Simple process for nutrient removal from food processing effluents

Food processing effluents often contain high levels of nutrients, particularly N. Conventionally, anaerobic ponds are used to purify these effluents in Australia, giving cost-effective removal of BOD but little nutrient removal. It has become apparent that disposal by irrigation as presently practised normally exceeds sustainable N application rates, thus reduction of nutrient levels before irrigation is becoming mandatory. Meatworks effluent is often discharged to country town sewers, frequently accounting for 50-75% of the nutrient load. Meatworks effluents contain 1,000-4,000 mg/L BOD, 200-400 mg/L TKN and 20-50 mg/L P. Conventional BNR technology can readily remove nutrients from such effluents, either alone or in combination with anaerobic ponds but sludge handling on such a small scale poses economic problems. Laboratory scale trials showed that both BOD removal from meatworks effluent and sludge disposal could be achieved readily in conventional anaerobic ponds. The pond effluent, together with the town sewage if required, could be treated in a sequencing batch reactor (SBR) designed for nitrification/denitrification service. Optimisation of the anaerobic pond operation was required to ensure production of the minimum BOD:N ratio needed for N removal. This paper will describe the design and commissioning of two plants; a demonstration plant installed at a typical sized meatworks in Gippsland, Victoria, and a full scale plant for treatment of combined domestic sewage and effluent from a large meatworks at Longford, Tasmania. In neither case (for different reasons) has P removal yet been required. It was demonstrated that 98% of BOD and up to 95% N removal may be cheaply and readily achieved in the SBR. Where lagoons are used, levels of N suitable for river discharge can be achieved. P can be readily removed by alum treatment when required.