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

The primary objective of this study was to compare the ability of various thermophilic anaerobic digestion processes to disinfect sludge so that it met U.S. EPA's Class A pathogen requirements (40 CFR Part 503). Three thermophilic processes were assessed for their ability to meet Class A requirements for fecal coliforms and pathogens: (1) two-phase, thermophilic acid phase/mesophilic methane phase; (2) single-stage thermophilic; and (3) two-phase, mesophilic acid phase/thermophilic methane phase. The thermophilic processes were compared to a control (mesophilic single-stage digester). Mesophilic and thermophilic digesters were operated at 35°C and 50°C, respectively. The laboratory-scale reactors (1.5-L) were spiked with three pathogens: Salmonella, poliovirus and helminth ova (Ascaris suum). All three thermophilic digesters outperformed the mesophilic single-stage digester control in terms of fecal coliform and pathogen destruction. Of the three thermophilic processes, only the two-phase, mesophilic acid phase/thermophilic methane phase consistently achieved the Class A fecal coliform and pathogen reduction requirements.