PATHOGEN DESTRUCTION EFFICIENCY IN HIGH TEMPERATURE ANAEROBIC DIGESTION

The primary objective of this study is to compare various thermophilic anaerobic digestion processes and determine their ability to disinfect sludge to meet U.S. EPA's Class A pathogen requirements (40 CRF Part 503). Three processes were assessed for their ability to consistently meet fecal coliform requirements: (1) two-stage, thermophilic acid phase/mesophilic methane phase; (2) single-stage thermophilic; and (3) two-stage, mesophilic acid phase/thermophilic methane phase. Each process was evaluated at three different thermophilic temperatures (48, 52, and 62°C) against a mesophilic control at 35°C. The laboratory-scale reactors (30-liters) were brought to thermophilic temperatures rapidly from a mesophilic seed sludge and operated in a draw/fill mode. At corresponding temperatures, the single stage process showed greater fecal coliform removals than the first stage (thermophilic acid phase) of the two-stage process. Temperatures greater than 52°C for Process 1 (2-day residence time) or 48°C for Process 2 (15-day residence time) produced average effluent fecal coliform densities less than 1,000 MPN/g. TS (limit for meeting Class A fecal coliform requirement). The third process (two-stage mesophilic acid phase/thermophilic methane phase) performed the best, with fecal reductions meeting Class A standards with the second-stage methanephase reactor as low as 35°C. Since all three processes were able to meet Class A fecal coliform standards, in work planned within the next year, all three processes will be further evaluated. These evaluations will include pathogen seeding and full-scale implementation.