Heat-activated Persulfate Oxidation Of Parabens In Aqueous Solution

Parabens(para-hydroxybenzoic acid esters)have been widely used as antimicrobial preservative agents in foodstuffs,medicines,and personal care products due to their broad-spectrum activity against yeasts,molds and bacteria.With a surge of usage,parabens may pollute water environment and do potential harm to human health.As parabens cannot be completely eliminated by conventional wastewater treatment plants,the novel treatment technologies with higher removal efficiency on these compounds are urgent and essential.Activated persulfate oxidation which has been recently considered as an efficient advanced oxidation process(AOP)has attracted much more attention.This process has been successfully applied in soil remediation and pollutants removal in the groundwater,showing broad application prospects.In this study,two representative parabens,namely methylparaben(MeP)and ethylparaben(EtP),were selected as target compounds to evaluate the oxidation efficiency of parabens by heat-activated persulfate process for the first time.The effects of different operational conditions including heating temperature,initial persulfate dosage,solution pH,chloride,alkalinity and humic acid(HA)were studied,along with assessing the reactive kinetics.The radical species were determined,then the TOC was analyzed.Additionally,the oxidation products were identified by LC-MS/MS and the possible reaction pathway was proposed.At last,the possibility of the application of the heat-activated persulfate process in the wastewater treatment was discussed.The results indicated that:(1)The degradation of both MeP and EtP were improved by increasing the heating temperature and initial persulfate dose.The oxidation effciency of parabens was found to be pH-dependent,decreasing in the order of pH 5.0 > 7.0 > 9.0.The degradation process could be well fitted by a pseudo-first-order reaction model.(2)The presence of chloride and bicarbonate was found to inhibit the degradation of the two parabens to some extent.Humic acid inhibited the removal of the two parabens significantly.When the initial HA concentrations was 10mg/L,the degradations of MeP and EtP significantly decreased by 80.7% and 82.6%,respectively.(3)Both sulfate and hydroxyl radicals contributed to the removal of the two parabens.The two parabens could be degraded to some intermediate products through the TOC analyzing in the MeP and EtP solutions.A possible degradation pathway of MeP in heat-activated persulfate process has been proposed,in which it primarily undergoes dealkylation of the methyl chain to produce p-hydroxybenzoic acid,followed by decarboxylation of the carboxyl chain and hydrolysis to produce p-dihydroxybenzene.(4)MeP and EtP in a real water were simultaneously removed by using heat-activated persulfate process.The removal rates was 67.1% and 73.4%,respectively,suggesting that this system may offer a potential method for treating paraben-containing wastewater samples.