular/ continuous basis. Hydrogen sulfide is regarded as the major odorous component (but certainly not the only component) of sewage gas. This was used as an indicator of odour generation, and formed the basis for plant monitoring of odours.

After numerous measurements by hand at the various sites, around North Head STP (using the Drager Pump), it was found that the most odorous site was the deaeration chamber. Measurements of 600 ppm hydrogen sulfide were obtained. However, this varied greatly with the time of day (i .e it was dependent on the flow to the p lant at the time) . In addition the air flow was of a pulse type presumably caused by level fluctuations in the drop shaft, ca using a pumping effect in the chamber. The air flow was only small but, surprisingly of great force (actually Ii fting the original metal lid of the chamber), particularly dur ing wet weather flow. Flow varied between 20-180 m 3 per minute. Hydrogen sulfide concentrat ions showed peaks about 7 .30-8.30 am, reached virtually zero in the middle of the day, and started picking up in the late afternoo n . This pattern was also borne through to the Ml vent stack. The deaeration chamber is connected to this stack via the air space in the effl uent channel, and was found to be the major contributor of odours releasing through the stack.

In addition to hydroge n sulfid e measurements, mercaptans were also measured occasionally using the Drage r pump. (Deareation chamber showed variations from I to 900 ppm, with H 2S being a major component of this measurement).

In September, continuous monitoring of t he Ml stack was commissioned. A typical pattern is shown in Figure 3. (These figures

WATER June 1992

27

lines . In the absence of dissolved nitroge,p, there was no formation of a float blanket.

14

Results Table 3 summarises average concentrations measured during these trials. (Note that the trials took place during winter when odour generation in general was lower than would have been experienced in summer cond itions).

Oxygen worked better than air in reducing both H2S a nd odours, although it is possible that the rate of oxygen inj ection was more than in the unmetered trials of a ir injection.

M1

12 10 w

0

I

0...

Table 3 -

8

Results from Trials of Air Injection and Oxygen Injection into the RS Pumps.

_J

DO Concen tration , mg/ L

::) (j)

lltm

Abo\(' <:round

Primar)

Sc,\agc

Influ ent

Effluent

Dcacration Chamber

Ml Srack

0 0 0

0.3 4.6 5.8

0.1 0.6 0.9

100 30 24

22 7 2

l) pc or Operation

E 6 0.

0.

orm al (n o injec1ion) Air lnjec1ion Oxygen l njec1ion

4

11 2S in Foul Air. ppm

NSOOS

2 0

12

0

24

TIME Fig. 3 -

Hydrogen Sulphide Emissions from the Air Stacks - Diurnal Plot

SOOS and MI Foul

are low since the plot was recorded during a period of oxygen injection of sewage). Measurements changed over the day from 2-3 ppm up to a maximum of JOO ppm on some days (although typically the peak was less then 50 ppm).

Table 2 shows airflows and average concentration of H 2S in the stacks.

Table 2 -

Results of Monitoring of Foul Air Sou rces at

orth Head STP

(prior to installation of oxygen dosing and sc rubbing).

So un:e

SOOS Siack Ml Stack Deaeration Chamber Blu e Fi sh St ack

Ai r Flon m3/ min

ljâ&#x20AC;˘pical 1-1,s

I 700 500 20- 150

2-5 30- 100 0- 600 0.5-1. 5

Range ppm

Daily Em ission of li ,S kg/ day

10 50 27

It is important to note that the effect of air/ oxygen dosing was imm ediate. Within seconds of commencement of air/ oxygen injection, the DO of the sewage increased in the riser and there was a reduction in su lfides emanating from the above ground influent channel. This was tested on several more occasions by switching the oxygen dosing system on and off, and measuring the hydrogen sulfide in the channel air space. There were instantaneous changes.

There was a definite lag period for increased DO in the primary effl uent. This was of the order of half an hour, and was indicative of the detention time of the sewage in the sett ling tanks.

As soon as DO in the effluent channel was increased, there was a correspondin g decrease (a lag time of a few seconds) in th e hydroge n sulfide concentration in the foul air in the deaeration chamber and Ml stack.

A temporary oxygen dosing system was installed and commissioned in October 1991. This served as an interim facility to allow tenders to be called and installation work carried out for a permanent unit, which came on line in March 1992. Figure 4 shows the oxygen storage facility, RS pumps and injection points respectively. ' The success of the system was shown by a marked reduction in odour complaints between the summer of 1990/ 91 and 1991/92. In fact, there was an obvious trend. During commissioning many odour complaints were received during times of failure of the oxygen dosing system .

In conj unction with the oxygen dosing system an ultrav iolet reaction chamber was constructed for the deaeration cham ber stack.

TRIALS ON ODOUR CONTROL Typically the DO in the raw sewage entering the plant is close to zero. At the top of the pump riser the DO is 3 mg/ L, but by the end of the sedimentation tanks it returns virtually to zero.

The thickener overflow recycle now increases suspended solids in the influent by some 20-35%, at zero DO. Air Injection Several trials on air injection into the raw sewage rise pump lines were carri ed out.

Compressed air was connected to a sparger placed in the suction well of the duty RS pump. The flow of air was not measured. It . was found to increase the DO at the top of the riser to about 5 mg/ L. This was carried through the sedimentation tanks, with about 0.5 mg/ L being measured at the outlets.

There was significant reduction in odour.

However, the injection of compressed air at the base of the 30 m riser resulted in a type of dissolved air flotation system being ge nerated (Thomas et al, 1991) . A blanket of floating so lids was generated on the surface of the sed imentation tank, far in excess of the removal capacity of the existing travelling bridge scraper. In consequence, air injection tria ls could only be operated for 3-4 hours maximum. Even so, they were operated in this mode during some periods of high odour emergency.

Oxygen Injection Trials were therefore initiated using pure oxygen, along the same

28

WATER June 1992

Fig. 4 - Oxygen Dosage Point to RS Pump Discharge

Out let air was recon nected to th e effl uent bypass channel. A ltho ugh a sig nifi ca nt reduction in odour units (50-80% ) was ac hi eved , hydroge n sulfid e redu ction was on a m·uch lesse r sca le (redu ct ion by abo ut 10-20 ppm was typicall y found).

More trial wo rk is required to determine the effecti ve ness a nd maintenance requirem ents of thi s process.

A 12 month ai r q ual ity st ud y is to be carried o ut around ort h H ead STP start ing mid 1992 . It wi ll include co mmunity surveys a nd quantification of odo ur p revalence in the surrounding community.

In December 1991 , chemi ca l sc rubb ers were insta lled o n three of the m a in vent stac ks a s a fina l preve ntative co ntrol meas ure at Nort h H ead STP. .

IMPLICATIONS OF INTRODUCING AIR OR OXYGEN INTO THE RISER PUMP The success o f the ox yge n/ ai r inj ecti o n trial work has major implica tions for upgrading o f the process at Nort h H ead (and ot her pl a nts).

The ' retrofit ' U-tu be Di sso lve d Air Flotation process for Nort h H ead (Thomas et al. 1991) would result in a signifi cant d ec rease in odour ge neration . Th is is interes ting sin ce con ventional DAF processes are ge nera ll y rega rd ed as being res ponsible for hi g her ge neration of odou rs through stripping.

T he m ain differe nce is that unlike co nvent io na l DAF processes, w hi ch aerate a sidesteam of the liquid , the U-t ub e DAF process in trodu ces oxygen, or ai r, into th e TOTAL fl ow, under press ure.

E ith er oxidation of di ss olved su lfides is being ac hi eved , o r a lternative ly th e DO is inhibiting th e furth er prod uct ion a nd re lease of H 2S. The impli cations of thi s a re as fo llows:

• if a p la nt was to be upgraded using the U-' ub e DAF process as th e ini tia l stage, the need fo r chem ica l scr ubbin g o r chemi ca l d osing wou ld be grea tl y red uced ; • so urce contro l as o pposed to end po int dosing is a key factor in odour co ntro l. Co nstru ction of a U-tube for p ress uri sat io n o f raw sewage co ul d a ll ow a ir/ oxygen do si ng at any plant ; • implemen tati o n of a retrofit OAF process wou ld reduce (or negate) th e requi rement fo r specific oxyge n d osing.

CONCLUSION AND SUMMARY Nort h H ead ST P has bee n the s ubj ec t o f numero us odour comp la int s. The m ain ca use of this has bee n th e recycle o f se pti c materi al (thi ckener overflow) back to th e head of th e plant .

O xyge n inj ection, un der press ure, to the p ump di sc harge lines has bee n introd uced to redu ce odo ur ge nera ti o n .

This source co nt ro l has proven ex tremely success ful a nd is rega rded a s the m ajor odour co ntrol met hod at the plant. It has succeed ed in signifi ca nt ly red ucing od o ur co mpl a int s. P ressurisat io n of incoming sewage follo wed by oxygen injec tion co uld be a pp li ca ble to other p la nts a nd in many cases would be the most cost e ffec ti ve (and envi ronmen ta ll y fri end ly) so luti o n to o d o ur control.

