| As the city life level unceasing enhancement,the output of our city garbage has increased sharply,sanitary landfill is still one of the main ways to disposal garbage in our country.In the process of municipal waste landfill,due to compaction and microbial decomposition,pollutants that garbage contains will dissovle out along with the water,and it will form the garbage leachate together with the rainfall,runoff, etc.Landfill leachate is a kind of high strength wastewater, it may contain large amounts of organic matter, inorganic matter and humic substance, ammonia nitrogen, heavy metals, chlorinated organic compounds and inorganic salts.Untreated leachate may lead to groundwater and surface water contamination by infiltrating to the groundwater or mixing with the surface water.Supercritical water oxidation (SCWO) can oxidate and decomposeo organic matters with supercritical water as reaction medium,in condations of higher than the critical temperature and pressure above the critical point of the water (374.3℃and22.1MPa).Adding oxidation agent, generally using of H2O2and O2, organic matter in the supercritical water can all be oxidized and decomposed into CO2,H2O,N2finally.Supercritical water oxidation technology has attracted great attention of experts all over the world because of its characteristics of high efficiency and environmental protection,it has the incomparable superiority in the treatment of refractory organics especially, such as fast reaction rate, high rate of organic matter processing and thorough decomposition.Based on the characteristics of supercritical water oxidation technology, the technology of supercritical water oxidation (SCWO) and catalytic supercritical water oxidation (CSCWO) are discussed, and the application of the two technologies in wastewater treatment areas in domestic and foreign are summarized.On this basis, the self-made landfill leachate was treated in conditions of supercritical water oxidation and catalytic supercritical oxidation sperately.The reactor is continuous straight tyre, H2O2is oxidizing agent, copper sulfate is catalyst.The experiment explored the removal effect of the COD and NH3-N in the landfill leachate. There are four main influential factors in the experiment:reaction temperature, reaction pressure, reaction time, peroxygen amount.The experiment was performed in comdations as folloW:the temperature range is420-480℃, the pressure range is24-28MPa, reaction time is3.3-10min, the results are as follows:(1)In the reaction of landfill leachate by supercritical water oxidation, increasing the amount of peroxide and the reaction temperature and the reaction pressure or prolonging the residence time are favorable for the removal of COD. With the changes of factors,organic matter degradation rate showed a trend of from fast to slow.By range analysis of orthogonal test,it showed that the effects of reaction temperature, reaction pressure, reaction time on COD and NH3-N’s removal rate from big to small are:reaction temperature, reaction pressure, reaction time.(2)In the supercritical water oxidation reaction, the optimum processing conditions of COD is480℃,28MPa, peroxide amount of5and residence time of lOmin, the highest efficiency is89.9%.(3)In the reaction of catalytic supercritical water oxidate the landfill leachate, the catalyst Cu2+concentration is0.5g/L, the egradation efficiency of organic matters is significantly higher than the non-catalytic reaction, the highest removal rate is96.2%.(4)Using the exponential equation model which is frequently used in dynamics research, on the basis of the experimental data, kinetic equation is established on conditions of supercritical water oxidation and catalytic supercritical water oxidation.The results show that:without catalyst,the reaction activation energy is151.023KJ· mol-1, pre-exponential factor is7.62×105; adding catalyst,s the activation energy of the reaction is115.514KJ·mol-1,the pre-exponential factor is1.08×108. |
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