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 (ty pically 55 degrees C) and the second stage operated at a mesophilic te mperature (typically 35 degrees C). The purpose of this laboratory stu dy was to compare the performance of the temperature-phased system wit h the conventional single-stage mesophilic system for treating domesti c wastewater sludge. Of particular interest in the research was a comp arison of the two systems from the standpoint of coliform reduction, v olatile solids destruction, and biogas production. The temperature-pha sed system achieved almost complete destruction of total and fecal col iforms over a range of solids retention times (SRTs) from 10 to 15 day s. The concentration of fecal coliforms in the effluent from the tempe rature-phased system never exceeded 1 000 MPN/g total solids, which ca n meet the U.S. federal fecal coliform requirements for Class A biosol ids. At SRTs ranging from 10 to 15 days, the temperature-phased system achieved an 18% higher destruction of volatile solids and 16% more me thane production than was possible with the single-stage mesophilic pr ocess.