Effects of different biosolids treatment systems on pathogen and pathogen indicator reduction

Abstract

In this study, the effectiveness of different treatment systems in reducing pathogenic density levels was evaluated according to the criteria established by the U.S. Environmental Protection Agency municipal sludge rule (40 CFR Part 503 Rule). In a year‐long effort, wastewater and biosolids samples were analyzed for both indicator and pathogenic organisms from different existing treatment systems. The results indicate that anaerobic digestion was superior to aerobic digestion in reducing pathogen density levels under the given field conditions. Composting was far more superior to both anaerobic and aerobic digestion. This study demonstrates that the Class B requirements under the 503 Rule are reasonable and can be achievable by most existing treatment systems, whereas the Class A requirements under the same rule may not be easily achieved by many existing treatment works. The effects of volatile solids loading rates on anaerobic and aerobic digester performance were investigated. Under anaerobic digestion conditions, the log reductions in fecal coliform and fecal streptococci appeared to be dependent on volatile suspended solids (VSS) loading rates. However, this trend was not evident in aerobic digestion systems sampled. Salmonella density reductions did not appear to be dependent on VSS loading rates in either case.