Bromate Formation During The Oxidation Of Bromide-containing Water By Ozone/peroxymonosulfate Process: Mechanisms And Control Method

Ozonation is a common water treatment oxidation method.However,ozonation has a certain selectivity and low oxidation efficiency.In addition,when bromide ions exist in water,bromate（BrO₃^-）may be formed as a by-product.Therefore,the advanced oxidation technology of O₃/H₂O₂ was proposed.The combination of O₃/H₂O₂can efficiently oxidize organic compounds in water and control the formation of bromate.However,hydrogen peroxide has the characteristics of difficult transportation,high cost and low utilization efficiency.On this basis,our group proposed an advanced oxidation system combining ozone/peroxymonosulfate（O₃/PMS）,in which the conversion efficiency of PMS was higher than that of hydrogen peroxide,and at the same time,high activity hydroxyl radicals（·OH）and sulfate radicals(SO₄^·-)were produced,which could degrade organic pollutants in water efficiently and rapidly.However,bromate formation process and mechanisms during the oxidative treatment of bromide-containing water by O₃/PMS process remains poorly understood.In this paper,the formation and control of bromate in the O₃/PMS system were studied in the following aspects:the influencing factors and reaction mechanism of bromate during the oxidation of bromine-containing water by O₃/PMS;the degradation effect of organic matter and the control of bromate formation in the O₃/PMS oxidation system by adding carbon-based catalysts;the degradation effect of organic matter and the control of bromate formation in the O₃/PMS process by adding carbon-based catalyst which supported with metal oxide.The main conclusions of this paper are as follows:（1）The influencing factors of bromate formation in O₃/PMS process were investigated,including the effects of PMS dose,initial bromide concentration,pH value and water quality.The results showed that,during the O₃/PMS process,increasing the PMS dosage and bromide concentrations promoted the bromate formation,which was also significantly improved by raising the pH from 4.0 to 10.0.Bromate formation was a result of the combined effect of molecular ozone,·OH,and SO₄^·-,and the HOBr/OBr^-was the essential intermediate species.（2）The addition of activated carbon（PAC）,carbon nanotubes（CNT）and graphene（GO）to the O₃/PMS system can promote the degradation efficiency of organic compounds（oxalic acid and p-chlorobenzoic acid）.The complete degradation time of p-chlorobenzoic acid was shortened,which can be completely degraded from25 min to 20 min,and the percentage of oxalic acid degradation was increased.As the catalyst input increased,the degradation effect on oxalic acid increased;On the other hand,the addition of carbon-based catalysts can effectively control the formation of bromate through reduction of intermediate.The inhibition effect of three carbon-based catalysts was GO>CNT>PAC,and the inhibition effect increased with the increase of carbon-based catalyst dosage.（3）The addition of carbon-based catalysts supported with metal oxides（CoFe₂O₄/CNT（GO）,CuFe₂O₄/CNT（GO）,CoCu₂O₄/CNT（GO）and so on）can promote the degradation of oxalic acid and inhibit the formation of bromate in O₃/PMS process.Among them,the degradation rate of oxalic acid by CoCu₂O₄/CNT（GO）and CuFe₂O₄/CNT（GO）was similar to that of CNT and GO alone,while the CoFe₂O₄/CNT（GO）was better than that of CNT or GO.On the other hand,the inhibition effect of bromate by CoCu₂O₄/CNT（GO）in the system was better than that of CNT or GO alone.（4）In actual water,the formation of bromate was inhibited in the process of oxidation of bromine-containing water by O₃/PMS process.Since the presence of humic acid,carbonate and ammonia will react with free radicals and intermediates.