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

Abstract

Auto-thermal aerobic digesters comprise a simple, robust, inexpensive technology
appropriate 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 liquors
arising from food processing and chemical plants, especially those with high levels of
biological oxygen demand (BOD), or for small-scale sewage treatment.
Liquid circulates around the reactor vessel by pumping through a venturi nozzle, which
draws air into the flow. As the microbial community develops, the system self-heats and
organic matter is removed as CO2, NH3 and water. The temperature of the insulated
vessel 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 aerobic
digestion (ATAD) acts faster than mesophilic or anerobic degradation and is very
resistant to organic toxins (pentachlorophenol) or metal pollutants (Cu2+
, Zn2+
, Ni2
J in
the waste.
Examples are shown of wastes and liquors successfully treated by pilot-scale ATAD
systems 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 waste
treatment in a climate of increasing demands from Regulatory Authorities and increasing
costs of conventional off-site waste disposal such as sewerage or landfill charges.