Electrochemical Oxidation Treatment Of Coal Tar Wastewater With Lead Dioxide Anode

In the present work,we first selected 4-methoxy-1-naphthol,a representative of coal tar waste water,as a simulated pollutant to investigate the feasibility and effectiveness of the electrocatalytic oxidation treatment of 4-methoxy-1-naphthol with lead dioxide electrode.Then we used electrocatalytic oxidation to degrade coal tar wastewater,and explore new and feasible treatment methods for the treatment of coal tar wastewater.The main research contents were as follows:In the process of electrocatalytic oxidation degradation of 4-methoxy-1-naphthol simulated wastewater,the operating parameters such as electrolyte concentration,current density,initial concentration of 4-methoxy-1-naphthol and solution pH were investigated.The effect of removal rate and COD,and the optimal operating conditions for the degradation of 4-methoxy-1-naphthol-containing wastewater were obtained.After degradation for 105 min under the optimal conditions at an electrolyte Na₂SO₄concentration of 0.2 mol L^-1,a current density of 20 m A cm^-2,and an initial concentration of 4-methoxy-1-naphthol at 25 mg L^-1 and pH 4.0,the removal rate of4-methoxy-1-naphthol and the removal rate of COD reached 99.9%and 87.7%,respectively.The degradation process follows the first-order reaction kinetics model.By scanning the spectrum of 4-methoxy-1-naphthol by UV-visible spectrophotometry and scanning the chromatogram of 4-methoxy-1-naphthol by HPLC,it can be found that4-methoxy-1-naphthol was almost completely degraded during the degradation process,but a large number of intermediate products were generated during the degradation process,and eventually these intermediates are gradually degraded.Finally,all the results show that the degradation of 4-methoxy-1-naphthol wastewater by the electrochemical oxidation method using the PbO₂ electrode as the anode can achieve the purpose of good degradation of organic matter.The coal tar wastewater was treated by the electrochemical oxidation technology using lead dioxide anodes.The influence of operating parameters,including applied current density,electrode gap and initial pH value,on the removal ratio of COD were investigated.The results demonstrated that the COD removal ratio reached 90.5%after 3.5 h electrolysis with the current density at 3 A dm^-2 and electrode gap at 1.0 cm.Correspondingly,the COD decreased from 5 125 mg L^-1 to 487 mg L^-1,which fitted the wastewater discharge standards of China,and the specific energy consumption(SEC_COD)was 35.3 k Wh kg^-1_COD.Not only was the COD removal ratio only 77.1%after 2 h electrolysis but the BOD₅/COD ratio of wastewater reached 0.44,which could be biochemically treated and the SEC_CODdecreased by 34.3%.Moreover,the main composition of pristine wastewater before and after 2 h electrolysis were analyzed by GC-MS,the disappearance of macromolecules(such as naphthalene derivatives,quinoline derivatives,anthracene,fluorene,etc.)and the production of small molecules(such as acetic acid,propane-1,3-diol,etc.)could improve the biodegradability of wastewater.Considering the treatment cost,combined treatment of electrochemical oxidation for 2 h and biological process is a promising treatment approach for real coal tar wastewater treatment than single-stage electrochemical oxidation.