Construction Of Electrochemical Wastewater Treatment System Based On High Efficiency H₂O₂ Cathode For Environmental Application

With the strengthening of environmental governance in our country,the sewage treatment rate has been continuously improved,but there are still a considerable part of refractory organic wastewater and decentralized organic sewage with poor treatment effect or low treatment rate.Electrochemical advanced oxidation processes（EAOPs）based on in-situ synthesis of H₂O₂ can generate strong oxidizing radicals to efficiently remove pollutants in wastewater.This type of technology has the advantages of fast start-up,strong controllability,high flexibility,and strong adaptability.However,the existing EAOPs and equipments still have problems such as high cost,low efficiency,and narrow applicable p H range,which seriously limit their practical application in organic wastewater treatment.Therefore,a high-performance,low-cost natural air diffusion electrode（NADE）was designed and fabricated for in situ electrosynthesis of H₂O₂.In order to improve the process efficiency,the H₂O₂ conversion and utilization efficiency in EAOPs was systematically explored and the NADE-MCF dual-cathode EF process,NADE-MCF dual-cathode PC process,and NADE/ACF/DSA floating sandwich EF process were constructed to promote Fe³⁺/Fe²⁺cycle efficiency,broaden the p H application range,and improve the treatment efficiency of organic wastewater.Finally,combined with the solar power supply system to form a solar-driven wastewater electrochemical integrated treatment technology and equipment to evaluate the actual wastewater treatment application,to prove its application feasibility,superiority and stability,so as to provide high efficiency and low consumption for refractory organic wastewater and decentralized wastewater.The main research contents and conclusions of this paper are as follows:（1）Based on the modification and regulation of the cathode catalytic interface and the innovation of the cathode structure,NADE without aeration was designed and fabricated.The use of hydrophobically modified CF as the air diffusion layer and substrate effectively improves the oxygen mass transfer efficiency.Compared with the gas diffusion layer of conventional GDE,the porosity of the modified CF exceeds 90%,and the oxygen mass transfer coefficient is increased by about 4.7 times.A stable superhydrophobic three-phase interface was constructed by adjusting the interface properties of the catalytic layer to improve the ORR efficiency.Electrochemical tests,pore structure analysis,and contact angle measurements were used to reveal the mechanism between the properties of the catalytic layer and the performance of H₂O₂electrosynthesis.Oxygen mass transfer,electron transfer,and interfacial stability jointly determine the ORR performance of the cathode.The influence of the catalyst layer loading（thickness）on the oxygen diffusion capacity,ORR performance and stability in the electrode was explored.It was found that the H₂O₂ yield and stability were better when the catalyst loading was 13.2 mg cm^-2.NADE has excellent oxygen mass transfer performance and high oxygen utilization efficiency（OUE:44.5-64.9%）,which can maintain high performance even at high current density(240 m A cm^-2).The H₂O₂ yield can reach 101.7 mg h^-1 cm^-2,the current efficiency is 66.8%,and the corresponding energy consumption is 19.4 k Wh kg^-1_H2O2.（2）A new type of non-aeration EAOPs based on NADE was constructed,and the H₂O₂ utilization efficiency（HUE）and the methods to improve the wastewater treatment efficiency were systematically studied.The HUE of the EF process is generally high in the early stages of processing,but decreases rapidly with increasing processing time.The decrease of HUE in EF process is mainly due to the low H₂O₂decomposition efficiency after the rapid consumption of Fe²⁺,and a large amount of H₂O₂ remains in the system.The PEF process can improve HUE by enhancing the regeneration of Fe²⁺and activating H₂O₂ by UV light,but its disadvantages are high energy consumption,easy to be affected by side reactions and reducing H₂O₂conversion efficiency.Using HUE as the process adjustment index,the constructed EF-PEF process can effectively reduce the energy consumption of sewage treatment(0.065-0.167 k Wh g TOC^-1),while maintaining high pollutant mineralization（87%mineralization in 2 h）.