Study On MFe₂O₄as Catalyst And The Application Of Photoelectro-fenton Process In Treatment Of Refractory Organic Pollutants

Photoelectro-Fenton technology （PE-Fenton） can improve treatment effect oforganic pollutants via the synergistic effect of light, electric and Fenton process. Thistechnology has been applied widely in treatment of refractory organic wastewater. In thispaper, some refractory organic compounds were used as the target pollutants degradedwith PE-Fenton process. The main results were as follows.（1） MFe₂O₄（M=Zn，Cu，Co） were used respectively as Fenton like catalyst in thedegradation of refractory organic pollutants, such as1H-Benzotriazole （BTA）,p-Nitrophenol （PNP） and2,4-Dichlorophenol （2,4-DCP）, with heterogeneous PE-Fentonlike process. MFe₂O₄（M=Zn, Cu, Co） nano-particles were prepared by aco-precipitation process and characterized respectively with transmission electronmicroscope （TEM）, X-ray fluorescence analysis （XRF）, X-ray diffraction analysis （XRD）and BET surface area. Then the catalysts were applied in PE-Fenton like process. First,the degradation of BTA with the heterogeneous PE-Fenton like process was studied using ZnFe₂O₄nanoparticles as catalyst. Under the optimum conditions, just as0.15mmol·L^-1BTA,0.05mol·L^-1Na₂SO₄, the electrical potentials of-0.6V （vs. SCE）, pH3.0,0.067g·L^-1 ZnFe₂O₄and UV irradiation, the180min BTA removal efficiency reached91.2%and the COD value was reduced by85.3%. Secondly, CuFe₂O₄as catalyst was employedto remove PNP by the heterogeneous PE-Fenton like process. For0.1mmol·L^-1PNP with0.05mol·L^-1Na₂SO₄and pH3.0, under the optimum conditions, namely the electricalpotentials of-0.6V （vs. SCE） and0.067g·L^-1CuFe₂O₄,92.8%of PNP was removed after180min treatment under UV irradiation and the corresponding COD removal efficiencywas81.4%. Moreover, CoFe₂O₄as catalyst was employed to remove2,4-DCP by theheterogeneous PE-Fenton like process. It was found that high2,4-DCP removal efficiencyof89.6%was obtained in the optimum condition of0.2mmol·L^-12,4-DCP,0.05mol·L^-1Na₂SO₄, the electrical potential-0.8V （vs. SCE）, pH3.0,0.067g·L^-1CoFe₂O₄and UVirradiation after180min treatment. At the same time, the COD removal efficiency reached84.2%. The results demonstrated that MFe₂O₄（M=Zn，Cu，Co）could be used as high efficiency catalyst and the heterogeneous PE-Fenton like process was a very effectivemothod in the degradation of organic pollutants. Compared with traditional treatmenttechnologies, a higher mineralization efficiency was obtained for the refractory organicpollutants.（2） UV/Fenton process and PE-Fenton process were respectively applied to treatthe sludge liquor, produced in deep dehydration of conditioned sludge. In the treatment ofthe sludge liquor with UV/Fenton process, response surface method was used to optimizethe operation parameters. The results showed that about60%COD removal efficiencywas obtained by the UV/Fenton process after50min treatment under the optimumcondition, namely pH3.0, H₂O₂31.7mmol·L^-1, FeSO41.59mmol·L^-1(NH₂O₂:NFe²⁺=20:1)and UV irradiation. A higher H₂O₂utilization ratio was also obtained. At the same time,the TOC, TN, NH₄⁺-N and TP removal efficiency could reach46.4%,12.8%,65.6%and95%, respectively.（3） Moreover, higher treatment efficiency was obtained in the treatment of sludgeliquor by the PE-Fenton process than UV/Fenton process. Under the optimum condition ofpH3.0, H₂O₂concentration of65.3mmol·L^-1，FeSO4concentration of6.53mmol·L^-1(NH₂O₂:NFe²⁺=10:1), the electrical potentials of7.5V and UV irradiation, only20min wasneeded for the COD removal efficiency to reach59%. The removal efficiency of TOC,TN, NH₄⁺-N and TP could reach50.6%,20.6%,73.6%and96.5%, respectively.Compared with the traditional Fenton process, UV/Fenton process and electro-Fentonprocess, the higher COD removal efficiency was obtained and TP was also effectivelyremoved in a short time. Moreover, this study had realistic meanings and provided apractical reference for the application of PE-Fenton process in wastewater treatment.