Temperature-phased anaerobic digestion of wastewater sludges

Abstract

The temperature-phased anaerobic bioreactor (TPAB) has been under study by Dague and co-workers at Iowa State University. The temperature-phased approach involves a two-stage reactor system with the first stage operated at a thermophilic temperature (commonly 55°C) and the second stage operated at a mesophilic temperature (commonly 35°C). The purpose of laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating mixtures of primary and waste activated sludge. 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 system achieved complete destruction of total and fecal coliforms over a range of SRTs from 11 to 28 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded 1000 MPN/g total solids (TS), which can meet the U.S. Code of Federal Regulations, Title 40 (40 CFR), Part 503 coliform requirements for Class A sludge. At the optimal SRTs ranging from 11 to 17 days, the capacity of 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.