Synergistic Benefits Between Ultraviolt Light and Chlorine-Based Disinfectants for the Inactivation of Escherichia coli

Ultraviolet light is increasing in popularity as a primary disinfectant in drinking water treatment because of its effectiveness against chlorine-resistant pathogens and lack of disinfection by-product (DBP) formation. Previous bench-scale studies have shown that there are possibly synergistic benefits in reducing heterotrophic bacteria when ultraviolet (UV) light is coupled with chlorine (Cl2) or monochloramine (NH2Cl). Additional experiments have demonstrated that synergy exists between various disinfectants in controlling numerous bacteria, viruses, and protozoan. Few studies, to date, have specifically investigated synergy with UV in combination with chlorine-based drinking water disinfectants including chlorine dioxide (ClO2), Cl2, and NH2Cl. This preliminary study looked at the effectiveness of seven disinfection strategies (UV, Cl2, ClO2, NH2Cl, UV/Cl2, UV/ClO2, and UV/NH2Cl) against Escherichia coli in a single-species system at various combinations of disinfectant dose and contact time. Spiked solutions containing E. coli were treated by UV alone, chemical disinfectant alone, or UV coupled with chemical disinfectant. It was found that the combined disinfection strategies achieved the highest removal. Data were additionally analyzed for synergistic benefits, and each combination had a positive result. Results suggest that drinking water utilities may see enhanced removal of bacteria and potentially other pathogens due to synergistic benefits when UV was used in combination with any chlorine-based disinfectant. However, more data are required to conclusively determine synergistic relationship(s) between UV light and chlorine-based disinfectants.