Performance And Mechanism Of Degradation Of Tetrabromobisphenol A In Water By Ozone And Ferrate(?) Oxidation Technology

Tetrabromobisphenol A(TBBPA)is the world's largest and most widely used brominated flame retardant,which has multiple toxicological properties.It would pose a threat to the safety of the receiving water with the release of waste water into the environment.Aiming at the potential pollution of TBBPA in water,some scholars have studied the degradation of TBBPA by ozone oxidation process.Although there was some removal effect,the systematic researches on the intermediate products,degradation mechanism and biological toxicity were still limited.In addition,it has the risks of forming bromate during ozone oxidation process.In recent years,the ferrate(?)oxidation process,which is gaining more and more attention,has been proved to have a good effect on many kinds of refractory organic pollutants.However,treatment of TBBPA by ferrate(?)oxidation process is basically very few.At the same time,a few studies have shown that the combination of the two processes can better promote the degradation of organic matter.Therefore,in this paper,the degradation efficiency and mechanism of TBBPA by ozone and ferrate(?)oxidation were studied separately,and the efficiency and mechanism of TBBPA treatment by combination technology were further investigated,which provided more selectivity for the degradation of TBBPA in water.The performance and mechanism of ozone oxidation degradation of TBBPA were studied.The results showed that TBBPA could be rapidly and efficiently degraded by ozone oxidation process.TBBPA(1.0 mg/L)could be completely degraded in only 2 min when ozone concentration was 2.0 mg/L(p H 7.0).The process showed high debromination level at the same time.When the reaction time was 30 min,the average debromination rate was as high as 65%.However,the higher debromination level led to the risk of bromate formation.At the ozone concentration of 4.0 mg/L,bromate concentration was up to 80.5 ?g/L.The ozone oxidation process can significantly control the toxicity of TBBPA degradation process,including acute and chronic toxicity and toxic intermediates;and prolong the reaction time and increase the concentration of ozone were conducive to the control of toxicity.The reaction mechanism analysis showed that the reaction pathway of ozone degradation of TBBPA mainly includes addition and hydrogen extraction channels,stepwise oxidative debromination and deprotonation channels.The performance and mechanism of oxidative degradation of TBBPA by ferrate(?)were studied.The experimental results showed that the ferrate(?)oxidation process can also rapidly and efficiently degrade TBBPA.The process adapts well to the solution p H and TBBPA could be significantly degraded under wide p H range(3-9).When the ferrate(?)concentration was 1 mg/L,the average debromination level for 1 mg/L TBBPA by 30 min exposure was 30%,which was lower than that by ozonation.When the ferrate(?)concentration increased to 5.0 mg/L,the desorption rate was as high as 64.65%,and there was no risk of bromate formation during the whole reaction.Similar to the ozonation process,the degradation of TBBPA by ferrate(?)oxidation process also via addition and hydrogen extraction,stepwise oxidative debromination,and deprotonation.Toxicity control studies showed that the control level of the acute toxicity by ferrate(?)oxidation process was level with that by ozonation process,and the control level of chronic toxicity was better than that by ozonation process.The toxic intermediate products 2,6-dibromophenol and BPA also have Significant degradation and toxicity control efficacy.By comparison,the advantages of the ferrate(?)-ozone combined process were proposed.The performance and mechanism of the combined process for degradation of TBBPA were further studied.The results showed that the combined process had high debromination level while efficiently degrading TBBPA,and ha d significant control efficacy on bromate and biological toxicity.When pre-oxidized by 0.1 mg/L ferrate(?)for 3 min and then reacted with 1.0 mg/L ozone for 30 min,1 mg/L of TBBPA could be completely degraded with a salinity of 80.5% and a debromination rate of 91.3%.No bromate was formed and the toxicity was better controlled as compared to the single process.Through the analysis of the experimental results combined with the relevant literature,the synergistic decontamination mechanism and bromate control mechanism were proposed.As to the synergistic degradation mechanism of TBBPA: firtly,there existed the superposition effect in the oxidation potential of the two oxidants;secondly,the intermediate products of ferrate(?)(such as hydrated iron ions,hydrated ferric oxide and ferric hydroxide etc.)could catalyze the decomposition of ozone to produce more hydroxyl radicals;furthermore,the low valence iron compounds of ferrate(?)could be oxidized to high valence ones,which could continue to play a role on TBBPA degradation.As to bromate control,the combined process could control bromate both formed from direct and indirect oxidation pathway.The main mechanism was due to the intermediates of ferrate(?)(Fe(III)?Fe(II)?H2O2?O2·-),which could result in the loss of hydroxyl radical,the reduction of bromate or its intermediates and the flocculation function.In summary,this paper provided a data support for the degradation of TBBPA in water by the separate oxidation process of ozone and ferrate(?),and revealed the degradation mechanism of TBBPA by two separate oxidation processes.In addition,the ferrate(?)-ozone combined process was proposed.The synergistic degradation of TBBPA efficacy,biological toxicity and bromate control role of the combined process were studied,which provided theoretical and technical support for the TBBPA wastewater treatment by the combined process.