REFERENCES T homas, P., La ginestra M. and Pearson , R. J.S. (1991). Di ssol ved air flotation system by simp le retro fit onh Head ST P. Water 18 , o.2, 27- 29.

ACKNOWLEDGMENTS I wo uld like to th ank th e fol lowing people fo r t hei r help in investigation, mon itoring and writing th is report: Phil Thomas , Matt H ardin, Simon Cou rt enay, Vlad Merku loff, Walter Meyer, Joanne Byrn es. I al so ack nowledge orth H ead STP personnel for their co-operat ion in the run ning of trials and during the in stallation work s.

UPDATE ON ODOUR CONTROL IN GEELONG'S WASTEWATER SYSTEM G. J Sew ard~ a nd D . J. Barkley con1in11ed from page 25

As wit h ultrav io let radiation , masking age nt s and deod o ri se rs are not co nsidered appropriate lo ng te rm so lu t io ns to the odour prob lems suffered at prese nt . In pa rticula r, co nce rn is held abo ut mask ing agents whi ch mi ght preve nt perso n nel from detect ing the p rese nce of noxio us gases, whi ch in turn mi gh t crea te haza rd o us co nditions. For th ese reasons, ex trem e cau tio n shou ld be exe rcised w ith use of t hi s type of chemi cal in enc lo sed lo ca tions. Th e ca use o f the o dour prob lem ideall y sho uld be identifi ed a nd eli m inated rat her than the od our simpl y hi dden.

Nevert heless, a m as kin g age nt is being used successfull y a t a sewe r ve nt adjacen t to a hi gh school in Geelong. Dur ing ce rtain wind co nditi o ns, foul a ir wafted in to a second sto rey window of a near by bu ilding. T he prob lem has bee n reso lved by inj ecti ng a gaseo us m ask ing agent direc tly in to the bot tom o f the ve nt using a small bat te ry dr iven compressor. The battery is kept charged by a sm a ll so la r panel suppor ted off the ve nt stack.

CHWRINE DIOXID E AT THE BLACK ROCK TREATMENT PLANT A chl orin e dioxide odou r control system was in stall ed durin g the co nstru cti o n of the Black Rock milli sc ree nin g pl a nt. Th is sys tem was se lec ted after co nside ration of severa l sys tems inclu di ng bio logical sc rubbin g, chemi ca l sc rub bing, ult ravio let ra diation and ac tiva ted ca rb o n a d so rp tio n. Th e chlorin e di ox ide syste m was de signed to trea t foul a ir co llec ted fro m th e coa rse scree nin g enclosure a nd from benea th th e fibreglass cove rs pro vided for the inlet sc rew pumps a nd th e milli sc ree ns. Howeve r, at th e tim e of d es ign , it was ass um ed that sulfid e control meas ures in th e main sewer sys tem wo uld be in place, and that the sewa ge arri ving at Black Rock wou ld co ntai n relative ly low sulfid e levels.

U nfo rtun ate ly, the sewer sul fid e co ntrol m eas ures are not yet in place, a nd the sewage co ntinu es to ca rr y ve r y high s ulfi d e co nce nt rat ions. These sulfid es are readil y re leased into th e fo ul ai r syste m und er the inlet sc rew pumps a nd th e milli sc reens, du e to the tu rbu lence. T he fou l ai r co nsequ ently ca rri es ve ry hi gh leve ls o f sulfid e gas a nd the chl orine di oxide ca nnot co pe with th em. As a res ul t, fo ul a ir is em itted from th e fou l air sys tem as we ll as from ot her loca tions at the plant.

Th e chl o rine dioxide system will be reta ined in it s present form a nd re-eva lu ated when ot her sewe r sulfid e co ntrol meas ures have bee n implemented to redu ce sulfid e va lues in th e fo ul a ir.

THE WAY AHEAD The measures imp lem ented to d a te by th e GDWB have a lready s hown some improvements. Sulfid e levels in the main sewe rs in the north ern part of the sys tem have bee n reduced by the add it ion o f oxyge n an d air. Major sources of co m plai nts, e.g. the Sa ltworks and Qu ee nscl iff ri sing ma in di sc harges, have been d ealt wit h . It is a nti cipated that o th er o d o ur problems will be elimi nated by use of ultraviolet radiat io n o r temporary use of d eod or ising chem ica ls.

Neve rth eless, th ere is sti ll quite a lo ng way to go to co ntrol the ge nerat ion of sulfid es in the sys tem. H owever, the major sources of th e prob lem have bee n identified a nd miti gation meas ures have bee n selected, including addi tion of oxygen at seve ra l point s to oxidi se existing sul fides and improve th e overa ll oxygen ba lance of th e sys tem.

REFERENCES Sewa'rd s, G. J . an d Carpenter, A . . (1988) Development of a long term corrosion and odour control strategy in a sewerage system. Austra lian Wastewater Assoc iation 13th Federa l onvention, Canberra, 6- 8t h March , 1989. Th e Institution of Engineers, Au stra li a Nat ional Co nferen ce Publica tion o 89/ 2.

WATER June 1992

29

TECHNOLOGY

Odour Control by Wet Scrubbers at North Head

by A. McDOUGALL INTRODUCTION Two wet scrubbing systems have been installed by Process and Pollution Contro l Pty Ltd at the North Head Treatment Plant of the (Sydney) Water Board . They have bee n tendered and installed on a BOOT co ntract sys tem , whereby Thiess Contractor's Environmental Division will own and operate them for five years for a fee, then transfer them to the Board .

The~ ~ere both installed on a 'fast track' basis, in order to try to min1m1se odo ur complaints from the public during the 1991-2 beach season at nearby Manly.

In retrospect, both the specifications and delivery targets were derived too hastily.

The contracts were let on October 8, 1991 and specifications amended as late as November 1991 , leaving a very tight time schedu le to be met.

The fir st system, sc rubbing the vent gas from the Northern Suburbs Ocean Outfall Sewer (NSOOS), was completed by January, and has operated satisfactori ly, except when chemical outages and some leak ing valves interrupted operation.

The second system, dealing with the foul air from the grit and sludge processes, (the Ml scrubber) is more complicated, and has been more difficult to optimise, particularly since the contractor did not have a full analysis of the foul air until the project was under way. Alt_hough the major components of odour are being removed, overdosing of hypochlorite has on occasion led to chlorine type odours being vented to atmosphere.

THE NSOOS SEWER VENT SCRUBBER . The design is based on the company's research and experi ence into a ll forms of odour remediation .

It is a two-stage hypochlorite oxidation in random-packed towers ' followed by polishing stage using PICA activated carbon.

The peculiar shape of the installation, as shown in the cover photograph of this Journal, was dictated by space limitations. The NSOOS sewer enters the plant area, and the head-space is isolated by an inverted gate. Fa~s draw off the fou l air, and force it up through the first of the absorpt10n towers (partly masked in the photograph).

The air is then ducted to the base of a second tower and from there to a hori zontal chamber containing the carbon ra~ks thence to a high ve locity outlet. ' The Absorption Towers The towers, 3.5 meters in d ia meter, are packed with Lanpac 3.5 which is a symmetrical expanded polypropylene, packed ran doml y: yet because of the even ly spaced drip points (30 000/ ft 3) it ge nerates very even distribution of both gas and liquid phases. The pressure drop at 2.9 m / sec air flow is 46 mm per metre.

The liquid phase in each tower is recirculated at 3 KL/ min and the sump levels are maintained by bleeds of up to 240 L/ hr'.

Sodium hydroxide at 4% w/ v is dosed to the sumps by two diaphragm pumps (I duty, I sta ndby) for each tower. A pH controller switches on the duty pump when the pH drop s below 9.7 until it reaches 10.0. If this value is not attained within 60 minutes a category ' B alarm is initiated.

Sodium hypo~hlorite at 12% w/ v is si milarly controlled by ox1dat1on/ redu ct10 n potential probes. When the ORP drops below 800 mv the duty dosing pump is switched on until the ORP reaches ~52 n:iv. If this is not attained in 15 minutes, the standby dosing pump 1s acuvated. If the ORP does not then reach the set point in a further 60 minutes, a category B alarm is initiated. . Pump redw:idancy and control strategies are commanded by a PLC wnh a scrolling sc reen di splay, and regu lar status reports and immediate alarms are printed out, in a form which can in future be connected to SCADA system s.

Angus McDougall is a Director of Process & Pollution Control .

Pty Ltd.

30

WATER June 1992

Activated Carbon The top of the second wet tower contains a demisting mesh , then the air is led hori zontall y through a chamber 9 m 2 cross-section, containing removable racks of foam impregnated with activated carbon. The PICA carbon can adsorb up to 500 mg of H S per gram, and acts as a fina l polish ing stage for both H 2S anct2 other odorous chemicals.

