The effect of thermophilic heat treatment on the anaerobic digestibility of primary sludge
Master Thesis
1992
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University of Cape Town
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Abstract
In a time when the world is becoming more environmentally conscious, and is looking for simple, efficient, economical, and environmentally friendly solutions to sewage and sludge treatment, the dual digestion system presents itself as an attractive alternative to other sludge treatment systems. The dual digestion system comprises an autoheated thermophilic (55-65°C) aerobic first stage and a mesophilic (37°C) anaerobic second stage. Past research into the dual digestion system has given rise, inter alia, to the following claims (de Villiers, et al, 1991): a) sludge disinfection and stabilisation occur in one process - disinfection .in the thermophilic aerobic first stage and stabilisation in the anaerobic second stage. b) the stability of the anaerobic stage is considerably 'improved by the increase in H2C03 * alkalinity and pH in the aerobic stage. c) in the aerobic stage the sludge is aerobically or thermally pretreated (conditioned) making it more readily digestible under anaerobic conditions, thereby allowing significantly reduced retention times from 25 to 30 days for normal digestion, to 8 to 10 days. Messenger (1991), in a full scale investigation at the Potsdam Wastewater Treatment Plant in Milnerton, Cape Town, verified claims (a) and (b), but was unable to verify claim ( c) above. It was the intention in this investigation to verify this claim at full scale using the existing dual digestion plant at Milnerton. However, after 9 months of starting up the plant, the fiberglass aerobic tank failed structurally along one of its seams. This failure was so extensive that the plant could not be started up again and the research project was terminated. The failure of the aerobic reactor necessitated continuing this thesis investigation in the laboratory.
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Bibliography: pages 61-2.
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Izzett, H. 1992. The effect of thermophilic heat treatment on the anaerobic digestibility of primary sludge. University of Cape Town.