Control of Aromatic Disinfection Byproducts in Potable Reuse Water by the UV₂₂₂/H₂O₂ vs UV₂₅₄/H₂O₂ Advanced Oxidation Processes

Research has demonstrated the difficulty associated with degrading the conventional 1-2 carbon aliphatic halogenated byproducts of disinfectant reactions with organic matter [disinfection byproducts (DBPs)] within advanced oxidation process (AOP) units in potable reuse trains, but the efficacy of AOP units for treating the emerging classes of halogenated aromatic DBPs is unclear. We herein demonstrate more effective removal of 28 halogenated aromatic DBPs in the UV/H₂O₂ AOP at 222 nm (UV₂₂₂) than in the conventional UV/H₂O₂ AOP at 254 nm. Direct photolysis of 28 halogenated aromatic DBPs was greatly enhanced at 222 nm with fluence-based photodecay rate constants of 4.31 × 10^-4-1.53 × 10^-2 cm² mJ^-1, which was mainly attributed to the higher molar absorption coefficients of halogenated aromatic DBPs at 222 nm than 254 nm. Generally, quantum yields of halogenated aromatic DBPs at both 222 and 254 nm followed the order of halophenols > halohydroxybenzaldehydes > halonitrophenols. All 28 halogenated aromatic DBPs exhibit high reactivity toward HO^• with second-order rate constants ranging from 2.18 × 10⁹ to 1.15 × 10¹⁰ M^-1 s^-1 determined by X-ray radiolysis. The UV fluence required to achieve 90% loss of halogenated aromatic DBPs in the UV₂₂₂/H₂O₂ AOP was 75-95% lower than that in the UV₂₅₄/H₂O₂ AOP, and 90% removal of most tested halogenated aromatic DBPs can be achieved in the UV₂₂₂/H₂O₂ AOP within the UV fluence levels commonly applied in potable reuse (700-1000 mJ cm^-2).