Application of the UV/Chlorine Advanced Oxidation Process for Drinking Water Treatment

This research investigated the feasibility of a novel advanced oxidation process (AOP) using ultraviolet light combined with free chlorine (UV/chlorine) in drinking water treatment. A bench-scale study using a medium pressure UV collimated beam apparatus showed that the UV/chlorine process was more efficient than the UV combined with hydrogen peroxide (UV/H2O2) AOP for the destruction of trichloroethylene (TCE) at pH 5 in a laboratory prepared water, but was less efficient than the latter at pH 7.5 and 10. A Matlab® mathematical model made accurate predictions of the observed experimental rates of TCE decay. The model predicted that increasing concentrations of hydroxyl radical scavengers in the treated water would tend to raise the pH at which UV/chlorine would remain competitive relative to UV/H2O2. Full-scale experiments at the City of Cornwall Water Purification Plant (Ontario, Canada) and pilot-scale tests in a Rayox® batch UV reactor using water from the Keswick Water Treatment Plant (Ontario, Canada) demonstrated comparable performance of UV/chlorine AOP to UV/H2O2 for geosmin, 2-methylisoborneol (MIB), and caffeine destruction. Organic and inorganic disinfection by-products (DBPs) were also monitored in the full- and pilot-scale tests. Minimal trihalomethane and haloacetic acid formation was observed across the UV reactor, while dichloroacetonitrile and bromochloroacetonitrile were produced rapidly, although overall concentrations were below 6 g L-1. Adsorbable organic halide was formed rapidly (up to 70 g Cl L-1) in water that had not been prechlorinated, while little formation was observed in previously chlorinated water. Chlorate and bromate were formed, equivalent to approximately 2-17% and 0.01-0.05% of the photolyzed chlorine, respectively, while no perchlorate or chlorite formation was observed. In addition, the 24 h organic DBP formation potential was increased by UV/chlorine pretreatment to an extent that was similar to that observed when the water was pretreated with UV/H2O2.Ph.D