| Landfill leachate is complex,it may contain large amounts of organic matter,inorganic matter,heavy metals,ammonia nitrogen,chlorinated organic compounds,where total organic carbon(TOC)and humic acid(HA)are important components.If the landfill leachate is not treated properly,it will cause serious harm to the environment and human health.The mature landfill leachate was collected to research in this experiment.The landfill leachate was treated by subcritical water oxidation technology with a batch reactor.Firstly,the influence of subcritical process parameters on the oxidation degradation of TOC in landfill leachate was investigated,the intermediate product of subcritical process were analyzed and identified systematically by gas chromatography coupled with mass spectrometry(GC-MS).The results showed that the effect of temperature on the degradation efficiency of TOC was the most significant.With the increase of temperature,the aromatics and acids were decomposed into low-molecular-weight hydrocarbons,the product species accounting for the largest area%at every temperature tested was C11-C15.Most of the aromatics in the original leachate were converted to hydrocarbons when the acidic subcritical water was used.With the increase of pH value,carbon products C6-C10 and C16-C20 first decreased and then increased,while C11-C15 increased firstly and then decreased.With the increase of the peroxide coefficient,the degradation of TOC first increased rapidly and then leveled off,the hydrocarbon showed the trend of increasing first and then decreasing,while the acid and aromatics showed the trend of decreasing and then increasing.It turns out that the free radical reaction dominates,however,oxidation reaction,hydrolysis reaction,pyrolytic reaction,hydrothermal synthesis,hydrogenation reaction and alkylation have also happened in subcritical oxidation process.Taking aniline and 2,4-dinitrotoluene as examples,they are easily removed and broken at high temperatures due to the oxidation of OH·,further oxidation decomposition for multiple linear or non linear paraffins,small molecule alcohol,formic acid,acetic acid,etc.Finally,they were completely oxidized to CO2 and H2O.Secondly,response surface methodology(RSM)was used to evaluate the effects of temperature(180-260?),peroxide coefficient(2.0-3.0),pH(4.0-8.0)and their interactive effects on TOC and HA removal efficiencies.The results demonstrated that RSM was an effective method for the optimization of experimental parameters in the treatment of landfill leachate.The effects on TOC removal efficiency were in the order:temperature>pH>peroxide coefficient,and that the order on HA removal efficiency was pH>temperature>peroxide coefficient.The interaction between reaction temperature and peroxide coefficient on the removal efficiency of TOC was significant,while peroxide coefficient at subcritical region has little effect on the decomposition of HA.Thirdly,in order to reduce the dependence on the operating conditions.The effects of different heterogeneous(CuO,ZnO)and homogeneous(CuSO4·5H2O,FeSO4·7H2O,and Cu(NO3)2·3H2O)catalysts on the treatment of TOC and HA in leachate were studied,the optimal parameters within the experimental range were:temperature of 260?,pH of 4.0,peroxide coefficient of 3.0 and Cu(NO3)2·3H2O of 0.03 mol/L.Under the optimum conditions,the TOC and HA removal efficiency can reach 86.42%and 66.10%,respectively.After the catalytic treatment of the five kinds of U.S.environmental protection agency(USEPA)in the list of priority pollutants were not detected.Catalytic subcritical oxidation combined with high temperature accelerated decomposition of macromolecular organic compounds(e.g.,long chain alkane,ketones,esters,amides,aromatic hydrocarbon,etc.),and then produce some more easy to be detected small organic molecule,such as short chain saturated alkane. |
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