Synergistic mechanism of combined UV-LEDs and peracetic acid treatment on inactivation of fungal spores

Photo-driven advanced oxidation process (AOP) with peracetic acid (PAA) has received increasing attention. In this study, a new PAA-based AOP (Ultraviolet light emitting diodes (UV-LEDs)/PAA process) was used to inactivate fungal spores. The synergistic factor of UV-LED265/PAA, UV-LED280/PAA and UV-LED265/280/PAA were 1.25, 1.14 and 1.19, respectively for Aspergillus niger. The results indicated there was a synergism in UVLEDs/PAA system, and it can be attributed to the radicals and other synergistic action. Each efficient composition of UV-LEDs, radicals, synergistic action and PAA varied in different disinfection evaluation methods (cultivability, membrane integrity, and oxidative stress) in UV-LEDs/PAA process. For example, UV-LEDs contributed the most (76-87 %) to spore damage in cultivability. The role of radicals (5-33 %) and synergies (23-65 %) mainly targeted in cell membrane damage. Radicals also can stimulate the increase in intracellular reactive oxygen species level (4-53 %). Compared with UV-LEDs alone, the inactivation rate constant of membrane damage (0.08-0.25 cm2 mJ-1) was much higher than cultivability and oxidative stress in UV-LEDs/ PAA process, suggesting that the synergism in UV-LEDs/PAA process was mainly reflected in the dramatic destruction of cell membranes (45-74 %). In addition, the control efficiency of fungal spores in UV-LEDs/PAA process were superior to solar/PAA and LP-UV, and the severe damage induced by UV-LEDs/PAA can control the spores in viable but not culturable states, suppressed the photoactivation, and decreased the possibility of fungal spore regrowth effectively.