Investigating log removals of bacteria and viruses at a full-scale enhanced coagulation contact filtration drinking water treatment plant

The effectiveness of pathogen removal from drinking water by conventional treatment has been evaluated in numerous studies. However, the reported log removals show a significant variation, depending on the source water quality, type of microorganism being studied, scale of experiments (laboratory, pilot, or full-scale), treatment operation conditions, and differences in treatment technology and process design. Additionally, data on the removal of bacteria and viruses using full-scale enhanced coagulation-contact filtration processes are very limited, and there is no available information on log removal rates under stressed conditions. In this study, the removal of spiked Enterococcus faecium (E. faecium) (ATCC® 8459™) and MS2 was investigated at a full-scale enhanced coagulation-contact filtration water treatment plant during optimal and stressed operational conditions. The log removals achieved under optimal coagulation conditions were ≥4.6 for E. faecium, ≥2.1 for infectious MS2 (PFU), and, on average, >2.3 for total MS2 (RT-qPCR), with variation ranging from 1 to >3.5 logs. The removal of naturally occurring coliforms was >3.4 logs. During suboptimal coagulation conditions, the concentration of E. faecium and total MS2 increased in the filter effluent. The removal for E. faecium was ≥4.1 logs, and the average total MS2 decreased by >1.8. Operational stress, such as increased filtration rates, reduced virus removal by over 2 logs. Compared to conventional treatment, the results suggest that enhanced coagulation-contact filtration is less sensitive to short-term stress and suboptimal operational conditions. The results of this study highlight the importance of optimizing operational conditions to ensure effective treatment barriers and safe drinking water.