Processes to Produce Disinfected Biosolids at Terminal Island Treatment Plant
Abstract:This paper discusses the disinfection of biosolids at Terminal Island Treatment Plant by thermophilic anaerobic digestion. The objective was to evaluate compliance with the U.S. EPA Part 503 Biosolids Rule requirements for Class A biosolids. Initial full-scale tests with analysis of the digester outflow demonstrated the reductions of fecal coliforms and Salmonella sp. in a single-stage continuous digester (Phase I), two-stage continuous digesters (Phase II), and single-stage sequencing batch digesters (Phase III). Salmonella sp. were always non-detect (<3 MPN/4 g dry wt), whereas fecal coliform densities were usually below the Class A limit of 1000 MPN/g dry wt. Recurrence of fecal coliforms during post-digestion handling of biosolids caused non-compliance with the Class A limit for fecal coliforms at the truck loading facility, which is the last point of plant control for compliance. Fecal coliform recurrence was tentatively attributed to: a) contamination of biosolids in post-digestion; b) reactivation and/or growth of fecal coliforms, which could have been facilitated by a large drop of the biosolids temperature during biosolids transport over conveyor belts. Subsequently, several design modifications of the postdigestion train were implemented to prevent the recurrence of fecal coliforms. Final certification tests were conducted with operation of the digesters as single-stage sequencing batch digesters according to the time-temperature requirement of Alternative 1 of the Part 503 Biosolids Rule. These tests demonstrated that both Class A limits for fecal coliforms and Salmonella sp. were met at the last point of control (truck loading facility), thereby achieving compliance with the federal standards for Class A biosolids (Alternative 1) as well as the stricter requirements for Class A biosolids in the Kern County ordinance.
Document Type: Research Article
Publication date: 2005-01-01
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