Producing enhanced quality biosolids through anaerobic digester optimization

The primary objective of this research was the development of a better understanding of the operation of anaerobic digesters in single and multi stage configurations, to improve process performance and pathogen destruction rate.; In each study phase, tested anaerobic digestion system was compared to single stage mesophilic digestion at the same HRT. During single stage temperature-HRT study the effect of elevated operating temperatures, and HRT on pathogen reduction was evaluated. In addition, an evaluation of pathogen reduction was assessed in digesters that were operated in a series configuration. The fate of indicator bacteria and bacterial pathogens was investigated in this study.; Results of the single stage study demonstrated that with the exception of Clostridium perfringens the concentrations of the microbial species in the digester effluents decreased as the temperature of operation increased. Operation at 55°C and 62°C resulted in essentially non-detectable concentrations of fecal coliforms, E. coli and Salmonella spp.. Operation at 42°C and 49°C resulted in incremental decreases in effluent concentrations as compared to operation at 35°C. With the exception of operation at 62°C, the effluent concentrations of Clostridium perfringens were observed to increase relative to the feed concentrations. The results suggest that Clostridium perfringens is not a useful indicator organism for the fate of pathogens in anaerobic digestion.; Staged operation of the digesters resulted in substantial improvements in pathogen destruction as compared to single stage digestion for all of the indicators. With the exception of E. coli all of the indicators were reduced to a greater extent in three stage digestion as compared to two stage digestion. With the exception of Salmonella spp. all of the indicators were removed to a greater extent when the first stage of the three stage system was operated at elevated temperature as compared to the three stage system that was operated at 35°C. This study revealed that fecal streptococci and Clostridium perfringens were more resistant to inactivation in the digesters as compared to Fecal coliform, E. coli. and Salmonella spp.; In addition, Denaturing Gradient Gel Electrophoresis (DGGE) testing of the digester effluents was performed to evaluate the impact of staging and temperature on the diversity of the microbial populations. DGGE testing revealed that staged operation resulted in a more diverse bacterial population that observed in single stage digesters that were operated under conventional conditions. The results of this study indicate that DGGE analysis can be a suitable and sensitive tool to support established engineering tools in the investigation of biological treatment processes.