WASTEWATER
60 50 40 ..J
Cl 30 E
20
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-1
:
-
- OXN
---
+ Ammonia N
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Figure 2. Longford SBR Effluent, July 99 - June 00
utilising only 8 aerators. Theoretically, this was insufficient for adequate mixing, but p revious operating experience with the aerated lagoon suggested otherwise. After th e de c anting sys t e m was completed (April 12, 1999), no sludge was wasted from the SBR for a further 45 days. Over this period, ammonia N dropped to about 2 mg/ L. Mixed liquor w ithdrawal then commenced at 500 kL/ d to achieve a sludge age of 30 d. M easured DO in the system grea tly exceeded 2 mg/L, so one further aerator was turned off to save power. T he result was catastrophi c because DO rose even further and efiluent ammonia rose very rapidly. M easurement of SS during the aeration stage suggested that the majority of the sludge was not being resuspended during the aerati on period. The plant performance recovered rapidly after the eighth aerator was tu rned on again. This demonstrated the need to maintain adequate power input for mixing. Efflue nt ammonia from the SBR has been between 0-3 mg/ L ever since (Figure 2). When all meatworks effiuent is directed to the CAL, oxidised N varies in a consistent fas hio n from 15mg/L on Monday rising to 30 mg/L by the end of the week. By-passing around the CAL, when optimised, reduced oxidised N to 5 - 10 mg/L (Figure 2) . Ammonia levels in Lagoon 6 (the plant effiuent) remained of concern for the remainder of the winter. Ammonia levels in Lagoon 6 started to drop rapidly in early summer (mid-Novemb er), presumably caused by increased algal activity. Total inorganic N remained below 3 mg/ L for four months, but both oxidised N and ammonia then rose and remained at about 5 and 10 mg/L respectively until the end ofJuly. It appears that ammonia is liberated from sludge stored in the lagoons, but is removed by algal activity during summer. Sludge wasted from the SBR will be returned to the CAL (as at Gippsland) when funds 38
WATER JULY 2001
permit. The improved condition of the lagoons has attracted over 65 species of birds to the lagoons.
New installations A treatment plant similar to the Gippsland plant is presently undergoing commissioning at C ranbourne Victoria , a large plant is being commissioned at Innisfail, Queensland and construction is about to commence at Ararat on a plant similar to the Gippsland Plant.
Conclusions Conversion of existing lagoon systems to SBR operation is a simple and economic upgrade for reduction of N disc harges. W e have shown in two fullscale plants that anaerobic treatment of the raw eff1u ent from meatworks, together with waste sludge from the SBR can achieve highly efficient removal of BOD and N in the downstream SBR, influent levels of 150 - 250 mg/L N being reduced by approximately 95%. Furthermore, sludge production, sludge handling and power consumption were minimised. Treatment of the effiuent with alum is straightfo rward and effective showing that river discharge and/ or reuse within the meatworks is a real possibility fo r the future. We are confident that other food manufacturing effluents (which also contain high levels of BOD and N) such as those from dairies, mil k processing, piggeries and feed lots would be equally amenable to treatment by such a process.
Acknowledgements Thanks are du e and tendered to Ms M. Kelly for h er contribution to the laboratory program and to M s. M . Caban for monitoring the commissioning of the Gippsland Plant. The Longford CAL was designed by GHD Pty Ltd. Special thanks are expressed to the management and operating staff of Longford plant for their support before during and after commissioning of that plant.
The Authors Bill Raper worked in CSIRO D ivision of Molecular Science and was an early proponent ofBNR, organising the first and second BNR Confere nces in Australia in Ballarat and Albury. Now retired, he is a consultant, specialising in nutrient removal process design. Wildern Consul ting Group, 8 D avies Street, Brighton E ast Vic 3187, Australia. (email: wildern@mira .net). John Green worked in the meat industry as a plant engineer and consultant and at CSIRO Meat R esearch Laboratories. He is now specialising in environment solutions for the meat and allied industries. Greeneng Pty Ltd, 12 Angle R oad, Balwyn Vic 3103, Australia. (email: greeneng@ mira.net).
References Coban M . (1996) . 'Sequencing Batch Reactor for R emoval of Nitrogen from Abattoir Wastewaters'. Minor Thesis for the degree of Master of Environmental Engineering, University of Melbourne. Ganczarczyk J (1983). Activated Sludge Process: Theory and Practice, Marcel Dekker, N ew York , USA Green J M, R aper W G C and Coban M. (1997) . Simple Process for Nutrient R emoval fro m Food Processing Effluents. Proceedings of the Australian Water and Wastewater Association 17th Federal Convention, Melbourne Australia. Hartley K J 1988. Operating the Activated Sludge Process. Gutteridge Haskins & Davey Pty. Ltd. Brisbane , Australia. R aper W G C and Green J M (1994) . 'Removal o f nutrients from effluents'. Australian Patent 701363 . R aper W G C. and Green J M, (1995). 'Low Capital Process for Removal of N from Abattoir Wastewater'. Proceerungs, Meat 95 Conference, Gold Coast, September, pp ll a-1 to lla-4. Subramaniam K, Greenfield PF, Ho KM.Johns MR and Keller J (1994). Efficient biological nutrient removal in high strength wastewater using combined anaerobic-sequencing batch reactor treatment. Water Sc ience & Technology 30 (6) 315-321