Kinetics of oxidation of odorous sulfur compounds in aqueous alkaline solution with H2O2

Sulfur species oxidation is a crucial issue in wastewater treatment. The pr oduction of sulfur compounds like H2S, CH3SH, C2H5SH, disulfides and dimeth yle sulfide generates odorous nuisances for the neighborhood. The oxidation of these species by H2O2 in alkaline solution has been investigated. The r esults showed that thiols CH3SH and C2H5SH react with H2O2 only in their di ssociated form RS- with rate constants respectively k = 8.81 +/- 0.48 M-1.s -1 and 8.37 +/- 0.63 M-1.s-1. Mercaptans oxidation produces 100 % of dimeth yldisulfide or diethyldisulfide. The oxidation of disulfides shows a differ ence of reactivity between H2O2 and HO2- towards sulfur species. Increasing the pH accelerates significantly the reactions in the case of CH3SSCH3. Th e oxidation rate can be described as: r = k[RSSR][H2O2][RSSR][H2O2] + k[RSS R][HO2-] [RSSR][HO2-] with k[RSSR][H2O2] = 1.2x10-4 +/- 0.2x10-4 M-1.s-1 an d k[RSSR][HO2-] = 3.4x10-4 +/- 0.6x10-4 M-1.s-1 for CH3SSCH3. Dimethyl sulf ide presents a reactivity different from disulfides. The oxidation rate can also be described as: r = k[CH3SCH3][H2O2][CH3SCH3][H2O2] + k[CH3SCH3][HO- ] [CH3SCH3][HO2-], however, oxidation rate decreases with pH increase. k[CH SCH3][H2O2] = 12.8x10-3 +/- 0.96x10-3 M-1.s-1 and k[CH3SCH3][HO2-] = 4x10-3 +/- 0.3x10-3 M-1.s-1.