FULL-SCALE SEQUENCING BATCH THERMOPHILIC ANAEROBIC SLUDGE DIGESTION TO MEET EPA CLASS A BIOSOLIDS REQUIREMENTS

The City of Los Angeles, Terminal Island Treatment Plant started thermophilic anaerobic digestion operation in Feb 2000. Mesophilic digesters were converted to thermophilic digestion using a rapid temperature increase to 130°F (54°C) without seeding. In May 2001, to meet the EPA 40 CFR 503, Alternative I (thermal treatment-temperature and time) requirement for pathogen destruction, anaerobic digestion was converted from a continuous feed and draw mode to a Sequencing Batch Reactor mode with a draw/fill/hold sequence to prevent short circulating and to allow all sludge particles to be heated for 24 h. Full-scale results show that the “rapid startup method” produced a robust thermophilic culture and stable digestion. The thermophilic SBR operating mode met Class A biosolids fecal coliform and Salmonella requirements. Fecal coliforms, but not Salmonella, regrew during the dewatering and centrifuged cake storage. Thermophilic digestion gave slightly higher pH, volatile acids and alkalinity than mesophilic digestion. Thermophilically digested sludge was more odorous than mesophilically digested sludge, but following centrifuge dewatering the reverse was true.