Counting of Total Number of Bacteria in Activated Sludges

Abstract

Activated sludge flocs were completely disrupted employing homogenization and sonication, and the total number of bacteria in activated sludges was microscopically counted with a Thoma blood corpuscle counting chamber after stain by methylene blue. In four different types of activated sludges, total numbers of bacteria were well correlated with MLVSS rather than MLSS, and the correlation coefficient was 0.99. The total number of bacteria per 1 mg MLSS was counted 1.02×10⁹ and that of bacteria per 1 mg MLVSS counted 1.32×10⁹, resulted in both numbers showing 10 to 100 times greater than the numbers of vial bacteria which were reported in many papers. The total number of bacteria increased according as an increase of SRT with which the activated sludge process was controlled in the bench scale plants, It, however, indi-cated to reach an upper limited value. Both numbers of bacteria per 1 mg MLSS and MLVSS showed a tendency to decrease when the process was controlled with longer SRT.