Oxidation of methylated arsenic species by UV/S2O82−

UV/S2O82− process was studied for the oxidation of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in aqueous solution. UV/H2O2 and UV/TiO2 were also applied to the oxidation of the target compounds. TiO2 was added at a low dosage (50 mg/L), considering a condition advantageous for catalyst separation. Under the experimental condition of this study ([S2O82−]0 = [H2O2]0 = 1 mM, [TiO2]0 = 50 mg/L), UV/S2O82− was more effective for oxidizing MMA and DMA than UV/H2O2 and UV/TiO2. The oxidation rate of DMA by UV/S2O82− could be accelerated by increasing the ratio of [S2O82−]/[DMA]. The oxidation efficiencies of MMA and DMA by UV/S2O82− were lower at initial pH 7 than at initial pH 3 and 10. This phenomenon was attributable to the radical-scavenging effect of bicarbonate, which was added as a pH-buffering solute. The results shown in this study show that UV/S2O82− is an effective oxidation process for MMA and DMA.