Study On The Kinetics Of Ferrous Iron Reduction Of Bromate And The Process And Mechanism Of Degradation Of Organic Pollutants

Bromate（BrO₃^-）is a common by-product of bromide（Br^-）or bromine containing organics in aqueous solution by ozonation disinfection,sulfate radicals-based advanced oxidation processes（AOPs）and chlorine activation systems assisted by metal oxides and UV irradiation.Due to potential human carcinogen and gene-toxicity,the maximum level of BrO₃^-is recommend as 10μg/L in drinking water by the WHO and US-EPA.The removal of BrO₃^-in the water body has attracted widespread attention.The traditional methods to remove BrO₃^-include ion adsorption,biological reaction and reduction method.Among these methods,reduction of BrO₃^-by ferrous ions(Fe²⁺)is one of most commonly used strategy.However,it still remains unknown that whether there are reactive oxygen species involved in the reaction of BrO₃^-with Fe²⁺.Moreover,the formation of reactive species definitely affects the reduction of BrO₃^-via their reactions with Fe²⁺or generated Br^-.However,how and to what extent the formed reactive species influence reduction of BrO₃^-by Fe²⁺have been seldom investigated.Further,it is not uncommon that organic pollutants co-exist with BrO₃^-in practical wastewater and groundwater.Therefore,the influence of organic pollutants on the reductive transformation of BrO₃^-by Fe²⁺should be clarified.In the view of environmental decontamination,the destination of co-existed organic pollutants under oxidation by reactive oxygen radicals（ROSs）in Fe²⁺/BrO₃^-system should be also taken into consideration.Therefore,the aim of the thesis is to identify all the involved reactive species during reduction of BrO₃^-by Fe²⁺,and investigate their effect on reduction of BrO₃^-and oxidation of co-existed organic pollutants.（1）Reduction kinetics and stoichiometry of reduction of BrO₃^-by Fe²⁺.Effects of dissolved oxygen（DO）,initial p H values,Fe²⁺concentrations and co-presence of organic pollutants on reduction of BrO₃^-by Fe²⁺were studied.It was found that DO and four organics（carbamazepine（CBZ）,ibuprofen（IBU）,Benzoic acid（BA）and phenol）had remarkable influence on reduction kinetics and stoichiometry of reduction of BrO₃^-.DO fastened hydrolysis and oxidation of Fe²⁺,decreasing concentration of available Fe²⁺,and inhibiting reduction of BrO₃^-.The co-presence of organics can consume formed O₂^·-,decreasing reductive recycle of Fe²⁺/Fe³⁺,and further increasing molar ratio of Fe²⁺oxidized to reduced BrO₃^-.（2）Radicals generation and organic pollutants oxidation during reduction of bromate by Fe²⁺.It was found that reduction of BrO₃^-by Fe²⁺ions produced O₂^·-and HO·through electron spin resonance（ESR）spectra and radical probe experiments.The generation of reactive bromine radicals（RBSs）was confirmed by detection of bromophenols by using phenol as a probe.By using phenol,CBZ,IBU and BA as model pollutants,the contribution of reactive species in their degradation was measured.·OH,O₂^·-and RBSs involved in phenol degradation,while·OH and O₂^·-were the main contributors for oxidation of CBZ and IBU.Through mineralization of phenol and BA（as a probe of HO·）,percentages of oxygen atoms released in the form of O₂^·-and HO·were determined as about 58%and 42%,respectively.Formation of brominated degradation products was confirmed during CBZ degradation by liquid chromatography-mass spectrometry.The formation of brominated by-products raises alarm and attention,and need further evaluation on its environmental toxicity.Degradation intermediates of CBZ in Fe²⁺/BrO₃^-system indicated that CBZ was mainly degraded via hydroxylation,followed by ring contraction and amine cleavage and bromination.It was also demonstrated that CBZ can be still degraded in practical wastewater.This study might shed new fundamental insights on reduction of bromate and its implication for transformation of co-existed organic pollutants.