Water Journal September 1974

I

1ssN.. 0310 - 035 7 1

Official Journal of the fflll-1 i if!1 • ~ fib) i #t iE ~ I•l WM-ii :1'4'l!l i =I iW!l-1-i•Il!l rt,. [I]~ I

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IVOL. 1 NO. 3 -

SEPT. 1974

Price $1.00

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EDITORIAL COMMITTEE Chairman: C.D.Parker Committee: G. R. Goffin F. R. Bishop Joan Powling A. G. Longstaff W. Burnett A. Macoun Hon. Editor: A.H. Truman

M. Dureau

L. C. Smith R. L. Clisby B. S. Sanders W. Nicholson A. F. Herath Publisher: John G. Craig

BRANCH CORRESPONDENTS

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IIssN 0310 - 03s1 I

Official Journal of the !AUSTRALIAN WATER~ ASTEWATER ASSOCIATION!

CONTENTS Editorial - The Association - Where to? ..

7

Association News

8

The Occurence of Nitrate in Groundwater R. L. Clisby

9

CANBERRA, A.C.T.:

A.Macoun, c/ - Dept. of Works, Phillip, 2606.

NEW SOUTH WALES: M. Dureau, Envirotech Australia Pty.Ltd., 1 Frederick Street, Artarmon.

VICTORIA: A. G. Longstaff, Gutteridge Haskins & Davey, 380 Lonsdale Street, Melbourne, 3000.

QUEENSLAND: LC. Smith, 24 Byambee Street, Kenmore, 4069.

Advanced Waste Water Treatment pt. 2 David M. Philp

11

Conference Calendar

19

Persistence of High Daily Demands in Australian Water Supply Systems - B. W. Gould

20

SOUTH AUSTRALIA: R. L. Clisby, c/ -E. &W.S. G.P.O. Box 1751, Adelaide, 5001 .

New Product and Projects

23

Subscriptions & Membership

25

WESTERN AUSTRALIA: B. S. Sanders, 39 Kalinda Drive, City Beach, 601 5.

Articles should be of original thought or reports on original work of interest to the members of the A.W.W.A. and preferably not more than 5,000 to 7,000 words.

INSTRUCTIONS TO AUTHORS Full instructions are available from Branch correspondents or the Editor.

TASMANIA:

W. Nicholson, 7 Swansea Court, Lindisfarne, 7015.

NORTHERN TERRITORY: A. F. Herath, 59 Allwright St., Casuarina, 5792.

Editorial Correspondence: Hon. Editor, A.H. Truman, c/- Davy-Ashmore Pty. Ltd., P.O. Box 4709, Melbourne, 3001.

Or to State Correspondents.

Advertising Enquiries: John Craig, 'Water' Box 175, Nunawading, 3131.

Phone: 874 2133.

FRONT COVER: Describing the Millewa district, in the far north-west Maliee area of Victoria as "heartbreak corner ", when he opened a new $3.2 million water reticulation scheme recently, Victoria 's Premier. Mr. R. J. Hamer, said, "what we are ensuring today is that heartbreak will never occur again - because what we are lacking until now, was an assured water supply for stock and domestic purposes.

The new scheme will provide continuous pressurized water supply to about 126 holdings on a total area of about 227 ,000 hectares.

About 644 km had to be laid and to keep to the contract rate of about 5 km per week meant the development of a highly efficient laying technique.

A system was devised by the pipelaying sub-contractors, D. G. Harding Pty. Ltd .. of Adelaide which meant that once asbestos cement pipes had been loaded onto a semi-trailer from James Hardie and Coy. Pty. Limited, Melbourne factory , they did not touch ground until placed directly into a pre-dug trench.

Tractor. trailer pipe rig and compressor operated as a single unit while pipe laying proceeded . The whole unit moved 3.96 m as each pipe length was laid.

Couplings, with rubber rings already installed . lubrication of the spigot end was all carried out in one continuous operation .

The whole scheme has been under the control of the State Rivers and Water Supply Commission of Victoria.

THE OCCURENCE OF NITRATE IN GROUNDWATER

by R. L. Clisby, B.E., B.Ec.

There are widespread areas in Australia where groundwater resources are of paramount importance. In recent years attention has been increasingly focussed on the occurrence of nitrate in some of these groundwater resources.

Nitrate-rich groundwaters occur in all Australian continental states including the Northern Territory. The medical importance of high nitrate waters for human consumption is emphasised by Johns. 1 There is also evidence to suggest that high nitrate waters may be responsible for abnormally high abortion rates in cattle and lowered milk production from dairy cows.

One of the nitrate-rich groundwater areas of Australia extends from the lower south-east of South Australia through the lower Western District of Victoria as far as Melbourne. In this area the South Australian Water Resources Management Authority has already experienced urban water supply problems as a result of the high nitrate levels. Two cases are cited : 1. Millicent Town Water Supply

Six bores, ranging in depth from 67 m to 201 m, supply underground water from the unconfined Gambier limestone aquifer.

One of the bores (No. 2) showed a higher nitrate level in 1965 analyses and by 1969 was withdrawn from service as the cdncentration had exceeded the limit of 45 mg/ I set for Potable water supplies. The fluctuations in nitrate level for this bore are shown in Table 1. The remaining bores showed no significant change in nitrate level and in October 1969 the means was 0. 7 mg / I. The TDS range for all bores was 616 to 907 mg/ I. Table 1. Results of Nitrate Analyses, Millicent No. 2 Bore Jan. July Jan. Jan. July Jan. Aug. Sept. Sept.

DATE

Nitrate (N03) mg/ I

8, 20, 5, 3, 7, 5, 2, 17, 24, 1965 1965 1966 1968 1968 1969 1969 1969 1969 11

16

13

29

5

116

88

90

2. Mount Gambier City Water Supply Th is city draws the bulk of its urban water supply from Blue Lake, a volcanic crater lake. Its nitrate level, monitored since 1927, has never exceeded 16 mg/I. To reduce distribution costs, water pressure had been maintained at a satisfactory level in the furthest parts of the distribution system by booster bores drawing water from the Gambier limestone aquifer.

The five pressure booster bores in the system, supplying only small quantities of water and commissioned 20-25 years ago, were all withdrawn from service by 1971 because of high nitrate concentrations. This necessitated the expenditure of $100,000 to enlarge the distribution system from Blue Lake.

These two cases provide palpable evidence of change in nitrate levels in underground waters over a short time and other cases of rapid changes are known . In Western Victoria, Mcvean Springs discharges over 4.5 Ml/d groundwater from ¡highly transmissive basalt on the southern shore of Lake Corangamite . Over a 50-year period the nitrate concentration in this water has risen from five to 50 mg / 1. 2 The water has a low TDS of 350 mg/ I which means that nitrate is one of the significant ions present.

Groundwater research in the United States, in the ChinoCorona dairy area of California, in 1969 revealed an interesting pattern of nitrate levels in soil profiles for various " land use" categories (see Table 2). The four categories chosen were : (i) Control or undisturbed sites with no manure or irrigation water applied;

(ii) Irrigated cropland which were disposal sites for barnyard manure, or liquid manure or both; (Iii) Irrigated pasture sites where wastes from milking operations where disposed of; and (iv) Corral sites where manures were generally scraped twice yearly and discharged to croplands or pastures.

Table 2.

Mean N0 3-N (in saturated paste extracts) in soil profiles under control (undisturbed), cropland, pasture and corral in the Chino-Corona dairy area (1969). 3

Depth (ft.)

Surface

5 10 20 31

Control

10 4 8 10 10

Nitrate-N (mg/I) Cropland

n 7 23 28 19

Pasture

Corral

5 39 38 39 17

100 140 80 86 33

The relatively high level of nitrate-N under corral will be noted.

From the American experience cited above it ,would seem that animals have played a major role in the increased nitrate concentrations of their ground waters. Some evidence for a similar situation exists in Australia.

Case 1: Water Supply Bore No. 2 at Millicent

Why is it that only one of the six water supply bores has been affected by high nitrate levels? All six bores serving Millicent are located on cattle and sheep pasture land beyond the urban built-up area. However, there is a stock saleyard located in the vicinity of No. 2 Bore and in 1965-66 a waste disposal lagoon was constructed with the discharge point about 300 m from the bore. The water used at the saleyards is high in nitrate and it seems reasonable to infer that the high levels detected at the bore are a result of concentrated animal activity at the nearby saleyards. However, no bacterial Pollution has been detected at the bore and it seems therefore that filtration through the limestone aquifer very effectively removes these bacteria from the effluent discharge.

