Development of ultraviolet disinfection systems to reduce photoreactivation of microorganisms in water

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Ultraviolet inactivation and photoreactivation of Escherichia coli, Cryptosporidium parvum and Legionella pneumophila were compared using a low-pressure UV lam (LP ; 254nm) or a medium-pressure UV lamp (MP ; 220nm-580nm). Filtration of the MP emissions was also carried out to investigate the effect of wavelengths on the characteristics of inactivation and photoreactivation of microorganisms. An endonuclease sensitive site (ESS) assay was applied to determine the number of UV-induced pyrimidine dimers in the genomic DNA, while a conventional cultivation or infectivity assay was also used to investigate the viability of microorganisms.This research indicated that (l) C. parvum can be effectively inactivated by UV without photoreactivation, (2) MP lamp can repress photoreactivation of E. coli probably by affecting photolyase (3) L. pneumophila performs evident photoreactivation either after LP or MP lamp inactivation. These conclusions may encourage a development of UV systems with high disinfection efficiency at low photoreactivation risk.