Volume 18, No. 6, December 1991
JOURNAL OF THE AUSTRALIAN WATER &WASTEWATER ASSOCIATION
FEDERAL SECRETARIAT PO Box 388, Artarmon 2064 Telephone (02) 413 1288 Facsimile (02) 413 1047 Office Manager - Margaret Bates
FEDERAL PRESIDENT Peter Norman, Phone (08) 226 2249
EXECUTIVE DIRECTOR Peter Hughes, Phone (02) 413 1288 Facsi mile (02) 948 1746
FEDERAL SECRETARY Greg Cawston, Phone (042) 29 0236
FEDERAL TREASURER John Molloy, Phone (03) 615 5991
BRANCH SECRETARIES Canberra, ACT Peter Cox, PO Box 306, Woden 2606 Phone (062) 498 522 New South Wales Nick Apostolidls, GCEC, 39 Regent Street Railway Square 2000 Phone (02) 699 9922 Victoria John Park, C/- Water Training Centre, PO Box 409, Werri bee 3030 Phone (03) 741 5844 Queensland Don Mackay, PO Box 412, West End 4101 Phone (07) 840 4844 South Australia Nell Palmer, Cl- State Water Laboratories, E&WS Private Mall Bag, Salisbury 5108 Phone (08) 381 0268 Western Australia Steve Gibson, CMPS, 200 Adelaide Terrace Perth 6000 Phone (09) 325 9366
CONTENTS 5 4
My Point of View President's Message It Seems to Me 5 Association News 11 IAWPRC News 12 Industry News
14 Maroochy Regional Conference and Operations
Features 16 Focus on some North Queensland Water Quality Issues A. Moss and J. Bennett 20 Clean Water Oxygenation and Mixing Tests for a Diffused-Air, Extended-Aeration Plant J. Charlton, K. Barr and S. Low 25 Design of Nitrogen Removal Plant with Sequencing Batch Reactor Capability J. Charlton 29 Water Quality in Lake Tinaroo, Atherton Tablelands, North Queensland J. Littlemore, M. MacKinnon, G. Sadler 32 Ecologically Sustainable Water Clarification at the Clear Water Lagoon, Mt. Isa T.J. Wrigley, P.O. Farrell and D.J, Griffiths 35 Water Supply Peaking Factors: Effect of Demand Management M. Clewett and L. Applegren 40 AWRC Water Technology Committee Report 42 Book Reviews 43 Plant, Products and Equipment 44 Conference Calendar
Tasmania Annette Ferguson, GPO Box 503E, Hobart 7001 Phone (002) 28 2757 Northern Territory Lindsay Monteith, PO Box 351, Darwin 0801 Phone (089) 81 5922
EDITORIAL CORRESPONDENCE E.A. (Bob) Swinton, 4 Pleasant View Crescent, Glen Waverley 3150 Office Phone-Fax (03) 560 4752 Home (03) 560 9306
ADVERTISING Ann Sykes-Smith, Applta, 191 Royal Parade, Parkville 3052 (03) 347 2377 Fax (03) 348 1206
White-water rafting is becoming a popular tourist attraction on the Tully River in North Queensland. The river has its source in the area of the Cardwell Range listed as World Herrtage, and though a series of falls, flows down to the coastal plains around Tul ly and empties into the Great Barrier Reef lagoon . The Tully River's catchment is located in the wettest area of the NorthEastern region and its potential for hydro-electricity generation with minimal impact on the environment is currently being assessed . The coastal plains are extensively cultivated for sugar cane which is processed at a mill adjacent to the township of Tully. Protecting the environmental values of this and other rivers from point and diffuse sources of pollution is the chal lenge facing the Queensland Department of Environment and Heritage. (see paper, page 16).
PUBLICATION Water Is bl-monthly. Nomlnal distribu tion times are the third weeks of February, April , June, August, Octobe r, December.
PRODUCTION EDITOR John Grainger, Appita, 191 Royal Parade, Parkville 3052 (03) 347 23TT Fax (03) 348 1206
The views expressed by the contributors are not necessarily endorsed by the Australlan Water and Wastewater Association . No reader should act or fall to act on the basis al any materlal contained herein. No responslbillty Is accepted by the Association , the Ed itor or the contributors for the accuracy of Information contained In the text and advertisements. The Australian Water and Wastewater reserves the right to alter or to omit any arllcle or advertisement submitted and requires indemnlly from advertisers and contributors against da mages which arise from material publlshed . AU material In Water Is copyright and should not be reproduc ed wholly or In pa rt without the written permiss ion ol the editor.
WATER December 1991
Focus on some North Queensland Water Quality Issues by A. MOSS and J. BENNETT SUMMARY This paper focuses on a range of water quality issues of relevance to the north-eastern coastal region of Queensland. Results of water quality investigations carried out by the Queensland Department of Environment and Heritage together with some data from other sources is presented and discussed. In addition to the regional focus, the major theme running through the paper is the contrast between the impacts of point and diffuse sources of pollutants. It is concluded that while point sources of pollutants are largely under control, much work remains before successful management of diffuse sources is achieved.
Andrew Moss, BSc(Hons), MSc is a Senior Environmental Officer with the Qaeensland Department of Environment and Heritage. He Joined the Queensland Government in 1974 and has since been involved in a wide range of water quality investigations.
INTRODUCTION In Queensland, powers for the control of water pollution and maintenance of environmental water quality are contained in the Clean Waters Act of 1971. The Act is administered by the Queensland Department of Environment and Heritage (DEH) (prior to 1989, the Water Quality Council of Queensland (WQC)). This paper draws on the experiences and results of water quality management and monitoring to focus on some important water quality issues in the north-eastern region of the State.
THE NORTH-EASTERN REGION AND ITS WATERS
John Bennett is a Senior Environmental Officer in the Department of Environment and Heritage. A civil engineering graduate of the University of Queensland, he went on to obtain his MSc in environmental engineering from the University of Newcastle-upon-Tyne in the UK. He has had 17 years experience in water quality investigations, including the application of mathematical modelling to these studies.
The region under consideration, (Fig. !), is the coastal fringe of North Queensland extending from the Burdekin River north to the i.,:...;: c,,
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CATCHMENT USES AND WATER QUALITY
The North-eastern Queensland region
WATER December 1991
Mossman River. In the north of the region, steep coastal ranges lie within a few kilometres of the coast while to the south, the main ranges are further inland and less steep. The region's climate is typified by wet summers and dry winters and stream flows reflect this pattern. Detailed discussion of hydrology is given in Hausler (1991). Mean annual rainfall isohyets, (Fig. 1), contrast the heavy coastal rainfall north of Ingham and the drier area to the south. In keeping with the region's topo~raphy, coastal streams north of Townsville are short and relatively fast flowing, entering estuaries that are also short but which nevertheless receive significant tidal influence due to a spring tidal range of up to three metres. While most larger streams are perennial, there is considerable annual variation. In dry years, flows can fall to very low levels during the August to November period. South of Townsville lies the Burdekin River which , unlike the coastal streams further north , drains an extensive inland catchment of 130 000 km2 • Streamflows in the Burdekin reflect lower and less reliable rainfall in its catchment but, due to its size, the Burdekin contributes a significant proportion of the total riverine inflow to coastal waters in this region. Offshore lies the Great Barrier Reef. The main reef is separated from the coast by the Great Barrier Reef Lagoon. This is about 50 km wide at Townsville narrowing to less than 25 km at Cairns. In low flow periods, river inflow has little impact on the lagoon but following major flood events, lowered salinity has been detected at offshore reefs (Wolanski and van Senden, 1983). Sediment studies indicate that particulates carried into the lagoon during floods are largely deposited within 15 km of the shoreline (Johnson and Carter, 1988). The region's major industry is sugar cane which is grown throughout the region and processed to raw sugar at local mills. The rapidly developing tourist industry is the region's other main income source, one major attraction being the Great Barrier Reef. This fact and the formation of two bodies, the Great Barrier Reef Marine Park Authority and the Australian Institute of Marine Science have served to focus much greater attention on the Reef area in recent years. Populations in the region are low and largely concentrated along the coast. The major urban centres are Townsville (pop. 110 000) and Cairns (pop. 80 000).
The influence of catchment land use on downstream water quality is now well recognised. Until recently, in Queensland, limited water quality monitoring resources have been focussed largely on the effects
of point source pollutants. However, a study carried out by DEH in the early 1980s, aimed at quantifying the effects of alluvial tin mining on turbidity in the Herbert River, provides some insight into the effects of changing land use on water quality. · Figure 2 shows the results of intensive sampling for suspended solids (SS) carried out in January and February 1981 (i.e. the wet season) at three sites in the Herbert River catchment. The sites were situated below three different sub-catchments (catchment areas shown in brackets): (1) the Millstream (325 km 2), a largely undeveloped forested area, (2) the Wild River (283 km2), an area of extensive alluvial tin mining and (3) the Stone River (490 km 2), a lowland cane farming area. The data show clear differences in SS values between the relatively undisturbed Millstream catchment and the other two catchments. It suggests that tin mining and agricultural practices have both res ulted in substantial increases in downstream particulate loads. The main conclusion from the study (WQC, 1981) in regard to tin mining was that it was only one of a number of factors affecting overall turbidity in the lower Herbert River. In general terms, the results are indicative of the effects of catchment development on water quality, and illustrate the potential for suspended particulate loads to be increased several fold. Associated with such particulates would be a range of pollutants related to specific catchment activities. Obviously, the main impact of diffuse sources on water quality would be felt during larger runoff events. During low flow periods, reduced dilution and the absence of catchment effects mean that impacts from point source discharges become more significant. The relative significance of the impacts of diffuse and point source pollutant loads is one focus of this paper.
SUGAR MILLS AND DISSOLVED OXYGEN Thirteen sugar mills are located between Ayr and Mossman. These mills process the harvested cane to raw sugar during the cooler, drier winter months of May to November. In the early 1970s, poorly treated and managed discharges of various waste streams from sugar mills were causing significant organic pollution in a number of streams, resulting in low dissolved oxygen (DO) levels and commensurate effects on the biota (Pearson and Penridge, 1979). A number of fish kill incidents were attributed to this cause. A gradua l but persistent up gradi ng of waste treatment andhousekeeping practices has greatly reduced pollution levels but, in a few mills, the discharge of cooling water remains a problem. Cooling water is used in the sugar crystallisation stage and, during this process, it entrains sugar juices and vapours. This results in typical effluent biochemical oxygen demand (BOD 5) values of 20-100 mg/ L. The other potential effect of cooling water discharges is an elevation in temperature of the receiving water. Cooling water is generally taken from an adjacent river. Some mills use a "single pass" through the mill and discharge back to the river. For a number of reasons, including demand for water exceeding the available yield of the river, recirculating cooling water systems using cooling towers or spray ponds have been introduced into the majority of mills. For most mills, this results in a small wastewater stream from the cooling water circuit which can be treated by conventional methods and/ or land disposal. However, some mills have a partially recirculating cooling system where river water
provides substantial make-up to the circuit. These systems can result in a more concentrated effluent so that organic loadings to the river are similar to those of "single pass" mills. Most mills are located adjacent to perennial streams or their estuarine systems. The impact of discharge of organically enriched loads on DO levels in these streams usually has two phases. In the riverine phase, a classical DO sag occurs downstream of the discharge, the degree and extent of DO depletion depending on available dilution and river velocities. Typically, organic loadings have not been completely exerted by the time the waters reach the estuarine phase of their travel. Here, downstream penetration of the loading is slowed by tidal influence. This results in greater organic loadings per unit length of river and gives the DO curve a greater slope as well as translating it up and down the river due to the tidal excursion. Figure 3 shows a typical DO sag curve in the South Johnstone River due to discharges from the "single pass" mill at South Johnstone and the "partially recirculating" mill at Mourilyan. The coincidence of the sugar mills' crushing season with North Queensland's dry winter months exacerbates DO depletions and supports the need for proper management of mill wastes. Mill discharges are thus a good example of point discharges dominating water quality during low flow periods. During the wetter months, DO levels may be significantly affected by diffuse sources. Figure 4 compares wet and dry weather DO profiles in the Mossman River estuary, north of Cairns. The "low flow" profile exhibits a typical dry weather DO sag downstream of the Mossman mill discharge. The "high flow" profile was measured before the crushing season (i.e. no mill discharge) and shortly after a major flow event. It shows the impact of organic loads, washed in from the catchment, exerting their oxygen demand during their passage through the estuary. Such wet weather effects are however transient and the dry weather DO profile re-establishes soon after the runoff recedes.
SEWAGE AND NUTRIENTS Sewage treatment in North Queensland is generally required to be to secondary standard but with no requirement for nutrient removal. The largest plants are at South Townsville with a connected population of 80 000 equivalent persons (EP) and two plants in the
So ulh John s t on e
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Es tuarin e Secti on
So uth Johnstone River dissolved oxygen profile
Ja n 2
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Feb 2 1
Suspended solids levels in Herbert River sub-catchments
High Flow Pe r iod
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Dis tance from Mouth (km) De pa rtme nt
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or Environme nt
Mossman River dissolved oxygen profiles WATER December 1991
Cairns area each around 40 000 EP. The majority of discharges are to estuarine or inshore coastal waters and in most cases these are located such that there is sufficient dilution and dispersion to preveJlt major effects on DO. Treated sewage discharges result in localised increases in nitrogen (N) and phosphorus (P) concentrations. Because local tidal waters are not suited to the growth of attached algae, the main impact of nutrient enrichment is increased phytoplankton production evidenced by increases in chlorophyll concentrations. In most cases, there is sufficient dilution and dispersion to prevent formation of significant blooms. For example, recent data from Trinity Inlet, Cairns (Cairns City Council, in prep.) indicated consistent mean chlorophyll levels (around 4 µg / L) throughout the Inlet, with no significant increase in the vicinity of the South Cairns sewage treatment plant (STP) discharge. In contrast, the STP discharge at North Townsville, to a poorly flushed tidal tributary of the Bohle River, results in frequent localised algal blooms. DEH has a policy of encouraging the reuse of sewage effluent and this has been assisted by the boom in the tourism industry. For example, effluent from the Northern Beaches STP north of Cairns is now completely reused on a tourist development golf course. Most of the effluent from the discharge to the Bohle River will be disposed of to land in the near future and a significant proportion of the South Townsville discharge is now being used as pasture irrigation. Nutrients and the Reef Sewage discharges are frequently cited in relation to the controversial question of nutrient enrichment of reef lagoon waters. To put this issue into perspective, it is useful to consider both the magnitude and potential effects of nutrient loads from all sources. Figure 5 shows estimated magnitudes of annual nutrient loadings to the reef lagoon from the following sources within the study area: (1) diffuse loads from mainland catchments, (2) mainland sewage discharges and (3) island resort discharges. Sources (2) and (3) can be quantified fairly accurately but estimates of diffuse loads are subject to much greater uncertainty. Measurements of nutrient loads discharged from the Burdekin River during a 30-day high flow period in January-February 1981 (DEH/ Queensland Department of Primary Industries data) gave values of 6500 tonnes of N and 2650 tonnes of P. Cosser (1988) estimated mean annual P loads from rivers between Cooktown and Innisfail at 9400 tonnes while recent field studies, (Mitchell et al, 1991) indicate somewhat lower values. More detailed studies are currently under way but it is clear from existing data that catchment loads are in the range of thousands to tens of thousands of tonnes compared with hundreds of tonnes from mainland sewage discharges and tens of tonnes from island resort discharges. Even though nutrients in sewage are more readily available, catchment sources are, overall, far more significant. Regarding effects on coral reefs, the small sewage discharges from resort islands may potentially have localised impacts, although studies at Hayman Island (Steven and van Woesik, 1990) indicate such impacts may be quite limited. Mainland sewage discharges are considerably larger but are generally too -distant from reefs to have direct impacts. It has been suggested that nutrients from Townsville's STP discharge to Cleveland Bay just south of the city could directly impact fringing reef areas on Magnetic Island. A recent grid survey of inorganic nutrients (DEH data) detected increased P
:, A A
A A 0
N Load., PLoad.,
Table 1 Mean metals concentrations in sediments from North Queensland rivers RIVER (Dlsl. from mouth in km) (No. samples)
S. Johnstone (3.9) (9) N . Johnstone (4.5) (9) N. Johnstone (13 .5) (9) Tully (9.0) (8) Mulgrave (2 .0) (10) Mulgrave (8.9) (10) Barron (12.9) (14)
METAL CONCENTRATION• Hg
(• Ail metals concentrations are expressed as total metal mg/kg (dry weight) in the < 0.063 mm sieve fraction except Hg which is the concentration mg/ kg (wet weight) in the total sample)
Increases in sediment metals levels above background are often detected in association with proximity of urban catchments. Miller (1987), in a survey of sediments of Trinity Inlet, Cairns, detected highest levels of Zn and Pb (peak values 224 mg/kg Zn and 62 mg/kg Pb) adjacent to the Cairns urban area with much lower levels in the non urbanised southern areas of the Inlet. Extensive surveys of metals in waters, sediment and biota in the Townsville region (Burdon-Jones et al, 1977) found that highest levels of a number of metals occurred in Towns ville Harbour, which receives runoff from much of the adjacent Townsville urban area. One potential point source of metals in North Queensland is the Queensland Nickel Refinery discharge to Halifax Bay, north of Townsville. However, studies of metal concentrations in sediments and biota (Burdon-Jones et al, 1977; Carey, 1981) were unable to detect any significant impacts from the discharge. In practice, the discharge is highly intermittent due to extensive water re-use and to evaporative losses from tailings dams .
