An Evaluation of 3 Stage Anaerobic Digestion of Municipal Wastewater Treatment Plant Sludges

Abstract

This study evaluated the efficiency of three stage operation of anaerobic digestion of municipal sewage sludge. In this study five sets of three stage anaerobic digesters operating in series were compared against a conventional single stage digester. Various combinations of conventional (35 o C) and non-conventional (42 and 49 o C) temperatures were evaluated in this study. The results showed that three stage operation was able to achieve enhanced Volatile Solids (VS) reduction as compared to single stage operation. Operation of the first stage of the three stage system at 42ºC and 49ºC resulted in an 8-12% increase in VS destruction. Stable operation of three stage configurations was indicated by low concentrations of total volatile fatty acids (TVFA) and substantial alkalinity generation. An increase in temperature to 42ºC in the second stage of the investigated system showed no significant change in final effluent quality of the digesters. For all of the indicators examined three stage operation resulted in a greater extent of removal when the first stage of the 3 stage system was operated at either 42 o C or 49 o C as compared to when the 3 stage system was operated at 35 o C. Clostridium perfringens were more resistant to inactivation in the digesters as compared to Fecal coliform, E. Coli. and Salmonella spp.