EVALUATION OF SURROGATES FOR MONITORING BIOSOLIDS DIGESTION PROCESSES

Abstract

Anaerobic digestion is a widely used method of treating the solid residuals from wastewater treatment processes. It produces both methane gas, which can be used as an energy source, and the product biosolids can be beneficially reused as a soil amendment. The USEPA (United States Environmental Protection Agency) has designated three organisms as representative of the pathogen content of biosolids: Salmonella sp., culturable enteric viruses, and helminth ova. Measurements of these pathogens is a difficult and time-consuming process, requiring over 30 hours of labor per sample and taking approximately one month to complete. This research proposes the use of surrogate organisms that can be enumerated more frequently than the pathogens and provide more rapid feedback of process efficiency. Semi-batch reactors were operated at mesophilic (36�C) and thermophilic (53-55�C) conditions with a 15 day solids retention time to analyze the inactivation of surrogate organisms and pathogens in anaerobic digestion processes. The reactors were three liters in volume and step-fed every other day. To assess the broader applicability of this study, four sets of experiments were carried out, each using biosolids from a different facility or in a different season. The extent and rates of inactivation of the proposed surrogate organisms were compared against that of the pathogens. Results indicate that male-specific coliphages were a promising potential surrogate organism for viruses. None of the tested surrogate organisms correlated well with helminth ova inactivation. There was a statistically significant difference in organism inactivation rates between the facilities tested, but not between the summer and winter seasons.