UV and solar photocatalytic disinfection of municipal wastewater: inactivation, reactivation and regrowth of bacterial pathogens

Pollution of water sources by pathogens is a major concern worldwide. This study investigated critical disinfection aspects such as bacterial regrowth or decay and evaluation of metal-ion leaching during photocatalytic disinfection. The inactivation of waterborne bacterial pathogens (Escherichia coli, Salmonella species, Shigella species and Vibrio cholerae) using ultraviolet and solar photocatalysis was evaluated. Bare and metal-ion (silver, copper and iron)-doped titanium dioxide photocatalysts were used to explore comparative performance. The influence of photocatalyst concentration (0.1-1.0g/L), source of radiation (ultraviolet or solar light) and water type (synthetic and municipal wastewater) was examined. The disinfection data were fitted to the pseudo-first-order model. The disinfection efficiency was higher in saline deionized water (99.9998-100%) that was spiked with the target pathogens (10(6) colony forming units/mL), compared to actual wastewater samples. Within 180min of treatment under solar irradiation, disinfection efficacy of 86.8-100% was achieved, while 99.4-100% disinfection efficacy was attained under ultraviolet irradiation within 60min. A significant difference (p<0.05) between ultraviolet and solar photocatalysis was observed, and silver-doped titanium dioxide displayed the best performance under all conditions tested. Nevertheless, after a contact time of 180min, there was no bacterial regrowth observed even for the solar photocatalysis processes; in fact, bacterial decay occurred. The elution of doping metals into the treated wastewater was insignificant. Therefore, the metal-ion-doped photocatalysts were effective under solar radiation, thus overcoming the limitation of bare titanium dioxide which is only effective under ultraviolet light and preventing bacterial regrowth.