Succession of bacterial community and enzymatic activities of activated sludge by heat-treatment for reduction of excess sludge

Heat-treatment has been used for the reduction of excess sludge as a simple process. To clarify the relationship between reduction efficiency and biological response of sludge matrix during heat-treatment, microbial population and hydrolytic enzyme (protease) activity of a municipal activated sludge were studied. Culture-dependent analysis showed the rapid increase in the population of thermophilic bacteria at the early stage of heat-treatment and the emergence of protease-secreting bacteria. Culture-independent analysis by denaturing gradient gel electrophoresis (DGGE) revealed that the Bacilli, which include most of thermophiles, became the dominant class in the community by the treatment. The protease activity in supernatant of the sludge increased instantly after I h heat-treatment, which was considered to be released from microbial cells by lysis. The protease activity succession was correlated with the microbial succession and also with the change in MLSS and TOC concentrations during heat-treatment, suggesting that the protease activity plays an important role in the lysis-cryptic growth induced by heat-treatment. (c) 2007 Elsevier B.V. All rights reserved.