Planar reactor with a serpentine channel for water disinfection by using ultraviolet C light-emitting diodes

Water sterilization efficiency is affected by water flow patterns and irradiance distribution, which in turn are affected by reactor design. In this study, a planar flow reactor with a serpentine channel was used to treat drinking water by using 278-nm ultraviolet (UV)-C light-emitting diodes. The effects of various water flow rates, channel widths, and baffle lengths were investigated to understand their effects on fluid mixing and flow trajectory. The experimental results revealed that the UV reactor with a channel width of 13 mm exhibited the highest log inactivation value for Escherichia coli among the reactors with three different channel widths. This is because this width maximized the exposure time and increased the secondary flow at the turn regions in the serpentine channel. Furthermore, the baffle length dramatically affected the flow trajectory, circulation zones, and microbial exposure time. This length was optimized at 22 mm for all the investigated flow rates. The developed UV reactor achieved an inactivation value of 4.0 log for E. coli at a maximum water flow rate of 80 mL/min.