Ultraviolet disinfection of filtered activated sludge effluent for reuse applications

An ultraviolet (UV) disinfection system was assessed in terms of the most stringent U.S. wastewater reuse standards. The UV inactivation of total and fecal coliform bacteria and seeded MS2 coliphages in filtered activated sludge effluent was tested continuously for 22 weeks. The most stringent coliform criterion, that the 7-day median not exceed 2.2 per 100 mL was met consistently in effluent exposed to an average UV dose of 168 and 112 mW/cm(2) . s for total and fecal coliforms, respectively. MS2 coliphages were more resistant to UV disinfection than the coliform group. Both the point source summation (PSS) and bioassay methods were used to estimate UV dose in the system. For a 95% confidence interval, the PSS method resulted in an equivalent estimate of UV dose when compared with the bioassay method.