Electrochemical Treatment Of Mature Landfill Leachate Using Ti/RuO₂-IrO₂ And Al Electrode:Optimization And Mechanism

With the rapid development of Chinese economic construction,expansion of urban-scale and improvement of living standards,the amount of municipal solid wastes is increasing.As the main technology of municipal solid waste treatment in China,landfill also brought new secondary pollution problems.Leachate generated by landfill is high concentration organic wastewater which has a great harm,containing amounts of refractory organic matters,ammonia nitrogen and heavy metals.If not properly handled it will cause serious pollution to the surrounding environment and groundwater.Because of the complexity of leachate,a certain kind of process technology cannot fully solve this problem.Today,improving the elimination of refractory pollutants in landfill leachate through electrochemical oxidation technology has attracted considerable attention.It had carried on the factor experiments,response surface optimization and its removal mechanism in this study.The factor experiments mainly studied the cathode materials,reaction time,electrode gap,current density,initial pH and the chloride ion concentration on COD and NH₃-N removal.The response surface methodology?RSM?method was adopted to optimize the electrochemical process.Three operating parameters were seted including current density,pH and the chloride ion concentration.Response values were seted as the removal efficient of COD and NH₃-N.through gas chromatography-mass spectrometry?GC-MS?,Environmental scanning electron microscopy coupled with Energy dispersive spectrometer?ESEM/EDS?and Fourier transform infrared spectroscopy?FT-IR?analysis of organic components in landfill leachate and sludge generated in cathode,a main degradation mechanism of pollutants was elucidated.The experiments showed that,a combination of anodic oxidation and cathodic coagulation process using Ti/RuO₂-IrO₂ and A1 electrode,was adopted to treat the mature landfill leachate with a very low biodegradability ratio?BOD5/COD?of 0.12.Based on the anodic oxidation,aluminium as the cathode could produce hydroxide at the expense of sacrificial aluminum,which had a promoting coagulation effect on pollutant removal.Compared with the pure electrochemical oxidation,structure of reaction tank could be optimized and the removal rate of pollutants was improved significantly.In the factor experiments,the most significant factors were current density,initial pH and the chloride ion concentration.COD and NH₃-N removal rates increased with an increase in current density.Under the acidic condition,the removal rate of COD was relatively high.In neutral or alkaline solution,it was more suitable for removal of NH₃-N.With the chloride ion concentration,the ability of electric conduction could be improved.Besides,it could be chemically converted to hypochlorite ion?OCl-?which accelerated the oxidaion of COD and NH₃-N indirectly.The optimum condition of 83.7%COD and 100%NH₃-N removal was achieved at current density 0.1A/cm2,pH 6.37,the chloride ion concentration 6.5 g/L and electrolytic time 150 min.In addition,heavy metals were partly removed.By GC-MS,ESEM/EDS and FT-IR analysis,it was evident that the species and mass percentage of organic compounds in landfill leachate were found to have considerably declined during electrochemical process.And the surface of sludge was coated with a layer of contaminant,most likely C,0,and Al species.Therefore,the main degradation mechanism of pollutants included oxidation,coagulation and precipitation.These results indicated that the electrochemical processes could be a convenient and efficient method for the treatment of landfill leachate.