COMPARISON OF THERMOPHILIC ANAEROBIC DIGESTION PROCESSES FOR MEETING BIOSOLIDS CLASS A PATHOGEN STANDARDS

The primary objective of this study was to determine the capabilities of various thermophilic anaerobic digestion processes to disinfect biosolids to meet the Class A pathogen requirements (40 CFR Part 503). Four anaerobic digestion processes were evaluated in parallel: (1) two-stage thermophilic acid phase/mesophilic methane phase, (2) single-stage thermophilic, (3) two-stage mesophilic acid phase/ thermophilic methane phase, and (4) single-stage mesophilic control. The raw feed sludge to these processes was spiked with three pathogens: (1) Salmonella, (2) helminth ova, and (3) poliovirus. The laboratory-scale reactors (1.5-liters) were operated in a draw/fill mode and fed on a semi-continuous basis for three HRTs (45 days). In addition to the pathogen destruction results, other process data, such as gas production, volatile solids destruction, total volatile acids, total alkalinity, and fecal coliform removal were collected. At the time of preparing this paper, results were not available. Concurrent with seeding raw feed sludge, an alternative method of helminth ova spiking using small plastic vials was evaluated for possible use in full-scale testing. Further work is planned to evaluate one or more thermophilic anaerobic digestion processes at full-scale.