Disinfection of Chlorine Resistent Enteroviruses in Ground Water by Ultraviolet Irradiation

Human enteroviruses, predominantly poliovirus type 1, occurring naturally in chalk well water, have been found to survive disinfection consisting of a nominal 1.0 mg/1 of free residual chlorine maintained for a minimum contact time of 15 minutes at a pH value of 7.2 and a temperature of 11°C. Disinfection with 1.5 mg/1 of chlorine under the same conditions resulted in virus inactivation and they were also destroyed by exposure to 25 mJ/cm² of ultraviolet light. It is considered that the apparent chlorine resistance of these viruses is due to their association with an organic floc rather than to any innate property of the virus or of the water. The implications of these results for the treatment of this water are discussed.