Medium-pressure UV for oocyst inactivation

Inactivation of Cryptosporidium parvum oocysts in finished drinking water b y medium-pressure ultraviolet (UV) light was investigated at bench scale us ing a collimated beam apparatus and at demonstration scale using a UV react or. Oocyst viability was assessed in vitro (using 4'.6-diamidino-2-phenylin dole with propidium iodide and maximized in vitro excystation) and in vivo (using neonatal mouse infectivity assays). In vivo bench-scale studies show ed > 4-log inactivation at UV dosages as low as 41 mJ cm(-2), although in v itro surrogate assays showed little or no inactivation at this or higher UV dosages. The in vitro assays, which indicate oocyst viability, grossly ove restimated the UV dosages required to prevent oocyst infection in susceptib le hosts. Results of demonstration studies, carried out under the Environme ntal Technology Verification program of the National Sanitation Foundation and the US Environmental Protection Agency, agreed with the bench-scale res ults and showed that a UV dosage as low as 19 mJ cm(-2) provided 3.9 mJ cm( -2) provided 3.9-log inactivation of Cryptosporidium oocysts.