THERMOPHILIC ANAEROBIC DIGESTION UNDER TIME TEMPERATURE TREATMENT PRODUCES CLASS A BIOSOLIDS AT TERMINAL ISLAND TREATMENT PLANT AFTER MODIFICATIONS OF POST-DIGESTION TRAIN
Abstract:Terminal Island Treatment Plant (TITP) operates a single-stage sequencing batch process with three thermophilic anaerobic digesters. This paper summarizes the certification tests for demonstrating compliance of this process with the Class A pathogen reduction requirements of Alternative 1 in the U.S. EPA 40 CFR Part 503 Biosolids Rule. The tests were conducted in April/May 2004 after implementation of several design modifications of the post-digestion train. This was to prevent the recurrence of fecal coliforms in post-digestion biosolids that was observed in 2001, 2002 and 2003. The modifications included insulation of the post-digestion train and replacement of the conveyor belts with transport of biosolids through pipes and pumps.
The digesters were operated with a batch holding time of 24 hours. The time-temperature requirement of Alternative 1 is that a temperature equal to or greater than 131°F shall be maintained if the batch holding time is 24 hours. Continuous monitoring of the digester temperatures at TITP demonstrated that the lowest temperature recorded during holding was 132.0°F.
The biosolids were sampled at the Truck Loading Facility and after three hours of transport by truck to simulate future sampling at the farm for land application, which are the last points of plant control where compliance with the Class A pathogen reduction requirements needs to be demonstrated. Salmonella sp. were never detected during the certification tests. Fecal coliforms were not detected in seven of nine samples, and counts were always well below the Class A limit if fecal coliforms were present. Thus, TITP biosolids met the time-temperature requirement for batch holding and the general pathogen reduction requirements of Alternative 1 (Class A limit for fecal coliforms or Salmonella sp.). TITP also met the stricter requirement of the Kern County ordinance that both Class A limits for fecal coliforms and Salmonella sp. shall be met. After these certification tests, TITP relocated the land application of its biosolids from Arizona to Kern County, California, thus achieving significant savings on hauling costs.
Document Type: Research Article
Publication date: January 1, 2005
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