Treatment Of Phenolic Wastewater By A Dual-chamber Oxidation System With Combining Anodic Photocatalysis And Cathodic Electro-Fenton Technology

As one of the common wastewater with refractory organic compound,phenol wastewater has the greatest risk and the boardest distribution,so that it threatens seriously ecological environment and human health.For this reason,the treatment of such wastewater has been worldwidely focused from all walks of life,and this task gradually becomes the emphasis of water environment pollution governance.Though traditional biological treatment processes was widely used in the current water plant,they can not effectively degrade phenol wastewater.In recent years,advanced oxidation technology has attracted the interests of researchers,because it can degrade and even completely mineralize most organic compounds by the in-situ generation of strong oxidative active substances,such as hydroxyl radical?·OH?.However,satisfactory results may not be obtained sometimes through the singular advanced oxidation technology.Therefore,in the present work,a dual-chamber oxidation system with combining anodic photocatalysis and cathodic electro-Fenton process was constructed to degrade phenol wastewater for high treatment efficiency.The Fe@Fe₂O₃/CF electro-Fenton cathode was prepared by ultrasonic immersion method with the optimal parameters as follows:FeCl₃·6H₂O concentration 3 g/L,ultrasonic time 20 min,NaBH₄ concentration 15 g/L,and drying time 90 min.The TiO₂/Ti photocatalysis anode was prepared by the anodic oxidation method with the optimal parameters as follows:H₂SO₄ concentration 1.0 mol/L,HF concentration 0.2mol/L,oxidation voltage 20 V,oxidation time 2 h,oxidation temperature 40?,calcination temperature 500?.Moreover,the characterization results indicated that both of them have good catalytic activity.A dual-chamber photo-electrochemical oxidation system with Fe@Fe₂O₃/CF cathode and TiO₂/Ti anode was constructed by combining cathodic electro-Fenton and anodic photocatalysis for treating phenol wastewater.Firstly,the effect of various factors on the system were evaluated by several single factor experiment.The optimal operating parameters were as follows:cathodic aeration rate 0.4 L/min,current density 10.0 mA/cm²,cathodic pH value 3,anodic pH value 7,electrolyte Na₂SO₄concentration 0.05 mol/L,and anodic light intensity 500 mW/cm².Under these conditions,after 180 min,total phenol and COD removal efficiency in the cathode chamber were 98.7%and 85.6%,respectively,and total phenol and COD removal efficiency in the anode chamber were 92.5%and 41.2%,respectively,indicating that the major organic pollutants were significantly reduced and the biodegradability was remarkablely enhanced,thereby the wastewater quality was improved.Meanwhile,the electricity consumption of the dual-chamber oxidation system is 6.4 kW·h,and the current efficiency of the cathode chamber and the anode chamber is 49.3%and 10.7%,respectively.According to a set of cyclic experiments,Fe@Fe₂O₃/CF cathode and TiO₂/Ti anode can be reused for 5 and 7 times,respectively,and maintain good degradation ability.Therefore,the oxidation system was high-efficiency,economic and stable.Under the optimal conditions,it was found that the variation of TOC in both chamber with reaction time followed the first-order reaction kinetics,and the rate constants were 0.009 min^-1 and 0.003 min^-1 for cathode and anode chamber,respectively.To deeply explore the mechanism of oxidation system,the trapping experiments with adding excess reactive oxidative species scavengers was carried out.The results showed that the order of oxidation strength of active substances in cathode chamber was as follows:·OH and·O₂^-,the order in anodic chamber was as follows:·OH,·O₂^-and h⁺.Based on these,a reasonable degradation mechanism was put forward by combining with electrochemistry and photochemistry related theoretical knowledge.According to the above discussion,high efficiency of the dual-chamber photo-electrochemical oxidation system is mainly attributed to the strong synergistic effect.On the one hand,the cathodic electro-Fenton attracts the electrons generated on the surface of anode,avoiding the combination of electrons and holes,and increasing the contact opportunities with organic pollutants,thereby improving the photocatalytic performance of anode.On the other hand,the anodic photocatalysis can provide more electrons for the dual-chamber oxidation system,strengthening free radical reaction,so that refractory organic pollutants can be rapidly degraded and even completely mineralized.