The Effect of Chlorine in Water on Enteric Viruses

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Abstract
Complete inactivation of enteric viruses was not achieved by the usual conditions for bacterial disinfection of water supplies, i.e., free residual Cl concentrations of 0.2 ppm for 10-minute contact at pH 7. Concentrations from 0.2 to 0.3 ppm inactivated viruses after 30 minutes of contact. Four hours of contact was necessary for inactivation by combined residual Cl concentrations of 0.7 ppm. Factors affecting inactivation of viruses were strain, pH level, free residual Cl concentration, exposure time, and temperature. Strains in decreasing order of sensitivity to Cl were: Coxsackie B 5, poliovirus 1 (Mahoney), poliovirus 2, Coxsackie B1, poliovirus 3, and poliovirus 1 (MK 500). Rises in Ph value of one unit above pH 7 more than doubled the contact period necessary for inactivation of several strains. Concentrations of free residual Cl greater than 0.2 ppm for contact periods longer than 10 minutes were necessary for inactivation, depending on virus strain, temperature, and pH level. A 20[degree] lowering of temperature slowed inactivation 2- to 15-fold. Results suggest that inactivation of enteric viruses in water at pH 7 at 25[degree]C requires a minimum free residual Cl concentration of 0.3 ppm for contact periods of at least 30 minutes; at higher pH levels or lower temperatures, more intensive chlorination is necessary.