Kinetics of Microbial Inactivation by UV-Disinfection in Water Treatment

Ultraviolet (UV) processing involves the use of radiation from the ultraviolet region of the electromagnetic spectrum for purposes of disinfection. Cryptosporidium parvum, an important health-related waterborne pathogen is very resistant to conventional water treatment processes, including chemical disinfection. The kinetics and extent of C. parvum inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage were studied. A UV collimated-beam apparatus was used to expose suspensions of purified C. parvum oocysts in phosphate-buffered saline (PBS), pH 7.2, at 25 °C to various doses of monochromatic LP UV. C. parvum infectivity reductions were rapid, showed first order kinetics. At UV doses of 0.8, 1.2, 3.0 and 5.0 mJ/cm2, the log10 reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.