Abstract
Inactivation of MS2 coliphage by sequential ultraviolet (UV) light/free chlorine exposure, sequential UV light/monochloramine exposure, simultaneous UV light/free chlorine exposure, and simultaneous UV light/monochloramine exposure using either low-pressure (LP) or medium-pressure (MP) UV lamps was evaluated in this study. At a UV dose of 51 mJ/cm2, the sequential exposure to UV or the simultaneous exposure in the primary disinfection stage enhanced MS2 inactivation rates during the secondary disinfection stage by chlorine by 1.5–2.7 times, compared to the rates solely by free chlorine. At the same dose, the sequential exposure to UV or the simultaneous exposure in the primary disinfection stage enhanced MS2 inactivation rates during the secondary disinfection stage by monochloramine by four to five times. The enhancement was similar with the different UV lamps but less significant with a UV dose of 17 mJ/cm2, while the enhancement from the sequential exposure was higher than that after the simultaneous exposure. During the simultaneous exposure, synergy (the log-inactivation under the simultaneous exposure was 1.1–5.3 times greater than the sum of inactivation achieved by using the two disinfectants separately at the same doses) occurred during the primary disinfection stage. Depending on the situation encountered, one combination among these tested ones may provide the best choice to give sufficient inactivation and shall be case-specifically evaluated.
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