[Acetate production by acidification-homoacetogenesis two-phase coupling process: effect of initial pH].

The effect of initial pH values on acetate production was studied in the acidification-homoacetogenesis two-phase coupling system using glucose as the substrate and the heat-treated and activated anaerobic sludge as the inoculum. Substrate degradation, product yield and pH variation during fermentation were examined at various initial pH values (5, 6, 7, 8, 9, 10 and 11). The results show that initial pH values affect volatile fatty acids and ethanol production not only in the acidification phase itself but also in the homoacetogenesis phase. Ethanol-type fermentation mainly takes place at initial pH 5 while butyrate-type fermentation at initial pH 6 and 7. But acetate is the dominant product at initial pH 8-11. The optimal initial pH value is 10 for acetate production in the two-phase coupling system. At initial pH 8-11, ethanol concentration is highest at the beginning of acidification, but there is a subsequent decline as ethanol is converted to acetate as a result of further metabolism of the microbes.