Up to four stages of carbon rack s can be used, to ensure effective removal of the odorous components which are not affected by the oxidation stages.

Performance The contract stipulated the follow ing co nditions: Outlet H 2S ... 0.05 ppm. Outlet Odour ... 100 ODU The plant was finally commissioned in January 1992, and the first full tests conducted on February 4. The results are summarised in Table I, and demonstrate that it was performing up to specification .

The performance since that date is summarised in Table 2, and shows that although the plant is generally meeting specification, there are occasions when it partially fai ls. Some of these have been due to chemical outages, and valve leakages .

Table I -

Profile of NSOOS Scrubber performed on 4 February 1992

(Odour S1rc ng1h sa mples taken at 8: 15 am, C hemical sa mples coll ected be1wecn &30 a m a nd 10:30am) After l-lypoch loritc

Odou r Strength Hydrogen Su lfide Su lfu r Dioxide Total Mercaptans Dim eth yl Sulfide Carbon Disulfide

Table 2 -

Date

30 04 14 05 10 12 17 24 01 12

Jan Feb Feb Mar Mar Mar Mar Mar Apr May

ODU mg/ ml mg/ m1 mg/ m1 Âľg / ml Âľg / m l

In let

Scrubb ers

Outler

354 2.21 I.2 I .4 535 }55

9 0.29 < 0.5 < 0.03 no data no data

17 < 0.1 < 0.5 < 0.03 I. I 181

Profile of NSOOS Scrubber, performed from 30 January 1992 to 12 May 1992.

Time

11:1 5 08:15 l0:40 09:45

am am am am

07:56 am 08:30 am 08: 10 am

ODU

u,s

ODU

u,s

In let

Inl et

Ou tlet

Outlet

757 354 32 2491 1027 980 986 414 171 1163

1.0

125 17 18 33 38 146 6 41 43 34

0.047

0.36

1.7 3.4 1.6

0.04 0.07

0.2 0.27

THE Ml SCRUBBER Design The Ml Building at North Head handles the solids collected by screenin g, sedimentation and dewatering. The Ml sc rubber was contracted to dea l with the fou l air from this building. A constriction on the design was that it had to be low profile, so as not to obtrude into the skyline as viewed from the adjacent Nat ional Park. Vertical absorption towers, as used for the NSOOS scrubber, were thereby ruled out, and crossflow packed towers were used, using the Lanpac packing.

The odour profile from a sludge handlin g plant is more co mplex than that derived from a sewer vent, and can contain any or all of the chemicals listed in Table 2. However, because of the decision to 'fast-track' the installation, the fu ll profile from the foul air system, and its variability, were not avai lable at the design stage. On the basis

Continued on pa~e 38

TECHNOLOGY

ODOUR CONTROL STRATEGIES AT BOLIVAR STP

by M. F. KENNEDY, P. M. THOMAS and K. P. YERRELL SUMMARY T he Engineering and Water Supply Department (EWS) of So uth Australia has in recent years und ertaken extensive investigatio n work a nd co mmissioned chemical dosing facilit ies for odour control at t he Bolivar Sewage Treatment Works (STW). This paper descr ibes the ea rl y odour contro l work und ertaken, the results of recent investigations und ertaken at Bolivar STW a nd impressions of th e status of odour co ntro l in New Zeala nd gained from a rece nt trip underta ken by two of the authors. Possible future strategies for odour co ntrol at Bolivar are discussed.

INTRODUCTION Metropolitan Adela ide has four major sewage treatment fac ilities sit uated at Bolivar, Port Adelaide, G lenelg a nd C hristies Beach .

Odour pro blems have bee n experienced part icul a rl y at Bo livar a nd Port Adelaide but sin ce odours have been la rgely eliminated at th e la tter plant , thi s paper wi ll concentra te on the current situa ti on at Bo li va r STW. The Bolivar STW is the largest plant operated by th e EWS and is located a pproxima tely I 8 km north of th e Adelaide Central Bus iness Distri ct. It is designed to serve 600 000 peop le, plus a 700 000 person eq ui va lent of industrial was tewater. Sewage a rrives at the pla nt through two gravit y trunk sewers; one from GawlerE li zabeth-Sali sbur y (Salisbury Trunk Sewer), a nother from the so uth ern area (Adelaide Trunk Sewer) which includes a large part of Adelaide.

At present Bolivar STW treats a n average of 135 ML of wastewater d ail y with a pollutiona l load of 50 tonnes BOD a nd 60 tonnes SS. Th e treatment process is phys ical a nd bio logical, consisting of screening, grit remova l, primary sedim entation, secondary treatment throu gh hi gh rate rock trick ling filters and humus sedimentation ta nks, a nd further treatment in sta bili sation lagoons. The final efflu ent is discharged via a 13 km open channel into the St. Vincent Gu lf.

Thirty yea rs ago when the Boli var site was chosen for a wastewater treatment facility it was isolated from existing residential areas. Since th en development has encroached to with in I km of th e works res ulting in increased odour complaints. However, comp laints rega rdin g odour emi ssions date as fa r back as the 1970s.

The odours have increased in severity with th e ageing of the pla nt, in creases in wastewater flow, longer detention times within sections of th e ex panding sewerage system , and an apparent increase in strengt h of trade waste discharges to th e sewerage system.

In 1989, an oxygen inj ection p lant was commi ssioned on th e Adelaide Trunk Sewer a nd in 1991 a temporary chlorine dosing fac ili ty was commissioned to augment th e oxygen inj ection plant.

ODOUR CONTROL INVESTIGATIONS Background In 1977 the EWS retained th e consulting eng ineering firm , Caldwell Connell Engineers (CCE) Pty Ltd, to investigate the odour prob lem at Bolivar a nd Port Adela ide STWs. This was the first specific inves ti gation into means of a lleviating odours at the Bolivar STW. The consultant's reco mmendat ions for th e Bo livar STW included covering the odorous areas, collecti ng the foul air a nd transporting it to biological odour removal towers for treatment . The a reas identified for covering included th e scree ned sewage channe l, preaera tion ta nks, settled sewage cha nnel , and the recirculation and bypass control st ru cture. Additional works proposed consisted of a building to house th e sewage screens a nd screen ings ha ndlin g area a nd level contro l equipment in th e settled sewage channe l to reduce tur bu lence and odour re lease. Coverin g of th e bio logical fi lters and

32

WATER June 1992

Martin Kennedy is a Senior Wastewater Treatm ent Engineer with th e Engineering and Water Department (EWS) in So uth A ustralia. He has 9 years experience in the water indust,y and is currently responsible for investigation and design work associated with wastewater treatmenl projecls.

Phil Thomas is a Senior chemist at the State

Water Laboratory (EWS). H e has over 16 years experience in th e areas of analy tical chem istry, water treatment particularly chloramination processes and is currently involved in the wastewater treatment field.

Kevin Yerrell is currently th e Treatment Enginee1; Bolivar (EWS). H e has JO years experience in wastewater collection and treatm ent and •is respon sible for th e operation, maintenance and upgrading of the Bolivar STW

treatment oft he co llected foul air was no t recommended due to the hi gh ca pita l cost.

Similar recommendations were made for the Port Adelaide works a nd th ese were subsequently imp lemented. Due to the hi gh costs of impl ementin g these m eas ures at Boliva r a nd prob le ms e nco untered with the system at Port Adelaide, these meas ures were not adopted for the Bolivar STW. T he Fou l Air coll ection a nd treatment system at Port Adelaide was later a ugmented by chem ical dosing facilities on th e larger rising mains to the works.

Recent Developments By the mid to late 1980s, the encroachment of residential deve lopment led to the department insta lli ng a trial side-stream ox ygen inj ection system on th e Ade laide Trunk Sewer. The oxygen injection system was commissioned in September 1989 in conjun ction with Commonwea lth Indust rial Gases (C IG).

The consulting engineerin g firm of Sincla ir Knight & Pa rtn ers (SKP) was engaged in June 1989 to provide a n overview of the oxygen inj ection system design for th e Adelaide Trunk Sewer a nd th e project's likely effectiveness. SKP. concluded that injection of oxygen into the Adelaide Trunk Sewer wo uld signifi cantly redu ce ma lodours.

However, it was stressed that thi s system was a tri a l a nd represented only one ste p of a wider strategy.

In la te January 1991 a temporary chlorine dosing facility was commissioned at Bo livar STW to a ugment the oxygen dosing a nd to assess whether an additional permanent chemica l dosing fac ility co uld be effect ive in furthe r reducing odours.

