Photoreactivation of Escherichia coli after inactivation by a low-pressure (LP) UV lamp (254 nm), by a medium-pressure (MP) UV lamp (220 to 580 nm), or by a filtered medium-pressure (MPF) UV lamp (300 to 580 nm) was investigated. An endonuclease sensitive site (ESS) assay was used to determine the number of UV-induced pyrimidine dimers in the genomic DNA of E. coli , while a conventional cultivation assay was used to investigate the colony-forming ability (CFA) of E. coli. In photoreactivation experiments, more than 80% of the pyrimidine dimers induced by LP or MPF UV irradiation were repaired, while almost no repair of dimers was observed after MP UV exposure. The CFA ratios of E. coli recovered so that they were equivalent to 0.9-, 2.3-, and 1.7-log inactivation after 3-log inactivation by LP, MP, and MPF UV irradiation, respectively. Photorepair treatment of DNA in vitro suggested that among the MP UV emissions, wavelengths of 220 to 300 nm reduced the subsequent photorepair of ESS, possibly by causing a disorder in endogenous photolyase, an enzyme specific for photoreactivation. On the other hand, the MP UV irradiation at wavelengths between 300 and 580 nm was observed to play an important role in reducing the subsequent recovery of CFA by inducing damage other than damage to pyrimidine dimers. Therefore, it was found that inactivating light at a broad range of wavelengths effectively reduced subsequent photoreactivation, which could be an advantage that MP UV irradiation has over conventional LP UV irradiation.

The seasonal profiles of microorganisms in raw sewage, secondary-treated sewage, and final effluent at a wastewater treatment plant in Tokyo, Japan, were quantitatively determined each month for one year, from July 2003 to June 2004. Human noroviruses, which were determined by real-time PCR, in raw sewage varied from 0.17–260 copies/mL for genotype 1 and from 2.4–1900 copies/mL for genotype 2, showing much higher values in winter, the epidemic season. The concentration of total coliforms, Escherichia coli, or F-specific phages in raw sewage was almost constant throughout the year. Human noroviruses of genotype 2 were removed most effectively (3.69 log₁₀ on average) at the wastewater treatment plant, followed by E. coli (3.37 log₁₀), total coliforms (3.05 log₁₀), F-specific phages (2.81 log₁₀), and human noroviruses of genotype 1 (2.27 log₁₀). The removal ratio of human noroviruses was almost constant, independent of the initial concentration of the viruses in raw sewage, which led to the increasing concentration of human noroviruses in final effluent in winter. None of the tested bacteria was judged to be a reliable indicator of human noroviruses in final effluent.

A ring-shaped disinfection apparatus has been developed containing twenty ultraviolet-light-emitting diodes (UV-LEDs) with emission at 285 nm. The apparatus was applied to Escherichia coli, Qβ, MS2, and adenovirus in water. The reduction-equivalent fluence in the apparatus was determined, based on a modification of the protocol for the bench-scale challenge test by low-pressure (LP) UV lamp systems (LPUV). All species demonstrated log-linear inactivation profiles versus the fluence, and the inactivation rate constants for E. coli, Qβ, MS2, and adenovirus were 0.157, 0.037, 0.029, and 0.023 cm2/mJ, respectively. The inactivation rate constant for adenovirus under the UV-LED exposure (kUV-LED′) was higher than that under a LPUV lamp (kLPUV′), and the ratio of kUV-LED′ to kLPUV′, which is approximated as a germicidal factor at 285 nm, was 1.15 for adenovirus. To conclude, this study demonstrated a high potential of the 285 nm UV-LEDs to inactivate microorganisms in water. The germicidal factor found...