TEMPERATURE-PHASED ANAEROBIC-DIGESTION OF WASTE-WATER SLUDGES

The temperature-phased anaerobic bioreactor (TPAB) has been under stud y by Dague and co-workers at Iowa State University. The temperature-ph ased approach involves a two-stage reactor system with the first stage operated at a thermophilic temperature (commonly 55 degrees C) and th e second stage operated at a mesophilic temperature (commonly 35 degre es C). The purpose of laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage me sophilic system for treating mixtures of primary and waste activated s ludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids (VS) destruction, and biogas production. The temperature-phased syste m achieved complete destruction of total and fecal coliforms over a ra nge of SRTs from 11 to 28 days. The concentration of fecal coliforms i n the effluent from the temperature-phased system never exceeded 1000 MPN/g total solids (TS), which can meet the U.S. Code of Federal Regul ations, Title 40 (40 CFR), Part 503 coliform requirements for Class A sludge. At the optimal SRTs ranging from 11 to 17 days, the capacity o f VS removal of temperature-phased system was more than double that of the conventional single-stage system. The foaming problem associated with the digestion of waste activated sludge was eliminated. (C) 1997 IAWQ. Published by Elsevier Science Ltd.