There is a range of aquaculture operations in North Queensland but the most commercially important are the culture of the brackish water prawns, Penaeus monodon and P. esculentis. The number of operations increased sharply between 1985 and 1990 but this rapid expansion has slowed as anticipated profits have failed to materialise.
Fig, S - Estimated magnitudes of annual nutrient loadings to the Great Barrier Reef lagoon
WATER December 1991
HEAVY METALS DEH has monitored heavy metals levels in the sediments of a number of rivers. Tobie 1 shows results for a range of waters not subject to significant anthropogenic influence. ·It is clear from these that there is considerable variation in background sediment metals levels. Concentrations in the Johnstone River in particular, considerably exceed those in other areas due, it is thought, to its highly basaltic catchment. This observed variation in background values underlines the need for care in interpretation of results.
Department ot Bnvirorunen1 and Hcrita,ae
concentrations in the Bay up to 10 km frolll the outfall. However no measurable elevations in nutrient concentrations in the reef areas were found in this survey. In general, nutrients from mainland discharges would be incorporated into inshore biomass well away from reef areas and the most legitimate concern with such discharges is their impact on inshore waters. In terms of effects over wider areas of the reef, mainland sewage discharges are best considered as a limited sub-set of overall mainland inputs. Settlement of North Queensland has clearly resulted in considerable increases in mainland diffuse loads of particulates and nutrients to the reef lagoon. Walker (1991) suggests the effect of increased inputs from mainland rivers would be to drive reef species back from the coast, but that as yet, the extent of this effect (metres, kilometres, tens of kilometres) is not well understood. Furnas (1991) concluded that, on the basis of data sets collected by the Australian Institute of Marine Science, there is no evidence that shelf waters of the Great Barrier Reef system are eutrophied to any appreciable degree at this time. Nevertheless, while there is no clear evidence of widespread impacts on the reef, efforts to contain and reverse the increase in catchment loads remain highly desirable, not only in terms of potential effects on the reef, but equally in terms of effects on freshwater, estuarine and inshore coastal systems.
The favoured location for prawn aquaculture ventures is near the mouth of a small creek. Estuarine areas of the creek provide saline waters for normal flushing of ponds (5% or more per day) while damming of upstream creek areas can provide the required freshwater makeup. Culture techniques are still under development but in many cases, ponds are maintained at high chlorophyll levels, up to 100 µg / L. Because culture operations involve discharge to State waters, a licence from DEH is required. Problems that may arise from aquaculture operations include (1) With large operations (some are planned to involve a hundred or more ponds) located on small creeks, the sheer volume of water required for exchange purposes has the potential to completely alter the natural hydrodynamic behaviour of creeks, with associated effects on the bed and biota. (2) Discharges from aquaculture operations can impose significant organic loadings on receiving waters. Twelve months monitoring of the effluent from one large operation in North Queensland gave BODs values in the range 1-20 mg/ L, with a mean of 8.5 mg/ L (n = 30). Much of the organic load from such discharges consists of algal cells. DEH monitoring results (Fig. 6) from Saltwater Creek, north of Townsville, show algae rich water from a local aquaculture discharge accumulating in the creek under neap tide conditions. This occurred because, in common with many small North Queensland creeks, tidal exchange during neap tide periods is severely restricted by a sand bar at its mouth. Prawn harvesting usually involves completely draining ponds with considerable disturbance of sediments. BODs levels in excess of 30 mg/ L have been recorded in drainage waters (Lotocki, 1987) so that, if untreated, total loads entering creeks over short periods could be considerable. Provision of settling ponds with a minimum of 24 hours retention for harvest drainage waters is included in DEH licence conditions. (3) Aquaculture discharges are often nutrient enriched (mainly in the organic form) compared to source waters so that the potential impacts of increased nutrient loading on receiving waters need to be considered . (4) Damming of creeks for freshwater supply may be required. Apart from affecting flushing characteristics, poorly designed and located dams may limit the movement and breeding of estuarine species. If culture techniques can be successfully refined, there is the potential for a very large aquaculture industry in North Queensland which will need proper management to prevent impacts on large numbers of creeks.
MICROBIOLOGICAL WATER QUALITY The National Health and Medical Research Council have recently published guidelines (NHMRC, 1990) for microbiological criteria for primary contact recreation waters. Under normal low flow conditions, virtually all recognised recreational waters in North Queensland would meet these criteria. Treated sewage discharges have been located away from recognised recreation areas. In contrast, under high flow conditions, microbiological contamination from diffuse catchment sources can result in some waters exceeding these criteria. Figure 7 shows faecal coliform values from three sites in the Barron River estuary in the vicinity of the North Cairns treated sewage discharge. Under low flow conditions, faecal coliform values are well within primary contact criteria limits (median < 150 colonies/100 mLs) but under high flows, faecal coliform values in excess of 800 colonies/ 100 mLs have been recorded. Interpretation of the significance of the high faecal coliform levels associated with stormwater runoff is difficult due
.......................... ···········• ························································
············- ································· ..................... • ........................... . ................................................ 0
1.5 2 Tidal Range [ml
............. ....................................................................................... ······•················••·····
. . .
• . .......................
20 25 Salinity (g/1)
Depal1ment a Envlronmern and Heritage
Fig. 7 - Faecal coliform levels at three sites in the lower Barron River estuary under low flow (high salinity) and high flow (low salinity) conditions (1984-1991)
to the lack of epidemiological data. Clearly however, the results of microbiological testing need careful interpretation in the light of prevailing conditions.
CONCLUSION The main conclusion is that while point sources of pollutants are to a large extent under control, runoff from catchments continues to impose large loads of particulates, organic matter and nutrients onto freshwater, estuarine and coastal ecosystems. In addition, metals and other contaminants from urban catchments and agricultural chemicals from rural areas have potential to impact on these ecosystems. The challenge is to control these diffuse pollutant sources, both in North Queensland and in other areas of the State.
ACKNOWLEDGMENT The authors acknowledge the permission of the Director and help of members of the staff of the Division of Environment.
REFERENCES Burdon-Jones, C., Denton, G.R.W., Jones, G .B. and McPhie, K .A. (1977) . Metals in marine organisms . Part 2, Regional and seasonal variations. Department of Marine Biology, James Cook University of North Queensland, Townsville . Cairns City Council (in prep). Environmental quality of the Barron River and Trinity Inlet. Report by the Working Group. , Carey, J. (1981). Nickel mining and refinery wastes in coral reef environs . Proc. Fourth Int. Coral Reef Symposium, Manila . Vol 1, 137- 146. Cosser , P.R. ( 1988). Phosphorus loading to the northern Great Barrier Reef from mainland runoff. Workshop on nutrients in the Great Barrier Reef region. Great Barrier Reef Marine Park Authority Workshop Series, No 10, 39-43. Furnas, M. (1991). Nutrient status and trends in waters of the Great Barrier Reef Marine Park . In: Land use patterns and nutrient loading of the Great Barrier Reef region . Sir George Fisher Centre for Tropical Marine Studies, James Cook University , Townsville. pp 162- 179. Hausler, G. (1991). Hydrology of North Queensland coastal streams and their groundwaters. In : Land use patterns and nutrient loading of the Great Barrier Reef-region. Sir George Fisher Centre for Tropical Marine Studies, James Cook University, Townsville. pp 90- 107 . Johnson, D.P. and Carter, R.M. (1988) . Sedimentary evidence on the seaward limit s of suspended materials from rivers . Workshop on nutrients in the Great Barrier Reef region . Great Barrier Reef Marine Park Authority Workshop Series, No 10, 23- 26. Lotocki , W. (1987). Water quality implications of aquaculture projects in Australia . Unpublished report of Queensland Department of Environment and Heritage. Miller, G . (1987) . Effects of waste disposal activities on water quality in Trinity Inlet, Cairns. Institute of Applied Environmental Research , Griffith University , Queensland. Mitchell, A., Rasmussen, C., Blake, S., Congdon, R., Reghenzani, J ., Saffigna, P. and Sturmey, H. (1991). Nutrient concentrations and fluxes in North Queensland coastal rivers and streams. In: Land use patterns and nutrient loading of the Great Barrier Reef Region. Sir George Fisher Centre for Tropical Marine Studies, James Cook University, Townsville. pp 39- 52. National Health and Medical Research Council (1990). Australian guidelines for recreational use of water. Australian Government Publishing Service. Pearson, R.G. and Penridge, L.K. (1979) . An ecological survey of selected rivers in Queensland . Department of Zoology, James Cook University of North Queensland, Townsville . Steven, A . and van Woesik, R. (1990). A multi-disciplinary examination of the Hayman Island fringing reef:influence of a secondary sewage discharge. Report to Great Barrier Reef Marine Park Authority . Water Quality Council of Qld. (1981) . Herbert River turbidity Study - Interim Report. Report to 95th Meeting of WQC. Walker, T .A. (1991). Is the Reef really threatened by chronic pollution? Search, Vol 22,4. Wolanski, E. and van Senden, D. (1983). Mixing of Burdekin River flood waters in the Great Barrier Reef. Australian J. of Mar. and Freshwater Res. 34, 49- 63 .
Depar1menl of Environment and Hernage
Fig. 6 - Saltwater Creek chlorophyll a levels under a range of tidal conditions WATER December 1991
Clean Water Oxygenation and Mixing Tests for a Diffused-Air, Extended-Aeration Plant by J. CHARLIDN, K. BARR and S. WW ABSTRACT Commissioning of the aeration system has been completed for the Waco! Wastewater Treatment Plant with the application of standard clean water oxygenation and mixing test procedures. The treatment plant employs an extended aeration process utilising a concentric circular basin configuration, with separated diffused air and propeller equipment to produce oxygenation and mixing capability. The novel process configuration has produced high oxygenation transfer efficiencies with an independent velocity pattern around the basin. Nitrogen removal is to be effected by an internal recirculation system between the concentric zones of the aeration basin, which -does not consume additional power. A test procedure for determining the hydraulics of the recirculation system was produced. This paper describes the test methodologies applied, and the impressive results associated with the oxygenation efficiency, mixing and recirculation hydraulics of the aeration system. In particular, clean water oxygenation efficiencies of up to 4 kg 0 / kW.hr were measured during the commissioning period.
All authors are employed in the Department of Water Supply and Sewerage of the Brisbane City Council. John Charlton is a chemical engineer with the Projects Design Section. He has spent three years in the Sewerage Operations Branch and six years in the Planning and Design Branch, being primarily involved in the detailed design of the Gibson Island and Waco/ Wastewater Treatment Plants.
Keith Barr is currently the Supervising Engineer for Sewerage Planning with the Investigation and Planning Section. He has previously been involved in the design, commissioning and operation of a number of wastewater treatment plants.
INTRODUCTION The Brisbane City Council has recently designed, constructed and commissioned Stage 1 of Waco! WWTP (Charlton, 1991) which is an extended-aeration plant with high energy efficiency. Clean water oxygenation efficiencies of up to 4 kg 0 / kW.hr (wire to water) were measured during commissioning. The first stage is sized for an equivalent population of 15 000 e.p. and was commissioned in December, 1990. Stage 2, also designed for 15 000 e.p. is currently programmed to be commissioned in 1992 and together, Stages 1 and 2 will be operated as a module with a total e.p. of 30 000. The plant is an extended-aeration system utilising a "Rotoflow" recirculation configuration for nitrogen removal. Each aeration basin consists of two concentric zones in a novel circular configuration. The aeration system for each stage consists of one circular basin, and the two stages will be interconnected to allow sequencing batch reactor operation. The source of oxygenation is fine bubble diffused air with a separate mixing system to generate the circulation velocity of the mixed liquor. With new plant designs, it is considered most important to specify the two key design characteristics of oxygen transfer and circulation velocity and that these be measured in clean water to determine equipment acceptance.
PLANT DESCRIPTION The aeration basins at Waco! consist of an inner anoxic zone for denitrification surrounded by an outer aerobic annulus for nitrification and removal of carbonaceous material. Influent wastewater and return activated sludge are initially mixed in a contact selector tank before entering the anoxic zone of the aeration basin. The flow then passes into the aerobic zone via a port in the wall separating the two zones. After oxidation, a portion of the flow reenters the anoxic zone via a recirculation port. No recirculation pump station is necessary, thus avoiding the associated power costs. Submersible propeller mixers produce a circulation velocity in the anoxic and aerobic zones to maintain the mixed liquor solids in suspension. The propeller mixers are of the large diameter, slow speed type, with adjustable, backward sloping blades. High speed centrifugal blowers produce air for the aerated annulus, which is delivered via several hundred pairs of fine bubble cylindrical rubber membrane diffusers in each 4.5 m deep basin. These diffusers are mounted on 20 independent and removable air drop pipes which facilitates maintenance of individual diffusers without significantly affecting the aeration performance. The propeller and diffuser systems have been built in Australia by Aquatec Maxcon Pty Ltd, under licence from GVA mbH of West Germany. The air blowers were manufactured by HY Turbo of Denmark. 20
WATER December 1991
Stuart ww is a civil engineer with the Projects Design Section. He has spent 12 months in the section, being primarily involved in the commissioning of the Waco/ Wastewater Treatment Plant.
