virus inactivation during disinfection of wastewater by chlorination and UV irradiation and the efficacy of F⁺ bacteriophage as a ‘viral indicator’

Wastewater disinfection has grown in popularity in recent years in the UK particularly for reducing faecal coliform levels in effluents impacting on bathing waters not compliant with EC Directive standards. Although disinfectants appear effective against bacterial indicators of faecal pollution, their efficiency against human viruses is still unclear. This has significance both for attainment of compliance with viral standards in the EC Bathing Waters Directive and, potentially, for protection against viruses likely to cause gastroenteritis. This study reports on bench scale disinfection of primary effluent treated with chlorination and secondary effluent treated with UV. Disinfection experiments comprised of wastewater, sterilised by gamma irradiation, seeded with monodispersed laboratory grown bacterial indicators (Escherichia coli and Enterococcus faecalis), human enterovirus (poliovirus) and F⁺ bacteriophage (MS2) – a potential ‘viral indicator’. Under the experimental conditions used, the inactivation of bacterial indicators was rapid in comparison to the inactivation of F⁺ bacteriophage which was very poor. Seeded poliovirus was significantly more susceptible to inactivation by chlorine and UV irradiation than F⁺ bacteriophage but was more resistant than bacterial indicators in both cases. These results indicate that the use of bacterial indicators alone to determine the effect of wastewater disinfection when using chlorination or UV irradiation underestimates human enteric virus inactivation, whereas the use of F⁺ bacteriophage is likely to give a conservative estimate of virus inactivation.