Comparison of the performance of pulsed and continuous UVC-LED irradiation in the inactivation of bacteria.

Ultraviolet light-emitting diode (UV-LED) is a newly emerging UV light source with a potential to replace the conventional chemical methods, mercury UV lamps and xenon lamps in water disinfection. UV-LEDs are characterized by the diversity in wavelengths and can be turned on and off with a high and adjustable frequency, making them an attractive candidate for pulsed light (PL) disinfection apart from the conventional continuous wave (CW) operation. Previous studies on comparison between the PL and CW UV-LED irradiations for the inactivation of bacterium in water disinfection are limited and results conflict. In this work, PL and CW UV-LED in the C-spectral band (UVC-LED) irradiations were compared at equivalent fluence in the inactivation and subsequent photoreactivation of E. coli bacteria. In addition, effect of different driving currents and ambient temperatures on solder temperature of the PL and CW UVC-LED irradiation was also examined. Under the equivalent fluences, the PL and CW UVC-LED irradiations brought comparable inactivation efficiency and similar photoreactivation of the E. coli. Moreover, the PL UVC-LED exhibited a much lower solder temperature than the CW UVC-LED irradiation. On the other hand, CW UVC-LED irradiation, higher ambient temperature and higher driving current increased the solder temperature that resulted to a negative impact on the wavelength, full width at half maximum, optical power and irradiance, which are key factors in the UVC-LED disinfection efficiency. In all, this work reports the comparison between PL and CW in UVC-LED irradiation for inactivating E. coli bacteria and firstly revealed the photoreactivation of the E. coli after the PL UVC-LEDs irradiation.