UV dose effects on the revival characteristics of microorganisms in darkness after UV disinfection: Evidence from a pilot study.

ABSTRACT

Ultraviolet (UV) disinfection during water supply treatment aims to reduce the number of bacteria. Although UV disinfection is effective at inactivating most microorganisms, some microbe species may be entirely impervious. A pilot study was conducted to compare the quantity and community component of bacteria in surface water collected from filtration effluent before UV disinfection with different doses of UV, and those 1 and 2 days afterwards, in darkness. The aim was to elucidate the relationship between the UV dose and the total revived microorganisms in darkness after UV disinfection. In the filtration effluent samples, Gammaproteobacteria, Bacilli, Actinobacteria, and Alphaproteobacteria were the predominant classes. After storage in the dark at a constant temperature of 19 °C, the UV-disinfected samples showed a considerable increase in Bacilli, while Gammaproteobacteria remained the predominant population. Genera such as Exiguobacterium, Citrobacter, Acinetobacter, and Pseudomonas presented a selective advantage in terms of revival in darkness after UV disinfection, irrespective of the UV dose and storage time. The lowest rate of microbial revival (5% day-1) was noted at a UV dose of 266.10 mJ m-2 (with an average UV illumination time of 124.4 s and an average intensity of 86.61 W m-2). Our results suggest that higher UV intensity and lower illumination time are key factors in minimizing the revival of microorganisms in darkness.