The Brisbane City Council performed the process design, with the aeration equipment being designed and supplied by Aquatec Maxcon Pty Ltd. A schematic of the aeration system is shown in Figure 1.
OXYGENATION TEST Purpose of Test The Brisbane City Council had determined an actual oxygenation requirement (AOR) of 280 kg 0 2 /hr for the aeration process which translates to a standard conditions oxygenation rate (SOR) of 420 kg 0 2 / hr in each of the aeration basins. The SOR is twice the MIXED LIQUOR TO CLARIFICATION
ANOX IC ZONE
RE'I\JRN ACTIVATED SLUDOE
Fig. 1 -
Wacol WWTP aeration system
normal requirement for such a process, as the Waco! Plant has been designed to allow sequencing batch reactor operation when Stage 2 is commissioned. To determine the SOR, oxygenation tests were specified so that the oxygenation capacity of the aeration equipment could be translated to standard conditions of 20°C, 1 atm pressure and clean deoxygenated water. The clean water tests were to be in general accordance with the American Society of Civil Engineers, "Measurement of Oxygen Transfer Rate in Clean Water". (1984) One test was required to ensure that the aeration equipment met the specified SOR under maximum conditions for the sequencing mode of operation, and two tests were performed to check the maximum SOR requirements for the normal unsequenced mode of operation. A further test was required to ensure the constraint of a 3:1 turndown ratio of the maximum SOR in the normal mode of operation. The requirements for oxygenation and energy efficiency are given in Table 1. Table 1 SOR and Energy Efficiency Requirements SOR
Air Flow Per
No. of Blowers
Guaranteed Energy Efficiency
Maximum (SBR Mode) Maximum (Normal Mode) Minimum
420 kg/ hr
6000 m3/ hr
3.39 kg O/ kW.hr 3.59 kg O/ kW.hr 3.01 kg O/ kW.hr
210 kg/ hr
3000 m3/ hr
70 kg/ hr
1000 m3/ hr
Non-linear regression is employed to fit the eQuation to the dissolved oxygen profile to obtain estimates of kL¾ and C,. An example of the fitted curve is shown on Figure 3. C Note that the above equation converts to ln Cs - T = kLar·t
assuming an initial dissolved oxygen concentration of zero. Hence it is possible to obtain a quick on-site estimation of the value of kL~ by plotting in C - CT versus time, t. This method also indicates
the degree of success of initial mixing of the test chemicals, since the semi-log plot should be linear. An example of this plot is attached as Figure 4. A temperature correction applied to kL 8.-r provides a standard conditions kL aw The standard conditions SOR is found from: SOR = kLa20 -V-C 520 The SOR was measured by the contractor, the Brisbane City Council and a third independent laboratory (Simmonds & Bristow Pty Ltd). The measured SOR efficiency includes the energy input from the propeller mixers as well as the blowers. The total power draw for the mixers was measured as approximately 9.3 kW. The data determined by non-linear regression from the independent analysis for the three conditions are given in Table 2. Table 2 Measured SOR and Energy Efficiency kLa20
Method • The recirculation ports between the inner anoxic zone and outer aerobic annulus were sealed to avoid any interplay between the zones. • Blowers were operated on minimum air output to assist mixing and distribution of chemicals added. • Initially the mixers were operating and a cobalt salt was added to the aerobic annulus to act as a catalyst to speed up the deoxygenation reaction. • A solution of sodium sulfite was added over three circulation times to completely de-oxygenate the aerobic annulus. • The blowers were set to the required output and the power draw for the blowers and mixers logged throughout the trials using a recording watt-meter. • When the dissolved oxygen began to rise, the DO was logged with time at six positions around the basin as shown in Figure 2. • After the dissolved oxygen met the saturated concentration and stopped increasing, the saturated DO was logged . Results Plots were obtained for all of the dissolved oxygen probes. A typical plot of Dissolved Oxygen versus time is attached as Figure 3. Discussion The kinetic model is an unsteady state re-aeration assuming a complete mix basin. Volume
= - (C _
=\__) 1m from_ --<2) CD--, floor Fig. 2 -
>3 .39 >3.59
Fig. 3 - Dissolved oxygen plot for maximum oxygenation run - Probe 1 6
.S -3 .0
The oxygenation tests were successful for all of the required conditions. Since all plots of In Cs - CT versus time were linear,
> 420 >210
•corrected for only I basin on-line.
TIM E (minal 14 16 18
!Imai 19 WI
B EB I~
Gr--- -Mid-Depth '---(5)(
13.04 Max. Normal Mode 6.75 (average of two runs *Min. Normal Mode 3.61
~ - 1 m from surface
Max. SBR Mode
C) k a
dt s LT where C is dissolved oxygen concentration, C is saturated value. k~ ¾, oxygen mass transfer coefficient, is temperature dependent kL¾ = kL a 20 • e<T- 20>. where 8 = temperature correction factor. T = temperature Integrating the differential equation gives C = Cs - (Cs - C) exp (-kL¾·f)
SOR (kg/ hr)
. . . .____, m from surf ace
-4 . 0
-----, m from surface
Location of dissolved oxygen probes
Fig. 4 -
In C~ C versus time, maxy oxygenation - Probe 1 s WATER December 1991
the addition of the sulfite solution to the outer annulus was consistent over the three circulation periods . The standard conditions transfer .efficiencies for the diffuser system expressed as g O/m3 air.m depth or as OJo oxygen transfer are given in Table 3, assuming a diffuser depth of 4.25 m, with no correction for relative humidity: Table 3 Measured Clean Water Transfer Efficiencies Alr Flow at
Clean Water Transfer Efficiency
o•c and3 1 aim (111
Max . SBR Mode Max. Normal Mode Min . Normal Mode
5800 2655 650
g0/ 111 3,m
20.0 22.5 25 .7
28.5 32 .2 36.6
Conclusion The oxygenation capacity and turndown ratio of the equipment met the requirements specified by the Brisbane City Council. In particular, the oxygenation efficiency was approximately 4 kg 0 2 I kW.hr wire to water, which is twice that typically measured for surface aeration systems. · It is recommended that wastewater projects be evaluated on capitalised running costs based on the discount interest rate, as well as initial capital costs, when comparing alternative tenders, as the diffused air and surface aeration systems have very different capital and running cost characteristics. Diffused air systems have higher initial capital costs, however, these costs can be quickly recouped in annual power costs savings.
The results of the velocity measurements are sho"~ following diagrams: a) Aerated Annulus Position 1 Position 2 Inner Wall Outer Wall Inner Wall O ~:Max. Oxygenation 0.39 0.64 0.61 0.42 0.48 0. 5] 0.21 0.36 0.51 0.31 0.38 0.5: 0.11 0.26 0.42 0.15 0.41 0.50 average = 0.39 mis average = 0.41 mis Min. Oxygenation 0.41 0.48 0.59 0.26 0.34 0.52 0.12 0.31 0.49 average = 0.39 mis No Oxygenation 0.22 0.52 0.58 0.22 0.35 0.55 0.20 0.37 0.51 average = 0.39 mis b) Anoxic Zone 0.11 0.27
MIXING TEST Purpose To maintain the mixed liquor solids in suspension and produce mixing of the basin contents in extended aeration systems, it is typical to specify circulating mixing velocities of 0.3 to 0.5 mis around the basin. The lower value is relevant for diffused air systems, as the air bubbles also produce mixing . The mixing velocity of 0.3 mi s has been found from previous experience to have sufficient turbulence to keep biological solids in suspension or to re-suspend material if mixing equipment is temporarily isolated. The Brisbane City Council specification for mixing velocity around the basin is given below in Table 4. Table 4 Specified Mixing Velocities
0.3 mis 0.35 mis
Maximum (100%) Minimum (33%)
Under maximum oxygenation conditions the fluid may tend to be slightly compressible due to the air bubbles, hence a lower circulation velocity was expected. The aim of the test was to determine if the circulation velocity produced by the submersible propellers met the specified requirements.
Method • ·The orientation of the propeller blades was predetermined and the mixers were turned on in the anoxic zone (1 unit) and the outer aerated annulus (2 units). • The velocity was measured across the annulus width at two positions as shown in Figure 5. An Ott velocity probe measured the velocity in a grid of nine positions, i.e. at 20, 50 and 800Jo of pass width and at 20, 50 and 800/o of water depth. • The velocity was also measured across the inner anoxic zone at position 3 as shown in the Figure 5. POSlllCJl 2
Outer Wall 800Jo (1> ::r: 500Jo ci<j' 200/o 800/o 500/o 200/o Width
Fig. 5 22
Mixing velocity measurement positions and cross section
WATER December 1991
0.51 0.51 0.48
Position 3 0.61 0.66 0.65 0.66 0.63 0.65 0 width from wall (m)
The average velocities measured over the aerated pass are in excess of the specified requirements, as shown in Tobie 5. Table 5 Measured Mixing Velocities Level of Oxygenation
Average Velocity in Aerated Annulus Velocity
0.17 0.46 0.58 0.22 0.48 0.55 0.35 0.41 0.51 average = 0.41 mis
0.3 mi s
0.4 mi s
0.35 mi s
The velocities tend to be higher at the surface and nearer the outer wall. The velocities in the inner anoxic zone range from 0.5 mis at about half the radius to 0.65 mis at the wall. Although the mixing velocity was lower near the centre of the tank, the influent pipe is also situated at that position hence the turbulence due to the influent ensures sufficient suspension of biological material.
Discussion Since the circulation velocity of the outer annulus is in excess of the 0.3 mis requirements, the flowrate around the basin is at least: I03L 0.3 mi s x 7.7 m wide x 4.5 m deep x - lm3
= 10,395 Lis, or 900 ML/d
Since the design dry weather flow, DWF, is 52 Lis or 4.5 MLld for Stage 1, the circulation flowrate is approximately: 900 ML/d = 200 x DWF 4.5 ML/d This high circulation rate converts the plug flow character of the outer annulus to a complete mix flow. Hence the outer annulus can be modelled as a complete mix basin. The average velocity of at least 0.3 mis is suitable to re-suspend biological solids after the clarifier phase of the sequencing batch reactor system ceases. Further, the diffuser system has the advantage of being evenly spread across the outer annulus and automatically re-suspends the mixed liquor solids when air is re-introduced during the aeration phase. Due to the diffusers being rubber membranes, they can flex during initial air injection so as to discard any accumulated sludge from the surface of the diffusers. The circulation velocity does not appear to be affected by the level of oxygenation.
Conclusion The circulation velocity in the outer aerobic annulus and the inner zone is greater than the required specification hence the associated turbulence is considered suitable to maintain mixed liquor soilds in suspension as well as produce complete mixing of contents in the inner and outer zones. Fig. 8 -
RECIRCULATION TEST Purpose To effect nitrogen removal, the nitrate associated with the Return Activated Sludge is denitrified in the initial anoxic zone. Ammonia and organic nitrogen entering with the influent wastewater pass through the anoxic zone to the aerobic zone where they are oxidised to nitrate. The flow is then partially returned to the anoxic zone via a recirculation gate for denitrification; the process train is shown in Figure 6. There is no method of flow measurement through the recirculation gate, however, the overall extent of nitrogen removal possible is dependent on the recirculation flowrate, a, and return activated sludge flow, s, as shown in Figure 7, which is determined from a mass balance of nitrogen in the system. The plot assumes a return activated sludge flow equivalent to the influent wastewater dry weather flow.
After the recirculation ports were opened, the concentration of salts dropped over time in the aerobic zone and increased in the inner zone until the concentration equalised. The concentration of salts will vary depending on the recirculation rate and may be measured by either sampling and analysing for sulfate, which would be tedious and costly requiring chemical analysis, or by measuring conductivity which is quick and cheap and only requires a calibrated conductivity meter operated by personnel without a chemistry background. As the total mass of sulfate or conductivity stays constant in the system, it was possible to sample both zones to obtain a check on the recirculation rate. Results The conductivity in the inner and outer zones varied with time as plotted in Figure 9.
Model for recirculation test
180 0 ~
1 150 0 '.:- 140 0
Recirculation , a
Fig. 6 -
Process train for nitrogen removal
Ell I NNE F TANK
130 0 120 0
110 0 100 0
90 0 ;
80 0 70
60 0 % Oenitrification •
50 0 ::,..
[ l +a+s
assume s = 1 x OW F 3
Fig, 9 -
a = recirculation rate.
Fig. 7 -
Denitrification versus recirculation rate
This assumes that maximum possible denitrification occurs in the anoxic zone and no denitrification occurs in the aerobic zone. However, this may underestimate the level of denitrification possible. (Jansen & Behrens, 1980). Full nitrification is also assumed in the aerobic zone. To meet a Total Nitrogen effluent constraint of 10 mg/ L with a peak influent Total Kjeldahl Nitrogen level of 50 mg/ L and assuming approximately 11 mg/L is converted to biomass, the level of denitrification required is: 50 mg! L influent - 11 mg! L biomass - JO mg/ L effluent (50 - 11)
10 = 80% which corresponds to a recirculation rate of 3 x DWF. 50 The aim of the test was to determine if the recirculation rate is at least two times dry weather flow. Method After the clean water oxygenation tests were performed in the outer annulus of the aeration basin, the concentration of sodium and sulfate ions was high in the outer annulus and low in the inner zone, as the recirculation ports were shut during the oxygenation tests. It was thus possible to do a tracer test by opening the inlet and outlet recirculation ports between the inner and outer zones to their operational positions. The system was modelled by two complete mi x basins interconnected in series, with the effluent of one basin acting as the influent to the other as shown in Figure 8.
