Combination of ultraviolet-C light-emitting diodes and a spiral-channel configuration in a water disinfection reactor

In this study, a water disinfection flow reactor with a spiral-channel configuration was developed to treat drinking water by using 278-nm ultraviolet (UV)-C light-emitting diodes. The effects of the flow rate, spiral pitch, and radiative power were investigated to improve the efficiency of sterilizing Escherichia coli. The spiral-channel configuration was used to induce Dean vortices and increase the microbial exposure time. The results of this study indicated that at all the examined flow rates, the flow reactor with a spiral pitch of 10 mm achieved the highest log inactivation among three reactors with different pitches. The shorter the spiral pitch, the higher was the Dean number and longer was the exposure time in the flow channel. Increasing the flow rate not only enhanced Dean effect but also reduced the microbial exposure time. Moreover, the exposure time and Dean number exhibited opposite trends under a varying flow rate. The optimal log inactivation was achieved at a flow rate of 60 mL/min, and a droop was observed in the fluence-response curve when the flow rate was less than 60 mL/min due to a decrease of Dean effect in the flow reactor. Under the same UV fluence, the shorter the spiral pitch, the higher was the sterilization efficiency of the flow reactor.