Case 2. Mt. Gambier City Water Supply Increasing concern for groundwater pollution in the southeast of South Australia led to the appointment in 1971 of a Committee on Water Pollution Control to examine the problem and make recommendations for control measures.

The Department of Mines examined. a total of 256 bores and sinkholes in a 1300 km 2 area around Mt. Gambier extending to the southern coast. The highest nitrate concentration recorded was 490 mg/I, and the distribution of results is given in Table 3.

9

Table 3. Nitrate distribution in 256 bores in the Mt. Gambier area

Frequency

Range mg/I - NO3

c,ver 300 100 and 50 and 20 and 10 and 0 and

4 11

4

7 14 43 79 43 66

200 and under 300 under under under under under

200

1 00 50 20 10

Cumulative Frequency

25 68 147 190

256

A careful ground examination of the immediate environment of some 50 bores within 8 km of Mt. Gambier was made but no direct correlation could be established between nitrate concentration and animal density, crop type (e.g. legumes), or local topography. This examination perhaps demonstrates the importance of not getting too close to the problem in order to clearly see it. The infiltration process and movements of underoround water may have so many local vagaries that to attempt correlations on a single bore basis is bound to fail.

The results from all bores have been used to construct the nitrate contours given in Figure 1. This figure has been compiled by dividing the entire area into squares of approximate size· 3 km x 3 km and plotting the mean nitrate level of all bores in each square at the centre of that square. The range

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of concentration is so great that, in order to obtain a manageable number of contour intervals (5) a log transform has been used. The high groundwater nitrate levels around the Blue Lake are clearly seen, although the reason for a comparatively low lake nitrate level is not fully understood.

The semblance of a plume of nitrate extends to the sea.

The area covered by the map is Karstic limestone with a relatively deep groundwater level and highly developed underground drainage leaving the ground surface free of swamps. The Glenelg River is incised into the limestone and is saline in its lower reaches for much of the year. The other surface streams constitute short distance flows from springs very near the coast. There are a limited number of volcanic craters and sinkholes which provide windows into the water table. All in all, there are few places for animals to obtain drinking water and it is concluded that the original native animal population could not have been high. Settlement began in the period 1830-1840. Expressing the introduced animals (sheep, cattle, horses, pigs, etc.) as equivalent sheep, it is seen that the population had reached 330,000 by 1915 and 860,000 by 1972. The estimated human population is 23,000 persons (1971 census) of whom 75 per cent live in Mt. Gambier city which was sewered in 1965-67 with the effluent piped directly to the sea although only about 60 per cent of all premises are connected to the municipal sewerage scheme. The total animal population in this area is now many times its original native level. case 3. Mc Vean Springs in Western Victoria The area drained by Mcvean Springs is an area of rich volcanic soil capable of supporting a high pasture production with a correspondingly high dairy cow population. This animal population level is again considered to be well in excess of the original native animal population level. case 4. Chino-Corona area of California This area has one of the highest concentrations of dairies in the world. The dairy area covers 67 km 2 and contains about 365 dairies with a total of nearly 125,000 cows.

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In the four cases discussed a correlation has been found between animal density and underground water nitrate concentration. The Mt. Gambier area is of interest because of the high degree of variability between nitrate levels recorded at different bores. This may indicate that the nitrate input to the groundwater comes from local areas (say around drinking troughs) where high levels of manure occur. Through microbiological transformations, the organic nitrogen in manure is converted to ammonia, then to nitrite and then to nitrate. This process is favoured by aerobic conditions. Crops recycle N by absorbing NO 3 or NH4 and converting it to proteins in plant tissue. However, some NO3 escapes the root zone with infiltrating rain water and eventually reaches the water table.

The dissolved oxygen level in the Mt. Gambier area groundwater is rarely less than 6 mg/I which would indicate that the partially saturated zone above the water table is aerobic below freely drained surface soils.

Under anaerobic conditions, which can occur at shallow depths in soils with clay subsoils of low permeability, soil nitrate can be denitrified to N2 or N2O and escape to the atmosphere in gaseous form. Groundwater under such soil could be expected to have lower NO 3 content.

The problem of nitrate-rich groundwater may therefore be a phenomena associated with the occurrence of animals and, perhaps, more particularly, the concentration of their manure in small areas. There may also be an association with freely drained soils and a relatively deep partially saturated zone above the water table which allows aerobic conditions to infiltrating water which has passed the bottom of the root zone.

REFERENCES:

MT. GAMBIER KARSTIC AREA LOG TRANSFORM NITRATE CONTOURS 10

1. Johns & Lawrence (1973), Med. J. Aust. 2: 925-7, Nitraterich groundwater in Australia.

2. Thompson, Bruce. Victorian Dept. of Mines. Pers. comm .

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ADVANCED WASTE WATER TREATMENT

by David M. Philp B.E.(Hon.) Sydney, M.I.E. Aust.

This is a continuation of Mr. Philp's article presented in the last issue (Vol. 1 No. 2 June 1974). The authors comments, acknowledgements and references appear at the end of part one.

Alternatively, consideration can be given to the conventional activated sludge process type with nutrient removal from the secondary effluent. .

Screening and primary sedimentation facilities would be similar to the plant proposed above with the activated sludge facilities being almost double in size. Air capacity would have to be increased by approximately 50 per cent.

Removal of phosphorous would be carried out in circular lime reactors or clarifiers followed by ammonia stripping towers for nitrogen removal on the effluent from the activated sludge plant.

Sludge disposal would be by incineration with lime recovery being undertaken. Flotation thickening of waste activated sludge would be required with incineration and dewatering facilities being the same as for the adopted process.

In considering an advanced waste water treatThe estimated cost of this proposal was $21'.1 million at ment plant for Lower Molonglo a number of alter- June 1973 costs. natives were examined. These alternatives includThe estimated cost of the plant for Lower Molonglo as ed consideration of a plant with nitrogen removal adopted is $21. 7 million at June 1973 costs. by ammonia stripping and biological oxidation of In addition , the cost of these advanced waste water treatthe oxygen demanding substances. However, ment facilities can be compared with the cost of a convenammonia stripping was not adopted due to a tional activated sludge plant without nutrient removal. This number of unknown factors described later in this plant would have to be designed for nitrification for the removal of ammonia and would require lime dosing facilities paper. to provide for alkalinity make up. Filtration would be required to achieve the reqJ,.Jired 800 5 and suspended solids with The capital cost of the Lower Molonglo Plant effluent chlorination for bacterial control. Sludge disposal can be compared with the cost of other types of would be by anaerobic digestion with land disposal. plants.

The estimated cost of this plant would be $24.3 million at Estimates were prepared for a treatment plant based on biological oxidation and removal of nitrogen with phosphorus removal by chemical precipitation in the activated sludge plant. Screening facilities would remain the same as proposed with primary sedimentation tanks being of a similar size to those of the adopted design. However the cost of the sedimentation facilities would be lower as the special provisions for handling lime and limed sludge would not be required . As BOD removal in the primary sedimentation facilities would be reduced due to the lack of chemical precipitation the aeration tank volume would be approximately twice the size of the proposed plant with the aeration blowers being of double capacity also. Phosphorus would be removed by alum addition to the activated sludge aeration tanks. However with Canberra's waste water, alkalinity would have to be added to meet the demand caused by the alum and nitrification. Phosphorus would be removed with the waste activated sludge . Nitrification would be carried out in the aeration tanks but operational difficulties could be expected due to the conflict between the optimum pH for alum removal of phosphorus and the optimum pH for nitrification.

The anoxic suspended growth reactors would be used for denitrification with the tanks having a capacity of approximately 30 per cent of that required for the activated sludge aeration tanks and sedimentation tanks similar to those for the activated sludge plant. Sludge disposal would be by incineration with flotation thickening of the waste activated sludge. The sludge voltJmes produced would be approximately 40 per cent of the sludge volumes produced in the proposed scheme .

The area of site development would be 30 per cent greater than that required for the proposed plant.

The estimated cost of this facility would approximate $26.8 million at June 1973 cost.

June 1973 costs at the Lower Molonglo Site.

