The effect of UV/H2O2 treatment on disinfection by-product formation potential under simulated distribution system conditions

Advanced oxidation with ultraviolet light and hydrogen peroxide (UV/H2O2) produces hydroxyl radicals that have the potential to degrade a wide-range of organic micro-pollutants in water. Yet, when this technology is used to reduce target contaminants, natural organic matter can be altered. This study evaluated disinfection by-product (DBP) precursor formation for UV/H2O2 while reducing trace organic contaminants in natural water (>90% for target pharmaceuticals, pesticides and taste and odor producing compounds and 80% atrazine degradation). A year-long UV/H2O2 pilot study was conducted to evaluate DBP precursor formation with varying water quality. The UV pilot reactors were operated to consistently achieve 80% atrazine degradation, allowing comparison of low pressure (LP) and medium pressure (MP) lamp technologies for DBP precursor formation. Two process waters of differing quality were used as pilot influent, i.e., before and after granular activated carbon adsorption. DBP precursors increased under most of the conditions studied. Regulated trihalomethane formation potential increased through the UV/H2O2 reactors from 20 to 118%, depending on temperature and water quality. When Post-GAC water served as reactor influent, less DBPs were produced in comparison to conventionally treated water. Haloacetic acid (HAA5) increased when conventionally treated water served as UV/H2O2 pilot influent, but only increased slightly (MP lamp) when GAC treated water served as pilot influent. No difference in 3-day simulated distribution system DBP concentration was observed between LP and MP UV reactors when 80% atrazine degradation was targeted.

► Trihalomethane formation potential increased through the UV/H2O2 reactors from 20 to 118%.
► Haloacetic acid increased when conventionally treated water served as UV/H2O2 pilot influent.
► DBP formation potential was similar for LP and MP UV reactors when 80% atrazine reduction was targeted.