Waterborne fungi have been recognized as an emerging environmental contaminant in recent years. In this work, sequential and combined applications of light-emitting diodes (UV-LEDs) with two wavelengths and chlorine (Cl2) were performed for fungal spores disinfection, the performance of LPUV (low pressure ultraviolet) and UV-LEDs was also compared. The results revealed that inactivation efficiency of fungal spores in the UV/Cl2 process was greatly enhanced compared to the sequential or individual processes, and an evident synergistic effect was observed. Take P. polonicum for example, pre-treatments by UV265 and UV280 (40 mJ/cm2) caused the log count reduction (LCR) of 1.05 log and 0.95 log, then the followed UV265/Cl2 and UV280/Cl2 at the same UV fluence caused additional LCR of 1.80 log and 2.00 log. The inactivation rates for Penicillium polonicum in the processes of UV265/Cl2, UV280/Cl2, UV265/280/Cl2 and LPUV/Cl2 was 0.142, 0.168, 0.174 and 0.106 cm2/mJ, respectively, which were all approximately 1.5-fold higher than that of UV alone. The synergistic effect of fungal spores inactivation by UV-LEDs/Cl2 and LPUV/Cl2 was due to the high level production of intracellular reactive oxygen species and the reaction of potential extracellular free radicals. Resistance of the tested fungal spores was as follows: Trichoderma harzianum &lt; Penicillium polonicum &lt; Aspergillus niger. In addition, the joint effect of DNA and other cellular damage resulted in the inhibition of photoreactivation of fungal spores inactivated by UV-LEDs/Cl2 and LPUV/Cl2. This study may provide reference for controlling the dissemination of waterborne fungi utilizing combined UV-LEDs and free chlorine processes.

Sequential and combined use of UV-LEDs irradiation and chlorine to disinfect waterborne fungal spores: Efficiency, mechanism and photoreactivation

ACS Spring 2022

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