In addition to chemical dosing a number of pla nt modifications a nd other act ions are being undertaken to alleviate odours. Among them are: • replacement of aged and ruptured pre-aeration pipework to redu ce turbulen ce • continuous remova l of humus sludge from th e humu s (secondary clarifi er) tanks

• replacement of trickling filter rotary distributors • the major trade waste dischargers have been investigated and a sign ificant contributor directed to ·red uce su lfide levels in it's effluent • sewers in the area surrounding Bolivar STW are being systematically clea ned.

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in th e seco ndar y areas. It was a lso noted that there was a lack of co rrela tion between wastewater sulfide leve ls and odo u r numbers.

Air Quality Testing and Community Involvement The air quality test ing program was condu cted by the Air Qua lity Branch (Department of E nvironme nt and Planning) an d co nsisted of two types of measurement. 0 1factometry assays were undertake n using a dynamic olfactometer in a ddition to an "expert panel" to determine strength and cha racte r of odours within th e plant.

In a ddition to the chemi cal a nd air quality monitorin g an interest ing feature of the assess ment process has been t he pub lic part icipation program whi ch was initiated to help better define the p ub lic's perceptio n of odours em a nat ing from the works. A number of advertise ments and news re leases were m a d e enco uraging local res idents to notify Bolivar when an odour is detected a nd a n in formation pamp hl et was di stributed in th e surrounding di stri cts.

Complaints via telephone have been recorded since early February 1991 wit h approximate ly 370 received to the end of December 199 1.

The peak number of co mplaints received in one day is 30, a lthough this immed iatel y followed the advert isem ents request ing people to phone th e works with the ir complamts. As a new initiati ve, 50 members of the public have a lso been recru ited as community observers. They have been tested and trained in odo ur detectio n a nd com men ced recordin g observations in May I 99 1. T hese observers a re located throu gho ut the a reas most likely to be affected to provide reg ular, re lia ble data about the type a nd frequency of odours they experience. These o bservers have been kept informed o f progress at Bolivar throu gh a seri es of newsletters.

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A monitorin g program was in sti ga ted in 1990/ 9 1 to eva lu ate the e ffe ct ive ness of chemi cal do sing. T he main fea tures of th e program we re: • Measurement of var io us li q ui d strea ms for chem ical a nd physical c hara c ter ist ics s uc h as pH, s ulfid es (tota l and so lubl e), temperat ure, redox potentia l • Assessment of the impact of ch lorin at ion on microbiology, particularly for the trickling filters • Olfactometer readings to quantify relative odour strength • Odou r panel to est imate odour st rengt h and chara cter • Dete rminat ion of adsorbable organic ha lide (AOX) and tri ha lomet ha n (T H M) formation • Use of lead acetate papers, to determine the re lative strength of atmosp heric hyd roge n sulfide (H ,S) at var ious locat io ns within the Boli var STW • Meas u rement o f oxygen upt ake rates to assess perfo rmance of oxygen inject ion.

Hi stori ca l sulfid e data from the Ade laide Trunk Sewer from 1977 10 the present is shown in Figure I. These resu lts represent the ave rage readings from 24- hour sur veys.

Resu lts of samp ling durin g February/ March 199 1 indi cated that so lubl e sulfide leve ls were reduced from 4. 1 mg / L to 1. 8 mg/ L by oxygen inj ect ion with a further drop to 0.5 mg/ L after chlorination (Figure 2) . A 24-hour survey of incoming sewage und erta ken in May 1991 showed sig ni fica nt variabi lit y in BOD a nd COD as we ll as s ulfid e leve ls. Thi s sur vey demon strated 11 01 on ly t he impact of unregu lated industrial d isc harges but a lso th e diffi culty th at chemi cal do sing has in co ntro ll ing slug load ings . An earlier exa mp le of a la rge d isc harge of waste from a ta nn ery is shown in Figu re 3.

Monitoring of wastewater sulfide levels and use of o lfactometry co n firmed that th e chemica l dosing has sig nifi ca ntly reduced odou rs in the primary treatment areas at Bolivar but has had no impact

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T he early res ults of the monitorin g program reinforced subjective assessment that the major remain ing odo ur generator was the trick ling filter area. Consequent ly odour co ntrol invest igation work has sin ce been focussed on the trickling filters.

In September 1991, Camp Scott Furphy Pty Ltd (CSF) was engaged to provide budget estimates and co nceptual layouts for cove rin g, coll ecting and treatment of odoro us air from th e primary a nd seco nd ary treatment areas at the Bolivar works.

CSF es timated the cos ts for cove rin g process uni ts and ducting a nd treat ing fo ul ai r in a two stage caustic sc rubber fo llowed by act ivated carbon . The indicative ca pita l cost for secondary treatment involving dome covers over the 12 50 111 diameter tr ickling fi lters was $26 .8 million. T hi s wou ld be reduced to $14.2 million if cocurrent forced air venti la tion could be adopted eliminating the need to cove r the filters. For each of these options, the running cos ts were estimated at $1.5 million per a nnum .

The budget a lso estimated the cos ts for co llection and treatment of foul ai r in th e primary area. Cap ital costs were estimated at $4.5 mi lli on with runnin g costs of $260 000 per a nnum .

Effect of oxygen and chlorine on soluble sulfide levels (Adelaide Trunk Sewer, 1991)

Both Aucklan d and C hristchurch in New Zealand have sewage treat m ent works of comparab le size to Bolivar, incorporatin g hi gh rate trick ling filters, thou gh both utilise plast ic m edia a nd therefo re have fewer filt ers tha n Bolivar (four a nd two respectively). At both locations extensive odour contro l investigation work has resu lted in the fi lters being covered wit h the foul a ir being extracted and

WATER June 1992

33

treated in soil filt ers. An in spec ti o n tri p to New Zeala nd was und erta ken in Febr u a ry 1992 to o bse rve fi rst ha nd t he ope ra ti o n o f cove red tr ick ling fil te r an d soi l fi lter o d ou r co ntro l sys te m s a nd to d iscuss th e odo u r co ntro l in vestiga ti o n wo r k und erta ke n prior to re so rtin g to covering t he fil ters. T he syste ms inspec ted we re fo un d to be hi g hl y success ful in ac hi eving o d ou r co n tro l. They we re a lso ve ry attrac ti ve fro m a n opera tio na l poin t of view beca use of the low mai nte na nce req uirement and abse nce oft he need to ha ndl e ca usti c an d ac id ic chem ica ls .

Christchurch Th e C hr istchurch Treatme n t Wor ks is a n 800 000 EP capac it y seco nd a ry trea tm ent pla nt .whi ch inco rpora tes sc reening, gri t rem oval a nd pre-aerati o n , p rim ary sedim ent at io n, b io logical fi ltra ti o n in p last ic medi a fi xed grow th reacto rs (FGRs), seco nda ry sedim ent atio n and ox idat ion po nd s.

Th e C hri stchurch Treatm ent Wo rk s was th e first wastewa ter t rea tm en t fac ilit y in New Zea la nd to instal l a so il filter fo r o d o ur co nt ro l with th e cove rin g o f their FG Rs a nd co nst ru ct io n of t he so il fil ter being compl eted in 1986.

Th e C hri stc hurch personn el u nde rtook exte n sive in vest iga ti o n wo rk in to t he id entifi ca ti on an d ch a ra cterisa ti o n o f odo urs fro m t he wo r ks . As a co nsequ ence o f thi s work th e ma in od o u r so urce at C hristc h urch was id enti fi ed as th e FG Rs but mo re im por ta nt ly th e ca use was ide ntifi ed as being du e to a str ipping ac ti on in th e FG Rs of vo latil e co mp o und s a lread y prese nt in th e raw sewage.

O nce th e str ipp ing m ec ha n ism was identified a s t he o d o ur ca use at C hri stchurc h t he in vest igat io n wor k cont inued in to t he des ign req uirements fo r cove ring t he FG Rs. T his wo rk in cl uded pilo t pla nt wo rk o n reacto rs to d eter min e minimum a ir fl ow requirem ents fo r cove red reacto rs a nd o n alte rn a ti ve fo ul ai r sc rubbing tec hniqu es .

Based o n th e invest iga ti on wo r k und erta ken a nd in form a ti o n from a n ove rseas in spect io n to ur t he fir st FG R was cove red wit h a fib reg la ss d om e, at a cos t of NZ$7 00 000 , a nd t he 75% bar k 25% so il fil te r was co nstru cted, a t a cost o f NZ$35 0 000 in 1986. The secon d FG R was su bseq uen tly covered by th e sa me co ntracto r a t a cos t o f NZ$ I milli o n (1986 cos ts).

The const ru cti o n o f th e FGR cove rs a nd so il fil te r effect ive ly so lved th e odo ur p robl ems at t he C hristc hurch Wo rk s.

