Enzyme activities under anaerobic and aerobic conditions in activated sludge sequencing batch reactor

An experimental study was performed to observe the effect of electron acceptor conditions on the enzyme activities in an anaerobic–aerobic activated sludge sequencing batch reactor (SBR). Four types of extra-cellular enzymes, i.e. alkaline phosphatase, acid phosphatase, α-glucosidase and protease were selected for the study. In addition to these enzymes, dehydrogenase, an intracellular enzyme, was also assayed. A lab scale anaerobic–aerobic SBR was operated and used for the experimental work. It was observed that the specific enzyme activities did not change significantly during anaerobic and aerobic phase of SBR. The enzymatic behavior of sludge observed under anaerobic and aerobic conditions was explained by considering three important factors: (1) enzyme synthesis under aerobic and anaerobic conditions, (2) location of enzymes, and (3) stability of enzymes in activated sludge. Based on the experimental results, it was established that, even though synthesis of the enzyme is to some extent affected depending on the anaerobic and aerobic incubation, it is the stable and the floc bound nature of these extra-cellular enzymes which results in no significant difference in enzyme activity under anaerobic and aerobic phase of a steady state operated single sludge anaerobic–aerobic system.