Destruction of Indicator Organisms in Wastewater Treatment Sludge using Thermophilic Anaerobic Digestion

Previous studies of thermophilic anaerobic digestion were reviewed. Batch digestion (55°C) was used to develop a thermophilic seed population from OWASA mesophilic digestion sludge. Buffering was deemed to be beneficial. A sequence of 3 digestions produced a strong, viable thermophilic population. A ratio, intermediate alkalinity to partial alkalinity, was shown to be a good measure of the important volatile acids to bicarbonate alkalinity ratio in anaerobic digestion. A continuous thermophilic anaerobic digester was operated at 10 days hydraulic residence time, at 55°C, with daily draw and feed. Operation was stable, with steady state achieved after two residence times. Volatile solids destruction was 43% and gas generated was 900 ml/g volatile solids destroyed. Fecal Coliforms and fecal streptococci were measured by the 5 tube Most Probable Number method. Fecal coliforms were reduced 5.8 logs, down to log[10]1.4. Fecal streptococci were reduced 2.75 logs down to log[10]3.19. Proposed Class A pathogen reduction requires log[10]2.00 for both indicator organisms. Therefore, the process will not meet the proposed Class A requirement based on indicator organism levels in the effluent. Additional work is needed on actual pathogen destruction using thermophilic anaerobic digestion.Master of Science in Environmental Engineerin