AWWA WQTC58793

A strain of pathogenic E. coli O157:H7 and non-pathogenic E. coli were exposed to ultraviolet (UV) radiation from both low- and medium-pressure lamps using a bench-scale collimated beam apparatus. E. coli O157:H7 was more sensitive to low doses of UV showing higher levels of inactivation. Following irradiation, samples were exposed to light and dark conditions to investigate photo and dark repair potential, respectively. Following low doses (5 and 8 mJ/cm²) of low-pressure UV exposure, E. coli O157:H7 was observed to reach maximum levels of photo repair more rapidly compared to a strain of non-pathogenic E. coli. Low levels of dark repair were also observed in E. coli O157:H7 following low-pressure UV exposure at these doses. Following higher low-pressure UV doses of 20 and 40 mJ/cm² low levels of photo repair of E. coli O157:H7 were evident; however, no dark repair was detected at these higher doses. Following medium-pressure UV exposure at low doses (5 and 8 mJ/cm²), limited photo repair was observed in both strains when exposed to light conditions. No dark repair was evident following medium-pressure UV exposure at these low doses. Includes 20 references, figures.