Auckl and Th e Ma nuka u Sewage Pu rifi ca ti o n Wo rk s (M S PW) in Auc kl a nd is a I 500 000 EP ca pac ity seco nda ry treat ment pla nt inco rp o ra ting sc ree nin g, gri t re mova l a nd pre-aerat ion, p rim ary sedim entat io n , bio logica l filt rat io n in plas ti c medi a FG Rs, seco nd a ry sedi me nt at io n a nd ox id a ti on po nd s. Ex tensive odo ur co nt ro l fac ili ties a re in place at t he MSPW du e to its p rox im ity to reside nti a l deve lopmen t . Th ese o d o ur co nt ro l fac iliti es we re co nst ru cted in two stages.

T he first stage of th e odo ur co nt ro l fac ili ties was co nstru cted by co nve rtin g one o f t he o ri g ina l rock med ia fil ters to a fo ul a ir sc ru bbin g filt er at t he tim e of t he co nstru cti o n of th e pl as ti c m edi a FG Rs. Fo ul air is du cted fro m t he inl et sewe rs, covered gr it rem ova l a nd preaeratio n ta nk s a nd cove red p rim a ry e fflu ent cha nn el to th e odo ur co n tro l filt er whi ch is fed with prima ry e fflu ent at a rate whi ch ma int a in s max imum nit rifi ca ti o n.

Fo r th e second stage o f the od o ur co nt ro l fac ili ties the FGRs we re covered with fibreglass domes a nd fo rce-ven til ated with the ex tracted fo ul a ir bein g trea ted in soil / scoria bi o log ica l bed s.

O d o ur co nt ro l inves ti gat io n wo r k a t t he MS PW res ulted in a numb er of ope rat io na l changes being im p lemente d to contro l th e

Fi g. 4 - A uckl a nd: C o"cred FG R's showin g fi b reg lass ductin g to soil filt er

34

WATER June 1992

growt h o f bio mass in th e FG Rs. T hi s wo ri. was successful in red ucing o d o urs bu t no t to a n accepta ble leve l fo r th e local co m mun it y.

The seco nd stage o f t he o d o u r co ntrol fac iliti es were co nstructed in 1990/ 91 at a n es tim a ted cos t of NZ$8 milli o n. The fac ili ty desig n was based o n so me o f t he work a lread y und erta ken in C hristchurch.

Dunedin T he Ta hun a Was tewater Treat m ent Pl a nt in Dunedin was a lso visited as it ha d rece ntl y co mmi ss io ned th e la rgest soil/ba r k fil te r in ew Zealan d . The Ta hun a Pla nt is a 100 000 E P ca pac ity prim a ry t rea tm e nt pl a n t in co rp ora tin g co mmut a ti o n a nd p rim a r y sedim entat io n.

The entire Ta hun a Pla nt , prim a ry trea tment a nd sludge ha ndlin g, is enclosed in buildings for o d o ur control du e to th e proximit y o f residentia l deve lo pment . The buildings are force-ve ntilated with th e ex tra cted foul a ir being treated in soil / ba rk bi o logical bed s .

FUTURE STRATEGIES C urren t invest igat io ns into o d o ur co ntrol a t th e Boli var ST W are linked with th e Bo li va r E fflu ent Ma nagement Stud y currentl y bein g und ert a ken by Ca mp Scott Furph y, as th e o utco me o f thi s stud y will d ete rmine th e fu tu re rol e o f th e tri cklin g filters. Give n t ha t th e t ri cklin g filte rs a re t he maj o r rem a ining co ntributo r to o d o urs e m a na tin g fro m Bo li va r, th e sh o rt term strat egy is to fo cus in vest igat io ns o n th e filt ers ra th er th a n p erm a nent facilities fo r th e head o f th e wo rk s.

Invest iga ti ons und erway in th e tri cklin g filt er area in clude: • F ield wo rk a nd la bora tory a n a lys is to d etermin e th e ex tent o f stri p pi ng o f foul gases in th e tric klin g filt ers a nd furth er ch a rac teri sati o n a nd fin gerprintin g o f o dours using G C / MS a na lysis, with the ass ista nce o f personnel fro m Flinders U ni versit y; • Field tri a l to evalu a te th e e ffec t o f co ntrollin g the we ight o f bi o m ass within th e filt ers by va rying the tri c klin g filt er irri ga ti o n int ensity (i.e. co nt ro lling t he speed o f rota ti o n o f the di stributo r a rm s); • Field trial to determin e th e feasibili ty o f drawing a ir down th ro ugh th e filt ers a nd furth er eva lua ti o n of th e off gases (using GC a nd GC / MS). If the fo rced ve ntil a tio n tri a l is successful pilo t p la nt trials of a va ri et y of fo ul ga s treat men t m eth o d s will be ca rri ed o ut. Fo ur trea tm ent method s proposed a re bi o logica l treat m ent in a so il bed , chem ical sc rubbin g in a pac ked o r misted tower, ac ti vated ca rbo n a d so rpti o n , a nd chl o rin e di oxide oxidat io n in a co nt ac t ch a m be r. ' The ex isting perm a nent oxygen inj ecti o n a nd te mp ora r y chl o rine d os in g fac iliti es have sub sta nti a ll y redu ced o d o urs fro m th e sc ree nin g, grit rem oval and pre-aerati o n a reas, a nd will be reta ined in th e short term in their present form . Investigations and preliminary d esign will be underta ken to re fin e th e existing systems and determine th e cos ts o f addi tio na l perma nent chemi cal d osing fac ili ties in t he Ade la id e a nd Sa li sbur y Trunk Sewers co m pa red to th e cost o f cove rin g a nd trea tin g of odo ro us gases fro m th e p rim a ry a rea.

ACKNOW LED GME NTS The a uth o rs wis h to th a nk the E nginee rin g an d Wa ter Supply Department for giving permi ss io n to pub li sh this paper a nd acknowledge th e co nsiderable in put from other members of the Boli va r O dour Co nt rol Steering Com mittee.

REFERENCES Caldwell Connel l Engi neers (1977) Odour Control Studies - Boli vara11d Port Adelaide Sewage Trea1111e111 Work s.

Ca mp Sco11 Furphy (1991) Collection and Ti-eat111e111 of Odorous Airfrom Process Umts al Ihe Bolivar Sewage Treatm ent f4'orks, November 1991.

Depart ment of Envi ro nment and Pl anning (1989) Bolivar Odour Study Interim Report - Phase /, Aug ust-September 1989.

Departm ent of Environ ment and Plan ni ng ( 199 1) Odour Testing P,vgram Boliva r S e wage Treatment Works - Report 2, May /991.

Engi neeri ng and Wat er Supply Department , SA (1991) Bolivar Sewage Treat111ent Works Odour Control - Status Report.

Si ncla ir Kni ght and Part ners (1989) Boli var Odour Co ntrol.

Yerrell KP and Thomas PM (1992) Odour Control Facilit ies at Se,vage Tiea1111e11t Works in Ne ,v Zealand - lnspectio11 To111; Febn1a1y 1992.

TECHNICAL NOTES

Olfactory Studies Related to Odour Emissions

by D.G. Laing and D. Barnett Background Odour Levels in Suburban Sydney In thi s study, th e goal was to es ta blish wheth er residents li ving close to th e Glenfi eld Sewage Pla nt in outer Sydn ey we re ex posed to hig her levels o f bac kground o d o urs tha n residents in Wahroo nga a t a locati o n di sta nt fro m a ny sewage plant , industri es a nd d ense tra ffi c movemen t. It was fea red th at residents li vi ng close to the sewage treatme nt pla nt at Glenfi eld m ay be ex posed to o d o urs tha t th ey co uld not d etect beca use o f o lfac to ry ad a ptat io n , a nd th a t such ex pos ure co uld be d etrimen tal to th eir health. Acco rdin gly, ai r sa mples were collec ted fro m both sites over several m o nth s. A t G lenfi eld , samples were collected when wind directi o n indicated tra nsport o f odo ur fro m the Glenfield plan t to residents' ho mes could occ u r. A t Wahro o nga, samples were collected irrespecti ve of wind direc ti o n . Sampl es we re co llected in 100 L Tedla r bags a nd tra nspo rted to th e CS IRO O dour Tes t Facili ty a t North Ryd e where their o dour stre ngt h a nd cha racteristi cs we re assessed by a hum a n pa nel. To achi eve this assess m ent a com puteri sed eight cha nn el air dilution ol factom eter built by Pro fess or Laing and Mr An drew Eddy (CS IRO) was used . The software d eveloped incorpo rated a forced cho ice tria ngle test to establish o dour thres ho lds. Sta tistical a na lyses o f the d a ta showed tha t there was no signifi ca nt difference between th e levels of odour to whi ch residents a t Glenfi eld a nd Wa hroon ga we re exposed , th e levels being 4.4 a nd 4 .8 o d o ur dilution units res pectively. Those levels were signi fica ntl y hi gher th an th e control sample (Medi cal a ir, 2.8 odour dilution units).

