The effect of halides on organic contaminant degradation efficiency was compared for UV/H2O2 and UV/S2O82- AOP treatments in saline waters. Benzoic acid, 3-cyclohexene-1-carboxylic acid and cyclohexanecarboxylic acid were used as models to represent aromatic, alkene and alkane constituents in saline water. In model freshwater, the apparent degradation rate of contaminant was higher by UV/S2O82- AOP because of the higher quantum efficiency for S2O82- than H2O2 photolysis. The presence of halides converted �OH and SO4�- radicals to less reactive halogen radicals and reduced the degradation efficiency of benzoic acid and cyclohexanecarboxylic acid. The UV/S2O82- AOP was more affected by Cl- than the UV/H2O2 AOP, because oxidation of Cl- is more favorable by SO4�- than �OH at pH 7. Degradation of 3-cyclohexene-1-carboxylic acid, was not affected by halides, likely due to the high reactivity of halogen radicals with alkenes. Despite its relatively low concentration in saline waters compared to Cl-, Br- was particularly important. Br- promoted halogen radical formation for both AOPs resulting in ClBr�-, Br2�-, and CO3�- concentrations orders of magnitude higher than �OH and SO4�- concentrations, and reducing differences in halide impacts between the two AOPs. Kinetic modeling of the UV/H2O2 AOP indicated a synergism between Br- and Cl-, with Br- scavenging of �OH leading to BrOH�-, and further reactions of Cl- with this and other brominated radicals promoting halogen radical concentrations. In contaminant mixtures, the conversion of �OH and SO4�- radicals to more selective CO3�- and halogen radicals favored attack on highly reactive reaction centers at the expense of less reactive reaction centers.The experiments with the RO concentrate showed that degradation of propranolol by indirect photolysis was the most efficient for both S2O82- and H2O2 photolysis.

Comparison of the efficiency of contaminant degradation by sulfate and hydroxyl radical-based advanced oxidation processes (AOPs) in saline water

248th National Meeting (2014)

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