Inactivation of Cryptosporidium parvum oocysts using medium- and low-pressure ultraviolet radiation

The effect of ultraviolet radiation from low- and medium-pressure mercury a re lamps on Cryptosporidium parvum oocysts was studied using a collimated b eam apparatus. Experiments were conducted using parasites suspended in both filtered surface water and phosphate buffered laboratory water. Inactivati on of oocysts was measured as reduction in infectivity using a CD-1 neonata l mouse model and was found to be a non-linear function of UV dose over the range of germicidal doses tested (0.8-119 mJ/cm(2)). Oocyst inactivation i ncreased rapidly with UV dose at doses less than 25 mJ/cm(2) with two and t hree log-units inactivation at approximately 10 and 25 mJ/cm(2), respective ly. The cause of significant leveling-off and tailing in the UV inactivatio n curve at higher doses was not determined. Maximum measured oocyst inactiv ation ranged from 3.4 to greater than 4.9 log-units and was dependent on di fferent batches of parasites. Water type and temperature, the concentration of oocysts in the suspension, and the UV irradiance did not have significa nt impacts on oocyst inactivation. When compared on the basis of germicidal UV dose, the oocysts were equally sensitive to low- and medium-pressure UV radiation. With respect to Cryptosporidium, both low- and medium-pressure ultraviolet radiation are attractive alternatives to conventional chemical disinfection methods in drinking water treatment. (C) 2001 Elsevier Science Ltd. All rights reserved