IWA Publishing

IWA Publishing

Effects of salinity on photoreactivation of Escherichia coli after UV disinfection


The effects of sodium chloride on photoreactivation of Escherichia coli were examined, assuming the discharge of ultraviolet (UV)-treated wastewater to water environment at different salinities. Suspensions of E. coli were first exposed to a low-pressure UV lamp in phosphate buffer to achieve 3 log inactivation, followed by an exposure to fluorescent light in NaCl solutions at the concentration of 1.0, 1.4, 1.9, 2.4 and 2.9 weight/volume %. When photoreactivation was completed in 3 h, survival ratio was recovered about 2 log in 1.0, 1.4, and 1.9% NaCl solutions, which was equivalent to the recovery observed in phosphate-buffered solution. Meanwhile, the recovery was suppressed to 0.8 log and −0.2 log in 2.4 and 2.9% NaCl solutions, respectively, which was significantly less than the recovery in phosphate buffer according to the t-test (p < 0.05). An endonuclease sensitive site assay demonstrated that the suppressed photoreactivation in 2.9% NaCl solution was due to the failure at repairing UV-induced pyrimidine dimers in the genome. In conclusion, photoreactivation of E. coli was significantly suppressed in NaCl solution at 2.4% or higher but not affected in NaCl solution at 1.9% or lower. This implies that photoreactivation of E. coli may potentially occur in brackish and coastal areas where salinity is rather low.

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