Coliphages as indicators of enteric viruses in activated sludge

The use of indigenous coliphage as indicators of enteric viruses during activated sludge treatment of domestic wastewater was examined. Enteric viruses, coliphage attacking three strains of Escherichia coli and a number of wastewater parameters were monitored in the primary effluent, secondary effluent and secondary sludge of a wastewater treatment plant. Removal of viruses during secondary treatment appeared to be the result of rapid adsorption of influent virions to mixed liquor suspended solids. Adsorption was followed by inactivation of the viruses during aeration of the mixed liquor. A larger proportion of influent enteric viruses than coliphage was recovered from the secondary sludge. This suggests that activated sludge treatment was less antagonistic towards enteric viruses than towards the coliphage. Coliphage plaques of less than or equal to 1 mm in diameter were composed of large viruses (approx. 100 nm in diameter). Plaques greater than 3 mm in diameter appeared to be the result of host infection by a much smaller virus (approx. 45 nm in diameter). Plaques between 1 and 3 mm in diameter were composed of both small and large coliphages. Coliphage concentrations could not be correlated with enteric virus concentrations in either primary or secondary effluent. However, it was found that coliphage giving rise to plaques greater than 3 mm in diameter were positively related with enteric viruses in the secondary effluent. This result suggests that this group of coliphage may serve as an indicator of the efficacy of activated sludge treatment of enteric viruses.