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

Abstract

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 × 109 M−1 s−1, respectively. A fraction of CHCl2I could be completely mineralized within 15 min 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−, SO42−, 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 16 mg L−1, respectively, which correspond to the lowest total energy consumption (EE/Ototal) of 0.2, 0.31, and 0.45 kWhm−3order−1.