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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.

Document Type: Research Article


Publication date: January 1, 2000

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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