Removal of phages and viral pathogens in a full-scale MBR: Implications for wastewater reuse and potable water

The aim of this study was to demonstrate how seasonal variability in the removal efficacy of enteric viral pathogens from an MBR-based water recycling system might affect risks to human health if the treated product were to be used for the augmentation of potable water supplies. Samples were taken over a twelve month period (March 2014- February 2015), from nine locations throughout a water recycling plant situated in East London and tested for faecal indicator bacteria (thermotolerant coliforms , intestinal enterococci n=108), phages (somatic coliphage , F-specific RNA phage and Bacteroides phage (GB-124) n=108), pathogenic viruses (adenovirus , hepatitis A , norovirus GI/GII n=48) and a range of physico-chemical parameters (suspended solids, DO, BOD, COD). Thermotolerant coliforms and intestinal enterococci were removed effectively by the water recycling plant throughout the study period. Significant mean log reductions of 3.9-5.6 were also observed for all three phage groups monitored. Concentrations of bacteria and phages did not vary significantly according to season (P<0.05; Kruskal-Wallis), though recorded levels of norovirus (GI) were significantly higher during autumn/winter months (P=0.027; Kruskal-Wallis). Log reduction values for norovirus and adenovirus following MBR treatment were 2.3 and 4.4, respectively. However, both adenovirus and norovirus were detected at low levels (2000 and 3240 gene copies/L, respectively) post chlorination in single samples. Whilst phage concentrations did correlate with viral pathogens, the results of this study suggest that phages may not be suitable surrogates, as viral pathogen concentrations varied to a greater degree seasonally than did the phage indicators and were detected on a number of occasions on which phages were not detected (false negative sample results).