The Effect Of Different Cathodes On Bromate Inhibition During Electrochemical Disinfection

The effect of different cathode on bromate formation and disinfenction rate during electrochemical disinfection is an important matter.For improving the theory and ensuring the safety of electrochemical disinfection,it is really significant to study the influence of different cathode on the law of brominated inorganic substance transformation and the DBPs inhibition mechanism of different cathode.The undivided electrochemical system was constructed using BDD anode and Ti、Cu、Zn、Ni、Cu/Zn、Cu/Pd cathoderespectively(Ti as an control-electrode)and the inhibition of cathode on bromate production during electrochemical disinfection was investigated by the cyclic electrolysis experiment.The main conclusions and prospect are follows:1.Under given condition(initial bromide comcentration=1 mg/L,pH=7,current density=5 mA/cm~2,electrode distance=2 cm),using Cu/Pd cathode produced lowest concentration of bromate,followed by Cu/Zn cathode,Zn cathode,Ni cathode,Cu cathode and Ti cathode.In this case,Cu/Pd and Cu/Zn cathode showed the most excellence capacity of bromate inhibition,the bromate concentration using Cu/Zn or Cu/Pd cathode is 32.20%and 25.85%of using Ti cathode respectively.2.Through the determination of oxidation material production rate,the experiment of electrolyzing bromate and electrochemical behavior characterization can be preliminarily inferenced that the production rate of oxidation material were not effected markedly by changing cathode.As for bromate inhibition,maybe due to the cathode reuduction rate were improved by its great capacity of catalytic reduction.And the distribution rlue of brominated inorganic by-products in the process of electrochemical disinfection were changed.3.From the perspective of thermodynamics,it can be inferred that the oxidation reaction and the reduction reaction can be carried out bidirectionally and synchronously under the experimental conditions.That is,the bromate reduction could occur in the electrochemical disinfection system and it can be further demonstrated that the bromate inhibition was realized through the reduction process on cathode surface.4.The first order continuous reaction kinetics model was established.The influence mechanism of different cathode materials on the of bromate formation was further clarified.The conclusion is that the conversion of bromine inorganic substance in the electrochemical system conformed to the first order bidirectional continuous reaction kinetic model.The bromate reduction path is different on different cathode surfaces,on the surface of Ti and Cu electrodes,the transformation path is mainly direct reduction:bromate got electrons and reduced to HBrO/BrO~-and Br~-gradually;the conversion path on the surface of Ni,Zn,Cu/Zn,Cu/Pd electrodes were mainly indirect reduction:H~+combined with electrons to form H*,and H*combined with bromate to form bromide.5.In the process of electrochemical disinfection,the production rate of bromate was increased with the initial bromide concentration under six different electrochemical systems.But the reaction rate of bromate reduction while using Cu/Pd and Cu/Zn cathode were faster than other cathodes.The potential of transforming bromide to bromate in acid addition is higher than the alkaline condition and benefit to the inhibition of bromate formation.The reaction rate of oxidation reaction and reduction reaction in the system was increased with the increasing of current density.However,in the electrochemical system with BDD anode,the main conversion of bromine was from low state to high state.Compared with other cathodes,Cu/Pd cathode showed excellent electrogenic H*ability under the condition of high current density.With the further extending of electrode distance,the ability of cathode electrogeneration of H*with better inhibition effect on bromate were affected by electron migration velocity,resulted in the inhibition on bromate in the disinfection system was weakened.In the presence of natural organic compounds,the production of bromate decreased significantly;cathodes which have stronger catalytic reduction capacity could inhibited the formation of bromine inorganic by-products and also the brominated organic DBPs were inhibited to a great degree.In the pratical disinfection,on the premise of the consistent disinfection rate,bromate formation could be inhibited using different cathode.And the higher initial bacterial concentration,the less bromate would be generated in the disinfection process.