A comparison was also made between the cost of anaerobic digestion and incineration for the treatment of sludge. It was estimated that the capital cost of anaerobic digestors at June 1973 cost would be $800,000 less than the cost of incineration. However, the value of lime recovered by incineration is expected to amount to $150,000 per annum when stage 1 reaches capacity. The cost difference does not include provision for the disposal of the treatecj sludge. The cost of land disposal is substantially higher than the cost of disposal of ash from incinerators. In Canberra only limited sites are available for the land disposal of sludge by lagoons and little suitablable land is available close to the site.

Consideration was also given to the cost savings which may be possible using gas from anaerobic digestion. It was estimated that approximately one-third of the power requirement for the plant could be generated using the gas; however, no substantial savings in the power cost could be achieved when compared with the cost of purchasing power from the electrical supply authority.

As can be seen from the,estimates for alternative schemes, the use of integrated facilities for nutrient removal offer the benefit of lower capital cost.

The difference between a conventional activated sludge plant and an advanced waste water treatment facilitiy lies mainly in the operation and maintenance costs.

The operation and maintenance cost (excluding capital charges) of the Lower Molonglo Plant at full capacity of stage 1 is expected to be $2.5 million per annum or $62 per megalitre.

The cost of operation and maintenance of a conventional treatment plant without nutrient removal could be expected to cost in the order of $1.3 million per annum or $33 per megalitre.

•oavid M. Philp, Supervising Engineer Sewerage and Treatment, Major Development Section, Department of Housing and Construction, Canberra, A.C.T. 11

REMOVAL OF PHOSPHORUS FROM WASTE WATER

A number of processes have been developed for the purpose of removing phosphorus from waste water. The alternative processes can be placed in three major categories: 1. Ion Exchange 2. Biological Removal 3. Chemical Precipitation However, only chemical precipitation processes have been developed to the stage where they can be seriously considered for major treatment facilities.

1. Ion Exchange A number of anion resins exist which are suitable for the removal of the phosphate ions from solution. These include: (al Several types of activated alumina regenerated with sodium hydroxide and carbon dioxide. (bl A macroporous resin (Amberlite TRA 68) regenerated with ammonium hydroxide and carbon dioxide.

Removal of phosphorus to very low residuals in the order of 0.05 mg/I can be achieved, with both orthophosphate and polyphosphates being removed.

With alumina resins, the waste water composition has little effect on removal efficiencies and they offer the advantage that¡ no extraneous ions are added as in the chemical precipitation processes. The treatment also does not alter the pH of the waste water.

The sodium hydroxide regenerant solution can be recovered by precipitating the phosphorus with lime thus producing practically no liquid waste and small volumes of solid waste.

Laboratory and pilot studies have demonstrated the feasibility of using alumina resins and they offer a potential for . economic and efficient removal of phosphorus.

However,.fouling of the ion exchange beds with solids and organic materials, combined in some cases with the disposal of the regenerant waste, still pose difficult problems.

3. Chemical Precipitation A large variety of chemical precipitation processes have been proposed for phosphorus removal ; however, these can be divided into three main types: (i) Addition of chemicals to secondary effluents. (ii) Addition of chemicals to aeration tanks of the activated sludge process. (iii) Addition of chemicals to primary sedimentation tanks.

II)

(i) Secondary Effluents

This technique is a proven method for the removal of phosphorus. A number of chemicals have been proposed. (al Lime Lime can be used on its own or with iron salts and/ or anionic polyelectrolytes.

Treatment followed by either one or two stage recarbonation and filtration may be used depending on the degree of phosphorus removal required and the waste water hardness. The process has the advantage of being separate from the conventional treatment plant and the upsets which can occur. However, this treatment results in substantially higher capital and operating costs.

Recovery of the lime can be practised with this process.

Operation at approximately pH 11 is generally used. (bl Alum Alum can be used on its own or with activated silica or anionic polyelectrolytes. The optimum pH with alum is in the order of 6. The process is used with rapid mixers, flocculators, clarifiers and/ or filters. No proven technique has been established for the recovery of the alum, although processes with alkaline and acid regeneration are under investigation. Again capital and operating costs are higher with this method when compared with additions.of chemical to the conventional plant.

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(cl Iron Salts Although iron salts are successful in precipitating phosphorus the process has found little application due to the residual iron remaining in the effluent.

2. Biological Removal Of the biological processes available for the treatment of waste waters, only the activated sludge process has been A number of commercial processes have been developed shown to be capable of achieving significant phosphorus for this technique using both clarifiers and/ or filters for the removal. removal of phosphorus contained in floes and precipitates.

Typical activated sludge plants operating on domestic Removals as high as 95 per cent have been achieved. The sewage can normally achieve a maximum removal of phos- costs involved in this process pose its main disadvantage. phorus in the order of 20 to 30 per cent. Over a period of 18 months removal of phosphorus at the Belconnen W.P.C.C. (ii) Aeration tank addition Aluminium and iron salts are applicable for use in the has averaged 18.2 per cent. This phosphorus has been shown to be removed by cell synthesis and can be released by cell removal of phosphorus in this process. Aluminium salts are generally preferred due to the possible carry over of iron in lysis. the effluent when iron salts are used.

To achieve maximum removal, the plant would have to be The process has the advantage of improving mixed liquor operated with short cell residence times to obtain maximum cell growth with little destruction of the cells and the plant settling enabling higher mixed liquor suspended solids to be would be subject to the problems associated with high food to maintained in the aeration tank. The hydrolysis of complex organism loadings such as sludge bulking and poor BOD phosphates to orthophosphate improves the efficiency of removal. Concentrations of 1 to 2 mg/ I of phosphorus in the _removals.

However, some plants have reported very high phosphorus effluent can be achieved. removals. Removals in the order of 90 per cent have been However the optimum pH 6 for the removal of phosphorus obtained at the Rillings Activated Sludge Plant at San is not compatible with nitrification. The optimum pH for Antonio, Texas, and the Back River Plant, Baltimore, nitrification is about 8.3 and it has been reported that where Maryland, with loadings in the order of 0.5 lb BOD per lb alum is used for phosphorus removal nitrification perforMixed Liquor Suspended Solids. The reasons for these high mance is diminished. removals is not understood and two hypotheses have been suggested. (iii) Primary waste water additions The chemicals used in Primary chemical precipitation (al Luxury Uptake by cells; (bl Chemical precipitation. include aluminium salts and iron salts with or without anionic polyeletrolytes and lime with or w ithout iron salts Since little success has been achieved in reproducing the and/ or anionic polyelectrolytes. above results the biological process can not be seriously conHowever lime with small additions of iron salts offers a sidered as a viable technique for significant phosphorus number of advantages. removal.

12

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(al Lime results in an increase in pH . A pH in the order of 11 .0 is required for good phosphorus remova l. At high pH acid and sulphide odour causing substances are supressed . (bl Lime sludges are more compact, are more easily dewatered and less subject to gas producing activity.

Alum tends to produce more bulky sludges which are less easily dewatered. The lower pHs at which alum is effective can result in decomposition activities that can cause sludge handling problems. (cl The addition of lime results in increased alkalinity which is advantageous with low alkalinity waste waters. Alkalinity is utilised in the nitrification process. The alkalinities present in Canberra's waste water are insufficient to meet these nitrification requirements. (d) The high pH resulting from lime treatment is rapidly reduced by the carbon dioxide in the aeration tanks. As the optimum pH for nitrification is around 8.3 the addition of lime which results in an overall increase in the pH of the mixed liquor is advantageous for the nitrification process. (el Lime can cause the precipitation of heavy metals providing added protection to the activated sludge process from the toxic effects of these heavy metals.

Phosphorus removal in the primary tanks offers a number of economic and operational benefits. (i) Chemical precipitation results in significant increases in BOD and suspended solids removal and produces a relatively clear effluent. The removal of BOD in the order of 70 per cent offers the economic advantage of a reduced size of aeration facilities. It has been determined that at the Lower Molonglo Plant the aeration tanks for nitrifi-

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cation would have to be more than twice as large if chemical precipitation was not used. (ii) No additional special facilities are required, such as additional clarifiers or filters as would be required with removal of phosphorus from secondary effluent. (iii) The high removal of BOD is beneficial for the nitrification process. (iv) The process of lime recovery described later with the use of a classification centrifuge has been demonstrated

by Brown and Caldwell to be a practical process suitable for full scale application . As all waste sludges can be handled through the primary sedimentation tanks the furnace for lime recovery can be used as a standby facility for the sludge disposal furnace. Less pipework and special facilities are required than if phosphorus removal was undertaken on the secondary effluent.

