Performance Evaluation of the Dual Digestion System

摘要

The dual digestion system (DDS) was developed to provide stabilized, pathogen free sludge. DDS consists of a 1-day detention time, pure-oxygen, covered aerobic digester (Step I) followed by an 8-day detention time anaerobic reactor. The temperature in the Step I digester is controlled by adjusting the pure oxygen feed rate. The heat generated through oxidation of volatile matter in the raw sludge is conserved in the Step I digester. No additional sludge heating is provided for anaerobic digestion in Step II so the biogas generated in Step II is available for other uses throughout the plant. Operation of DDS during the special study at the Lackawanna Wastewater Treatment Plant demonstrated that adequate total volatile solids reduction could be achieved relative to processes to significantly reduce pathogens (PSRP) and processes to further reduce pathogens (PFRP). Reductions of the three indicator microbiological parameters of interest through DDS treatment were greater than those achieved by PSRPs and greater than or equal to those achieved by thermophilic aerobic digestion, a PFRP. Salmonella spp. data were difficult to compare, but it appears that greater reductions of the pathogenic bacteria can be achieved with PSRPs. Regrowth of Salmonella spp. in the Step II digester was not observed during the study.