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 degrees 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/cm(2), the logo 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.