At Lower Molonglo it is proposed to add lime upstream of the aerated grit chambers and to utilise these chambers for promoting flocculation. The use of the grit chambers is to provide for the separation of grit .from the sludge removal system. Grit removal is necessary for the satisfactory operation of the centrifuges. The grit is introduced to the top of the sludge furnace separate from the lime recovery process. The addition of iron salts to improve the removal of phosphorus is proposed. Sedimentation of the limed waste water will be carried out in horizontal sed imentation tanks. It is expected that sludges containing approximately 7 per cent sol ids will be achieved from these sedimentation tanks permitting direct feed of the sludge to the classification centrifuge.

The use of chemical precipitation with lime on primary waste water provides the most economical solution to the problem of phosphorus removal at the Lower Molonglo Plant, with many operational benefits over other available processes.

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BIOLOGICAL

NITRIFICATION -

DENITRIFICATION

WITH SETTLED SEWAGE AS CARBON SOURCE

( Barnard)

13

THE REDUCTION OF NITROGEN IN WASTE WATER

Four main processes are generally recognised for the removal of nitrogen compounds from waste waters.

These are : 1. Chlorination 2. Ion Exchange 3. AmmoniaStripping 4. Biological Nitrification-Denitrification Of the available nitrogen removal processes, only two were given serious consideration for the Lower Molonglo Plant.

These were ammonia stripping and biological nitrificationdenitrification with chlorination resulting in further reduction of the ammonia concentrations released in the plant effluent.

1. Chlorination The U.S. Environment Protection Agency at their Blue Plains Pilot Plant. Washington D.C., have demonstrated that ammonia may be removed using chlorine . Controlled pH and chlorine dosage with good mixing and sufficient reaction time can result in the conversion of ammonia to nitrogen gas which is subsequently released to the atmosphere. However, large dosages of chlorine are required . Appro ximately 10 mg/ I of chlorine is required for each mg/ I of ammonia.

Consequently with the usual quantities of ammonia found in waste waters the process is costly and results in excessive chloride concentrations in the pJant effluent.

2. Ion Exchange Several ion exchange resins have been demonstrated as being capable of removing ammonium and nitrate ions.

A process utilizing zeolite-clinoptilolite is selective for ammonium ions in the presence of sodium , magnesium and calcium ions . The removal of ammonium ions by ion · exchange has some potential for full scale operation.

The removal of nitrate ions will only be feasible when resins highly selective for nitrate over other ions normally found in waste water are developed . The Duca Process based on a two column process with Strong Acid-Weak Base resins will remove nitrate ions; however, the process has also a high selectivity for the sulphate ions.

Ions exchange techniques result in concentration of the particular ions. Approximately 400 to 1 has been achieved with ammonium ions.

Liquid wastes resulting from the regeneration of the ion exchange beds pose a problem of disposal. Ammonia stripping has been considered for overcoming this difficulty with the ammonium ion exchange process; however, no suitable techniques have been developed for the nitrate ion exchange regenerated.

Organic fouling of resins present some difficulties and consequently the process only holds promise for the treatment of secondary effluents. The cost of this process is currently much higher than other ammonia removal processes.

Two treatment plants in the vicinity of Washington D.C. are proposed which will use the ion exchange technique for nitrogen removal.

3. Ammonia Stripping Ammonia stripping depends on the conversion of the ammonium ion to ammonia. This conversion is approximately 98 per cent complete at pH 11 and a temperature ,of 2O°c .

Ammonia can be stripped from the waste water by bringing it into contact with ammonia free air.

Removal of ammonia is enhanced by the continual formation of droplets, therefore towers filled with packing are generally used for the stripping process. At South Tahoe Public Utility District Tertiary Waste Water Treatment Plant a 14

24 ft high tower filled with 1½ in x 2 in timber packing , loaded at 1.7 gpm / sq ft gives approximately 95 per cent removal of ammonia with an air supply of 480 cu ft/gal at an effluent temperature of 2O° C. However, a number of limitations exist with this process:

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(a) Freezing

At air temperatures below o0c the waste water freezes at tht air inlets thus making the towers inoperative.

During the winter months in Canberra sub zero temperatures are regularly achieved with the average minimum air temperature in July being - 1°c. Thus freezing can be considered as a potential difficulty for the Lower Mo long lo Plant.

(b)

Low efficiency at low temperatures The solubility of ammonia increases with decrease in liquid temperature, consequently greater quantities of air are required to achieve good ammonia removal as the temperature becomes lower. Approximately 1000 cu ft / gal is required as the effluent temperature approaches O°C and this increased air requirement significantly increases the cost of operation .

th th di u~ of

1.

(c ) Tower Scaling

As the waste water entering the tower has been treated with lime to achieve the required pH it is saturated with calcium carbonate. The calcium carbonate tends to precipitate forming a scale on the tower packing . This scale has been found to vary in nature and composition . Some scales have been found to be soft and easy to remove such as the Lake Tahoe plant while others are reportedly hard and difficult to remove as at the E.P.A. Blue Plains Plant .

Counter flow rather than cross flow with the pH adjusted to 10.8 has been found to minimise scaling with the towers being constructed for easy access to enable flushing of accumulated scale. 'This offers a potential for control of the scaling problem.

The d ifficulties in predicting the type of scale which forms points to the need for pilot plant studies and present a further difficulty in the selection of this process.

In addition , at the Lower Molonglo Plant two other main factors were considered as possibly detrimental to the adoption of ammonia stripping: (i) Air Pollution

The atmosphere around Canberra is relatively clear with no major industrial air pollution. Frequent temperature inversions are a feature of the climate and despite a somewhat favourable meterological report for the area surrounding the plant, concern was felt for the possible effects of discharging large volumes of ammonia into the atmosphere. (i i) Environmental Effects In the February 1970 A.W.W.A. Committee report on the chemistry of nitrogen and phosphorus in water it was pointed out that rainfall in its function of cleaning the air usually contains larger amounts of ammonia than other nitrogen oxides and their derivative acids. Ammonia is known to be highly soluble in water, approximately 0.525 kg/ I at 2O0c, and tras significant sorption properties.

Therefore concern was felt that ammonia stripped from wastes at Lower Molonglo could be precipitated in the surrounding area and within the Murrumbidgee catchment. The Murrumbidgee catchment is extensive in the vicinity of the plant, the nearest catchment boundary being some 55 km to the east. Thus it was possible that ammonia removed at the plant could be returned to the Murrumbidgee River and the Burrinjuck Reservoir.

These possible unknowns lead to further consideration of other alternatives for nitrogen removal.

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4. Biological Nitrification-Denitrification Biological nitrification-denitrification has been adopted as the nitrogen removal process for the Lower Mo long lo Plant.

activated sludge process effluent an external source of organic carbon must be found.

In the nitrification process ammonia is oxidised to nitrite and then nitrate by the autotrophic organisms nitrosomonas and nitrobacter respectively. These nitrifiers have much slower growth rates than the heterotrophic bacteria responsible for the oxidation of carbon in the biological processes.

·(al Settled Sewage

Two main possibilities exist for carbon sources: Processes using settled sewage direct to the denitrification process after biological oxidation have not been successful due to the carry over of ammonia, phosphorous and BOD in the plant effluent. However, research work in South Africa (Barnard) has shown some promise for utilisation of settled sewage as a carbon source. This process requires a recirculation rate of approximately four times the incoming waste water flow rate and tankage for 14 hours' detention. Due to the slope of the site the cost of recirculation would be significant and the capital cost of tankage much higher than for the proposed process at the Lower Molonglo Plant.

Nitrification-denitrification in the oxidation ditch process has also achieved some success.

At the Lower Molonglo Plant nitrification and carbon oxidation will be carried out by an activated sludge process. Due to the slower growth rate of the nitrifiers, adequate cell residence times or sludge ages must be achieved to permit nitrification otherwise the organisms would be "washed out" of the process. The required cell residence times are dependant on temperature and pH .

The nitrification process is well documented and many activated sludge plants both in the U.S.A. and Great Britain have been operated for many years to achieve nitrification.

