The study compared conventional, anaerobic sludge digestion and three stage, anaerobic sludge digestion. The conventional digester and the first two stages of the multiple stage system were operated at 35 deg C; the third stage was maintained at 49 deg C. The influent feed sludge was a mixture of primary and secondary sludges. Tests were run in three phases with solids retention times of 9, 15, and 20 days. The results of the study indicated that multiple stage digestion outperformed conventional single stage digestion in terms of COD and VS destruction, and methane production. The first two stages of the multiple stage system, by themselves, achieved a greater degree of sludge stabilization and destruction, and methane production than the conventional system. The effluent sludges from both processes were further treated by wet air oxidation (WAO). The WAO tests were performed at a pressure of 1.4 x 10 to the 7th power Pa (2,100 psi) and temperatures up to 300 deg C.

Caption title. "December 1986." "EPA/600/2-86/118." Microfiche.