Study On The Degradation Of Landfill Leachate By Electroassisted Activated Persulfate

Since the reform and opening up,China’s economy has developed rapidly and urbanization has been steadily increasing.Still,at the same time the production of municipal solid waste has been rising,which in turn has led to the production of landfill leachate increasing with each passing day.Landfill leachate is a kind of highly concentrated polluted wastewater,containing a variety of hard-to-degrade organic pollutants,with substantial toxicity,high color,and odor,which poses a serious threat to environmental safety and human health when discharged directly.At present,the treatment of landfill leachate in China is costly and prone to secondary pollution.Therefore,properly treating landfill leachate has become an urgent task for water treatment workers.The new persulfate（PS）advanced oxidation process and electrochemical（EC）oxidation process are both advanced technologies in the field of landfill leachate treatment and have sound effects on landfill leachate treatment.In this paper,combined with these two technologies,Ti/IrO₂-RuO₂-TiO₂ anodic oxidation system,Fe²⁺/UV composite activated PS system,and electroassisted zero-valent iron/UV composite activated PS system were used to treat landfill leachate,respectively.Guided by the reduction of COD,NH₃-N,and other water quality indexes,the degradation efficiency of each system on landfill leachate was investigated,the transformation of landfill leachate characteristics before and after treatment was explored,and the degradation mechanism of pollutants in landfill leachate was clarified.In the experiment of treating landfill leachate with Ti/IrO₂-RuO₂-TiO₂ anodic oxidation system,the influences of initial pH value,current density,electrode plate spacing,and other factors on the degradation effect of landfill leachate were studied,and the biodegradability difference of landfill leachate before and after treatment was investigated.At the same time,the ultraviolet-visible spectrum and three-dimensional fluorescence spectrum of landfill leachate before and after treatment were analyzed.The results show that under the optimal reaction conditions of initial pH 3.0,current density 87.5 m A/cm²,and electrode spacing 1.5cm,the content and molecular weight of organic compounds including aromatic compounds in the landfill leachate treated by the system decreased for 6h,and some humic acids and fuluric acids were removed.The removal rates of COD and NH₃-N reached the maximum of 22.42%and 48.41%,respectively.Biodegradability was slightly improved,with BOD₅/COD increasing from 0.23 to 0.28.In the experiment of treating landfill leachate with Fe²⁺/UV composite activated PS system,the influence of initial pH value,PS dosage,Fe²⁺dosage,and other factors on the degradation effect of landfill leachate was studied,and the difference of biodegradability of landfill leachate before and after treatment was investigated.At the same time,the ultraviolet-visible spectrum and three-dimensional fluorescence spectrum were analyzed for landfill leachate before and after treatment.The results showed that under the optimal reaction conditions of initial pH value 3.0,Fe²⁺concentration 71.94mM and PS₀ concentration 80.63 mM,the aromatics and hydrophobicity of soluble organic matter（DOM）in the treated landfill leachate decreased significantly,and the content and molecular weight of organic compounds decreased.The removal effects of COD and NH₃-N were 71.42%and 58.69%,respectively.The biodegradability of BOD₅/COD increased from 0.23 to 0.38.In addition,it was found that the system had a good effect on the removal of fulvic acids and soluble microbial metabolic byproducts,but a relatively poor impact on the removal of humic acids.In the experiment of treating landfill leachate with an electroassisted ZVI/UV composite-activated PS system,the effects of the dosage of PS and ZVI,initial pH value,and current density on the removal effect of COD and NH₃-N in landfill leachate were studied.The treatment effects of single PS,single electrochemistry,UV/PS,electroassisted ZVI-activated PS,and electroassisted UV/ZVI composite-activated PS were compared.At the same time,the ultraviolet-visible spectrum and three-dimensional fluorescence spectrum of landfill leachate before and after treatment were analyzed.The results show that under the optimal reaction conditions of initial pH 3.0,PS dosage 40.31mM,ZVI dosage 1.5g/L,and current density of 62.5 mA/cm²,most of the humic acid,fulvic acid,and other macromolecular organic materials are removed when the system runs for 6 h.The removal efficiency of COD,NH₃-N,and chroma reached 81.99%,89.90%,and 99.75%,respectively,and Chroma reached 81.99%,89.90%,and 99.75%,respectively,and the BOD₅/COD value increased from 0.23 to 0.46.In addition,the BOD₅/COD value increased from 0.23 to 0.46.the free radical identification results show that the degradation of COD is caused by the interaction of sulfate free radicals(SO₄^·-)and hydroxyl free radicals（·OH）,and SO₄^·-is dominant.The effect of combined activation PS on landfill leachate was significantly stronger than that of.And SO₄^·-is dominant.The effect of combined activation Ps on landfill leachate was significantly stronger than that of single activation PS,which confirmed that electroassisted ZVI/UV combined activation PS is a promising treatment method for landfill leachate.