Study On Construction Of Three Dimensional Electrode Ozone Process And Its Proference Of Removing Refractory Organic Pollutants In Water

In recent decades,with the continuous development of industrialization,a large number of industrial wastewaters had caused a serious threat to surface water environment and ecosystem.Especially,various persistent refractory organics in industrial wastewater are highly carcinogenic,mutagenic,and teratogenic.Meanwhile,They are difficult to degraded completely by conventional wastewater treatment processes.Therefore,the organic pollutants could accumulate in natural environment and cause serious harm to human health and natural biodiversity.In hence,The AOPs(advanced oxidation processes)based ozone have attracted more attentions.As for the electrocatalytic ozonation process,ozone molecules in the solution could reduce into a large number of hydroxyl radicals(·OH),which has highly oxidative ability(E₀=2.7V),and then could completely decompose organic pollutants into biodegradable small molecular acids,water and carbon dioxide.However,some drawbacks,such as low reaction mass transfer efficiency,low utilization rate of ozone,and low current efficiency,still limit the wide application of electrocatalytic ozonation technologies.On the other side,as for three-dimensional electrochemical oxidation,it has high mass transfer efficiency,high current efficiency and high reactive area due to the presence of particle electrodes.Nevertheless,low degradation rate of target pollutants and the inactivation of particle electrodes are inescapable disadvantages for three-dimensional electrode oxidation.Based on the characteristics of two advanced oxidation technologies,we proposed and constructed a three-dimensional electro-ozonation coupling process.In the process,the decomposition efficiency of ozone and the mass transfer efficiency could be improved due to the presence of particle electrodes.In addition,under the long-term operation,the particle electrodes could maintain high catalytic activity.In this study,granular activated carbon(GAC)and zero-valent iron particles(Fe⁰)are selected as two types of particle electrodes.The oxidation capacity of E-GAC-O₃process and E-Fe⁰-O₃ process was investigated systematically.Meanwhile,the degradation experiments of different water substrates,actual water bodies and various organic pollutants were used to evaluate the practical application prospects of three-dimensional electro-ozonation process.Accroding to the results of various quenching experiments,the types of active free radicals and generation pathways in the process were evaluated,and then quantizing the relative contribution of target pollutant.Through repeated use of particle electrodes,the stability of three-dimensional electro-ozone process was evaluated,and various characterization methods were used to compare the changes in the physical structure and chemical group of the particle electrode before and after the reaction in the process.The main research contents and conclusions are as follows:(1)In the E-GAC-O₃ process,the removal efficiency of nitrobenzene(NB)obtained94.04%,which was much higher than the electrocatalytic ozonation process(E-O₃)and conventional three-dimensional electrode oxidation process(E-GAC).Meanwhile,the presence of Cl^-could improve the removal rate of NB,whereas PO₄^3-?HCO₃^-and NOMs had inhibitory effect.Application potential evaluation experiments shown E-GAC-O₃process also had certain oxidative capacity for NB in different actual waters,and can efficiently remove various persistent organic pollutants(DMF,BAT,IBP).(2)As for E-GAC-O₃ process,hydroxyl radical(·OH),hydrogen peroxide(H₂O₂)and superoxide radical(O₂^·-)were all involved in the oxidation removal of target pollutant.In addition,hydroxyl radical(·OH)was the main oxidation radical,the oxidation contribution was 92.30%.After reusing GAC 50 times,the E-GAC-O₃ process maintained stable removal efficiency of NB.It is because that GAC in the E-GAC-O₃process can replenish electrons by polarizing internal electron accumulation and colliding with the cathode surface,so as to avoid the damage of ozone and free radical oxidation,and then kept stable catalytic activity.(3)When selected zero-valent iron(Fe⁰)as the particle electrodes,the removal efficiency of NB in the E-Fe⁰-O₃ process achieved 90.45%within 20 min,which was much higher than that of E-O₃process(64.72%)and E-Fe⁰ process(37.08%).Meanwhile,after 120 min reaction,the removal rate of TOC in the E-Fe⁰-O₃ process reached 85.19%with lower energy consumption.In addition,the E-Fe⁰-O₃ process also had a stable removal rate of NB under different water quality conditions;Meanwhile,as for different ozone-resistant organic pollutants(CB,IBP,ATZ,BA),E-Fe⁰-O₃ process also achieved efficient removal efficiency.(4)In the E-Fe⁰-O₃ process,hydroxyl radical(·OH)was main oxidation radical.the oxidation contribution rate of hydroxyl radical(·OH)was 92.83%.Comparing the yield of hydroxyl radicals in different processes,it is found that the concentration of hydroxyl radical(·OH)in the E-Fe⁰-O₃ process is 2.45×10^-9 m M,which was higher 1.86 times than that of E-O₃ process.After reusing zero-valent iron(Fe⁰)particles 10 times,the E-Fe⁰-O₃process maintained stable removal effciency of NB.It becaused that the applied electric field could improve the decomposition efficiency of zero-valent iron particles,and produce numerous iron oxides on the surface.Consequently,zero-valent iron particles in the E-Fe⁰-O₃ process can keep the stable catalytic activity.(5)When selected zero-valent iron(Fe⁰)and GAC(1:1)as the particle electrodes,the removal efficiency of NB(24 mg L^-1)in the E-Fe⁰/GAC-O₃ process achieved 95.54%within 20 min,which was much higher than that of E-O₃process(73.47%)and E-Fe⁰process(58.19%).In addition,the E-Fe⁰/GAC-O₃ process also had a stable removal rate of NB under different water quality conditions;Meanwhile,as for different ozone-resistant organic pollutants(CB,IBP,ATZ,BA),E-Fe⁰/GAC-O₃ process also achieved efficient removal efficiency.