EFFECTS OF DIFFERENT BIOSOLIDS TREATMENT SYSTEMS ON PATHOGEN AND PATHOGEN INDICATOR REDUCTION

In this study, the effectiveness of different treatment systems in red ucing pathogenic density levels was evaluated according to the criteri a established by the U.S. Environmental Protection Agency municipal sl udge rule (40 CFR Part 503 Rule). In a year-long effort, wastewater an d biosolids samples were analyzed for both indicator, and pathogenic o rganisms from different existing treatment systems. The results indica te that anaerobic digestion was superior to aerobic digestion in reduc ing pathogen density levels under the given field conditions. Composti ng was far more superior to both anaerobic and aerobic digestion. This study demonstrates that the Class B requirements under the 503 Rule a re reasonable and can be achievable by most existing treatment systems , whereas the Class A requirements under the same rule may not be easi ly achieved by many existing treatment works. The effects of volatile solids loading rates on anaerobic and aerobic digester performance wer e investigated. Under anaerobic digestion conditions, the log reductio ns in fecal coliform and fecal streptococci appeared to be dependent o n volatile suspended solids (VSS) loading rates. However, this trend w as not evident in aerobic digestion systems sampled. Salmonella densit y reductions did not appear to be dependent on VSS loading rates in ei ther case.