Synergistic Effect of Self-Doped TiO2 Nanotube Arrays and Ultraviolet (UV) on Enhanced Disinfection of Rainwater

Rainwater has been used in areas that have limited water resources. In this scenario, ultraviolet (UV) disinfection is often used to improve the quality of rainwater before its reuse. However, the technology is weakened by photoreactivation and dark repair for promoting the regrowth of microbes in treated rainwater. In this work, a system integrating UV and self-doped TiO2 nanotube arrays (the UV-TiO2 system) was used to solve the issue. The effects of the power of UV lamps, pH value, the area of TiO2 nanotube arrays, biomass concentration, humic acid, sulfate, and nitrate concentration on the disinfection effect of the two systems were also studied. To achieve the standard of drinking water quality, the single UV system and UV-TiO2 system needed 17 s and 12 s respectively for the rainwater treatment at medium biomass concentration. Increasing the area of TiO2 nanotube arrays would improve UV-TiO2 disinfection efficiency. Furthermore, the UV-TiO2 system could better adapt to the changes in biomass concentration and low pH conditions than the UV system. The total colony count disinfected by the UV system was approximately 3.2 times higher than that by the UV-TiO2 system after 8-h exposure to fluorescence light. The experimental results showed that the UV-TiO2 system was better than the UV system in terms of disinfection, faster and more efficient inactivation, and inhibition of photoreactivation and dark repair.