The very low level o f odours at each location provoked no specia l d escription by th e assessors. Importa ntly, th e o dours at Glenfi eld were not o bviously different fro m those a t Wa hroon ga a nd did no t resemble sewage odo urs. It would a ppea r th at apa rt from the occasio na l exposure to sewage odours th a t ge nerall y las ts betwee n a few minutes a nd a few hours, th a t residents at G lenfi eld can slee p soundly ass ured th a t they a re no t being unn ecessa ril y exposed to sewage odou rs the m ajority of times the wind blows in their di recti o n from th e treatm en t pla nt .

Predicting The Strength and Characteristics of Sewage Odours from th eir Composition Predicting the strength and characteristics o f mixtures of the m ajo r co mpon ents o f sewage, nam ely hydrogen sulfid e, isova leric acid , butyl m ercapta n a nd skatole is not a simple exercise, but is necessary if we a re going to predi ct how far from a sewage plant odours can travel a nd what they will smell like a long th e pa th the o dour plume travels. To achi eve this Laing a nd Edd y constructed a uniqu e computerised 16 cha nnel a ir dilution olfactom eter whi ch a llowed th em to mi x th e fo ur o d o urs in a ny ratio, co mposition o r strength .

Again using a hum a n panel in a year- lo ng st ud y, th ey found , unfortunately, that mixtures o f these odours are far more unpleasant th a n a ny of the indi vidual o dours a nd th at the odour strength o f th e mi xtures is significan tly greater th a n tha t o f a ny of th e constitu ents of a mixture. H oweve r, not a ll th e news is ba d .

A ll the unpleasant odours in a mixture are not al ways detected .

Stron g m ask ing of o ne odour by a nother was not un common , wi th hydrogen sulfid e being th e leas t suppressed constitu ent a nd ska to le a nd isovaleri c acid the most suppressed . Overall, this study has given a n insight to how th e major co nstituents of sewage odours can affect th e perception o f eac h o th er in mi xtures. Va ri ati o ns in th e co mposition o f sewage emissio ns need to be considered when m o d elling odour plumes from treatm ent pla nts, in pa rticul a r, the increased annoyance likely to ari se from th e greater unpl easa ntn ess o f mi xtures, compa red to emissions d o min a ted by one m ajor component such a s hydrogen sulfide.

C urrently pla ns are in place fo r a new a pproach to m o d elling o dour plumes. From both underwater stud ies with lobsters a nd aeria l studies with insects by researchers overseas, La ing has proposed th at a m ajor problem with cur rent odour plume models is th a t they are not in keeping wi th the latest understa ndin g of th e mi crostructure o f o dour plumes. C u rrent kn owled ge no t acco mmod a ted by Ausplume, for example, is that odorants in a plume travel in "packets" of ever diminishing size, a nd that these " pac kets" o f o d ora nts trave l co nsiderably furth er th a n predictions based . o n di ffu sion a nd

36

WATER June 1992

di spersio n m odels. Accordin g to bio lo gists these "packets" appea r to be enco un tered in 100-200 msec bo uts, occ urin g freq uentl y close to a so urce. H owever, a lth o ugh their frequ ency dec reases with di sta nce, the co ncentrat io n of o d o ur in a " packet" d oes no t a ppea r to d ecrease as rap id ly as p redi cted by class ica l diffu sio n a nd di spersio n theo ry. Since a " pac ket" o f od our is perceived by th e nose as a co ncent rated pulse, o ur thresho ld for a n od o ur ca n be dec rea sed by o ne o r two o rd ers o f m ag ni tud e. T he end res ult is th at we may sm e ll o d o urs to be mu ch stro nge r a nd at grea ter d istances fro m th e emi ssio n source t ha n predi cted by current plume m o d e ls. A colla bo rative st ud y with ANSTO, Uni ofNSW, BH P, an d th e Sydney Wa ter Boa rd a imed at tes tin g this proposal, is cur rently under review by th e C RC fo r Waste Ma nage ment (Uni versit y of NSW ) a nd it is ho ped will be und erway sho rtl y.

Elec tronic Biosensors for Odours O ne o f the too ls req uired by was te ma nagers is a se nso r sys tem fo r m o nitoring odour emissio n to identify which processes in a pla nt are fun cti o ning properl y. Ove r three yea rs La ing a nd Ba rn ett , in colla borati o n with co lleag ues in severa l CS IRO Di visio ns a nd th e U ni versiti es of Sydn ey a nd Wo llo ngo ng, have bee n work ing o n the deve lo pment o f a new genera ti o n of se nso rs th a t will be sensitive a nd specific enough for di fferen t processes. T hese wo uld a lso provide a n ea rl y warnin g system to trigger va ri o us co unteract ions to prevent o d o urs reac hin g levels th a t wo uld resul t in co mpl ain t fro m nea rby co mmunities.

Two of the p rojects invo lve th e d evelo p m en t of highl y se nsiti ve senso rs fo r hydrogen sulfid e p rima ril y fo r use in sewage trea tme nt pla nts and for p-cresol fo r m o ni to ring odo ur fro m pig feedlots. The la tter sensor has invo lved the p reparation a nd isola ti o n of a n a ntibo d y to p-creso l. Meth o d s for attachin g the an tibo d y to a piezoelect ri c- based elec troni c device a re in p rog ress.

Production o f th ese se nsors wo uld all ow moni to rs to be placed in strategic locatio ns on the bo und aries of sewage pla nts and feedlots in conjunction with a meteo rological source to p rovi d e th e so rt of earl y wa rning system s was te m a nage rs drea m a bo ut.

Footnote

Dr David Laing, whilst in CSIRO, was involved for many years with human responses to odours, and was a member of the Panel which originated the Odour Survey for the Werribee Treatment Complex (page 16). H e is currently Professor of Food Technology, University of Western Sydney.

Dr Don Barnett is a Principal,Research Scientist in the CSJRO Division of Food Processing, and is involved in research into the identification of tastes and odours in both food products and wastes.

EDITORIAL MATTERS: T he Journ a l Co mmittee welcome the submi ssion of papers relating to wa ter resources, hydrol ogy, trea tment , supply, wastewater treatm ent and disposal, a nd related scientific a nd man agem ent matters. A length o f 3000- 5000 words is preferred. M ateria l should be submitted to the Editor a s hard co py, typed or printed d o uble space, with wid e ma rgins (fo r the convenience of th e referees a nd the editor) . Two copies a re preferred .

Once a pa per has been accepted , perha ps after so me a mendments required by the re ferees, a uth o rs should , if possible, a lso submit a copy o f th e a m ended m a teria l on a di sk (IBM o r Macin to sh , p re ferably in ASCII 'text onl y', o r in a sta nd a rd word-processing fo r m a t) . A ltern ati vely, pages from electri c typew riter or lase r prin ters (n ot dot m at ri x p rinters) can be computer-sca nned by the ty pesetter.

The Reference style preferred is th e CSIRO style - see p revious issues for examples.

Diag rams must be sui table fo r pho to-redu ctio n to a wid th o f 57mm or 90mm without loss o f clarity. (This can be checked by using a photo-copier with a reduction fac ilit y).

Ph o to grap hs can be either B & W or colo ur p rints, provided th a t the cont rast is a d equ ate.

Eac h a uthor is required to supply brief bioda ta relevant to the pa rti cular pa per, a nd a persona l photograph (B & W o r colour) .

The Co mmittee a lso we lcom es brief progress reports o r papers of a bout 1000- 1500 word s which ca n be published less form a ll y as Techni cal N otes, rather th a n as full pa pers.

TECHNICAL NOTE

ODOUR CONTROL BY WET SCRUBBERS AT NORTH HEAD, A.McDougall Continued from page 30

ODOUR CONTROL SOME QUEENSLAND NOTES

by L. CHAPPLE Below are two examples of novel odour control infrastructure, which are relatively inexpensive and effective.

INDUCTED Affi HEATING IN SEWAGE WET WELIS This a patented system developed by Suncoast Wastewater Management to overcome odour complaints and corrosion problems .

The process involves the continuous heating of the inducted air by means of a flame from an LP gas source or by an electrical element. The warm air enters the wet well and is exhausted by means of a high level vent. As the exhausted air is warmer than the surrounding atmosphere it rises to a high altitude, in normally prevailing weather conditions. By the time the flume of odorous vented air reaches ground level it has usually travelled a long distance and the odorous gases have been diluted to levels below the odour threshold.

The continuous induction of warm air into the wet well causes the atmosphere to become dry. This dry atmosphere ensures that any hydrogen sulfide gas generated in the wet well is not converted to corrosive sulfuric acid through the reaction with water, and there is no acidic condensation in the pump station .

Care has to be taken to ensure that the system is safe, as there is always a possibility that petrol or other flammable compounds may be illegally dumped into the sewer system. An LP gas installation should have three safety features, namely: • a solenoid valve which shuts off when there is a power fai lure, or the fan is switched off • a pressure differential switch which shuts off the solenoid valve if there is no downward air flow through the inlet vent • a flame failure valve that shuts if the flame is extinguished.

