Survival of indicators of bacterial and viral contamination in wastewater subjected to low temperatures and freezing:: application to cold climate waste stabilisation ponds

The survival of bacterial and viral pollution indicators and Salmonella in urban wastewaters under freezing conditions (-14degreesC for up to 60 days) is reported. Presumptive, total and faecal coliforms (PC, TC, FC), salmonellae and coliphages were tested. The dynamics of somatic coliphage (E coli C) and F-pili specific coliphage inactivation were compared at 4degreesC and 25degreesC over various run times. On freezing of the wastewater, it was found that PC, TC and FC showed a first rapid phase (days) of inactivation followed by a slower second phase (up to 4 weeks) and then stabilisation at between 1-10% of the initial population size, depending on the wastewater sample used. Salmonella spp. were detectable in 0.1 ml of raw wastewater and were still detected up to 2 days after freezing but none were detected in 100 ml samples after 4, 42 and 60 days, although microbiologically similar but antigenically different forms were found. Viral indicators of pollution showed a slow but constant decrease in viability during the first month but then stabilised at between 10-20% survivors (10% in somatic E coli C phages, 15.8% in somatic Salmonella phages and 17.9% in F-pili specific coliphages). Using electron microscopy, no difference in susceptibility to freezing could be detected with respect to morphological phage types, which were either small icosahedral particles or complex tailed phages. The study of viral indicators at 4degreesC versus 25degreesC showed a higher survival of the various coliphages over time at 4degreesC. F-pili specific leviviridae were particularly susceptible to the antiviral factors at 25degreesC and no viable units per ml were detected after one month at that temperature, whereas somatic coliphages were detected in higher numbers after this period, especially at 4degreesC.