The aerobic treatment of reverse osmosis (R/O) permeate was investigated to determine its suitability for reuse in the dairy industry. The biodegradability was characterised by a series of batch tests and the biokinetic parameters μm, Ks and Y were found to be 2.4 d−1, 38 mg L−1 and 0.45 mg TSS/mg Chemical Oxygen Demand (COD) respectively. The permeate was treated aerobically in a 5 litre reactor resulting in an effluent soluble COD of 18 mg L−1. The feasibility of biotreatment was also tested at a pilot plant level. Soluble COD removal efficiencies of over 90% were achieved in trials at 10 and 20-hour hydraulic retention times. True steady state operation was never achieved due to highly variable influent substrate concentrations. The Sludge Volume Index was in the range of 40 to 50 at an HRT of 10 hours, and increased to 70 to 140 at a 20 hour HRT. The test showed that R/O permeate has biodegradability comparable to general dairy effluent, and can potentially be reused after secondary treatment.

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