50 60 TIME Cminel
Conductivity versus time for recirculation test
As the volume of aerobic zone is V 1 = 3500 m 3 and volume of anoxic zone V2 = 2050 m3, a mass balance was performed to check that there was no loss in the system. The initial mass, M, of sulfate or conductivity in the system was: v1c10 + v 2c20 = M where C 10 was initial conductivity in aerobic zone at time = 0 C 20 was initial conductivity in anoxic zone at time = o, At time t, the total mass of sulfate is the same and equals: v1c1
Hence V 1C 10 + V2C 20
= V 1C 1 +
Hence a recirculation rate of 2 x DWF is required under peak conditions. If we disregard the nitrogen required for the biomass, the extent of denitrification required under peak conditions is
v 2c 2
V2C 2 or,
v2c20 = v2c2
A check on the mass balance of conductivity revealed a value close to unity, implying there was no loss or gain of conductivity in the system over time, as shown in Table 6, and the results are therefore considered to be reliable. Table 6 Mass Balance for Conductivity
v1c10 + v1czo v,c, + v,c,
0 10 15 20 25 30 40 50 60 70 80 90
1900 1880 1860 1850 1830 1820 1800 1770 1750 1730 17 10 1690
740 755 792 840 850 873 934 972 1010 1054 1074 1100
1.00 1.00 1.00 1.00 1.00 1.00 0.99 1.00 1.00 0.99 1.00 1.00
WAT E R December 1991
Table 7 ~ Determination of Recirculation Rate
Discussion A kinetic reaction equation can be developed assuming the recirculation model shown in Figure 8. Assuming complete mixing in each basin, with recirculation flowrate , a, mass balance on Aerobic Volume V 1I gives: aC2 Inlet Outlet aC1 l
c20 V2) - cl vi (2) v2 Substituting (2) into (1) and solving the differential equation gives: In
v1c 10 +
v 2c 20 - (V1
+ Vi)C 1 = - a(V1 + Vi)t
- 0.00752 min-1
0.182 m 3 /s or 3.5 DWF
0.162 m 3 /s or 3.1 DWF
vi v 2
V/C20 - Clo) Hence if we plot In VICIO +
The separated diffused air and mixing systems have successfully met all performance requirements specified by the Brisbane City Council. In particular, the measured energy efficiency of 4.0 kg 0 2/ kW .hr is believed to be one of the highest obtained from any extended aeration plant in Australia. The measured recirculation flowrate allows the possibility of at least 80 % level of denitrification.
versus time, the slope will be - a( Vi + V2) v1 v 2
Solving for the recirculation rate, a
Vi V2 vi+ v 2
Similarly, a mass balance on the anoxic volume V2 indicates that if we plot In (VI + V2)C2 - vlclO Vl(C20 - CIO)
The Brisbane City Council wishes to acknowledge personnel from Aquatec Maxcon Pty Ltd who supplied and installed the aeration equipment and conducted the aeration system tests in conjunction with Brisbane City Council personnel. Simmonds and Bristow Pty Ltd provided analytical services as an independent party.
v 2c 20 versus time, the
- a( VI + V2) v1 v2
slope will be
Conclusion The measured recirculation rate ranges from 3 .1 to 3. 5 times dry weather flow, hence the level of denitrification expected corresponds to over 80%. Note , however, that under process conditions the return recirculation gate from the aerobic zone to the anoxic zone must pass about 3 .1 to 3 .5 x DWF. However, the gate that transmits flow from the inner anoxic zone to the outer aerobic zone must allow the maximum combined flow of the influent wastewater in wet weather periods (3 x DWF), the maximum RAS (1.5 x DWF) and the recirculation flow (3 .1 to 3.5 x DWF). The gate has not been tested to determine if over 7.5 x DWF passes through it and a future test will evaluate this aspect.
= (CIO vi +
therefore c 2
aC1 + dC1 · V1
Accumulation Therefore aC2
Thus we have two methods of checking the recirculation rate, a, based on measurements in the aerobic zone and the anoxic zone. The semi-logarithmic plots for the anoxic and aerobic volumes are attached as Figure 10. Linear regression of the data provides the slopes as given in Table 7.
Charlton, J. (1991). Design of nitrogen removal plant with sequencing batch reactor capability . This Journal. ' American Society of Civil Engineers (1984) . Measurement of Oxygen Transfer Rate in Clean Water. Jansen, J .L.C . and Behrens , J.C. (1980) . Periodic parameter variation in a full scale treatment plant with alternating operation . Prag. Wat. Tech. Vol 12, No. 5 pp 521-532.
I 2 0· 2
Tl ME ( mins)
Fig. 10 24
Recirculation test -
WATER December 1991
rate of change of conductivity for recirculation test
AEROBIC ZONE ANOX IC ZONE
Design of Nitrogen Removal Plant with Sequencing Batch Reactor Capability by J. CHARLTON ABSTRACT This paper describes the design of Waco! Wastewater Treatment Plant Stages 1 and 2, sized for 30 000 e.p., which is an extended aeration recirculation process for nitrogen removal, with additional capability for sequencing batch reactor mode of operation. The design includes a diffused air aeration system and separated propellor mixing, with an associated standard conditions oxygenation energy efficiency measured at over 4 kg 0 2 / kW hr at the time of commissioning, which is considered relatively high. The design of each of the unit processes is detailed.
John Charlton is a chemical engineer with the Projects Design Section of the Brisbane City Council. He has spent three years in the Sewerage Operations Branch and six years in the Planning and Design Branch, being primarily involved in the detailed design of the Gibson Island and Waco! Wastewater Treatment Plants.
INTRODUCTION The Waco! Wastewater Treatment Plant Stages 1 and 2 is an extended aeration system designed for a total equivalent population of 30 000. Stages 1 and 2 are each 15 000 e.p. sub-modules with Stage 1 commissioned in 1990 and Stage 2 currently schedul~d for commissioning in 1992. The treatment plant catchments will include the Brisbane sewerage schemes of Bellbowrie and Mt Ommaney. Pump stations at each of these locations will pump the wastes to the surge chamber at the treatment plant site via an interconnected series of rising mains. The treatment plant discharges effluent via a submerged outfall located 60 km upstream from the mouth of the Brisbane River. The site is sized for two additional 30 000 e.p. modules, which may require full nutrient removal. The treatment process is designed as a "Rotoflow" recirculation process for nitrogen removal with sequencing batch reactor capability. The sources of oxygenation and mixing in the circular aeration basins have been separated, with oxygenation being produced by a diffused air system, and mixing by submersible propellor mixers. The standard conditions oxygenation efficiency based on clean water at 20Â°C and atmospheric pressure has been measured at over 4kg O /kW.hr at the time of commissioning (Charlton et al. 1991), which is relatively high compared to traditional surface aeration efficiencies of 1.7-2.3 kg 0 2 / kW.hr. This paper describes the design of the unit processes contained in the treatment plant.
INFLUENT CHARACTERISTICS A program of sampling and analysis was determined to measure the average values and variation of influent characteristics from the catchments. The treatment plant has been designed for 95 percentile values for the influent characteristics, which corresponds to the sample average plus approximately two standard deviations. These peak 95 % influent parameters and the associated arithmetic means are summarised in Table 1. Table 1 Influent Parameters Parameter
Biochemical Oxygen Demand (5 day) Suspended Solids Ammonia Organic Nitrogen Total Phosphorus
185 mg/ L 210 mg/ L 23 mg/ L 13 mg/ L IJ mg/ L
275 mg/ L 285 mg/ L 30 mg/ L 20 mg/ L 15 mg/L
No diurnal factor was applied to the influent parameters in the design of the treatment plant as the treatment process chosen was an extended aeration system with a conservative sludge age of 25 days specifically for sludge stabilisation, hence the considerable buffering capacity reduces the impacts of the diurnal variation. Dry weather flowrates have been previously determined for the general Brisbane area as 300 L/ h.d. A study of the Mt Ommaney catchm~nt indicated that a predominantly domestic equivalent population of up to 15 000 e.p. was required for design of Stage 1. However the Stage 2 scheme indicated that a predominantly trade waste equivalent population of up to 15 000 e.p. was required, leading
to a total of 30 000 e.p. and a design ADWF of 9 ML/d . The associated dry weather flowrate was calculated as: 30 000 e.p. x 300 L/h.d . x 10-6 ML/L = 9 ML/d. During periods of wet weather, the influent flowrate typically increases to four times dry weather flow, hence Wet Weather Flow = 36 ML/ d. This compares with State Government Guidelines of five times dry weather flow at 230 L/h.d. which corresponds to 34.5 ML/d.
EFFLUENT LICENCE REQUIREMENTS The Queensland Department of Environment and Heritage has issued a licence to discharge wastes to the Brisbane River from the Waco! Wastewater Treatment Plant Stages 1 and 2, which includes the following major effluent water quality criteria, which are not to be exceeded: , Biochemical Oxygen Demand (5 day) < 20 mg/ L < 30 mg/ L Suspended Solids Total Nitrogen < 10 mg/ L Dissolved Oxygen > 2 mg/ L 1 pH range 6.5 to 8.5 In particular, the total nitrogen constraint determined the types of treatment processes that were initially evaluated for the treatment plant. Note that although there is currently no phosphorus limitation, the State Government may introduce a phosphorus constraint in the future when phosphorus loads to the Brisbane River from all sources become significant.
TREATMENT PROCESS The diffused air treatment process was chosen from a variety of alternatives, including surface aeration systems. Although the initial capital cost for the diffused air process in circular aeration basins is higher than that for surface aeration systems in racetrack basins, the power costs are significantly less. For example, the annual power costs of the diffused air system were originally estimated at approximately $70 000 p.a. compared to the traditional vertical shaft surface aeration system of $120 000 p.a. When capitalised over the life of the equipment, the total costs estimated for the diffused air system were lower than those of the surface aeration system. Wastewater is pumped from pump stations located up to 4 km from the site to the on-site surge chamber. This consists of a standpipe located within a concentric chamber, with the discharge level of the stand-pipe designed to maintain a full rising main at all times. The flow is initially screened, de-aerated and de-gritted in the preliminary system. Screenings are pressed and stored, before disposal as landfill on-site. The flow from 30 000 e.p. will be treated in an extended aeration activated sludge system which consists of a contact selector tank, two aeration basins, a distribution chamber, four clarifiers and a return activated sludge pump station. A fraction of the sludge is wasted to the thickening system which consists of two picket fence thickeners. A pump station transfers the thickened sludge to the dewatering system. The dewatering system consists of beltfilter presses and an associated polyelectrolyte dosing system. Filtrate and thickener WATER December 1991
supernatant are returned to .the plant downstream of the grit chambers. Dewatered sludge is dried on sludge pans before disposal as landfill on site. 'Ireatment plant effluent is piped from the clarifiers to the effluent pumping station which feeds high pressure effluent to the screens' washwater system, belt press polyelectrolyte dilution and washwater, general hose-down and irrigation requirements. Excess effluent is piped to the river via a submerged circular outfall. Figure 1 shows the general layout of the treatment plant.
2 SCJU!DII BUil.DiNO I OE-AERATION QWilllDl 4
lll.OWl!R """""" DJSTRletm:ON <JW.l8EJl
ORITOtAMBIJII (DrffACr TNIC
SETJUl«J TAHU 10 EFF'1.J.Eff PlAF ITATION 11 RAS. PUliP STATION
12 PJcn.,' F9D ntICICDEtS
ACTIVATED SLUDGE SYSTEM The activated sludge system consists of an initial contact tank, two aeration basins, a distribution tank, four clarifiers and a return activated sludge pump station. Contact tank
SITE LAYOUT STAGES 1 AND 2
and dewater 85 OJo of the grit with a specific.gravity of greater than 2.6 or an equivalent diameter greater than 0.3 mm during periods of wet weather flowrates . For the ultimate capacity of the plant, there will be three duty chambers for peak wet weather flows.
Early studies indicated that a pre-selector contact tank may be utilised to exploit the difference in growth characteristics between floe forming micro-organisms which produce good settling sludges in the clarifiers, and filamentous organisms which may hinder settling if their growth is not controlled. The growth characteristics of these micro-organism types are shown in Figure 2 (van den Eynde et al. 1982). 14 T.W.A.8. PUMP STATION 16 8LU)(£ 8ALAHCJNO TANK 11 Bn.TFtLffR PR£88 BUil.DiNO 17 MEQi. l El.EC. W0RXSH0P 1t ADMINIS'MATION BUILDlHO
_ _ _ _ _ FLOC FORMERS
Although the two aeration basins may be operated in the normal parallel mode, they are also interconnected and may operate in series in either of two experimental sequenced batch reactor (SBR) modes. One mode allows for redundancy of the clarifiers and RAS pump station by dedicating one basin aerobic and the second acts as a clarifier. The second mode allows greater nitrogen removal by dedicating one basin aerobic and the second anoxic. In the SBR modes of operation the functions of the two aeration basins are reversed after an appropriate length of time. If the sequencing modes are found to be successful, they may be employed for future augmentations either to reduce the associated capital costs or to reduce nutrient loads to the receiving water bodies. The plant is designed to operate automatically, with provision for manual operation, and is to be manned 8 hours/ day for 5 days per week. An alarm priority system relays high priority alarms to a centralised city control room for after-hours emergency situations. The control system consists basically of four programmable logic controllers connected via a data highway to a central data logger.
PRELIMINARY TREATMENT SYSTEM
When the influent waste concentration is low, the growth rate of filamentous organisms may be greater than that of floe formers, hence low concentrations favour the poorer settling organisms. The level of influent waste absorption is dependent on time and is shown in Fig. 3 (Eikelboom et al. 1982) 100¾
The preliminary treatment system consists of a screens system and an associated de-aeration chamber, a screenings disposal system and grit removal system. Screens system
The screens system includes one duty and one standby "Contrashear" rotary wedgewire drum screen, each sized for wet weather flows of up to 36 ML/ d, plus lOOJo surcharge. The wedgewire slot width is 3.0 mm. As the screened sewage collection tray is so shallow, the vertical flow of sewage leaving the screen drum and striking the tray entrains air, hence requiring a significantly greater hydraulic head to allow the design flow through the pipework. A de-aeration chamber has been installed to remove the air bubbles entrained in the flow exiting the screen discharge trough. For the ultimate capacity of the plant, there will be three duty screens for peak wet weather flows. Screenings disposal system
Screenings captured and discharged from the rotary drum screens fall vertically to a rising conveyor belt which discharges to a "Warren Engineering" press. The press is designed to reduce the volume of rags by at least a ratio of 3.5 to 1 with an influent screenings moisture content of 900Jo. Pressed screenings are stored in standard rubbish bins in a storage carousel before being disposed in a landfill area on-site. Grit removal system
Normally, the Brisbane City Council utilises spiral flow aerated grit channels. However, due to the likelihood of future requirements for biological nutrient removal, methods that entrain air have been purposely avoided. Grit traps have been employed utilising grit removal pumps rather than the conventional air lift pumps. "Pista" grit chambers, one duty and one standby, are installed to remove grit from the influent flow. The flow enters a circular basin where a rotating grit paddle produces a circulating flow which allows heavier grit to fall to the base of the chamber. Grit slurry is then pumped from the basin to a cyclone and wedgewire screen to capture 26
WATER December 1991
To control the growth rate of filamentous organisms, a selector contact tank was constructed with a detention time of nominally 20 minutes based on the total flow entering the basin. The contact tank is 8.4 m diameter and 4.5 m deep. The basin pre-mixes the return sludge with the influent wastewater at high concentrations, thus selecting for floe-forming micro-organisms. Although aerobic conditions increase the quantity of wastes removed, an anoxic contact tank has been installed. The contact tank has the advantages of: (i) selecting for filamentous organism control (ii) initial denitrification of Return Activated Sludge (iii) produces a well mixed influent to the aeration basins (iv) facility for phosphorus removal experiments (v) forcing anoxic conditions in appropriate zone of aeration basin. Current literature e.g. as discussed in Gabb et al. (1991) indicates that the selector mechanism is not as simple as initially proposed and may require extensive research to refine the mechanisms involved. Aeration tanks
A number of configurations were investigated for the site. Based on overall economics, process considerations and the availability of formwork from a recently constructed wastewater treatment plant, concentric aeration basins were adopted utilising a diffused air aeration source and submersible propeller mixers. This is labelled a "Rotoflow" system. 1\vo duty and one standby "HV Turbo" KA2S blowers supply air to the 400 pairs of "GVA" rubber membrane diffusers in each of two circular aeration basins. Each aeration basin consists of an inner anoxic denitrification zone where the influent and return sludge initially enters, and an outer aerated annulus where the influent is then oxidised and either recirculates back to the inner denitrification zone or is piped to the clarifiers. The process train is a recirculation system as shown in Figure 4.
