Treatment Of Actual Industrial Wastewater Using Electrochemical Oxidation Technology With Ti/SnO₂-Sb-Ni Anode And Air-cathode

With the rapid development of coking,pharmaceutical,petrochemical,printing and dyeing,chemical and other industries,the ecological problems caused by wastewater containing various refractory organic matter have become more and more serious.It is of great significance to develop high-efficiency refractory organic wastewater treatment and reuse technologies for China’s sustainable development.Electrochemical oxidation technology has attracted widespread attention from researchers at home and abroad for its advantages such as high oxidizing ability,low investment in chemical agents,strong adaptability,and easy operation.Therefore,an efficient and low-energy consumption electrochemical oxidation system was constructed to treat actual coal chemical wastewater and dyeing wastewater.Ni-doped Ti/SnO₂-Sb electrodes were used as the anodes of the electrochemical oxidation system.Ti/SnO₂-Sb-Ni anodes were prepared by impregnation method and its electrochemical properties,surface characteristics,and phase structure were analyzed by CV,SEM,XRD and EDS.Doping of Ni can effectively improve the catalytic activity of the electrodes.The anodes obtained the highest oxidation current when the average load of the oxide coating was 3.601 mg/cm²,corresponding to 9 times of dipping when prepare anodes using impregnation method.XRD results showed that the coating in anodes was mainly SnO₂ with tetragonal rutile phase.Doping of Sb and Ni did not change the crystal structure of the material,and the average particle size of SnO₂ was 22.39 nm.SEM showed that the surface of the Ti/SnO₂-Sb-Ni anodes had many shallow cracks,also was loose and porous with a high specific surface area.The electrochemical system with Ti/SnO₂-Sb-Ni anodes and air-cathodes can effectively treat high concentration coal chemical sulfurous wastewater.Sulfurous wastewater contained sulfur-containing substances,aliphatic hydrocarbons and their derivatives,aromatic hydrocarbons and their derivatives.The effects of current density and air-cathodes on COD removal,color removal,energy consumption and current efficiency were analyzed.The COD removal rate of sulfurous wastewater increased with the current density.When current density was 20 mA/cm²⁵0 mA/cm²,the COD degradation of sulfur wastewater conformed to the zero-order kinetic model.40mA/cm² was identified as the optimum current density for this system with the highest current efficiency of 94.27%and the lowest energy consumption of 9.41 kWh/kg COD.At the optimum current density of 40 mA/cm²,99.05%COD,94.52%TOC,and 100%color can be removed within 24 hours.The removal of TOC conformed to first-order kinetics.Air-cathodes had a significant promotion on the removal of COD and color,which improved the current efficiency of 97.83%and reduces the energy consumption of 59.03%.The main reasons were that the introduction of air-cathodes significantly increased the cathodes potential and reduced the electrolysis voltage by 28.41%.At the same time,the higher cathode potential limited the reduction ability of the cathodes,improved the utilization of electrons,and thus improved the current efficiency and COD degradation.The oxidation mechanisms were combination of the direct and indirect anodization of the anodes.Most of the long-chain aliphatic hydrocarbon derivatives in the wastewater were completely oxidatively degraded and removed,and sulfur-containing substances such as organic sulfide or elemental S₈ were completely oxidized to sulfate SO₄^2-.The electrochemical system with Ti/SnO₂-Sb-Ni anodes and air-cathodes can also effectively treat dyeing wastewater.The effects of current density,electrode spacing,and in-tandem mode or parallel mode on COD removal,color removal,energy consumption and current efficiency were analyzed.At a current density of 5mA/cm²²0 mA/cm²,the removal of COD conformed to a first-order kinetic.When the current density was 10 mA/cm²,the current efficiency was 46.52%and the energy consumption was 5.92 kWh/m³ when the COD of the wastewater was reduced to below50 mg/L.The electrode spacing had no significant effect on the removal of COD,but the energy consumption was linearly related to the electrode spacing with a correlation coefficient R² of 0.996.The parallel mode was more conducive to the removal of COD.When the current density was 10 mA/cm²,the COD removal in parallel mode for 20minutes was higher than that of in-tandem mode by 18.59%.The current efficiency in series and parallel modes were 56.00%and 33.21%,respectively,and the energy consumption were 5.30 kWh/m³ and 5.10 kWh/m³,respectively.