The electrical heating method is appropriate for wet well installations with no superstructure. However, operating costs are reported to be 20% greater than the LP gas system.

COMPOSTING FILTER As part of the UASB (Up flow Anaerobic Sludge Blanket) digestion system supplied by Aquatec Maxcon Pty Ltd for the Golden Circle Factory, an odour control system was required. Odours were primarily generated in the pre-acidification section where complex organics are broken down to short chain molecules liberating sulfur dioxide. The conventional solution would be a caustic scrubbing system, which involves considerable mechanical componentry, control systems, maintenance and chemical consumption.

The composting filter overcomes these problems although it requires more space and specialised design.

The system involves construction of an under-bed plenum constructed of a timber grillage. The grillage supports gravel which in turn supports compost. The system then requires a fan to pressurise it, induced draft being impractical.

Design parameters include surface loading rate, bed depth and available pressure.

As the composting process involves the conversion of SO to H 2SO 4 the compost life is limited. This can be extended by blending lime with the compost.

Operational problems centred around finding a suitable compost.

In Europe, where such filters are more common, blends of domestic compost and municipal sludge are available, which are biologically active and friable.

Australian commercial composts are generally too heavy so a tailor made blend was eventually developed which provided a bed life of one year. In dry weather, the bed is prone to drying out, requiring a sprinkler system to wet it. The system is very successful in reducing odours while requiring minimum upkeep, maintenance and having a very low operating cost.

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WATER June 1992

of what was known, it was decided to install a sulfuric acid chamber, followed by two stages of alkaline hypochlorite, a demister, and a final active carbon stage.

Performance The plant was completed in January to a very tight time schedule.

It immediately demonstrated that it could reduce 8iS to very low levels.

However, the foul air feed is very variable, with H2S ranging from practically zero up to 200 ppm, and the other components being dependent on the variables of the processing operations. It has proved difficult to adjust chemical dosing to relate to demand.

The tests to date show that as well a$ H S, the normal sewagetype odours (indoles, skatole, mercaptans) are being effectively removed, but the dynamic olfactometer tests show that the odours are not being removed effectively. However, this test does not differentiate between types of odour. On some occasions at least, high ODOs in the outlet were chlorinous odours rather than the usual malodours of sludge. Optimisation is proceeding, and the unit is currently being assessed for acceptance.

Odour-producing compounds produced from sludge

ammonia, methylamine, dimethylamine, trimethylamine, ethlyamines, amylamines, butylamines. hydrogen sulfide, methyl mercaptan, butyl mercaptan, dimethyl sulfide, dimethyl disulfide, diphenyl sulfide, thiophene, indoles, skatole.

Urban Water Research Association of Australia Publications Available from Jim Greer, c/- Melbourne Water, Box 4342 Melbourne 3001. Fax: (03) 615 4408 Price List UWRAA Research Reports - $30 each (include postage and packaging) , Except: No 13 - $15, and No 19 - $50

Hydrogen Sulphide Control Manual (MUWAA Technological Standing Committee on Hydrogen Sulphide Corrosion in Sewerage Works, 1989) - $125 (plus $10 postage in Australia) Current Urban Water Research in Australia: July 1991 Survey - $55 (includes postage and packaging) Cleaning and disinfection practices for water mains (MUWAA Specialist Workshop No 21 November 1987 Melbourne) - $20 (includes postage and packaging) Organisations who do not at present receive the Urban Water Research Newsletters may apply to the above address to be included in the circulation list.

HAZARDOUS & SOLID WASTE CONFERENCE PROCEEDINGS All copies of the proceedings from the 1st National Hazardous & Solid Waste Convention held at Darling Harbour Sydney in March 1992 have been sold.

Due to additional requests for these proceedings we are considering a reprint. However to be able to do this we must have at least 85 firm orders by early July. If your organisation would like a copy of the proceedings will you ring Kelly or Stephanie at our Federal Office on (02) 413 1288. The cost for the two volumes is $100 including postage.

Reprints of individual papers presented at this convention will always be available at the cost of $10 (members) and $12 (non-members) from the AWWA Bookshop (tel 02 413 1288, fax 02 413 1047).

TECHNICAL NOfE

Effective Sulfide Deodorization

by K.L. CLARK INTRODUCTION Historically, the treatment of sewage by traditional waste water treatment methods has been assoc iated with the release of greater or lesser quantities of gaseous hydrogen sulfide, which is formed by the action of su lfate-reducing bacteria during the anaerobic decomposition of organic and mineral matter containing sulfur (typical components of domestic and certa in industrial effl uents from tanneries, paper mill , petrochemical plants etc). Hydrogen sulfide and its organic derivatives, the mercaptans, produce very unpleasant odours and are detectable by olfactory methods at very low levels of less than lppm. Thus, while because of the occurrence of olfactory fatigue at higher concentrations, hydrogen sulfide is treated as a material with poor warning properties, the unpleasant odour at low concentrations causes many complaints in areas adjacent to where waste treatment is carried out.

In attempts to surmount the problems of malodours resulting from waste water treatment, several methods have been proposed and appl ied over the years. These deodori zation methods may be classified into four types as follows : • Odour replacement or fragrance en hancement.

• Physical adsorption.

• Biological or enzymatic treatment.

• Chemical reaction with the odour-producing agents.

Of these methods, the first method does not remove the source of the malodour, but attempts to "mask" or cover it with yet another odour which may in some cases actually en hance or produce an even more disagreeable odour.

The use of adsorption methods often leads to the adsorption of other components present, which are not in themselves part of the problem, rendering the process uneconomic.

The biological processes are generall y too slow in operation to be effective in abating malodours.

For these reasons most recent methods utilize some form of chemical reaction with the odour producing agents, most commonly involving oxidative treatments with chemicals such as ozone, chlorine, or potassium permanganate. Because of the presence of relatively large quantities of other oxidi zable matter in the wastewater, oxidative methods can prove overly expensive in dealing wit h odour complaints. Attention has recently centred on nonoxidative chemical reactions that may significantly reduce su lfide odours emanating from the treatment. One such treatment utilizes 'Neutrapo l 7 C'. ' eutropol' odour neutralisers are a Japanese development which convert noxious gases to non-odorous compounds by chemical reuctions. For example, an organic acid is converted to a salt , an ami ne or mercaptan to non-odorous ionic compounds.

TESTING OF NEUTRAPOL N7 C The Environmental Engineering laboratory of Dept. of Civil Engineering - National University of Si ngapore (Koe, 1992) was commi ss ioned to evaluate the effecti veness of Neutrapol N7 C, in reducing hydrogen su lfide emissions from municipal waste waters.

SEWAGE SAMPLES Sewage samples for the laboratory tests were collected from a nearby municipal wastewater treatment works which handles approximately 286 ML/ day of municipal wastewater. The samples were collected from one of the primary sedimentation tanks which was known to be handling sewage that is fairly septic and has a history of emitting significant levels of H 2S gas. For this study, two batches of sewage sample, each on a separate day, were collected from the treatment works and each batch of sewage was subjected to five different dosages of Neutrapol N7 C . A ll sewage samples were stored in bulk plastic containers and immediately transported to the laboratory.

EXPERIMENTAL METHODS Approximately 1-L sewage samples were first poured from the bulk plastic container into a measuring container. The sample was then

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WATER Jun e 1992

dosed with the relevant amount of Neutrapol N7 C concentrate and allowed to mix for about JO minutes. After this initial mixing, the mixture was then slowl y poured into a 2-L conical flask which had been fitted to enable the passage of a nitrogen airstream throu gh the sewage sample. The nitrogen flowrate was set at 5-L per minute and this was adequate to allow sufficient agitat ion of the sewage sample and to enable the collection of volatilized air in Tedlar plastic bags. Approximately 25 L volume of vo latilized air sample was collected during the initial 5 minutes of volatilization. The collected sample was then imm ediately analysed for its H 2S concentration with a GC-FPD ana lyser.

The five Neutrapol dosages used were: 0.005%, 0.0JOJo, 0.05%, 0 .1% and 0.5% by vo lum e of sewage sample.

Table 1 gives a summary of the H2S concentration for each of the co llected air samples at the various Neutrapol dosages.

Table 1 Nc utrapol dose ( 0/o )

0 (undosed) 0.005 0.01 0.05 0 .1 0 .5

H 2S concentrat ion (ppm) for Neutrapol N7 C Sewage Batch # I O/o H2S

H2S

(ppm)

162 87 51 34 37 0

remo\·ed

46.3 68.5 79. 0

77.2 100.0

Sewage Batch # 2

H 2S co ne.

