Microorganisms inactivation by continuous and pulsed irradiation of ultraviolet light-emitting diodes (UV-LEDs)

Abstract

Ultraviolet light-emitting diode (UV-LED) is an emerging UV source and has a number of features that do not exist in conventional mercury based UV lamps. One such feature is the ability to turn the radiation on and off with a high frequency, which enables pulsed irradiation with flexible pulse patterns by UV-LEDs. In this study, the inactivation of different microorganisms by continuous and pulsed irradiation was investigated using UV-LEDs, in order to utilize this unique feature to distinguish the effect of pulsation on inactivation, and to explore the potential benefits of UV-LEDs pulsed irradiation for water disinfection. The analysis was based on the equivalent UV fluence between continuous and pulsed irradiation using two types of actinometry techniques (iodide-iodate and ferrioxalate) for UV fluence determination. The disinfection study involved the inactivation of E. coli and coliphage MS2 in laboratory water, as well as E. coli and total coliform in wastewater. The effects of pulse patterns including frequency (i.e., the number of on-off cycles per second) and duty rate (i.e., the percentage of irradiation time in each on-off cycle) on the inactivation effectiveness were also examined for these microorganisms. The results showed comparable inactivation of all the examined microorganisms by 265 nm UV-LED continuous and pulsed irradiation with various pulse patterns under equivalent UV fluence. The findings in this study were compared with those from conventional xenon lamps pulsed irradiation studies, which not only distinguished the role of pulsed UV irradiation on microorganisms inactivation, but also revealed a key feature of UV-LEDs pulsed irradiation with respect to improved thermal management, potentially affecting application of high output UV-LEDs for water disinfection.