| In recent years,municipal solid waste production continuously and explosively increases in China,and consequently a large amount of landfill leachate from sanitary landfill has currently become the dominant environmental concern,due to its complex compositions,poor biodegradability and high ecotoxicity.Note that only utilizing biological treatment process,the mainstream water treatment widely applied in China,is difficult to meet the discharge standard,and it is therefore essential to carry out advanced treatment for landfill leachate.Dielectric barrier discharge plasma（i.e.,DBD）process,as an advanced oxidation technology,has been widely attracted wide attention due to its highly removal capacity without causing secondary pollution.Nonetheless,the DBD system is easily affected by impurities in water during advanced wastewater treatment.Considering the above points,this study established a combined process of coagulation-DBD system and employed it to treat landfill leachate after biochemical effluent,comprehensively investigated the degradation mechanism for the contained pollutants in landfill leachate during the treatment process,evaluated ecological toxicity of landfill leachate treated by coagulation-DBD system,and briefly assessed the process feasibility of such treatment technology.The dominant results are displayed as follows:（1）The effects of diverse process conditions by coagulation-DBD system upon the advanced treatment for landfill leachate were comprehensively investigated.The result shows that the polyferric sulfate（PFS,the concentration adjusted as 5 g/L）possessed the best coagulation efficiency on chemical oxygen demand（COD,60%）,UV254（84%）and chroma（96%）of landfill leachate.Furthermore,the treatment effects of diversified pH regulators,initial pH values,discharge voltages,gas types and initial concentrations for landfill leachate by DBD system were evaluated.It was found that the Ca（OH）2 as pH regulator showed the better removal efficiency upon pollutants than Na OH,and under strong alkali,high discharge voltage and blown oxygen circumstances,the removal rate upon the pollutant in landfill leachate by DBD system was relatively at a good performance.Hence,after treating 60minutes under the conditions of PFS as coagulant,initial pH adjusted to 12.95,discharge voltage adjusted to 10.4 k V,and O2 as inlet gas,the removal rates of COD and UV254 reached to 82%and 99%,respectively.（2）The degradation mechanism of landfill leachate by coagulation-DBD system was comprehensively investigated.The UV-vis incorporated with its characteristic ratio,3D-EEM,FT-IR and GC-MS techniques were jointly employed to investigate the degradation process upon organic matter in landfill leachate.Along with the increase of treatment time,the intensity of infrared absorption peaks for organic functional groups decreased synchronously,implying destruction of macromolecular organic matter;meanwhile,most of the aromatic compounds were effectively removed,and the types of substituents on the aromatic rings were gradually declined.After 60 min of discharge,organic substances（i.e.,alcohols,carboxylic acids and ketones）and humic substances（i.e.,fulvic acid and humic acid）were completely degraded into small molecules or mineralized into CO2 and H2O.Furthermore,through the free radical quenching experiment and determination of the variations of O3 concentration in the system,it was evidenced that the free radicals（i.e.,·OH、1O2and·O2-）generated from DBD systems played a key role upon degradating organic matter,and the produced O3 also further promoted their degradation.（3）The ecological toxicity variability and process feasibility were quantified during advanced treatment of landfill leachate by coagulation-DBD system.Through ryegrass seed germination test and chlorella toxicity experiments,the variations of ecological toxicity in landfill leachate were evaluated,and the varying of the production of disinfection by-products were comprehensively investigated by determining the changing of bromate concentration in landfill leachate during treatment.The result shows that the inhibition from the treated landfill leachate upon the germination and growth of ryegrass was obviously alleviated,and the chlorella cultured with low concentration landfill leachate showed strong growth ability.Along with the increase of treatment time,the bromate concentration in water increased gradually,which therefore requires to further control the bromate content in this treatment system.In this study,the feasibility of coagulation-DBD system was assessed,and it was found that the cost of water treatment is nearly 10～30 yuan/ton,indicating a good engineering application prospect.The coagulation-DBD system provides a high-efficiency treatment approach for advanced treatment for landfill leachate,simultaneously showing a good performance of reduction for its organic pollutants and ecological toxicity.In general,coagulation-DBD system in our study is an efficient and advanced treatment technology with widely engineering application prospects. |
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