（3）In order to simultaneously improve the H₂O₂ yield,Fe³⁺/Fe²⁺cycle efficiency and p H application range of the process,NADE and modified carbon felt（MCF）dual cathode EF systems were constructed.Characterization by electrochemical analysis,SEM,BET,contact angle,and XPS indicated that nitric acid modification enhanced the electrochemical active area,hydrophilicity and electron transfer efficiency of the cathode.The modified MCF cathode had more oxygen-containing functional groups and increased O=C–O can promote the complexation and reduction of Fe³⁺/Fe（III）,and the MCF cathode realizes the efficient regeneration of Fe²⁺/Fe（II）.The Fe²⁺regeneration rate of the MCF cathode was 1.2 and 4.7 times higher than that of the CF cathode at p H 3 and 7,respectively.MCF accelerates the dissolution and catalytic conversion of solid ferric hydroxide formed under neutral and alkaline conditions,increases the content of soluble iron in the system,and promotes the formation of≡Fe（II）,enhancing homogeneous and heterogeneous Fenton reaction.（4）In order to simplify the wastewater treatment process and enhance the treatment efficiency of high p H organic wastewater,a dual-cathode PC system was constructed with NADE and MCF as cathodes and Fe and DSA as anodes without external oxidants and catalysts.Compared with the conventional PC process,the dual-cathode PC improves the treatment performance of neutral and alkaline sewage,the mineralization rate of the target pollutant SMT is increased by more than 2.7 times,and the treatment energy consumption is reduced by 37%-62%.The main active species in the dual-cathode PC system are^·OH and O₂^·-,the homogeneous and heterogeneous Fenton reactions on MCF play an important role in the degradation of pollutants,and the^·OH yield is 4.1 times that of the conventional PC system.Comparing the treatment performance of dual cathode PC and conventional PC process on actual wastewater,the results show that the former improves the TOC removal rate of wastewater by 84%-105%and more than 85%of the TOC removal is contributed by the oxidation process.The amount of iron sludge produced in the treatment process is only a quarter of that of conventional PC processes.（5）In order to improve the removal efficiency of low concentration pollutants and enhance the oxidation efficiency of the process,a floating NADE/ACF/DSA sandwich-type EF system was constructed.The N/（A）/D electrode takes into account both the H₂O₂ yield and Fe²⁺regeneration,and the^·OH yield is the highest.The removal rate constants of the N/（A）/D-EF system for CBZ are 7.6 times and 2.1 times of N/D-EF and ACF adsorption,respectively.Different from the conventional EF process,the N/（A）/D-EF system has a good removal of CBZ in the concentration range of 0.1-30mg L^-1,and the pollutant removal efficiency is less affected by the change of pollutant concentration.The removal efficiency and energy consumption advantages of low-concentration organic matter help to improve the space-time efficiency of deep purification of sewage.NADE can electrosynthesize H₂O₂ efficiently,and ACF plays two roles of adsorption and enrichment of pollutants and Fe³⁺reduction at the same time,which effectively improves the removal efficiency of pollutants.（6）Based on the NADE cathode and the constructed EAOPs,combined with the solar power supply system,a solar-driven electrochemical integrated wastewater treatment equipment was developed to treat refractory organic wastewater and decentralized organic wastewater.The non-aeration H₂O₂electrosynthesis system constructed with NADE has efficient and stable H₂O₂ production,and the H₂O₂production of a single electrochemical generator can be maintained between 1474-1535mg h^-1 during the electrochemical reaction process for up to 50 h,and the current efficiency is between 77.4%-80.6%.The electrochemical integrated sewage treatment system is coupled with dual-cathode EF,PC and PEF,which effectively improves the conversion and utilization efficiency of H₂O₂.It integrates^·OH,O₂^·-,electro-oxidation and UV/H₂O₂ oxidation and Fe（OH）₃-dominated flocculation,which can efficiently remove various pollutants in wastewater.The integrated sewage treatment equipment has realized the successful treatment of a marine aquaculture wastewater and a rural distributed domestic sewage in the northwest.It has the advantages of no need to lay sewage collection pipe network,no low temperature restriction,convenient start-up,efficient and fast treatment process,and low treatment cost.In this study,an efficient NADE cathode was prepared for in situ electrosynthesis of H₂O₂.The utilization efficiency of H₂O₂ in EAOPs was systematically explored,and a series of improved EAOPs based on NADE were constructed to improve the efficiency of organic wastewater treatment.Finally,a solar-driven wastewater electrochemical integrated treatment technology and equipment were formed for practical wastewater treatment application demonstrations.