A critical aspect of nitrification for Canberra's waste water is the utilization of alkalinity. For each mg/ I of ammonia oxidised some 5.9 mg/I of alkalinity is required . The alkalinity of Canberra 's sewage is as low as 155 mg/ I with ammonia concentrations averaging 37 mg/ I. The use of lime precipitation for phosphorus removal in the primary sedimentation facilities offers an advantage in respect.

In biological denitrification nitrate is reduced to nitrogen gas. In this process denitrifiers such as Achromobacter, Pseudomonas and Micrococcus are used. These organisms are heterotrophic utilising organic carbon as sources of energy. As the denitrifying process is carried out on an

SE.CONDA RV E.FFLUENT

Clarifiu

(bl External Carbon Source At the Lower Molonglo Plant it is proposed to use methanol as an external source of energy. Other carbon sources have been studied but methanol has received the widest application. The lower cell growths obtained with methanol are advantageous to denitrification in the trickling column. The dosages of methanol must be closely controlled to achieve efficient removal. Dosages of 3 to 1 methanol to nitrate nitrogen are required. Insufficient methanol results in leakage of nitrate in the effluent while excessive doses are costly and increase the BOD of the effluent. The denitrification process occurs in anoxic conditions and dissolved oxygen must be removed before the organisms will commence to use the nitrate as the oxygen source or electron acceptor.

R•carbonator

Clarifio:r

Carbon Dioxidt Sludg• to or

Slak<d Lim•

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Filter

TREATED EFFLUENT

Carbon Oioxid<

R<colcinator disposal

PHOSPHOROUS REMOVAL Slaked

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SECONDARY EFFLLENT

Flocculant

Scum

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Screen

RAW

Primary PRIMARY Sedim•ntation 1------E-F..

F•LU-ENT

WASTEWATER

Grit for disposal

PHOSPHOROUS REMOVAL

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RAW WASTEWATER 15

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t BIOLOGICAL

NITRIFICATION -

DENITRIFICATION

EXTERNAL CARBON SOURCE

The denitrification trickling column has been developed in experimental work at the Centr.al Contra Costa Sanitary District waste water treatment plant. Brown and Caldwell are carrying out an investigation into various advanced waste water treatment process as consultants to the district and as part of the design of a water reclamation plant for the district.

The design of the trickling column for Lower Molonglo will be based on work at this plant.

The process of biological nitrification-denitrification adopted for the Lower Molonglo Plant using a nitrifying activated sludge process with methanol addition and denitrifying trickling columns offers a number of advantages over other processes: (a) Effective removal of nitrogen under all temperature conditions likely to occur in Canberra as the efficiency of nitrification-denitrification is not reduced to the same degree as ammonia stripping with decreasing temperatures. (b) The end product of nitrification-denitrification is nitrogen gas which is compatible with the composition of the atmosphere. (c) Removal of ammonia is more complete with this process than with ammonia stripping which has advantages in effluent chlorination. (d) The process is more stable than ammonia stripping which is subject to upset by variations in flow rate, temperature, and air volumes. (e) Greater variations in the flow rate through this process can be accommodated. Economic considerations llmit ammonia stripping towers to a maximum flow rate of 1.5 average dry weather flow before bypass is necessary.

However, the proposed process wi.11 allow for 3.0 average dry weather flow before bypass is required. This flow rate is only exceeded under extreme storm conditions.

16

(METHANOL)

Three main denitrification processes have been developed: (i) Mechanically Mixed Anoxic Tanks

This process consists of a tank with approximately two hours' detention, fitted with mechanical mixing equipment. Sedimentation and sludge return facilities are requ ired to retain the denitrifying growths in th~ system. (ii) The Flooded Column In this process columns 3 m to 6 m deep filled with an inert media are used. In experimental studies loading rates of 5. 7 lps/ m2 with actual detention times between five and 15 minutes have achieved nitrate removals of 90 per cent. Coarse sand or 20 mm stone media can be used. The flooded column can be used as a tertiary filter for removal of suspended solids but air binding due to nitrogen re lease can cause difficulties with the finer medias. Backwashing of the columns is necessary but this results in removal of the denitrifying organisms from the columns. A settling-in period occurs after backwashing when nitrate removals are lower than just prior to backwashing. (iii) The Packed Trickling Column

This process consists of a packed column approximately 11 m high. The denitrifying growth is retained on the 5.8 m deep packing in much the same way as with a trickling filter. Air is prevented from entering the column by maintaining a slight positive pressure in the column with provision being made for the escape of nitrogen gas.

In view of the head available at the Lower Molonglo Plant the use of 11 m high columns is an economic proposition as no pumping is requ ired. A further advantage of these columns is the possible future use of natural gas as a carbon source. Should work with natural gas prove successful the columns offer a ready means for introduction of the gas.

(fl

The use of mixed media filters to polish the effluent prior to chlorination is compatible with denitrifying columns and will prevent any growths which "slough off" the column packing from being discharged in the effluent.

(h) Ammonia removal from the waste water would be required irrespective of the decision to adopt a nitrogen removal process to prevent the discharge of ammonia due to the toxic effects and oxygen demand of ammonia on river systems. Thus the denitrifying column can be bypassed in the event that nitrogen discharge is found to be acceptable at certain times. Such operation offers a significant reduction in operating costs. However, ammonia stripping towers would require continual operation to prevent ammonia discharge.

Thus the proposed process for Lower Molonglo offers the most satisfactory and economic solution to the removal of nitrogen compounds.

SLUDGE DISPOSAL AND HANDLING SYSTEMS

The disposal of sludges resulting from waste water treatment has in the past posed and will in the future pose a major problem. It has posed operating difficulties and accounts for a significant portion of capital and operating costs in waste water treatment. With the development of advanced waste water treatment new problems of solids disposal have had to be solved.

The need for elimination of odours, the scarcity of land at the site for the Lower Molonglo Water Quality Control Centre and the need for a high quality of effluent necessitates consideration of the alternatives for sludge disposal.

Alternatives considered include: (i) Anaerobic Digestion (ii) Wet Oxidation (iii) Heat Conditioning (iv) Incineration Anaerobic digestion followed by land disposal has been the most common method of sludge disposal used for many years. Anaerobic digestion is currently used at existing Canberra waste water treatment plants. Heated primary digestors with both gas and mechanical mixing and secondary digestors are used. At least 50 per cent reductions of volatile solids are generally achieved with a gas production of approximately 1.0 m3 /kg volatile solids destroyed consisting of approximately 64 per cent methane and 35 per cent carbon dioxide.

Disposal of sludge from these digestors is mainly by sludge lagoons with sludge drying beds being used at the Fyshwick plant. Sludge lagoons offer the most economic solution to the disposal of the sludge provided sufficient land is available.

However, anaerobic digestion poses some difficulties: (al Odour production from the disposal of digester gases and sludge; (bl The possibility of use of new industrial and domestic chemicals which could inhibit the biological digestion process; (cl The large space requirements necessary for anaerobic digestion with land disposal, over other methods of disposal; (dl The safety hazard of having to handle a highly combustible gas; (el The increased loading on the waste water treatment facilities caused by supernatant liquors returned to the waste water flow.

The use of anaerobic digestion has been shown to be feasible with limed sludge after the sludge has been treated in the classifying centrifuge. The centrate from the centrifuge has a pH of approximately 9 and after further thickening can be fed to the digestors.

Wet Oxidation

The wet oxidation process is marKeted commercially under the name "Zimpro Process". In this process the sludge is first ground and fed through a heat exchanger. Air is added to the sludge before heating. The sludge is heated to a temperature ofapproximately 260°Cat a pressure of 2100 KPa. The sludae is then fed to a reactor where it is oxidised. Steam can be used to achieve the required temperature particularly in the initial start up; however, the sludge generally contains sufficient volatile material to sustain the reaction without the addition of external heat. The sludge is then fed back through the heat exchanger to transfer the heat to the incoming sludge. The gas is separated from the sludge and the sludge is easily dewatered by mechanical means. The gas is oxidised in a catalytic burner for odour control. The sludge is stable and can be disposed by burial or incineration. The liquid faction is high in BOD and is normally treated with the other plant liquid wastes.

The disadvantage of this process is that the return liquor increases the load on the treatment plant.

