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Processes to Produce Disinfected Biosolids at Hyperion Treatment Plant

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This paper describes Phases III, IV and V of full-scale testing at the City of Los Angeles Hyperion Treatment Plant (HTP) of the production of Exceptional Quality (EQ) biosolids (U.S. EPA Part 503 Biosolids Rule) by thermophilic anaerobic digestion. The tests were conducted after complete conversion of HTP to thermophilic operation and insulation and electrical heat-tracing of the post-digestion train. The Phase III process contained two stages, both of which were operated in a continuous mode. Pathogens (Salmonella sp., helminth ova and enteric viruses) in silo and farm biosolids were non-detectable, whereas fecal coliform densities were in general below the Class A limit of 1000 MPN/g dry wt. The Phase IV process was a two-stage continuous/batch process that complied with the time-temperature relation for batch treatment, defined in Alternative 1 of the Part 503 Biosolids Rule. The batch stage provided 16 hours holding at a temperature of 56.6°C. Farm biosolids produced by this process did not contain fecal coliforms or Salmonella sp., thus providing full compliance with the Class A pathogen reduction requirements. However, an increase of the production of methyl mercaptan was observed when the temperature was raised to meet the minimum temperature of 56.3°C at 16 hours holding. Subsequently, the digester temperatures were lowered to minimize potential odor nuisance to HTP neighbors. As the time-temperature relation for batch treatment would not be met, Phase V tests were conducted to evaluate compliance with Alternative 3 of the Part 503 Biosolids Rule (extended pathogen monitoring). Although the temperature of the thermophilic digesters was reduced, biosolids at HTP's silos and at the farm for land application showed non-detectable levels of Salmonella sp., helminth ova and enteric viruses, whereas fecal coliform densities were about 100 times less than the Class A limit.
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Document Type: Research Article

Publication date: 2005-01-01

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