CLAR If IER
I N F L UL ~ _ _ _ _-_ ~~~~c-c=·c=-:--=:cc;,=' ~cc-----''-- - - ~ - f f , l UEHT
RETURN ACT IVATEO SLUDGE
A unique feature of this configuration includes an internal recirculation of over three times dry weather flow, without the use of a pump station, by simply employing adjustable butterfly gates. The angle of inclination to the direction of motion of the flow can be adjusted as required . The two aeration basins are interconnected as shown in plan view in Figure 5.
BAS I N
The actual oxygenation requirement (AOR) for the process was calculated from the following relations, assuming 800Jo level of denitrification: kg 02 AOR = 0.65 kg BOD dest + 4.57 0.625
BLOWERS MIXERS DI FF USERS
~ BLOWERS -1*-VALVES
The blowers are each capable of supplying 3000 m 3/ hr of air at 20°C and 1 atm pressure. The three mixers in each basin provide a fluid velocity of at least 0.3 mi s around the basin to keep the mixed liquor solids in suspension and produce a complete mix regime in the basin. This avoids the potential for variations in dissolved oxygen levels in the aeration zone which is characteristic of surface aeration or diffused air systems in a racetrack configuration. Cylindrical rubber membranes diffusers provide fine bubbles. There are 20 separate diffuser headers in each basin, with each header supplying air to 20 pairs of diffusers. Each header can be isolated and removed from the basin without affecting the basin contents. Further, the mixers are removable from the basin. The "Rotoflow" type system readily lends itself to the removal of any piece of equipment from service for maintenance without significantly affecting the treatment process. The two aeration basins are interconnected to allow either of two modes of sequencing batch reactor operation. The first mode of SBR operation attempts to make the clarifiers and RAS pump station redundant by dedicating one aeration basin as an aeration tank while the other one acts as a clarifier. After a pre-set time, the function of the two basins are reversed to avoid sludge accumulation, as indicated in Figure 6.
PHASE 1 CLARIFIER
+ M.V.r20 .
4.57 _ _k_g---'02,...__ kg N denitrified
M = Mixed Liquor Suspended solids = 5000 mg/ L V = Volume of aeration basins = 11,100 m 3 r = respiration rate at 20°C = 2.2 mg 0/ g MLSS.hr 0 = temperature correction factor = 1.07 T = temperature = 26°C (maximum) where, to meet the licence requirements: BOD load dest = (275 - 5) mg/ L x 9 ML/d = 2430 kg/ d N load dest = (0.9 x 30 mg/L + 0.6 +20 mg/ L) x 9 ML/d = 2025 kg/ d The standard conditions oxygenation rate (S.O.R.) for the process was calculated from the following equation: SOR
AOR x SOR AOR
where SOR AOR where
Csc a(/3.Csc - qerT-20)
Csc is saturated oxygen concentration corrected for mid-depth C is dissolved oxygen in aerated annulus a = ratio of kLa process fluid = 0.85 kLa water
ratio of Cs process fluid = 0.95 Cs water 8 = temperature correction factor = 1.024 T = temperature = 26°C (maximum) Tuble 2 summarises the oxygenation requirements for the total 0f stages 1 and 2.
Table 2 Summary of Oxygen Requirements for 30 000 e.p. 20' C
220 kg/ hr
280 kg/ hr
330 kg/ hr
420 kg/ hr
kg 02 kg N nitrified
The second SBR mode attempts to maximise nitrogen removal by dedicating the contents of one of the aeration basins to be anoxic, thus ensuring sufficient time for denitrification, as shown in Figure 7. For the SBR mode of operation, each basin is equipped with twice the normal oxygenation capacity. Times for the various phase lengths are operator adjustable to suit variations in influent characteristics.
Due to the sequencing batch reactor operation, the maximum SOR requirement to be met by the aeration equipment was 420 kg/hr in each basin. Under the normal parallel operating mode, the maximum SOR required was 210 kg/hr per basin with a 3:1 oxygenation turndown ratio. The SOR measured for the aeration equipment is summarised in Tuble 3. WATER December 1991 27
Table 3 Summary of Standard Conditions Oxygenation Requirements SOR of Basin
Maximum SBR Maximum Normal Minimum Normal
420 kg/hr 210 kg/ hr 70 kg/ hr
493 kg/ hr 255 kg/ hr 71 kg/ hr
The average mixing velocities measured are compared to the required velocities in Table 4. Table 4 Summary of Velocity Requirements Velocity
Aerobic Annulus - Max Oxygenation - Min Oxygenation Anoxic Zone
0.3 mi s 0.35 mi s 0.35 mi s
0.4 mi s 0.6 mi s
0.4 mi s
The recirculation flowrate from the aerobic zone to the anoxic zone was measured as greater than three times dry weather flow which corresponds to a theoretical level of denitrification of over Âˇ80%. It should be noted that too low a recirculation rate does not return sufficient nitrate to the anoxic zone to produce an acceptable level of denitrification. However, too high a recirculation rate returns more nitrate than the anoxic zone can manage, and dissolved oxygen returned with the recirculation flow hinders anoxic conditions. Hence there is an optimum recirculation flowrate, typically three to four times the influent wastewater flowrate. The SBR process has the capability of further increasing the extent of denitrification as mentioned previously, by virtue of being able to dedicate an entire aeration basin as anoxic. A dissolved oxygen control system is utilised to maintain the DO in the aerated annulus at 2 mg/ L. One of a number of DO probe positions may be selected as the duty probe to control the dissolved oxygen level to a specific set-point. Distribution tank The distribution tank consists of an inner zone which evenly distributes the mixed liquor to each of the four clarifiers. It also has an outer annulus which evenly collects the return sludge from the four clarifiers, thus ensuring equivalent operation of all of the clarifiers. The basin is 4.5 m deep and has an inner zone diameter of 2.0 m and an external annulus diameter of 4.0 m. The only items housed in the basin are the mixed liquor isolation penstocks. In the design stage, the case of asymetrical flow distribution to the final settling tanks was considered . To cater for this, valve pits on each of the return activated sludge lines to the Distribution Tonk annulus were sized to accommodate flow meter and control valves if required. Final settling tanks Four final settling tanks are used to clarify the mixed liquor to produce an effluent suitable to be discharged to the outfall. The basins are 4.5 m deep and 24 m diameter, and are sized on a solids flux of 5.5 kg/ m2 .hr during wet weather flows. The sludge removal mechanism consists of a full diameter bridge which hydrostatically lifts the sludge collected on the flat bottom floor and transports it to a radial launder via updraught tubes. The return sludge travels along the radial launder to the central column mechanism which then pipes the sludge back to the distribution chamber annulus. The return sludge flow from the clarifiers is set equal to the influent wastewater flowrate, within the range of 0.7 to 1.5 times design dry weather flows . However, fixed position sludge blanket detectors override the control system if the sludge blanket level becomes high, and increases the return sludge flowrate until the sludge blanket level is reduced . Return activated sludge pump station The RAS pump station consists of a baffled entry segment which distributes the flow evenly to two duty and one standby "Forrers" submersible pumps located in the RAS pump station wet well. One pump produces a flow equivalent to design dry weather flow, and two pumps operating in parallel produce a total flow of 150% of design dry weather flow, which is the RAS flow during wet weather periods or under conditions of high sludge blanket levels. The advantage of submersible pumps is that the RAS is not aerated . Aeration may cause problems in the future if phosphorus removal is required, as aeration will reduce the readily assimilable feedstock to the phosphorus-removal micro-orgal')isms. 28
WATER December 1991
THICKENING SYSTEM The aim of the thickening system is to produce a feedstock to the dewatering system. It consists of two picket fence thickeners and a pump station which pumps the thickened sludge to the dewatering system. Picket fence thickeners For maintenance purposes, two picket fence gravity thickeners will be employed to thicken the waste activated sludge from a nominal concentration of 1OJo to 2.5% . The thickeners are 8.4 m diameter and 4.5 m deep with flat floors and have been designed for a solids flux of at least 20 kg/ m 2 .hr. The waste activated sludge flowrate is controlled to a constant flow set-point or to meet a constant sludge age. If a phosphorus removal constraint is applied to the treatment plant in future, the gravity thickeners may be converted to dissolved air flotation units to avoid release of phosphorus in anaerobic conditions. Thickened waste activated sludge pump station Helical rotor positive displacement pumps (one duty and one standby) are employed to transfer TWAS from the thickener system to the dewatering system. Each is designed to deliver a nominal flowrate of 10 kL/hr at 2.5% solids. The TWAS removal rate is controlled by solids blanket electrodes at fixed position in the thickeners.
DEWATERING SYSTEM The aim of the dewatering system is to produce a sludge cake that is manageable for disposal. It consists of a sludge balance tank which acts as a hydraulic break between the thickened waste activated sludge positive displacement pumps and the belt-filter press feed pumps, which are also positive displacement type. The sludge is dewatered via a belt-filter press and associated polyelectrolyte make-up system. Sludge balancing tank The level control system in the sludge balance tank has the potential to initiate operation of the belt-filter press system when the sludge level rises in the balance tank due to sludge feed from the thickeners. The sludge storage capacity in the balancing tank has been sized to allow the maximum number of stop-starts for the thickened sludge pumps. For the ultimate capacity of the plant, there will be three sludge balancing tanks. Belt-filter press "Sulzer" belt-filter presses (one duty plus one standby) are used to dewater the thickened waste activated sludge from approximately 2.5% influent solids to a cake of not less than 16% solids with at least 90% solids capture efficiency and a polyelectrolyte consumption of less than 3.5 kg/ t of dry solids. Dewatered cake discharges onto a common conveyor belt which transfers the sludge to a stacker conveyor to be stored on a concrete pad. Sludge is then transferred to a medium term sludge pan for final drying before disposal onsite in stock piles. Polyelectrolyte is batched by transferring dry powder polyelectrolyte to be dissolved with potable water and mixed in a mixing tank to approximately 0.3% solution. The solution is pumped to a dosing tank where it is diluted to approximately 0.025% solution by treatment plant effluent water, then dosed to the thickened waste activated sludge. The polyelectrolyte and sludge mixture is initially mixed in a flocculating basin before being distributed to the pre-dewatering gravity drainage zone of the belt press. The sludge is dewatered via a series of rollers which gradually increase the belt pressure. Each belt-filter press is designed for a nominal sludge flowrate of 10 kL/ hr and one duty press operates 8 hours/ day. For the ultimate capacity of the plant, there will be three duty presses operating 8 hours/ day.
POTENTIAL FOR FUTURE MODIFICATIONS RETROFITTING FOR PHOSPHORUS REMOVAL The aeration basin configuration as shown in Figure 8 may be suitable for biological nitrogen and phosphorus removal with a recirculation type system. The system has sufficient flexibility for a number of process trains including a modified UCT type system, modified Bardenpho type system, Johannesburg variation and Bio-denipho type system as
continued on page 31
Water Quality in Lake Tinaroo, Atherton Tablelands, North Queensland by J. LITILEMORE, M. MacKINNON, G. SADLER SUMMARY This paper reports the findings of a study of lake water nutrient status of Lake Tinaroo, Atherton Tableland, north Queensland, from December 1987 to June 1990. The nutrients NO 3 -N, PO 4 -P and K, and pH and electrical conductivity were measured at six sites within the storage, eight sites on streams entering the lake and two sites on water being released from the lake. Sediment samples were collected from the lake floor and from stream mouths when the lake water level fell to 47% capacity. These samples were analysed for total P and trace element components Cu, Zn, Mn and Fe.
John Littlemore was a chemist with the Department of Primary Industries in Mareeba during the water quality monitoring in Lake Tinaroo in North Queensland. He has a B.App.Sc. from the QUT and a MSc from James Cook University ofNorth Queensland. He now works as a Senior Chemist with the Queensland Department of Transport, Brisbane. Malcolm MacKinnon has a B.Sc from the University of New England and has been a fisheries biologist with the Department of Primary Industries since 1974. He has wide practical experience in freshwater ecology and aquaculture with emphasis on reservoir fisheries enhancement.
INTRODUCTION Lake Tinaroo is situated on the Atherton Tableland, north Queensland approximately 80 km from Cairns and is 500 m above sea level. The climate is temperate with winter temperatures of 15 to 27°C and summer temperatures of 21 to 35°C with 800Jo of the rainfall occurring during the period December to March. The lake is a multi-purpose storage providing water for irrigation, power generation, town water supply, recreation and tourism. Since the dam wall completion in 1959, considerable development has occurred within the catchment of the storage and along the lake foreshore. As a result of this development, and because of the importance of the lake to the local economy, concern has .been expressed from various community sectors over the possible deterioration of water quality in the storage. The Queensland Water Resources Commission, under the relevant provisions of the irrigation and Water Acts, gazetted the Lake Tinaroo Catchment Area in 1973 which has enabled the Commission to control land use and subdivision within the catchment and to protect water quality and the environment generally. However, because of the growing pressure for further subdivision along the lake foreshore, and the changing agricultural practices within the catchment area, the Commission is now proposing to develop a Storage Management Plan in consultation with local authorities and relevant government departments. An interdepartmental advisory committee was established to investigate factors which affect water quality in the lake, and the potential effects of current land use trends on the "pollutant" load. The initial approach was to examine very closely the water quality of the storage and its streams, so that the problem could be better identified.
Grant Sadler is District Engineer, Water Resources Commission, Department of Primary Industries, Mareeba, and is responsible for the management of the Mareeba-Dimbulah irrigation area for which Lake Tinaroo is the source of irrigation water. He has a REng(Civil) from the QUT.
Lake nnaroo Samples 1 Tobacco Hill (TH) Dam Wall (OW)
2 3 4 s
Barron River Mouth (BRM) Forsetry (F) lakeside (L) 6 Mazlin Creek Mouth (MCM)
METHODS Water samples were collected monthly at six sites (Fig. 1) from the water surface and at a point approximately one metre from the lake floor. The samples were chilled in ice, then frozen until analysis · as a batch of 60-80 samples. At sampling, dissolved oxygen and temperature measurements were also made, with a sub-sample being forwarded to Cairns City Council Water laboratory for chlorophyll A analysis. The water samples were transported to Department of Primary Industries laboratories, Mareeba for nutrient analysis of Nitrate N, Phosphate -P, K, and pH and electrical conductivity using methodology from "Standard Methods for the Examination of Water and Waste Water", APHA, 13th edition, 1974. All concentrations are expressed in mg/m 3 (ppb) (P. Cullen, pers. comm, 1988). During 1988, when the lake fell to 47% capacity, several sediment profile samples were collected from the mouths of the principal streams that discharge into the lake for Cs 137 analysis to date the sediments as part of a separate study. These soil samples were also analysed for total P by the fusion method of Blackmore et al. (1987). Sediment samples from seven sites were taken by dredge, oven dried at 70°C, sieved to pass through a 2 mm screen to remove leaf litter and small stones, and then analysed for total P. The trace elements Fe, Mn, Zn, and Cu were determined by atomic absorption spectroscopy following digestion of 10 g of sediment in 15 ml concentrated nitric acid and dilution to 50 ml in a volumetric flask.
