Study On DSA Electrode Modification For Electrochemical Treatment Of Low Concentration Ammonia Nitrogen Wastewater

A water purification plant in the pollution interception system around the Dianchi Lake adopts the Membrane Bio-Reactor（MBR）process to treat agricultural non-point source wastewater.After optimizing the operating parameters and combining chemical methods to strengthen phosphorus removal,the effluent can be guaranteed to meet the standard.However,considering the high cost of chemical methods,membrane pollution and other issues,as well as the fact that it is imperative to increase the standard phosphorus discharge（TP<0.3 mg/L）in the Dianchi Lake Basin,the research group built an electrochemical reaction pilot plant in the early stage,and directly treated it.In the agricultural non-point source sewage in the Dianchi Lake Basin,the CODcr and TP in the effluent meet the discharge standard of Class A of the Pollutant Discharge Standard for Urban Sewage Treatment Plants（GB18918-2002）,and the phosphorus removal effect is remarkable.However,due to the use of electrocatalysis in the device graphite anode with poor oxidation performance,so the denitrification effect is not good.Even if the HRT is prolonged and the electrolyte is added,the nitrogen in the effluent is still not up to the standard.Since the performance of electrode materials in electrochemical devices is one of the decisive factors for the degradation effect of electrochemical processes on NH₃-N,At the same time,in order to develop a high-efficiency and low-consumption technology to reduce the agricultural non-point source pollution load flowing into Dianchi Lake,it provides a solution for the treatment of low-concentration ammonia nitrogen wastewater.The new solution,based on the electrochemical device designed in the previous stage,explores the use of DSA anode with high electrocatalytic oxidation activity and good NH₃-N degradation effect to replace the graphite anode with low electrocatalytic oxidation activity in the previous device;Adding an interlayer and optimizing the preparation conditions of the interlayer can improve the electrochemical performance of the DSA electrode,in order to be better applied to the electrochemical process.The thermal decomposition method was used to prepare Ti/MnO₂,Ti/Sb₂O₄,Ti/SnO₂,and compared with the NH₃-N degradation effect of the electrochemical device using it as the anode,the DSA electrode with the better degradation effect was selected as the best choice.Based on this,the DSA electrode was prepared by adding the interlayer of MnO₂,Sb₂O₄,and SnO₂,and the degradation effect of NH₃-N was investigated in the electrochemical device using it as the anode.Finally,by changing the preparation temperature and composition ratio of the DSA electrode interlayer,the electrochemical performance of the DSA electrode after the change was discussed,and the optimized scheme of the interlayer preparation temperature and composition ratio was obtained,in order to obtain high electrocatalytic oxidation activity.DSA electrodes with longer electrode life and electrochemical stability.The main research results are as follows:（1）The Ti/SnO₂ prepared by thermal decomposition was used as the anode of the electrochemical device,the current density was controlled to be 5 m A/cm²,the Cl-was controlled to be 2000 mg/L,and the NH₃-N was controlled to be 25 mg/L.The temperature was maintained at room temperature 25°C and the p H was 7.After 2 h of reaction,the removal rate of NH₃-N can reach 100%,and the removal effect is the best.Compared with MnO₂ and Sb₂O₄,SnO₂ is an ideal active layer component of DSA electrode,and Ti/SnO₂ has the best electrocatalytic oxidation effect of NH₃-N.（2）The electrochemical device with Ti/MnO2+Sb2O4+SnO2/SnO2 as the anode has better NH₃-N degradation effect,and the average concentration of NH₃-N has dropped to2.96 mg/L when the reaction reaches 90 min,reaching the emission level A standard.The chlorine evolution potential is lower at 1.48 V,and the oxygen evolution potential is higher at 1.96 V.It has a wider electrochemical potential window,and the electrocatalytic oxidation performance of the electrode plate is better.At the same time,by adding MnO2+Sb2O4+SnO2 intermediate layer,the growth of the solid solution on the surface of the electrode plate is promoted,the bonding force between the coating and the substrate is better,and the solid solution formed on the electrode surface is more stable.The crystal form on the surface of the coating is relatively complete,the shape is relatively fine,and the titanium matrix is not easy to passivate,so it has the longest service life and the best electrochemical stability.（3）Compared with the electrodes with the interlayer preparation temperature of400℃and 600℃,the electrochemical performance of Ti/MnO2+Sb2O4+SnO2/SnO2 is the best at the interlayer preparation temperature of 500℃.The chlorine evolution potential is as low as 1.48 V,and the oxygen evolution potential is as high as 1.96 V.The chlorine evolution performance is the best,the oxygen evolution side reaction activity is low,the electrochemical potential window is 0.48 V,and the q*of the electrode is the largest,up to 24.5 m C,and there are many active sites on the surface of the electrode plate,and its electrocatalytic oxidation performance most.At the same time,the grains on the surface of the electrode are more densely arranged,the crystal growth condition is better,the number of cracks is less,the characteristic peak intensity of MnO2+Sb2O4+SnO2 oxide is higher,the crystal growth condition of the intermediate layer is good,the bonding strength between the active coating and the substrate is better,and the electrode The lifespan is longer up to 80.4 h,and the electrochemical stability of the electrode plate is stronger.（4）Compared with the electrodes prepared with the interlayer composition ratio of Mn:Sn:Sb=1:3:1 and Mn:Sn:Sb=1:1:3,the interlayer composition ratio is Mn:Sn:Sb=3:1:1 Ti/MnO₂+Sb₂O₄+SnO₂/SnO₂ electrode has the best electrochemical performance.Its chlorine evolution electricity is relatively low at 1.28 V,oxygen evolution potential is as high as 1.85 V,and the electrochemical potential window is wider at 0.57 V.At the same time,there are a large number of tiny pores on the surface of the electrode plate,the maximum q*is 26.67 m C,and the specific surface area of the electrode is relatively high.Large,more active sites for electrochemical reactions,and the best electrocatalytic oxidation performance.Moreover,the grains on the surface of the electrode plate are fine and dense,the crystal arrangement is dense and orderly,without obvious cracks,the characteristic peak intensity of MnO₂+Sb₂O₄+SnO₂ mixed oxide is higher,the grain growth condition is better,the crystallinity is better,and the electrode life is the longest.It can be up to 105 h,and the electrochemical stability is good.