Oxidation of methylated arsenic species by UV/S2O82−

Abstract UV/S 2 O 8 2− process was studied for the oxidation of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in aqueous solution. UV/H 2 O 2 and UV/TiO 2 were also applied to the oxidation of the target compounds. TiO 2 was added at a low dosage (50 mg/L), considering a condition advantageous for catalyst separation. Under the experimental condition of this study ([S 2 O 8 2− ] 0  = [H 2 O 2 ] 0  = 1 mM, [TiO 2 ] 0  = 50 mg/L), UV/S 2 O 8 2− was more effective for oxidizing MMA and DMA than UV/H 2 O 2 and UV/TiO 2 . The oxidation rate of DMA by UV/S 2 O 8 2− could be accelerated by increasing the ratio of [S 2 O 8 2− ]/[DMA]. The oxidation efficiencies of MMA and DMA by UV/S 2 O 8 2− 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/S 2 O 8 2− is an effective oxidation process for MMA and DMA.