Creek/River Samoles A Kauri Ck. B Mazlln Ck. Sewerage Treatment Plant C Mazlin Ck. Fox Bridge 0 Maztin Ck. Atherton E Severin Ck. F Peterson Ck.
G Barron River, Picnic Crossing H Barron River, Temp Gauge I Barron River, Downstream of Wall J West. Barron Main Channel
Fig. 1 -
Lake Tinaroo water quality sampling sites WATER December 1991
RESULTS AND DISCUSSION
Very definite cycles are evident for pH (data not presented) but are little cause for concern from an agricultural view point because the water is always close to a neutral pH. It is known that several dairy pastures in the Barron River/ Peterson Creek catchment have soil pH (1:5 H,O) as low as 3.5 with a typical result of 4.5 to 5.0. These lower pfl soils do not seem to influence the pH of the lake storage and this is significant. Hart (1982) noted that as a lake becomes acidic, then the heavy metal concentration (particularly Al) in the water column increases as a result of dissolution of metals in the sediment and particulate matter. In this multi-use storage it is imperative that this does not happen. The principal nutrients NO 3 - N and PO 4 - P have presented interesting results. The PO4 - P concentration in the storage does not appear to be increasing from that found at the beginning of the sampling (Fig. 2). The high results observed between December 1987 and February 1988 are most probably a result of the inflow during storm events. From March 1988 until June 1990, very little PO4 - P was detected in the storage with the concentration regularly at the limit of detection of 5 mgP/ m3 • Nitrate -N concentration is cyclic and it appears to be rising slightly with time (Fig. 3). This observation is supported by monitoring of the N:P ratio which shows a very definite upward trend from an N:P ratio in April 1988 of 12, to N:P ratios in 1990 of 30 to 70. Ryding and Rast (1989) have determined that a mass ratio of 7-8N:1P appears to be the reasonable boundary for defining the potential limiting nutrient for most known algal growth. The result, then, demonstrates we have a situation where P is the limiting nutrient and that, in future, emphasis should be placed on the quantity of P entering the storage from either agricultural or residential sources. Examination of the NO3 - N concentrations at the mouths of the Barron River, Mazlin Creek and the lake grand average (Fig. 4) demonstrates that the NO 3 - N is entering the storage body both from the agricultural area and from Atherton township sewerage treatment plant at about the same concentration as is present in the lake water. In a comparison of Mazlin and Kauri Creeks (which drain forestry areas) it was observed that very little contribution to the lake NO 3 -N came via Kauri Creek. The Department of Primary Industries is concerned about high N use by dairy farmers in the upper catchment areas of the Barron River and Peterson Creek, and studies are currently being initiated to determine the fate of the N applied to dairy pastures. This study will include leaching studies
1N1 - ·- - - •- - - - - ___
,,.. _ _ _ _- + - 1NO--
Fig. 4 - Nitrate-Nat Barron River and Mazlin Creek mouth vs. dam average
to determine if some of this N is eventually entering Lake Tinaroo in these streams. Potassium concentrations in the storage also appear to be of a cyclic nature with marked increases seen in the months August to October, then steady decreases in the months of April to June (Fig. 5). The end result is an "annual" K concentration approximately 1700-1800 mg/ m 3 , with no evidence of increase. This is not surprising because K application, by way of fertiliser to the agricultural catchment area, is about one quarter of that of N (P. Valentine, J.C.U., unpublished results, 1988). Electrical conductivity was measured to investigate the possible correlation with NO -N, PO 4 - P, and K. Unfortunately no correlation was found for storage waters. However, electrical conductivity in the storage has a trend of its own. In 1988 as the lake level fell, the conductivity rose significantly from 45 mS/m- 2 to a high of 80 in December, then with the storm events of early 1989 it fell to 55 in April, then steadily rose to remain at about 75 mS/ m-2 (Fig. 6). Lake turnover is very evident. In the cooler months of May- July the "bottom" conductivity measurement is lower than that of the "surface" one whereas throughout the majority of the year, it is normally the other way around with the "bottom" being 3- 5 mS/ m-2 higher than the "surface". , ,00
a s urta •
lOO 400 K 110
Phospha t e-P
ttlt - !- -- ·- - - - -1- --·- - - - --+·
,.,-+-- - -·-- - ---+-- - -·- - -- - - -·- -
Fig. S - Potassium In surface and bottom sample
Fig. 2 - Phosphate-P In surface and bottom sample 100
" " E . C:.
" " " so
___________ _____~_,..,_ P
Fig. 3 - Nltrate-N In surface and bottom sample 30 WATER December 1991
" "+--il-t--+-+-t-+--t-t-1---t--t-,1-t--+-+-t--l-+-t-1---+-+-,1-t--t-+-i---+-i DJP
11111-·----·- - - - - - - -·-- - - - -
Fig. 6 - Electrical conductivity In surface and bottom sample
Total Pin sediment samples (Tobie 1) was found to be concentrated in the surface 30 cm for Barron River and Peterson Creek (which has as part of its catchment the township of Yungaburra). The concentration of nearly 2000 mg/kg is very significantly higher than those for Kauri or Severin Creeks whose principal catchment is a forestry area which is undisturbed and unfertilised. (Mazlin Creek samples were taken but inadvertently discarded before analysis). Sediment samples taken by a dredge (Table 2) from the lake floor at project commencement in 1987 have total P analyses which are in reasonably good agreement with those of the sediments taken by soil auger, especially the Forestry result of 480 mg/kg which approximates the average of 600 and 320 mg/kg for Kauri and Severin Creeks. Williams et al. (1971) noted similar variable and large amounts of inorganic P in a study of sediments from lakes in
J. CHARLTON continued from page 28
shown in Figure 9. The Johannesburg variation utilises an anoxic basin located on the return sludge line to denitrify the return activated sludge. The pipework flexibility allows bypass of the selector basin as well as partial feeding of the influent or RAS to the primary anoxic zone to denitrify the return sludge. TO CLAR IF IERS
Table 1 Total P in sediments at stream mouths in Lake Tinaroo, 1988 (mg/ kg). Barron
0-10 10-20 20-30 30- 40 40-50 50-60 60-70 70-80 80- 90 90-100 100-110 110- 120 120-130 130-140 140- 150 150-160 160-170 170-180
1640 1720 1840 1600 680 920 1040 440 320 320 360 280 280 200 NS NS NS NS
600 520 680 680 520 440 440 560 480 400 520 440 480 440 560 640 NS NS
320 360 480 440 400 320 360 360 400 320 320 320 280 280 280 400 360 280
1600 1440 1080 920 920 780 880 840 780 NS NS NS NS NS NS NS NS NS
AEROBIC ANOXIC ANAEROB IC
Table 2 Analysis of dredged sediments for Total P, Fe, Mn and Cu (mg/kg) Site
Barron River Mouth Mazlin Creek Mouth Petersen Creek Mouth Lake Side Tobacco Hill Darn Wall Forestry
MODIFIED BARDEN PHO TYPE (STAGE 3) ANAEROBIC
2090 2520 2480 880 2580 1720 480
70800 78900 71000 31600 78850 53600 8900
960 1400 1055 560 950 915 105
123 164 139 49 140 103 14
56 71 48 21 58 36 4
' BID ÂˇDEN I PHO TYPE ANAEROBIC
BASIN 2. AER09 1C
BASIN 1. ANOXIC
PHASE A R."5 .
Wisconsin, USA, but they did not indicate the catchment area the sediments were derived from. The trace element composition of the dredged sediments reveals that Fe can be considered to be largely responsible for the adsorption of the P. This observation is supported by the finding of Williams et al. (1971). In a separate study, using an uncultivated soil sample collected from the native forest at Kairi Research Station, we observed that this basalt-derived soil was capable of irreversibly absorbing 2000 mg/kg PO 4 - P. This result is in excellent agreement with the P found in both batches of sediment samples. Overall, it would appear by good luck rather than good planning, that Lake Tinaroo has a catchment area with high P fixing soils which will result in low P concentration in the storage water.
REFERENCES Blackmore, L.C., P.L. Searle, and B.K . Daly (1987). Methods for Chemical Analysis of soils. NZ Soil Bureau Scientific Report 80. Hart, B.T. (1982). Australian Water Quality Criteria for Heavy Metals. Aust. Water Resources Council, Tech . Paper 77. Ryding, S.O., and W. Rast (1989). The Control of Eutrophication of Lakes and Resovoirs, Vol. I, Man and the Biosphere series. UNESCO and The Parthenon Publishing Group. Williams, J.D.H., J.K. Syers, D.E . Armstrong, and R.F. Harris (1971). Characterization of Inorganic Phosphate in Noncalcerious Lake Sediments. Soil Sci Soc. Amer. Proc. Vol. 35, 556- 561.
BASIN 2 AtÂŤJX I(
ACKNOWLEDGEMENTS The author wishes to acknowledge the support and effort of all those involved with the Waco! Project from its inception to commissioning. REFERENCES Charlton, J., Barr, K.G. & Low, S. (1991) Clean water oxygenation and mixing tests for a diffused-air extended-aeration plant. This Journal. Eikelboom, D.H. (1982). Biosorption and prevention of bulking sludge by means of a high floe loading. In Chambers, B. & Tomlinson, E.J. (ed). Bulking of Activated Sludge - Prevention and Remedial Measures. Ellis Horwood Ltd, Chichester. Gabb, D.M.D., Still, D.A., Ekama, G.A., Jenkins, D. and Marais, G.v.R. (1991). The selector effect of filamentous bulking in long sludge age activated sludge systems. Water Science in Technology. Vol 23 No. 4 to 6. Van den Eynde, E ., Houtmeyers, J., and Verachtert, H. (1982). Relation between substrate feeding pattern and development of filamentous bacteria in activated sludge. In Chambers, B. & Tomlinson, E.J. (ed) Bulking of Activated Sludge Prevention and Remedial Measures. Ellis Horwood Ltd, Chichester.
WATER December 1991
Ecologically Sustainable Water Clarification at the Clear Water Lagoon, Mt. Isa by T.J. WRIGLEY, P.D. FARRELL and D.J. GRIFFITHS SUMMARY A reliable cost-effective water clarification system has been developed, and monitored for over ten years. It supplies 70 ML/ d to the township and mine complex of Mt. Isa, Queensland, and consistently reduces a very variable turbid inflow from the storage reservoir to less than 2 NTU. It consists of a relatively shallow lagoon, with a nominal retention time of 30 days, which is maintained at a constant level to encourage the growth of a diverse population of rooted macrophytes. Influent turbidities of up to 100 NTU resulting from wet season inflows necessitate occasional dosing of flocculant to the inlet flume, but otherwise the system is ecologically sustainable. . This paper outlines the construction and operation of the Clear Water Lagoon and the biological processes which are important to its success.
INTRODUCTION The Clear Water Lagoon (CWL) is a small but integral part of the water supply system of the town of Mt. Isa (24 000 population) and Mount Isa Mines, the operator of one of the world's largest underground base metal mining complexes (Figure 1). Water from the two man-made lakes on the Leichardt River, Lake Moondarra and Lake Julius, is pumped to the CWL, then chlorinated at Lake Moondarra and the Mt Isa water treatment plant before distribution to the reticulation system.
- - - ____ !:~~ _Jf------Capricorn
Fig. 1 - Map of Queensland showing the location of Mount Isa and water storage dams 32
WATER December 1991
Tim Wrigley is the Environmental Science Program Manager ofMt. Isa Mines, Mount Isa. He has published papers on limnological research for Southern Africa, Western Australia and the Northern Territory.
D.l Griffiths is Professor and Head of the
Department of Botany, School of Biological Sciences, James Cook University of North Queensland. His main research interests include studies of the biology of marine and freshwater algae and the limnology of tropical lakes and reservoirs.
Peter Farrell is an Environmental Biologist
with the consultancy firm AGC WoodwardClyde. He studied Botany and Marine Biology at James Cook University and completed MSc studies examining the hydrobiology of a natural water clarification system whilst being funded by a Mt Isa Mines scholarship. His particular area of interest is water quality and ecosystem interactions.
At certain times of the year, the water of Lake Moondarra is unsuitable for domestic use because of its high turbidity. Standard methods for reducing water turbidity may involve flocculation, pH adjustment and sedimentation or filtration, all of which are costly. Even though turbidity levels of Lake Julius downstream of Lake Moondarra are much lower, they still exceed acceptable levels during periods of inflow. Pumping costs also negate the continued use of Lake Julius water except during times of drought or exceptionally high demand. The concept of a storage lagoon was first mooted in 1968, when a shallow depression next to Lake Moondarra was dammed to receive water during periods of low turbidity in Lake Moondarra. The water was transferred to the Clear Water Lagoon from a floating pump station. This depression was to provide a temporary water storage (30 days) for Mt. Isa during periods of high turbidity in Lake Moondarra. The Clear Water Lagoon has now been extensively modified to form an indispensable part of the Mt. Isa water treatment system. Its standing crop of macrophytes providing a cleansing system which gives Mt. Isa a year-round supply of water of acceptable quality.
CONSTRUCTION AND OPERATION OF THE CWL In 1968, a natural depression south of Lake Moondarra was dammed to the west with earth fill while to the south the road was re-routed and raised (Figure 2). The lagoon covers an area of 0.67 km2 and water is pumped in at a maximum rate of 70 000 m 3 day- 1 to maintain a lagoon volume of 2.19 x 106 m 3 â€˘ Over the years, substantial improvements to the operation of the Clear Water Lagoon have been carried out. The most significant was the maintenance of conditions allowing establishment and continued growth of a range of macrophytes. Early observations that water stored temporarily in the Clear Water Lagoon showed a marked
The turbid waters of Lake Moondarra in the foreground and the brilliant blue water of the clear water lagoon in the background.
poly aluminium chloride (PAC) is used to dose incoming water. A tank and dosing pump located at the main pump station distributes the chemical solution through a spray bar at the end of a turbulent section of the flume. Baffles in the flume downstream from the spraybar ensure that the PAC is well mixed in the water. A settling pond constructed at the end of the flume collects the floe obtained from dosing before the water enters the main body of the lagoon. A compressed air destratifier located close to the offtake operates in automatic mode throughout the year to maintain good mixing in the water column.
