Thermophilic Aerobic Digestion of Activated Sludge; Reduction of Solids and Pathogenic Microorganisms

In the temperature range of 10 to 80 ºC and in a batch digester, a typical activated sludge was digested aerobically. Reaction rate constants were determined by measuring the amounts of volatiles removed from the suspended solids at different time intervals during the process. The maximum value of the reaction rate constant (0.45 d-1) occurred in the temperature range of 55-60˚C. Removal of indicator organisms (pathogens) in the sludge, during the batch digestion, was also studied. Sludge digestion at 60 ºC provided a noticeable difference in reduction of the indicator organisms as compared to digestion carried out at 55 ºC. Optimum thermophilic aerobic digestion for high rate removal of volatile suspended solids and effective inactivation of pathogens happened in temperature range of 60-65 ºC.