Quantification of pathogen removal in activated sludge treatment

Smaller and regional Wastewater Treatment Plants (WWTPs) have the capacity to recycle wastewater for agricultural use, but the cost of obtaining regulatory approval or ‘accreditation’ is prohibitive. One reason for this is that each WWTP must demonstrate that its processes and operations consistently remove pathogens that cause infectious diseases in humans. Operating conditions include flow rate through the WWTP, and temperature in the activated sludge component of the WWTPs. Although pathogen ‘log removal values (LVR)’ were obtained for a WWTP at 19-20°C in Part I of this project (WQRA project 2001), these values cannot also be attributed to summer temperatures of 26°C. This research determined LRVs for ‘new’ WWTP operating conditions and combined the data with data from Phase I (Project 2001) for analysis. One of the conclusions from Part II was that faster flow rates associated with increased rainfall reduced pathogen LRVs.