Changes in composition and microbial communities in excess sludge after heat-alkaline treatment and acclimation

This study examined the effects of combining heat-alkaline treatment (HAT) with an acclimation process on sludge reduction. Changes in sludge components and microbial communities in both the mixed liquor suspended solids (MLSS) and supernatant fractions were monitored throughout the process. HAT was performed under different pH conditions (pH 7, pH 11 and pH 13) at 60 °C. Approximately 42–62% of the released materials were proteins. After an 8-day acclimation of sludge, the protein concentration in the supernatant had significantly decreased under all conditions. Treatment conditions at pH 11 were optimal for sludge reduction due to the increased efficiency and reduced consumption of chemicals to adjust the pH. A molecular analysis showed that the microbial consortia in both fractions after the cell lysis differed depending on the pH and temperature, and only a few types of bacteria were resistant under extreme conditions. The microbial communities in the MLSS under different conditions were similar after the 8-day acclimation.