O-/oH,S

(pp m)

rc mo;cd

20.3 15. 1 5.4 4.7 3.6 0 .0

25.6 73.4 76.8 82.3 100.0

DISCUSSION Results shown in Table I clearly illustrate that Neutrapol N7 C reacted with the municipal sewage to cause a reduction in the potential of the sewage to emit H 2S. At the 0.5% level, Neutrapol N7 C was found to completely eliminate the potential of H 2S emission from both batches of sewage tested. At the lower dosage level of 0.1%, the efficiency of H 2S reduction reduces to between 77-82%. At the very low dosage level of0.01, about 70% reduction in H 2S emission potential was still achieved .

It should be noted that these llests were carried out in a closed environment under laboratory conditions and indicated that total chemical H.,S removal could be obtained. However, field tests have indicated that Neutrapo l N7 C, when employed at much lower concentrations, significantly reduces the olfactory effects of sulfide odours.

For example, a series of tests employing six different chemica l odour treatments was performed at the Honolulu City and County Waste Water Management, to determine their effectiveness in controlling sewage odours. These tests, which utilized measurement of H 2S in the atmosphere and olfactory tests by a panel of eight assessors, indicated that only one product, namely Neutrapol N7 C, (marketed in Japan and USA as Epoleon) met all their requirements.

The districts of Kanaone and Kailua are using Epo leon (Neutrapol) N7 C to control odours from their primary clarifiers and thickener tanks, at the rate of 40-50 li tres per day, which has had the dramatic effect of reducing the odours from the plant while at the same time significantly decreasing the quanity of peroxide and iron chelate being employed and effectively reducing treatment costs. These references were confirmed under local conditions where E&WS at Port Adelaide have reported success in sewage odour abatement by using Neutrapol N7 C in the form of a fine mist spray on conveyor belts and storage bins.

CONCLUSIONS Neutrapol N7 C has been tested under laboratory conditions for its reaction with municipal sewage samples. The chemical has been found to be capable of reducing the potential of sewage to emit volatile sulfide odours. This laboratory determination has been confirmed by field tests in Hawaii and Australia, where satisfactory abatement of sewage odours has been achieved.

REFERENCE L. C. Koe, Dept of C ivil Engineer ing . National University of Singapore. Pri vate commumca t1on.

Ken Clark is a consultant chemist working for Rusden Environmental Services Pty Ltd.

ENVIRONMENTAL NOTES

OBSERVATIONS ON WATER POLLUTION FROM A TRAIN

by Stephen Davis An occasional series from Mallesons Stephen Jaques, Solicitors and Notaries At the end of November last year I headed off to Shanghai, China, to attend the third IAWPRC Regional Conference on Development and Water Pollution Control.

From Shanghai I travelled to Beijing and boarded the Trans-Siberian railway. The 16 000 km journey took me through China, Mongolia and into the crumbling USSR, where I stoppped in Irkutsk, Siberia, before traversing Russia by train to Moscow and then into Eastern Europe. I saw firsthand much of the environmental degradation which afflicts those countries. The sad part ¡ is that with the amazing political changes which have swept through that region in the past 18 months, it is unlikely that they will concentrate on environmental controls for sometime to come.

USSR Prior to 1988, the protestations of Soviet scientists on environmental degradation occurring in that country went largely unheard, whilst the protests against pollution and the warnings in the press were ignored. In January that year, however, the situation appeared to change as various industrial and energy projects were abandoned by Soviet a uthorities on environmental grounds and Goskompriroda, the State Committee for Protection of the Environment, was established. In November 1989, the Supreme Soviet made environmental protection a priority in a resolution containing guidelines for action until the year 2005 .

With the disintegration of the Soviet Union, one can only lament over the fact that environmental issues are likely to be a small priority for many years to come. As with many significant environmental problems, there is often a conflict between environmental remediation and economic development. One only has to stand in a food queue in Moscow to know which side will win. As Gorbachev commented while visiting Leningrad in July 1989: "I will say frankly that the environment has us by the throat". In January 1990 at a global forum in Moscow on environmental protection and development for human survival, Gorbachev acknowledged the Soviet Union's past neglect of ecological issues and the seriousness of problems such as atmospheric pollution, endangered water resources and soil degradation.

Even back in 1989, Salykov, the Chairman of the Committee for Ecology, told the Supreme Soviet that atmospheric pollution was 10 times the maximum permitted levels in 103 towns, affecting more than 50 million people. In addition, two-thirds of water resources reportedly below health standards while drinking water was inadequately purified in 600 towns. The annual application of pesticides in parts of Crasnodar Kray, Sverdlovsk Oblast, Tajikistan, Armenia, Kirghizia and

Turkmenia were at least 5 times higher than the average for the country.

Even prior to the dissolution of the Soviet Union, however, little action had been taken.

Figures released in October 1989 suggested that of the 158 environmental clean-up projects ordered at the beginning of that year, only 10 had been commenced. At a conference of European Community in Eastern European environment ministers in Dublin on June 16, 1990, the Chairman of Goskompriroda said that the USSR placed the passing of environmental laws as a high priority. These laws would a llow citizens harmed by pollution to sue offenders, including the State. It is unlikely, however, that any such laws will be passed by the Republics for many years to come.

The pollution of Russia's rivers is something I saw first hand on my trip. Lake Baikal is located in the so uth of Eastern Siberia and covers an amazing area of 31 500 square kilometres. Its water base occupies about 557 000 square kilometres and contains approximately 23 000 cu.km of water, which represents about one fifth of the world's reserves of fresh surface water.

Baikal is also the deepest lake in the world with an average depth of 730 metres and a maximum depth of 1620 metres. I was told be a local scientist that it would take all the rivers of the world - the Volga and Don, Dnieper and Yenisei, Ural and Ob, Ganges and Orinoko, Amazon and Thames, Seine and Oder - nearly one year to fill Lake Baikal.

Lake Baikal is blessed with rich and diverse wildlife, including over 1 200 species of animals and 50 species of fish from seven families. Tragically, however, the lake is being heavily polluted by a pulp and paper plant on the southern shore which every year releases approximately 100 million tonnes of cellulose waste into the river. The waste has only been partially treated by an inadequate purification system prior to release. Anot her hundred or so similar enterprises in the Baikal basin have no purification facilities at all. If that was not bad enough, more than 700 farms dump fertiliser and pesticides into the water.

Gorbachev left Irkutsk in Siberia the week before I arrived and the local residents in Listvyanka were angry as he had made no promises to stem the pollution of Lake Baikal from which they feed and work. Yet water pollution is not the only ecological problem I observed in the region surrounding Baikal. There have been campaigns to attempt to reduce the logging of Angara pine and Siberian cedars in the Taiga forest, which have proved largely unsuccessful. During my stay in Irkutsk, the capital of Siberia , I met severa l representatives from foreign timber countries whose express aim was to export as much timber as they cou ld from Siberia before strict environmental controls were imposed. Then they feared they may have

to comply with better logging practices and reforestation.

St. Petersburg's main water supplies are also seriously polluted. Lake Ladoga has been seriously contaminated by the effluent from several cellulose paper mills built prior to the second World War and by untreated effluent from cattle farms. Although the largest paper mill at Priozersk was closed in 1986 due to public pressure, the situation is still serious. The past three years have seen some progress, however, as more than 150 enterprises have ceased discharging untreated effluent into the Baltic sea and Lake Ladoga and pesticides have been banned in the area.

On the Volga River and around the Caspian Sea, industrial and agricultu ral development has diverted water from traditional fish breeding grounds and is polluting the water which remains. Even catches of the famous sturgeon and salmon are falling as large hydroelectric schemes divert water for large scale rice growing.

Pesticides also pour into the Volga from the Deltas ricefields, as do wastes from industries further up river. At a large gas plant about 60 km t'rom Astrakhan, which began operating in 1988, eq uipment failure and lack of trained manpower have resulted in accidents in which clouds of sulphur1 laden gas have been em itted to the atmosphere. Villagers near the plant have been issued with gasmasks and people complain that they can no longer grow vegetables. The Chernobyl disaster was a public nightmare, but one gets the impression that there are many others, more and more deadly.

In the summary, the outlook is bleak.

Whilst the Republics devote the majority of their attention to territorial disputes and building their political and economic systems, the environment is unlikely to be a high priority. One can only hope however, lhat once capitalism becomes firmly entrenched and the private enterprise system is developed, private property rights may provide individual incentives to landowners to protect their own resources. Perhaps environmental protection agencies will also be established to control industry as it develops. The sad part is the Soviet braindrain has resulted in many of the ex-USS R's top scientists being drawn to Canada and the USA on salaries they could only previously dream of. Even the yo un ger scientists are leaving the profession. I met a young scientist called Sasha on the TransSiberian who had left his job to sell books and magazines. He could earn five times his previous salary and was having a great time being an "Ameri can business man". I hope Australia with its hi gh standard of environmental scientists and engineers can play a developing role in protecting the environment in the new Soviet Union.

WATER June 1992

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