BIOWGICAL FUNCTIONS Turbidity
Fig. 2 -
Lake Moondarra showing location of the Clear Water Lagoon.
improvement in quality led to the decision in 1982 to pass all lake water through the Clear Water Lagoon before chlorination and distribution. The critical element was the maintenance of a constant water level in the Clear Water Lagoon thus preventing the adverse effects on rooted water plants resulting from drawdown and refilling. To enhance the performance of the Clear Water Lagoon, an open earth flume was constructed around the northern edge of the lagoon to place the lagoon water inlet as far as possible away from the offtake to the treatment plant (Figure 3). During periods of high turbidity,
Turbidity in Lake Moondarra is highest during the Northern Australian wet season (December, January and February). Turbidities up to 100 NTU have been recorded during these months while values are uniformly low (less than 10 NTU) during the dry season (March through to November) (Figure 4). Turbidity in the lake is related to inflow as estimated from changes in lake volume (Griffiths and Farrell, 1991) (Figure 5 (a)). Lake Moondarra is a relatively shallow lake with a single deep basin (maximum depth 22 m) near the dam wall. Over 250Jo of the lake area water has a depth which is less than the critical depth of mixing under the average prevailing conditions. During the dry season when there is no significant inflow, the fine substrate material is subject to resuspension under the influence of turbulent water movement resulting from wind-generated wave action. Turbidity in the lake is correlated with the wind transport factor, a value that describes the wind energy received at a point on the lake surface 100.0 - - - - - -- - - - - - - - - - - - - , r- - ,
o.t-l---~~~-----,-~-~- - . ------,--,-- - - , -. -- . - ~ JUL
Lake Moondarra Clear Water Lagoon Lake Julius
Fig. 3 - The Gear Water Lagoon showing depth contours (M) and water circulation pattern.
Fig. 4 -
Turbidity levels in Lake Julius and Lake Moondarra and after passage through the Clear Water Lagoon, 1989-1990. WATER December 1991
[] Hydrilla verticillata ~ Potamogeton tricarinatus
Vallisneria spiralis Typha domingensis
• • •
• *Fig. 6 - Distribution of four major macrophyte species in the Clear Water Lagoon.
WTF index Fig. 5 - Turbidity in Lake Moondarra in relation to inflow and wind energy (at times of 1.ero nflow). Dec. 1986-April 1988. WTF = Wind Transfer Factor.
(U.S. Army Coastal Engineering Research Centre, 1973, Griffiths and Farrell 1991) (Figure 5 (b)). Passage of this turbidity-laden water through the CWL produces a water consistently less than 2 NTU and usually below 1 NTU (Figure 4). Lagoon Vegetation Approximately 82% of the surface area of the lagoon has a vegetation cover (extending from the shore-line to a depth of approximately 5 m) comprising four dominant species of rooted macrophytes (Figure 6). There are three major habitat types each with a characteristic pattern of vegetation reflecting the texture and slope of the substrate and the exposure to wind/ wave energy (Griffiths and Farrell, 1991). Habitats dominated by Typha showed a marked seasonal fluctuation in total biomass with a maximum in December and minimum in June. The pattern suggests a synchronized pattern of seasonal growth and decline. Habitats dominated by Hydrilla exhibited a less marked seasonal pattern suggesting an almost continuous replacement of plants throughout the year but with a slightly lower standing stock during the winter months. The third habitat containing a mixture of plants also showed a strong seasonal variation of biomass but with a minimum harvest in October and a maximum in April (Griffiths and Farrell, 1991). The Clarification Process Entrapment of particles on Hydrilla, the dominant macrophyte in the lagoon, occurred through two mechanisms: • lodgement of particles against plant surfaces at the leading edge especially at the joints between leaf whorls and stem; • entrainment into localized swirling vortices resulting from the drag force downstream of the plant body causing the particles to spiral downwards to the nearest substrate. 34
WATER December 1991
Individual plants periodically slump to the substratum carrying with them their silt loading thus facilitating downward transport of the particulate matter and its incorporation and stabilization within the sediment. Maximum sedimentation occurred within the basin; the sediment being transported there by water movement from other parts of the lagoon . A gradual build-up of sediment will result over time in a slow migration of the front of the delta into the lagoon and gradual reduction in the depth of the lagoon basin. At current rates of accretion it is estimated that the depth of the basin will be reduced to a maximum of 6 m within a period of approximately 20 years (Griffiths and Farrell, 1991).
CONCLUSIONS The innovative use of an ecologically sustainable system has provided the city and industry of Mt. Isa with a reliable cost-effective water treatment system. The Clear Water Lagoon, the only documented case of this form of water treatment within Australia, has been an outstanding success. A similar capacity conventional water treatment plant would cost in the order of $10-20 million to design and build (pers. comm., Popple, Mt. Isa Water Board). There is now, in Australia, a much greater interest in the use of macrophyte based systems to meet water discharge requirements. The major stumbling block to a more widespread implementation of such systems has been the lack of information on suitable design criteria treatment process for drinking water quality. The Lake Moondarra Clear Water Lagoon system offers a design plan for an ecologically sustainable water treatment process without a large expenditure on capital works. It represents an economically attractive and ecologically sound method of meeting the now more stringent requirements relating to the provision of potable water.
REFERENCES Griffiths D.J. and Farrell P.O. (1991): Turbidity and Water Quality in Tropical Reservoirs in Northern Australia. Verh. Internal. Verein. Limnol. 24: 1465- 1470. U.S. Army Coastal Engineering Research Centre (1973): Shore Protection M anual Vol 1 U.S . Government Printing Office, Washington .
Note: Figures 2, 3, 5 and 6 are reproduced with permission from Verh Internal. Verein. Limnol.
WATER SUPPLY PEAKING FACIDRS: EFFECT OF DEMAND MANAGEMENT by M. CLEWETT and L. APPLEGREN
SUMMARY This paper deals with two aspects of water supply design peaking factors. Firstly, it shows how design factors have been determined for Toowoomba city as a whole and for selected pressure zones within the city's overall reticulation system. Secondly, it examines the effect on the total city factors of substantial changes in water consumption patterns caused by the introduction of demand management measures.
Murray Clewett is an Engineer specialising in water supply and sewerage works with Toowoomba City Council. For over 20 years, he has been closely associated with demand management of the water supply system.
INTRODUCTION Traditionally the design of water supply system components has used various multiplier or peaking factors to account for the persistence of high demand periods. Where demand data for specific localities are not available water authorities have recommended nominal values for design purposes. In Queensland, the Water Resources Commission (WRC) recommends the use of the following factors and values in its Guideline for Planning and Design of Urban Water Supply Schemes (1989) for those situations where there are no actual data. Maximum Day (Max D) 2.25 Average Day
Lex Appelgren is an Associate of Sinclair Knight where he specialises in water supply and sewerage works. While previously working for Toowoomba City Council he developed an interest in demand persiste nee and management.
Mean Day of Maximum Month (MDMM) 1.5 Average Day The Public Works Department (PWD) of NSW uses design criteria based on annual peak day and peak instantaneous demand. This methodology appears not to place as much emphasis on demand persistence but Anderson and Vickers (1989) report a number of examples of terminal storage systems constructed by PWD which utilise demand persistence techniques for design and operation. If the WRC values shown above are adopted without critical assessment then it is likely that the various components of the water supply scheme may be under or over-designed. In either case the optimum value for the dollar spent may not be obtained. This paper shows the development of the WRC demand persistence parameter values for Toowoomba city. The techniques used can be readily adapted for developing demand persistence design values for other authorities. The paper also examines the effect that the introduction of universal water metering and pricing policy demand measures have had on the values and relationships of the WRC demand persistence design factors.
PERSISTENCE OF PEAK DEMANDS Basic techniques for demand persistence analysis have been presented by Gould (1976), Clewett (1979) and have been further developed by Anderson and Vickers (1989). Gould showed that by using the Goodrich Formula as presented by Steel (1960) it was possible to predict the persistence of high daily demand in a water supply system. He plotted on a log-log scale the ratio of the average demand in peak t consecutive days to the average flow for 365 days versus time in days for a number of Australian cities and found that the results approximated to the Goodrich type formula . p (1) R•t" when P = Ratio Average demand in peak t consecutive days Average demand for 365 days R = Ratio Average demand on maximum day Average demand for 365 days t = number of consecutive days of peak flow demand. n = index, the value of which indicates the degree of persistence of high demand. A high numerical value means that the high demand is relatively short lived while a lower value means that the line has a flatter slope and the high demand period persists for a longer time. If both sides of equation (1) are multiplied by the average demand (A) over 365 days then: P•A
when P•A R•A
= Average demand over peak t consecutive days = Average demand on the maximum day.
The advantage of expressing consumption in the Goodrich form is that the average demand for any numqer of consecutive days up to at least 49 can be easily calculated. Note that if t = 1, the Max D consumption can be calculated and if t = 31 the MDMM consumption is also obtained.
TOOWOOMBA WATER SUPPLY Toowoomba city is a regional centre with a population approaching 85 000. It is located 120 km west of Brisbane on the edge of the Great Dividing Range and at an elevation of 700 metres. Annual rainfall is 960 mm but, unlike that for the majority of Queensland, it is well distributed with 105 rain days per annum. The climate is temperate with a summer average temperature of27° and a winter average of l7 °C. Because Toowoomba's climate is significantly different from that of the majority of Queensland it is reasonable to expect the WRC parameter values to be at variance with the state average or norms. Tobie 1 - Historical Water Data for Toowoomba, summarises populations, total city and per capita water consumption for the 1950/ 51 to 1990/ 91 period. It also presents Max D and MDMM ratios based on the raw water consumption data. This paper examines the effect that regression trend analysis of Avg D consumptions has on these ratios. The Toowoomba Water Supply reticulation system is divided into eight different water supply zones but for the purposes of this paper a number of zones have been combined and only the following zones are considered: (a) Mt Lofty/Picnic Point/ Gabbinbar (b) Mt Kynoch / Platz (c) Mt Kynoch Treated Water comprising (a) + (b) (d) Homers (e) City (f) Total Toowoomba comprising (c) + (d) + (e) Mt Kynoch Treated Water is obtained from surface storages while Homers and City Zones are supplied with softened underground water. Both sources are treated to a high standard and it is considered unlikely that water source influences demand patterns in Toowoomba.
GOODRICH ANALYSIS OF DATA The data for each of the zones and combined zones for each financial year on a daily basis from 1982/83 to 1990/91 were analysed WATER December 1991
Historical water data for Toowoomba YEAR
PER CAPITA CONSUMPTION
1950/51 1951/52 1952/53 1953/54 1954/55 1955/56 1956/57 1957/58 1958/59 1959/60
37902 39354 40834 42370 43619 44561 45523 46507 47513 48540
1960/61 1961 /62 1962163 1963/64. 1964/65. 1965/66. 1966/6r 1967/68' 1968/69 1969/70
49603 50674 51766 52887 54027 55186 56262 57247 58248 59267
1970/71 1971/72 1972/73 1973/74 1974/75 1975/76 1976/77 19TT/78 1978/79 1979/80
62685 63933 65673 67590 68895 69780 70520 71115 71735
1980/81 1981/82 1982/83 1983/84 1984/85 1985/86 1986/87 1987/88. 1988/89 1989/90 1990/91
72575 73560 74560 75555 76580 TT615 78620 79585 80560 81550 83030
16.320 16.834 12.725 17.702 19.394 18.262 15.016 17.189
8.374 11 .958 10.899 12.267 9.827 9.843 14.210 13.648 12.164 13.956
5627 5738 6913 7593 8028 8190 TT32 8924 8984 9622
34.578 30.618 37.660 41.529 41 .992
19.107 20.262 24 .276 25.685 25.940 30.036 24 .431 29.454 30.339 32.484
15.416 15.721 18.939 20.803 21 .994 22.437 21 .184 24.451 24.6 14 26 .362
40.5TT 45.015 56.408 50.628 59.334 54.032 51 .617 61 .073 44.370 49.053
30.505 31 .285 39.030 37.166 43.672 35.919 36.692 46.669 29.452 33.498
26.921 25.530 32.263 30.274 32.082 30.014 30.115 33.447 26.433 27.3TT
40.806 40.090 49.640 35 .2TT 44 .579 40.587 49.331 33.635 51 .299 59.473 59.545
33.989 26.523 37.435 25.549 32.330 33.707 34.051 26.598 36.635 38.500 46.103
24.304 23.721 26.732 23.003 25.767
3978 4477 3587 3593 5187 4982
11TT6 11050 11710 10985 10992 12208 9648
10020 8871 8658 9757 8419 9405
9725 10062 9110 10481 111 35 13088
27.567 24.891 28.715 30.507 35.858
713 709 673 718 882 TT 1 878 784 740
385 400 469
393 407 407 377 427 423 445
662 414 467
335 322 359
468 361 502 338 422 434
467 582 523 627 423 637 729 717
1.507 1.763 1.748 1.672 1.849 1.800 1.714 1.826 1.679 1.792
1.233 1.225 1.210 1.228 1.361 1.197 1.218 1.395 1.114 1.224
1.679 1.690 1.857 1.534 1.730 1.523 1.789 1.351 1.786 1.949 1.661
1.398 1.118 1.400 1.111 1.255 1.265 1.235 1.069 1.276 1.262 1.286
407 505 461 475 436 432 474 372 382
1.541 1.445 1.540 1.687 1.593
1.239 1.289 1.282 1.235 1.179 1.339 1.153 1.205 1.233 1.232
506 499 610
1.497 1.372 1.295 1.798 1.365 1.338 1.234 1.232
225 221 312 293
544 434 515 521 548
221 304 267
400 397 292 397 426 393 316
343 351 313
455 472 555
• Water Restrictions AppUed
using a Lotus 1-2-3 spreadsheet. Daily flows and reservoir levels were entered into the spreadsheet from each 13 May (to accommodate the 49 day moving average) to 30 June the following year. The spreadsheet then calculated the moving averages for 1, 2, 3, 5, 7, 14, 31 and 49 previous day flows and divided each by the annual daily average to obtain the respective ratios. The maximum ratios were then found for each category for the nine years of record. Thble 2 - Toowoomba Water Supply Goodrich Analysis shows the analysis results for each of the pressure zones and zone combinations studied. The Maximum Ratios were obtained using actual Avg D values. The Maximum Adjusted Ratios have been calculated using smoothed regression trend Avg D values. This exercise resulted in higher Max D ratios than for the raw data as the highest ratios often occurred in above average years. It is considered that this better represents assumed future conditions as projected average flows are usually smooth curves. The Adjusted Maximum Ratio data are presented in a log-log format on Figure 1 - Toowoomba Water Zones Goodrich Curves and in a more familiar format with linear scales on Figure 2. The following conclusions may be drawn from Figure 1: • With the exception of City Zone the log-log relationship is reasonably linear for each zone or combination of zones thus substantiating the validity of using equation (1) to predict consumption; • With the exception of City Zone the slope of the curves is approximately the same thus indicating a similar degree of persistence of demand. Calculated values of "n" are shown in Tobie 3. It is not surprising that City Zone exhibits markedly different characteristics as it is predominantly commercial and industrial with very little residential demand and therefore different in nature. In Figure 3 - Max D and MDMM Ratios v Population, the Max D and MDMM ratios have been plotted for each of the zone populations as shown above. For Max D consumption the ratio 36
WATER December 1991
TABLE 2 Toowoomba Water Supply: Goodrich Analysis 0AYS LOG (DAYS)
2.36 2.50 0.40
2.19 2.30 0.36
2.03 2.01 0.30
1.96 1.94 0.29
1.93 1.91 0.26
1.8 1.78 0.25
1.63 1.61 0.21
1.52 1.50 0.18
2.19 2.05 0.31
2.16 2.03 0.31
1.82 1.71 0.23
1.6 1.50 0.18
1.5 1.41 0.15
1.3 1.32 0.12
1.26 1.25 0.10
1.2 1.22 0.09
HORNEAS ZONE 1982/83 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED) CITY ZONE 1982/83 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED)
LOFTYJl'ICNIC POINT/GA88IN8AR ZONES 1962/83 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED)
2.25 2.26 0.35
2.02 2.03 0.31
1.97 1.98 0.30
1.89 1.95 0.29
1.85 1.92 0.28
1.7 1.77 0.25
1.56 1.57 0.20
1.44 1.44 0.18
2.07 1.95 0.29
2.01 1.90 0.28
1.91 1.80 0.26
1.84 1.55 0.19
1.53 1.44 0.16
1.98 1.69 0.28
1.91 1.84 0. 27
1.83 1.76 0.25
1.78 1.70 0.23
1.62 1.56 0.19
1.48 1.43 0.15
1.9 1.83 0.26
1.82 1.76 0.24
1.76 1.71 0.23
1.68 1.62 0.21
1.54 1.49 0.17
1.42 1.38 0.14
MT KYNOCH/Pl.ATZ ZONES 1983/82 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED)
2.34 2.21 0.34
2.1 1.98 0.30
MT KYNOCH TREATED WATER ZONES 1982/83 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED)
2.15 2.07 0.32
1.98 1.91 0.28
TOOWOOMBA TOTAL ZONES 1982/83 TO 1990/91 MAXIMUM RATIOS ADJUSTED RATIOS LOG (ADJUSTED)
2.09 2.02 0.30
1.9 1.84 0.26
decreases as the population increases. This finding is consistent with the observation of Anderson and Vickers (1989) who found that larger cities have a lower peak day to average day ratio due to a greater diversity of demand and larger base load demands from industrial users. It is interesting to note in Toowoomba that all zones do not necessarily experience their maximum consumption at the same time and this would also contribute to the decrease in the Max D ratio with increase in population. The MDMM ratio exhibits a similar trend to Max D but is not as marked.
