The Effect Of Coexisting Ions On The Formation Of Bromate During Electrochemicial Dsinfection Drinking Water

When using electrochemical technology to disinfect bromide-containing drinking water,the influence of coexisting ions on the formation process of BrO3-by-products is an unavoidable problem.To ascertain the effect of common inorganic coexisting ions on the formation of BrO3-in electrochemical system is of great practical significance for promoting the large-scale and safe application of electrochemical disinfection technology.In this study,Ti/Pt and BDD anodes with different catalytic oxidation mechanisms were used as anodes.Under the conditions of 0.5cm anode spacing and 5mA/cm2 current density,the common ions in water under neutral environment were investigated.The influence of(SO42-,Cl-,HCO3-,NO3-,NH4,Ca2+,Mg2+)on the formation of Br03-was studied.The effect of coexisting ions on the formation of BrO3-was investigated under different pH and isoionic compositions.Combined with electrochemical line,thermodynamics,kinetics and analysis of the bromine conversion process,the following main conclusions have been reached:1.When SO42-coexisted,the increase of SO42-concentration inhibited the formation of BrO3-in the Pt anode oxidation system.SO4-Formation of peroxosulfate and peroxosulfate on the Pt anode occupies the surface-active sites of the anode,reducing the probability of Br-being directly oxidized by the anode surface,thereby reducing the rate of BrO3-formation.The increase of SO42-concentration in the coexistence promotes the formation of BrO3-in the BDD anode system.Electrobiogenic ·OH excitation of SO4-generated SO4-·,may be the main reason for the promotion.2.Cl-coexisted,Pt anode and BDD anode electrogenic hypochlorous acid promote the formation of BrO3-.The HOCl/OCl-generated by the Pt anode with strong chlorine evolution ability would oxidize the bromide to BrO3-and accelerated the formation rate of BrO3-.The oxidation of BDD anode mainly depended on the indirect oxidation of OH.It not only reacted with Br-to form BrO3-,but also oxidized Cl-to ClOH-·,and formed with the participation of Br-,which promoted the formation of BrO3-.3.When HCO3-coexisted,the increase of the pH of the reaction solution in both anode oxidation systems can promote the formation of BrO3-.When HCO3-coexisted in the Pt anode system,the generated strong oxidizing H2O2 accelerated the reaction rate of BrO3-generated bromide;in the BDD anode system,the reaction between the electrogenerated OH energy and the HCO3-/·CO32-reacted with the OBr-reaction.The formation of BrO-,HCO3·/·CO3-,which may be the main reason for the coexistence of HCO3-to promoted the formation of BrO3-.4.The promoting effect of NO3-coexistence on BrO3-formation are more obvious.Under the condition of coexist NO3-15mg/L and initial bromide ion concentration of 2mg/L,the BrO3-increased by 121.43%and 278.36%,respectively,in the Pt anode and BDD anode system compared with no addition of NO3-.NO3-facilitated the reduction reaction at the cathode,reduced the contact probability of BrO3-at the cathode and H+,and reduced BrO3-reduction,thereby increasing the concentration of BrO3-generated.5.The coexistence of NH4+ could lead to lower pH of the reaction solution and indirect inhibition of BrO3-formation;NH4+ reacted with HOBr/OBr-to form bromo-amine,which reduced the formation of BrO3-.The greater the concentration of NH4+,the stronger the inhibition was.The initial bromide ion concentration was 2 mg/L,compared with no NH4+ addition,after adding NH4+2 mg/L,the active bromine concentration in Pt anode and BDD anode system decreased by 11.76%and 24.00%,respectively.6.Combined with thermodynamic and kinetic analysis,it was found that when ions coexisted,the first-order reaction could show the concentration changes of BrO3-,Br-and active bromine.Compared to the Pt anode,the non-selective oxidation of ·OH in the BDD anode system resulted in no significant accumulation of active bromine.This study focused on the study of BrO3-formation mechanism in the early stage of the project,and explored the formation law and influence mechanism of BrO3-in the presence of major coexist ions.The results of the study can enrich the mechanism of disinfecting bromine-containing water by electrochemical technology and provide a more complete theoretical basis for the application of electrochemical technology.