Heat Conditioning

This process is commercially marketed under the name of the "Porteous Process" and is similar to the wet oxidation process except that air is not mixed with the sludge. The process operates at a lower pressure of 1700 KPa and a temperature of 180°C. Steam is added to the sludge before it enters the reactor. The sludge produced is easily dewatered and is biologically stable. The dewatered sludge can be disposed by incineration or burial. The liquor removed from the treated sludge is high in BOD and poses the same disadvantage as the wet oxidation process.

Incineration

Two types of furnaces are generally used for the disposal of waste water sludges: (al Multiple Hearth Furance (bl Fluidised Bed Furnace The multiple hearth furnace is available in a wide range of capacities from five tonne to 1250 tonne per day. The larger furnaces are 6.7 m diameter with some 12 hearths.

Sludge material is fed into the top of the furnace and sludge material is raked by the rabble arms to the centre of the furnace where it falls through to the lower hearth. The sludge is then raked to the outside of the second hearth where it falls through to the third hearth. In this way the sludge is fed through the furnace.

The upper hearths of the furnace are used for drying the sludge material with the centre hearths being used for burning. The bottom hearths are used for cooling the sludge material.

Cooling air is circulated through the centre shaft and rabble arms and this heated air is then used as preheated combustion air.

The burners are automatically controlled to achieve the required temperature on the hearth.

At Lower Molonglo multiple hearth furnaces are proposed due to the economics of lime recovery and the high cost of land disposal for anaerobic digestion for the Lower Molonglo site. The proposal to use lime recovery enables two furnaces to be used, one for sludge disposal, while the other is used for lime recovery. Additional capacity is provided in each furnace to provide standby facilities. In the event of a furnace failure all sludge material can be fed to one furnace.

The fluidised bed furnace consists of a single burning chamber lined with refractory material. The chamber is partly filled with silica sand. Air is blown through the sand bed to 17

expand and fluidise the sand . Sludr,e and fuel are fed into the solids from this centrifuge consisting of 75 per cent calcium sand bed where incineration is undertaken at temperatures carbonate, 20 per cent organics and 5 per cent other about aoo 0 c. However, the ashed material in these furnaces is materials. The cake is then fed to contain between 50 and 60 removed with the exhaust gases. The exhaust gases are fed per cent solids. It is then fed to the recalcining furnace. Ash to a scrubber unit for the removal of the ashed material. As -material from the furnace is fed to a dry cyclone classifier to the exhaust gases contain a significant concentration of separate the lighter calcium phosphate compound from the carbon dioxide the pH of the scrubber water is reduced ash. The rejects are then fed to the ash hopper while the causing phosphorus compounds to be redisolved. As all the accepts are fed to the lime storage hopper. ashed material passes through the scrubber units a major Centrate from the classifying centrifuge is fed to a balance portion of phosphorus removed from the waste water wou ld tank where screenings are added to aid thickening . be present in the scrubber waste water posing a disposal problem for this waste.

The feed to the sludge clarification centrifuge is expected to contain 4 per cent solids with the cake from the centrifuge Solids Handling containing between 14 per cent and 19 per cent solids and The use of sludge furnaces has a significant effect on the the centrate containing 1 per cent solids. The centrate will be types of primary sludge cond itioning which can be used. The returned to the balance tank with overflow from the tank two main primary conditioning requirements are classification being fed to the raw waste water. An anionic polyelectrolyte and drying . Sludge drying is important with furnaces due to will be added to aid solids capture and to reduce the cake the fuel required to evaporate the water from the sludge. moisture content.

Grit and scum removed in the primary processes are to be delivered direct to the sludge burning furnace after dewatering. Grit will be washed and dewatered and fed to the second hearth of the furnace while scum is fed to the first burning hearth.

The cake will then be fed to the sludge furnace. After incineration the remaining ash will be stored in a hopper prior to disposal. The ash will be trucked to land fill disposal through other uses for the ash are being considered .

The C.S.I.R .O. are undertaking research work into the disAs lime precipitation is being used in the primary sedimentation tanks waste nitrified sludge is returned to these posal of nutrient rich sludges and intend examining the sedimentation facilit ies for removal with the primary sludge. effects of applying lime sludges to soils and intend examining The primary sludge is to be fed direct from the sedimentation the effects of applying lime sludges to soils as fertilisers. It is tanks to the classification centifuge. Two methods are avail- proposed to study the soil conditioning and fertilising properable for the classification process either wet or dry classifica- ties of the lime classification centrate and sludge clarification tion. Dry classification can be carried out using air after the cake as well as the primary lime sludge. sludge has been burnt in the furnace. Research work carried However initial research work carried out using raw limed out by Brown and Caldwell and other workers has shown that wet classification is more efficient and a two stage centrifuge sludge from the C S.I.R.O. experimental plant at Lower Plenty process has been adopted at Lower Molonglo as the most has not been encouraging. The major portion of the research programme has now been deferred until the completion of satisfactory process for sludge conditioning . the Lower Molonglo Plant when a greater variety of profive centrifuges are to be installed at the Lower Molonglo cessed sludges and supernatants will be available.

Plant and each will be arranged in such a way as to allow them to perform either a classification or sludge clarification The San Francisco standards are stringent and as Canberra duty. does not suffer from the air pollution stress of this area it is In considering the use of a sludge furnace for the Lower proposed and considered reasonab le to adopt a somewhat Molonglo Plant it became necessary to determine the accept- lower emission requirement. However the design for the able stack emission requirements for the furnaces. Within the incinerators is capable of being modified and operated to A.C.T. at present there are no statutary regulations laid down achieve more stringent standards. to cover emission standards. The Victorian Clean Air Act of Emission quality is controlled by two factors : 1965 and the associated Clean Air Regulations of 1965 provide standards for emissions from industrial plants. (a) Furnace outlet temperature.

However it is expected that the Victorian Environmental (bl Gas scrubber efficiency.

Protection Authority will in the future impose more strict An afterburner will be provided on the gas outlet of the furregulations approaching those now in force in California. naces capable of raising the gas temperature to 760°C. This temperature is required to reduce the concentrations of San Francisco Characteristic Victorian EPA hydrocarbon and carbonyls. It is expected that heating to this Bay Area temperature will not be required under the present emission Max. Concentration Air Pollution Control requirements however it is expected that some heating may District be required to control odours.

Max. Concen.

No darker than Visible Emissions No darker than When gas temperatures must be raised to 760°C-870°C to Ringelmann No. 2 Ringelmann No. 1 meet new standards being considered for the San Francisco 0.23 g/ m3 (S.T.P.) Sulphur Trioxide Bay Area, fuel costs become very high and sludge inciner0.02 ppm (vol) Hydrogen Sulphide 5.0 ppm (vol) ation may become uneconomic unless some of this heat 3 Oxides of Nitrogen 2.29 g/ m (S .T.P.) 225 ppm energy can be recovered . By increasing the existing temperaParticulate matter 0.46 g/ m3 (S.T.P.) 0 .11 g/ m3 (S .T.P.) ture from 420°C to 870°C fuel requirements can be increased 0.5 ppm (vol) Sulphur Dioxide by4½ times. at ground level (stack emission 300 The operation of the afterburner at Lower Molonglo will be ppm (vol)) controlled by the need to meet higher emission standards Hydrocarbons and and to suppress odours.

25 ppm (each) carbonyls Lower Molonglo furnaces are expected to be able to meet The classification centrifuge is expected to recover the following emission requirements for most operating conapproximately 90 per cent of the calcium oxide with the cake ditions.

18

Characteristic

Maximum Concentration

Visible Emissions Particulated Material (at STP) Hydrocarbons-Carbonyls Sulphur Dioxide

Ringelmann No. 1 0.023 g/m 3 25 ppm (vol) (each) less than 300 ppm (vol) (stack emission)

ation of water resources in rivers downstream of these cities.

Meterological studies have been undertaken at the site of the plant and in the surrounding areas. The studies include the examination of temperature inversions and light non dispersive wind effects. lnformatiol"l from these studies .will be used in the operation of the furnaces and the establishment of the necessary emission requirements for the plant.

CONCLUSION

1. In view of Australia's limited water resources the development of inland cities will result in the need for advanced waste water treatment facilities to enable maximum utilis-

ASSOCIATION NEWS South Australia (cont.)

The final meeting for 1974 will be in the form of a Ladies¡ Night. This meeting will be held on Friday, October 25th, at which Mr. R. C. Williams will speak on "Water Treatment for Adelaide".