o. , 0.38 0,36
0.34 0.32 0.3
0 .26 0.2 4 0 .22 0.2 Q. 18
0.16 0 . 14
0. 12 0.1 0 .08
LOG( NUMB[ R H0 RN[ RS
Fig. 1 -
l /PP /G
KY N/ PL
T t.4 8A
Toowoomba water zones Goodrich curves 2.5
only 508 mm, the lowest annual total since-records commenced in 1868. This climatic condition combined with a lack of enforced water restrictions and continued population growth has led to the high 1991 water consumption. Figure 5 - Per Capita Water Consumption from 1969 to 1991 shows Max D, MDMM, Avg D and Min D data expressed in per capita terms. This period of data has been chosen because it is free of enforced water restrictions apart from a brief period from August 1987 to February 1988. It also includes the periods of water consumption decline and regrowth. The interesting feature of this data is the apparent sympathy between Avg D and the other ratios. The subsequent figures in this paper examine this relationship more closely. The trend noted in Figure 4 is also apparent in the per capita water consumptions shown on Figure 5 - Per Capita Water Consumption. Per capita consumption since 1988 has increased markedly. It is considered this has been influenced by the drop in real money terms of excess water charges which have remained constant in dollar terms since 1984/ 85 . It is also apparent that modification to the present pricing policy will soon be necessary if future water consumption growth is to be effectively controlled. Figure 6 - Toowoomba Per Capita Regression, presents a regression analysis trending of the data. This analysis was carried out on daily average per capita consumptions in three steps. Firstly, for the period 1969 to 1978; then from 1978 to 1981 and finally for 1981 to 1991. This was done to accommodate the discontinuity in
Table 3 Zonal Data Summary
Fig. 2 -
Max D Ratio
2.50 2.26 2.21 2. 07 2.02
1.61 1.57 1.55 1.56 1.49
-0.1 3 -0. 11 -0. 10 -0.08 -0.09
500 000 700 700 200
Toowoomba water zones Goodrich curves
9 30 37 67 78
Homers Zone Mt Lofty/ Picnic Pt/Gabbinbar Zone Mt Kynoch/ Platz Zone Mt Ky noch Treated Zone Toowoomba
1.2 1. 1 50 20
YEAR ENDIN G JUNE 19_
(Tho usands) WATER ZONE POPULATION C
Fig. 3 -
Fig. 4 -
Max D and MDMM rations v.population
For Toowoomba the Max D ratio ranges from 2.02 to 2.50 while the MDMM ratio ranges from 1.49 to 1.61 depending on the zone. As these values are significantly different from those given in the WRC Guidelines (1989) they should be used in water supply analysis for Toowoomba.
EFFECT OF WATER METERING ON MAXIMUM DAY CONSUMPTION Figure 4 - City Water Consumption, was plotted from the data in Table 1 - Historical Water Data for Toowoomba. It shows a significant growth in water consumption from 1950 to 1978. In 1978 universal water metering was introduced along with a base charge, 324 kL/a allowance and excess rate water pricing policy (Clewett, 1987). From 1978 to 1981 total water consumption declined as the impact of the metering/ pricing policy was experienced by consumers. Since 1981 the growth in total water consumption has resumed and in 1991 consumption exceeded the 1978 level. Rainfall in 1990 was 38
WATER December 1991
Toowoomba city water consumption 900
~z 3 >
, oo 300
YCAR EN0INC JUNE 19_ C
Fig. 5 -
MAX DA Y
Per capita water consumption
AV DA Y
MIN DA Y
consumer behaviour caused by the introduction of universal water metering. Figure 7 - Toowoomba Maximum Day Regression, shows a plot of Avg D consumptions with its associated regression trend line for the period 1969 to 1991. When an envelope of 2.02 times the Avg D trend values is plotted the envelope encompasses all of the Max D values. Figure 8 - Toowoomba MDMM Regression, show a similar outcome when an envelope of 1.49 times the Avg D trend values is plotted. This is a somewhat unexpected result. Conventional wisdom would suggest that Max D and to a lesser extent MDMM consumptions would be influenced by short term climatic phenomena and would not be so closely related to Avg D trends (particularly when Avg D trends are being driven by demand management policies) . The 2.02 and 1.49 multipliers in Figure 7 and 8 respectively have been selected as the maximum adjusted Max D and MDMM ratios for Toowoomba from Table 2. If the relationship can be applied to
ii:, ~ z
CONCLUSIONS • The Goodrich type equation P = R*t" gives a reasonable design basis for all water supply zones within Toowoomba with the exception of the City Zone which is predominantly commercial and industrial in nature. • Ratios for maximum day (Max D) demand and mean day maximum month (MDMM) demand need to be based on the smoothed average trend line for each year rather than on the actual average day (Avg D) flow. • Ratios for maximum day (Max D) flows for different water supply zones within Toowoomba decrease with increasing population while the ratio for mean day maximum month (MDMM) exhibits this trend less strongly. • Demand management of Toowoomba's water supply since 1978 has significantly reduced average annual demand until the last three years when pricing policies have been relaxed. • Demand management has not affected maximum day (Max D) and mean day maximum month (MDMM) ratios thereby reducing peak demand stresses on Toowoomba's water supply system.
' ~ u
other localities, populations and operatilli situations then different envelope widths would be expected.
77 79 81 8.3 85 87 89 91 76 78 80 82 84 86 88 90 HAR ENDING JUNE 19_
Steel, E.W. 1960, Water Supply and Sewerage, McGraw Hill, New York, p 18. Gould , B.W. 1974, "Persistence of High Daily Demands in Australian Water Suppl y Systems", Water Journal of the Australian Water and Wastewater Association, Vol. 1, No. 3, pp. 20-22. Clewell, M.A. 1979, "Towards Rationalising the Sizes of Trunk Mains and Service Reservoirs", Proceedings of the Thirtieth Conference of Local Authority Engineers, Townsville, Queensland, October, 1979. Clewell, M.A. 1987, "Water Meters, Pricing and Water Consumption in Toowoomba". Australian Water Resources Council & Western Australia Water Resources Council , Working Paper for the National Workshop on Urban Water Demand Management, Perth. Anderson, J.M. and Vickers, R.J. 1989, "Sizing and Operation of Terminal Storages", Proceedings of the Thirteenth Federal Convention of the Australian Water and Wastewater Association, Canberra, Australian CapitaJTerritory, 6-10 March, 1989 . Guidelines fo r Planning and Design of Urban Water Supply Schemes, 1989, Local Authority Planning Division, Water Resources Commission , Queensland .
AV DAY R(GR(S SION
Fig. 6 - Toowoomba per capita regression 80
J 3 z a
Treating Water Properly
Design and manufacture of municipal and industrial filtration equipment for:
71 70 0
"Fig. 7 -
;;J 3 z a
77 79 81 83 85 87 89 91 76 78 80 82 64 86 88 90 YEAR ENDING JU NE 19_ MAX DAY
• • • • •
Toowoomba maximum day regression
FULL SERVICE SUPPORT THROUGHOUT AUSTRALIA
~ a u
Potable Water Waste Water Treatment and Re-use Sewage Treatment Industrial Waste Treatment UV Disinfection
Locked Mall Bag No.1
Windsor NSW 2756 69
YEAR ENDING JUNE 1 g_ 0
Fig. 8 -
(045) n-seoo (045) n-6804
2/45 Klngtel Place Geebung QLD 4034 Tel: (07) 265-4388 Fax: (07) 265-3502
Toowoomba MDMM regression WATER December 1991
AWRC Water Technology Committee At the 14th meeting held in Darwin in September and after three very busy years, Peter Manoel, Engineering & Water Supply Department, South Australia stepped down as Chair of Water Technology Committee. The work of Peter and his Technical Secretary, Mary Drikas, is acknowledged. The new Chair is Barry Sanders, Manager, Headworks & Treatment, Water Authority of Western Australia. Mr Sanders has been WA's representative for three years. The Committee has four new members Peter Cooper (SA), Roger Payne (Vic), Fred King (NSW) and Neil McDonald (Commonwealth).
KEY PROJECTS NH&MRC and AWRC Drinking Water Guidelines NH&MRC and AWRC have agreed that the 1987 Guidelines for Drinking Water Quality in Australia will be revised and issued in .late 1992 or early 1993. The purpose of the guidelines is to provide a framework in which drinking water quality decisions can be made which are consistent with the protection of public health and the provision of an acceptable drinking water supply to the community. A joint Co-ordinating Committee has been established comprising three representatives and an observer from both AWRC and NH&MRC, an independent Chair, Doug Lane, and a Secretariat provided by NH&MRC. The procedure for review has been agreed upon and technical reference panels established. A research officer is to be engaged to enable the panels to begin their various tasks. The revision will take into consideration the soon to be released WHO guidelines. Release of the draft document is scheduled for the middle of 1992. Contact: D Bursill (08) 226 2501.
A workshop on Automatic Meter Reading Systems was organised for November 1991 in Melbourne. Lagoon Workshop A workshop for the design and operation of wastewater treatment lagoons has been tentatively scheduled for late 1992. Contact R Payne (03) 615 4747.
WATCHING BRIEFS WTC is maintaining watching briefs on, or is initiating research into, the following: • Greywater Reuse • Algal Toxin Removal • Point of Use Devices • Phosphorus in Detergents • Pipe Materials • Trenchless Technology • Wind and Solar Powered Systems
SITE VISIT Members visited a remote Aboriginal community, Paradale, a community of some 40 people, about 200 km SSW of Darwin. Paradale is completely surrounded by areas subject to inundation and so can be cut off from road transport for several months. Water is supplied from a solar powered bore. The visit highlighted the vast differences between remote communities and large urban areas, a fact which is particularly pertinent when considering the draft national guidelines. The Committee's thanks go to Norm Allen and to the people of Para dale.
NEXT MEETING The next Water Technology Committee Meeting will be held in Adelaide in March 1992.
Guidelines for Sewerage Systems • Effluent Management Guidelines. As a first step, Camp Scott Furphy Pty Ltd was engaged to produce a 'Review of Effluent Disposal Practices' which has now been published under the AWRC Water Management Series (No 20). Copies are available for about $25 from the Secretary. Draft guidelines are being revised and are to be submitted to Standing Committee in November. • Sludge Management Guidelines. A Working Group, chaired by Peter Dalglish, has been working on draft guidelines, which following revision are to be submitted to Standing Committee in November. • Guidelines for Acceptance of Wastes into Sewerage Systems. Draft guidelines have been prepared by a Working Group, chaired by Tony Catalano, and following revision are to be submitted to Standing Committee in November. Contact: B Sheedy (03) 615 5885
WA, Mr B Sanders (Chairman), (09) 420 2453; NT, Mr N Allen, (089) 82 6103; TAS, Mr B Cash, (002) 30 8033; SA, Mr P Cooper, (08) 226 2247; QLD, Mr D Gardiner, (07) 224 2655; NSW, Mr F King, (02) 228 4238; COMM, Dr N McDonald, (06) 615 4757; VIC, Mr R Payne, (03) 615 4757. Invited Specialist, CSIRO Dr B Bolto (03) 542 2231 Technical Secretary: Mr L. Edmonds (09) 420 2460 Water Authority of W.A. PO Box 100 Leederville W Aust 6005
Water Efficient Appliances and Plumbing (WEAP) WTC endorsed the WEAP group's recommendations and will recommend to Standing Committee that: (a) As from January l, 1993, all new or replacement WC cisterns and pans shall be of the 6/3 litre dual flush type with matching pans, or approved equivalent. (b) The new national Water Conservation Rating Scheme for water efficient domestic appliances, similar to Melbourne Water's scheme which is already in place, be actively and financially supported by authorities.
Synopses by February 28, 1992 Completed papers (if accepted) will be required by April 30, 1992
OTHER PROJECTS Asset Management The report on the workshop held in Melbourne in November 1990 was tabled. To implement the recommendations requires significant resources and means of implementation are being explored. Contact: R Vass (03) 615 4340 Information Technology Organisation of a national workshop on Telemetry has been deferred until 1993. 40
WATER December 1991
COMMITTEE MEMBERS t
Recycled Water Seminar Charles Stuart University, Wagga Wagga, NSW May 191/s 20, 1992
CALL FOR PAPERS
Themes - Regulatory framework and controls - Overseas experience - Practical applications in Australia - Theoretical/scientific aspects J. Patruno, Secretary NSW Recycled Water Co-ordinating Committee Cl- Public Works Department 12th Floor State Office Block Phillip Street SYDNEY, NSW, 2000 Information: Phone (02) 228 4751 - Fax (02) 228 3100