Laboratory studies on the temperature phased anaerobic digestion of domestic primary sludge

The temperature-phased anaerobic process involves a two-stage reactor system with the first stage operated at a thermophilic temperature (typically 55 degrees C) and the second stage operated at a mesophilic temperature (typically 35 degrees C). The purpose of this laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating domestic wastewater sludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids destruction, and biogas production. The temperature-phased system achieved almost complete destruction of total and fecal coliforms over a range of solids retention times (SRTs) from 10 to 15 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded 1 000 MPN/g total solids, which can meet the U.S. federal fecal coliform requirements for Class A biosolids. At SRTs ranging from 10 to 15 days, the temperature-phased system achieved an 18% higher destruction of volatile solids and 16% more methane production than was possible with the single-stage mesophilic process.