Kinetic modeling and energy efficiency of UV/H₂O₂ treatment of iodinated trihalomethanes

Photodegradation of I-THMs including CHCl₂I and CHI₃ by the UV/H₂O₂ system was investigated in this study. CHCl₂I and CHI₃ react rapidly with hydroxyl radical (OH) produced by the UV/H₂O₂ system, with second-order rate constants of 8.0×10⁹ and 8.9×10⁹M^-1s^-1, respectively. A fraction of CHCl₂I could be completely mineralized within 15min and the remaining fraction was mainly converted to formic acid (HCO₂H). Cl^- and I^- were identified as the predominant end-products. No ClO₃^- was observed during the photodegradation process, while IO₃^- was detected but at less than 2% of the total liberated iodine species at the end of the reaction. The effects of pH, H₂O₂ dose, and matrix species such as humic acid (HA), HCO₃^-, SO₄^2-, Cl^-, NO₃^- on the photodegradation kinetics were evaluated. The steady-state kinetic model has been proven to successfully predict the destruction of CHCl₂I and CHI₃ by UV/H₂O₂ in different water matrices. On this basis, the kinetic model combined with electrical energy per order (EE/O) concept was applied to evaluate the efficiency of the photodegradation process and to optimize the H₂O₂ dose for different scenarios. The optimal H₂O₂ doses in deionized (DI) water, model natural water, and surface water are estimated at 5, 12, and 16mgL^-1, respectively, which correspond to the lowest total energy consumption (EE/O_total) of 0.2, 0.31, and 0.45kWhm^-3order^-1.