ANOTHER LOOK AT THERMOPHILIC ANAEROBIC-DIGESTION OF WASTE-WATER SLUDGE

New federal regulations on wastewater sludge management will be implemented in the near future and will have an impact on virtually every biosolids disposal method, including application to agricultural land. Current regulations on land application restrict land use according to the sludge treatment technology, whereas the new regulations will restrict land use based on pathogen destruction criteria. The most flexible land use practices will be allowed for biosolids with low pathogen content (Class A biosolids); for high-temperature sludge treatment processes (greater than 53-degrees-C), indicator organism destruction can be used as a measure of pathogen destruction. The purpose of this study was to evaluate the indicator organism destruction capability of thermophilic anaerobic digestion. For the conditions studied, thermophilic digestion achieved the expected Class A limits on fecal coliforms; data are also presented on fecal streptococci destruction. Rapid startup of the thermophilic reactor (contrasting startup procedures used in the most recent full-scale studies reported in the literature) and preliminary experiments on stability of the thermophilic population are described as well. Based on the results of this study, it appears that thermophilic anaerobic digestion can be a viable process for achieving Class A biosolids criteria.