A short account of the Branch May and August Meetings is given below: Friday, May 31st: Mr. C. J. M. Glover

A singularly interesting address was given by Mr. C. J. M. Glover, Curator of Fishes, South Australian Museum, on "Conservation of Inland Fishes". Mr. Glover detailed some of the problems facing our native freshwater fish. These are all of marine origins recently adapated to the freshwater habitat and rather specialised in their adaptation, from the Eyeless Blind Gudgeon living in wells of the North West Cape region to the Desert Goby which can withstand salinity from distilled water to seawater strength and temoeratures from 40°C to freezing.

The stabilising of the Murray River with dams, having reduced the extremes of temperature, flow and salinity and restricted access, now favours the introduced European species.

Friday, August 23rd: Dr. J.C. Dodd

Dr. J. C. Dodd of Caldwell Conell Engineers Pty. Ltd . presented a paper on "algae harvesting and its use as a cattle fodder" at this Branch Annual General Meeting . A method of harvesting algae was described employing a belt-type filter with integral dewatering and drying. Paper precoat and algae mat was dewatered and dried to form a composite feedstuff, the paper supplying roughage for ruminant livestock and the algae supplying protein and other food values.

Dr. Dodd is continuing pilot scale work on this process at Werribee Sewage Farm , Victoria.

2. Advanced waste water treatment utilising a multi-purpose function from the various process units of the plant in the majority of cases will result in a lower capital and operating cost when compared to those plants using tertiary treatment facilities.

3. The Lower Molonglo Water Quality Control Centre is due to be commissioned for operation in mid 1976 and will offer a first hand opportunity for Australia to examine advanced waste water treatment in operation. This plant is being designed by Caldwell Connell Engineers as consultants to the Department of Housing and Construction for and on behalf of the National Capital Development Commission .

River basin studies which are expected to extend into the operation period of the plant will provide a case study under inland Australian conditions for the quality control of waters downstream of major inland centres of population .

CONFERENCE CALENDAR A.W.W.A. SUMMER SCHOOL Applications have closed for the A.W.W.A. residential Summer School to be held at the Australian National University in Canberra from 3rd to 7th February 1975, on the theme "Water in the Urban Environment".

The School programme comprises 5 days of lectures, workshops and a panel discussion presented by eminent Australian and overseas authorities in the water and wastewater field .

46th A.N.Z.A.A.S. CONGRESS, CANBERRA, JAN. 20-24, 1975 SECTION 5 (ENGINEERING)

This is one of the twenty five sections of the Congress and covers four topics including "Resources". This topic is presented on Monday, 20th January, 1975, under the chairmanship of Mr. N. Body and includes: Future requirements and costs of providing water supply, sewerage and drainage facilities for Australian Urban Development.

Speaker: Mr. Hay, Engineer in Chief M.W.S. - D.B. Sydney.

Rural Versus Urban Requirefllents for water supply in Australia.

Speaker: Mr. Groxford - Chairman M.M.B.W. Future Australian Requir~ments for Energy; 50 year point of view. Speaker: Dept. of Minerals and Energy.

INTERNATIONAL ASSOCIATION FOR WATER POLLUTION RESEARCH 8TH INTERNATIONAL CONFERENCE SYDNEY SEPTEMBER 12-17, 1976

Official Opening: The Opera House Venue: The Wentworth Hotel CONGRESS SECRETARIAT G.P.O. BOX 2609, SYDNEY, N.S.W., 2001.

Telephone (02) 27 6940 Preliminary Brochures and Details regarding Registration and Submission of Papers are available from the Secretariat and from : Dr. M . Flynn, Secretary-Treasurer, I.A.W.P.R. Australian Committee I.A.W.P.R. G.P.O. Box A53, Sydney, 2001 .

All A .W.W.A. State and Federal Secretaries.

The A.W.W.A. is a member of the I.A.W.P.R. and recommends your support for the 8th International Conference.

19

PERSISTENCE OF HIGH DAILY DEMANDS IN AUSTRALIAN WATER SUPPLY SYSTEMS

By B. W. Gould* (Member, N.S.W. Branch; SYNOPSIS A study of the persistence of high daily demands in some Australian water supply systems has been made. This study underlines the importance of considering variations in both climate and type of urban development when planning combinations of trunk mains and storages.

INTRODUCTION

In the design of transmission systems for town water supply, it is often advantageous to combine pipelines and storages (dams or reservoirs) for the sake of economy. When a storage is built at the downstream end of a pipeline, the necessary flow capacity of the pipeline does not have to be as great as the peak demand flow, and hence there can be savings in the cost of the pipeline to offset the cost of the storage reservoir. s requir~s that the Good stewardship of public monie_ system should not only operate without obvious inadequacies, but also be such ' that unwarranted extravagance of design is avoided. As well as ensuring functional adequacy and protecting his public image, the designer should try to avoid overdesign with its consequent wastage of resources of materials and manpower.

Such is the nature of many engineering projects that construction must take place before it is possible to obtain all the data required for a strictly logical design. For example, a water supply system is designed for a demand expected at the end of the design period - some years hence. In spite of the varying degrees of care taken to predict the design demand, the demand for that future time can be verified only long after construction should have been completed .

Uncertainties in design may be reduced by making the best use of all available data.

The likely magnitude and persistence of high demands from a water supply system affect the sizing of economical pipeline-storage combinations. The relative sizes of the peak daily demand and the average peak demands over other time periods will be affected by the type of development in the town, the climate, and the amount and type of industrialisation.

The adoption of "blanket " values for ratios like that of peak weekly flow to peak daily flow, without due regard to circumstances, could give a bias to the estimate of storage for any particular situation. To give an indication of the variability of the magnitude and persistence of peak flows in different localities in Australia, the statistics for a number of towns were examined , and the peak flow pattern compared with the values given by the American Goodrich equation.

THE GOODRICH FORMULA

The Goodrich formula (Ref. 1) for the average daily flow rate during the highest demand for t consecutive days, as a proportion (Pl of the average annual flow rate, is

pt =1 .8t-01 The factor 1.8 implies that the average demand flow on the peak day is 1.8 times the average annual demand flow (i.e. when t= 1 ). In the varied Australian climate, it is well known that the ratio of peak day flow to the annual average flow varies from city to city.

20

The index , -0 .1, is an indication of the persistence of high demand , and implies a constant persistence regardless of location. This does not conform to Australian experience. A higher numerical value of the index would mean that the high demand would probably be short-lived, whereas a lower value would indicate a more persistent high demand. One would expect that in some areas where regular cool changes bring relief from hot, dry conditions, the index would have a higher numerical value than either in areas of summer rainfall where the peak day flow may not be so large, or in inland areas where heat without rain can persist for weeks at a time. It would therefore be improper to apply factors and indices based on American average values to the design of Australian systems - it could lead either to underdesign, or to waste.

DATA COLLECTION

The Authorities supplying water to a number of Australian towns and cities supplied daily consumption records for analysis.

Each Authority which co-operated was asked to supply a continuous daily record of demand extending over a period of from two to five years. Some Authorities supplied continuous records extending over this period , or even over two independent periods each of five years, with practically no missing data. However, some sets of records had omissions because either the measuring equipment had been out of order, or the officer responsible for reading the meter had been on leave, or for some other cause. Most of these omitted brief periods in the records accepted for analysis, were at times of the year when peak flows would not be expected.

Because the method of analysis used required complete records, some substitute values had to be inserted to make up for the missing records. When these missing periods were not in a season when peak flows could be expected , the substitute values were so chosen that the average flow for the missing period was the mean of the average flows for the immediately preceding and following periods of the same length, thus maintaining season trends.

In the cases where no readings were made at weekends, the large Monday reading was divided by three. This could affect the determination of the peak day flow, but there is no simple way to make a correction to take account¡of probable peak day flows at weekends if the records have not been kept.

DAILY FLOW RATIOS

For the purposes of the following analysis, a daily flow ratio was obtained by dividing the flow for each day by an annual mean daily flow rate. Because of the trends caused by population increase and increasing per capita consumption, the annual mean flow could not be taken as the mean flow for the calendar year - if it were, the relativity between the demand ratios for December 31st and January 1st, for example, could be misleading. The annual mean flow was therefore taken , as far as practicable, as the moving 365 day average, with the day in question being the middle day of the period . This could not apply to the first and last 182 days of the record .

