Study On The Characteristics And Mechanism Of Removal Of Typical Pesticides In Water By Electrochemical Oxidation Of BDD Electrode

Water environment has always been the concern of human society,and with the increase of pesticide species and use,water pollution is becoming more and more serious.Pesticide waste water pollution is widely distributed,toxic and difficult to degrade,becoming a stubborn disease of water treatment.At present,most of the pesticide wastewater is not treated strictly,and some of them are discharged directly into the natural water body,which will make the water pollution problem more and more serious.Since the emergence of advanced oxidation processes,researchers have paid much attention to it,and electrochemical anodic oxidation is an important part.Among the advanced oxidation technologies,hydroxyl radical and sulfate radical are always hot spots.In this paper,boron-doped diamond electrode is mainly used to degrade typical pesticide by anodizing.First of all,the method of electrochemical oxidation was used to degrade the diuron one of Phenyl urea herbicide by BDD electrode,with the removal rate of 91%.The degradation mechanism and degradation effect of BDD electrode with MMO electrode and Pt electrode were compared.The effects of electrolyte type,initial concentration,current density,electrode immersion area and initial pH value were investigated mainly in the research.Through the analysis of experimental results,it is concluded that the degradation effect was far better than the other two electrodes when the BDD electrode was used as anode.However,when the chloride ion was present in the solution,the degradation efficiency of MMO electrode was quite high,and the degradation efficiency of BDD and MMO electrodes were 97%and 93%respectively.With the increase of the initial concentration of diuron,the degradation rate of diuron was first increased and then decreased when the BDD electrode was used.With the increase of the current density,the degradation rate of the diuron increased gradually,and the energy consumption increased accordingly.The degradation rate increased with the increase of electrode immersion area.Under the different initial pH value of solutions,the rate order of degradation reaction of diuron was:strong acid>strong basic>neutral.The second part of this project mainly studies the degradation of atrazine(ATZ)by BDD/PS system.There was almost no degradation when persulfate was used alone,while the degradation of 78.2%was achieved using the system of BDD/PS with low concentration of electrolyte.This part mainly studies the degradation mechanism,influencing factors,degradation pathways and products of the atrazine's degradation in the BDD/PS system,with a view to providing guidance for practical application.By comparing the degradation effect of different systems,the oxidative degradation ability of the BDD/PS system with low concentration electrolyte was proved to be better.Through the quenching experiment(scavenger used methanol and tert-butyl alcohol)and degradation experiment of nitrobenzene using BDD/PS system,it was proved that the degradation of ATZ were the effect of sulfate radical,hydroxyl radicals and the non-radical way.In addition,the paper mainly discusses some factors' influence on degradation of ATZ in BDD/PS system.The increase of current density is beneficial to the degradation of atrazine,but it can decrease the current efficiency and increase the energy consumption.The high initial sulfate concentration and low initial pH value promoted the degradation of atrazine.The presence of dihydrogen phosphate,bicarbonate and nitrate would inhibit the degradation of ATZ,and the inhibitory effect follows the following order:HCO3->H2PO4->NO3-.In addition,the deethylatrazine(DEA)and deisopropyl atrazine(DIA)are the two main substances produced through the system of BDD/PS removing ATZ,and the ratio of the DEA/DIA is about 2.De-alkylation,de-chlorination and hydroxylation are three main reactions occurred in BDD/PS system to degrade ATZ with analysis of product.