Treatment of high-strength liquid wastes by auto-thermal aerobic digestion

Abstract

Auto-thermal aerobic digesters comprise a simple, robust, inexpensive technologyappropriate for on-site liquid waste treatment by small- and medium-sized enterprises.They have been shown to be effective at treating a wide range of effluents and liquorsarising from food processing and chemical plants, especially those with high levels ofbiological oxygen demand (BOD), or for small-scale sewage treatment.Liquid circulates around the reactor vessel by pumping through a venturi nozzle, whichdraws air into the flow. As the microbial community develops, the system self-heats andorganic matter is removed as CO2, NH3 and water. The temperature of the insulatedvessel may rise to 55e°C or more as the thermophilic community becomes established.BOD levels typically reduce by 90% over a 3-5 day residence time. Auto-thermal aerobicdigestion (ATAD) acts faster than mesophilic or anerobic degradation and is veryresistant to organic toxins (pentachlorophenol) or metal pollutants (Cu2+, Zn2+, Ni2J inthe waste.Examples are shown of wastes and liquors successfully treated by pilot-scale ATADsystems up to I 000 litres in size. These include effluents from food processing (icecream, chocolate, egg pasteurisation, brewing), chemical plants (wood processing,phenolic liquor) and silage pit effluent.Auto-thermal aerobic digestion offers a versatile, cost-effective solution for liquid wastetreatment in a climate of increasing demands from Regulatory Authorities and increasingcosts of conventional off-site waste disposal such as sewerage or landfill charges.