For the first and last 182-day periods of the record, a substitute moving average value was obtained in the following way: (al Estimate the ratio between the average flow for the first (or last) 182-day period, and the average flow in the corresponding period in the following (or preceding) year; (bl Obtain the substitute moving average value by multiplying the 365-day moving average for the corresponding day in the following (or preceding) year by the flow ratios for the two corresponding periods.

The daily flow ratios thus obtained constitute a series of numbers based on the daily flow records, but the general trends due to population increase and changed habits of water use as reflected in the 365-day moving average have been removed .

ANALYSIS OF FLOW RATIOS All calculations were carried out using a digital computer.

The flow ratios were examined year by year to find the highest individual one (peak day), and the highest totals for periods of various lengths from two consecutive days to 35 consecutive days.

The Goodrich form of:

2·75

2·50

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Figure 1 - Graph of peak T-day flow ratios, as a function of time.

SymLocation Code bol Adelaide, S.A., 1/7/68-31/ 5/72.

AD AL X Albany, W.A., 1/7/68-30/ 6/ 71.

D Canberra, A.C.T., 1/ 3/ 69-30/ ~ '71 .

C CQ1 0 Canberra & Queanbeyan, 1/1 / o · ·31/12/ 65.

Canberra & Queanbeyan, 1/7 ' c;6-30/6/71.

CQ2 Darwin, N.T., Apr. '67-May '72.

D 0 () Gold Coast City, 1/11/66-31 / 10/ 71 GC (excepting 10/1/69-5/ 2/70). fl Ipswich, Qld., 1/1/65-31/ 12/ 69.

M 0 Melbourne, Vic., 1/7/68-31 /12/71.

NC1 0 Newcastle, N.S.W., 1/1/64-31 / 12/ 66.

Newcastle, N.S.W., 28/12/66-31 / 12/71 .

NC2 Northam, W.A., 1/4/69-30/4/72.

NO p Perth, W.A., May '67-June '72.

•

.

+• •

was used as a model, and the values of A and n determined for the line of best fit for the log of the geometric mean of the annual maxima for the various lengths, and the log of the period of peak flow in days (t).

Graphs of P vs t (19g-log scales) indicated that when the peak day flow was less than about twice the average flow (i.e.

P, 2), the general form of the Goodrich equation was acceptable, but for towns with greater values of P,. the loglog plot was curved.

In figure 1, the plot for Toowoomba (Tl is curved, but the data for this plot included the flow to the reticulation system plus the flow to the service reservoirs. The inclusion of the service reservoirs would tend to reduce the recorded peak daily flows, but would have little effect on the average demands for the peak fortnight, or longer.

Tropical Port Moresby (PM) has the lowest peak dai ly flow to annual flow ratio, and the lowest numerical value of the persistence index.

For all centres with a high peak day flow ratio, the plots tend to be curved, with short-term high demand tending to persist for periods of two or three days, but for longer periods there is a substantial reduction in average flows for maximum consumption periods. Several of the curves are S-shaped.

This could possibly be a result of regular cm,. changes followed by a renewal of hot dry conditions during the seas on of high demands.

Where two separate sets of records for the one town have been examined , there are differences in the characteristic curves for the two sets (see CQ1 and CO2 ; and NC1 and NC2). This shows that an examination of a limited amount of data can give an indication of the general magnitude of the peak flow ratio and the persistence, but the more data that is examined , the more accurate are the conclusions reached. A study of variations on a basis of climatic variations could possibly yield data wh ich could be extrapolated.

Figure 2 shows the relationship between the peak day flow ratios (from the line of best fit), and the mean January rainfal l.

Other parameters may give better correlation, but they are not as readily available as is monthly temperature or rainfall data as given in " Climatic Averages" (Ref. 2). January rainfall was found to give a much better correlation than January temperature. Where information is available, the year to year variations may fit better to a multiple regression using, for example, number of consecutive rain-free days, and temperature and humidity on these days. As would be expected, those areas having a high summer rainfall do not have such relatively high peak flows as those with a dry summer, even though they may have a high average temperature. The points which deviate most markedly from the general trend are those for Newcastle and Sydney South Coast (including Wollongong) which have low ratios (NC1 , NC2, SSC). and Canberra and the. Gold Coast which have higher ratios than the general trend (C, GC).

PM R

+

s

+

SSC

T

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•

Port Moresby (P.N.G.) Richmond (Sydney M.W. S. & D.B.) 1/ 7/ 61-30/ 6/ 65.

Sydney Main Supply, 1/ 7/ 60-30/ 6/ 65.

Sydney South Coast (Wollongong etc. Sydney M.W.S. & D.B.) 1/7/60-30/ 6/ 65.

Toowomba, Qld., 1/7/ 67-30/6/72 (Residential & Service Reservoirs) 21

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1--------------~---'2.00 50 100 150 o January Average Rain (mm)

Figure 2 - Plot of peak day flow ratio vs. the average January rain. (Code as for figure 1 ).

Probable causes to account for some of the discrepancy could be that Newcastle and Wollongong each have industries which use large amounts of water regardless of the season , and hence the ratio between peak and average flows would be expected to be less, whereas Canberra and the Gold Coast are areas with little industry, but perhaps a morethan-average amount of parks which require watering during the summer period. In addition, the Gold Coast could have a fluctuating population of tourists, which would tend to increase the peak flows during the summer.

Figure 3 is a plot of the peak day ratio and persistence index for the lines of best fit calculated for the several towns and cities examined. There is a general tendency for the persistence index to increase with an increase in the peak day ratio. The three sets of records which appear to depart most from the general trend are those for Northam and Perth (W.A.), and Adelaide (S.A.). In these places the persistence index is less than would be expected from the peak day ratio, indicating more prolonged periods of high demand, as compared with other places with a similar daily peak flow ratio.

NEW WATER MONITORING STATION INCORPORATES AUTOMATIC CLEANING OF SENSORS AND CALIBRATION Fully engineered to run unattended for long periods, independently or within networks for total waterway surveillance.

Current operating experience with Philips automatic water pollution monitoring station confirms the major contribution it can make in the field of water quality management.

Wide range of parameters measured Automatic measure of any combination of pH, Redox, pCI, conductivity, 22

1 0

0¡04

0-08

0¡12

Persistence Index (rll

Figure 3 - Plot of peak day flow ratio vs. the persistence index, n, in the formula Pt= At-n.(Code as for figure 1 ).

CONCLUSIONS

The pattern of peak flow for various lengths of time shows considerable variation over the continent of Australia, where climatic conditions span from tropical areas to cool temperate areas. Local variations can be induced by the degree of industrialization or the interest of the inhabitants in gardening , or fluctuating tourist populations.

Where daily records of water consumption have been kept over a considerable period, they may be very useful in determining the local trends of persistence of high demands, for use in designing future extensions to the supply system in an economical manner. Although the cost and trouble of record collection and analysis may appear to be considerable, it is negligible in comparison with the costs of trunk main systems, and the savings that may be made by basing designs on reliable local data.

REFERENCES

1. Steel. E. W. , Water Supply and Sewerage, McGraw-Hill, New York (1960), p. 18.

2. Climatic Averages Australia. Comm. of Aust. , Bureau of Meteorology, Melbourne, 1969, 108pp.

By B. W. Gould* (Member, N.S.W. Branch)

* Associate Professor in Civil Engineering, The University of New South Wales.

dissolved oxygen , temperature and turbidity, also level/flow and meteorological parameters can be incorporated.

Sampling System

Along with the station, Philips provide the complete sampling system, drawing water from a constant depth by a submersible, floating pump rising and falling in a plastic cylinder, with guards to prevent debris reaching the pump.

Fully Automatic

Automatic cleaning sensors by ultrasonic and calibration of sensors enables a station to run unattended for periods of several weeks.

Optional sample collection/storage

A separate unit can be installed within

the station to collect samples at fixed intervals, or proportional to an external variable level or flow, then store these under refrigerated conditions for eventual investigation by laboratory analysis. Capacity is twelve 2000 cc containers-. ti lied in turn.

Emergency alarms can also be signalled to a measuring centre enabling preventative action to be taken.

Single station and Network operation

Measurements can be recorded 'instation' on charts or magnetic tape; alternatively transmission to a remote measuring centre is available.

Total waterway surveillance uses a network of stations connected to a measuring centre.