| Similar tocatalytic ozonation, Fenton reagents and photocatalytic oxidation,sulfate radicals (SO4-) are frequently investigated and used as alternativeadvanced oxidation technologies (AOTs). SO4-can be generated via persulfate (PS,such as peroxymonosulfate (PMS) and perdisulfate (PDS)) activation by light, heat,transition metals and other methods. Experimental results showed thatultraviolet(UV)/PS system could efficiently eliminate organic matters inmicro-polluted waters. However, the major drawback for these AOTs application isthe formation of undesired by-products, such as bromate (BrO3-). BrO3-isclassified as a B2, probable human carcinogen, and is generally formed duringozonation of bromide-containing waters.This paper (i) investigated the time-dependent BrO3-formation in UV/PSsystem, along with the influence factors;(ii) revealed the mechanism of BrO3-formation in SO4-based-AOTs. The experimental procedures were:(i)500mLsolutions containing desired concentrations of reagents were prepared andtranfered into the UV reactor;(ii) beginning with the UV irradiation, samples werewithdrawn at designed time intervals for Br species determination;(iii) Br-andBrO3-were determined by ion chromatography with conductivity detector, andHOBr/OBr-was determined by HPLC after reaction with phenol.In the UV/perdisulfate (PDS) system, the transformation efficiency of Br-toBrO3-increased from6.05%to100%with the increase of concentrations of PDSfrom50μM to2000μM. The increase of concentration of Br-from5μM up to50μM, resulted in the decrease of the transformation efficiency from99.71%to4.33%. As the pH increased from7to10, transformation efficiency of BrO3-decreased drastically from75%to0%. At pH>10and pH <7, the efficiencieswere kept constant with0%and75%, respectively.In the UV/peroxymonosulfate (PMS) system, the transformation efficiency ofBr-to BrO3-increased from4.53%to47.43%with concentrations of PMS from100μM to1000μM. As the concentration of Br-increased from5μM to50μM, theransformation efficiency decreased from47.43%to1.27%. The transformationefficiencies of BrO3-were47.43%,19.94%,3.64%and0%at pH=7.0,8.0,9.0,and10.0, respectively, and kept constant to be75%at pH <7.0and0%at pH>10.0, respectively.Furthermore, with model compounds such as humic acid (HA), methanol (MeOH), tert-butyl alcohol (tBuOH), benzoic acid (BA) and p-chlorobenzoic acid(pCBA) added in the UV/PDS system, it was found that as the concentrations ofadded organic matters increased, the production rates of BrO3-gradually sloweddown with the initial time of the detection of BrO3-gradually postponed.According to the time-depended variation of concentrations of Br-,HOBr/BrO-and BrO3-, it can be speculated that HOBr/BrO-is an importantintermediate product for the generation of BrO3-. In the presence of organicmatters, the H2O2formed in the reactions of radicals (SO4-and/or OH) withorganic matters played a significant role on BrO3-inhibition in the UV/PDSsystem. |
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