| Landfill leachate is a kind of harmful wastewater containing high concentration organic compounds, and it is called one of most resistant to treatment wastewater. Landfill leachate could pollute the around environment and the substrate of landfill site, which comes from precipitation and the water in landfill. The pollutants of landfill leachate were more complicated, COD can reach 70000mg/L, BOD5 can reach 38000mg/L, ammonia nitrogen (NH3-N) can reach 1700mg/L and high concentrated highweight metal of Fe, Pb et al. The main compounds were aromatic hydrocarbons, Alkanes, alkenes, oragnic acids, lipids, alcohols, carbonyl compounds. Because of its serious pollution to the circumjacent environment and substrate of the landfill, the long-term maintenance of pollution, and the secondary pollution, it is an urgent problem to collect and treat the landfill leachates effectively in city environments. The treatment mothed of landfill leachate is a hotspot studies over the world.At present, the main singleness methods to treat landfill leachates include biological methods, physical-chemical methods and the synthesis of different methods. Biological method was easy to operation, the running cost was lower, and the operation technique is relative perfect, so the method was applied extensively. Some wastewater such as low biodegradability, refractory orgnic matter, and poisonous wastewater was not suitable to be treated by biological method, but physical-chemical method was much better. The commen physical-chemical methods include photocatalysis oxidation, Fenton, adsorption, chemical precipitation, membrane separation, electrolytic oxidation method and catalytic wet air oxidation, et al.Catalytic wet air oxidation (CWAO) is a kind of physical-chemical method, this method is suitable to treat the high concentrated organic wastewater which is too dilute to incinerate and too concentrated for biological treatment. CWAO could be applied abroadly, the treating speed is rapidly, the degradation efficiency is higher, the treating cost is lower and have no second pollution. Since CWAO was invented, the method was favoured by researchers. CWAO is carried out under a high pressure of oxygen at elevated temperatures to decompose organic pollutants contained in wastewaters over catalyst. These years, the investigated results that applying CWAO to treat many kinds of high concentrated wastewater were achieved by many researchers, the decomposed effects were influenced by the character of catalyst, reaction temperature, reaction time, the concentration of wastewater and oxygen partial pressure.Mn/Ce catalyst showed very high catalytic activity over many CWAOs, in this paper Mn/Ce compoud catalysts were prepared by citric complex method, and the preparation conditions were optimized over the interactive orthogonal design. The best preparation conditions were concluded according the study results of calcination temperature, metal ratio and calcination time. The physical properties of the Mn/Ce catalyst was charactorized, then the relations of the physical properties and catalytic activities were analysised. The influence factors of degrading acetic acid, n-butyric acid and n-hexanoic acid over CWAO were investigated, and the interact of the above organic acid were also analysised. N-butyric acid was as model wastewater of landfill leachate, heating process forecast model and constand temperature kinetics model were established by study the parameters of the reaction temperature, reacion time, catalyt dosage, TOC concentration, oxygen partial pressure and pH value. The activity difference of Mn/Ce and Co/Bi catalysts over oxidating acetic, n-butyric, n-hexanoic and landfill leachate were analyzed, then the interact between NH3-N and low molecular weight organic acids were discussed over CWAO. Finally, the decomposition mechanism of landfill leachate were further analyzed.The reactivity of the catalysts which were prepared by citric complex method were superior to Co/Bi catalysts over the n-butyric solution oxidation, and the CeO2 was the main component of the Mn/Ce catalyst. These experiment data showed that the catalytic activity had no notable difference while calcination temperature discrepancy was smaller than 100℃with the metal bulk ratio was Mn/Ce=7/3, and calcination time have no notable influence on catalytic activity. The best preparation conditions were: Mn: Ce=3: 7, calcination temperature of 500℃and calcinations time of 5 hours through the analysis of interactive orthogonal design, the prepared catalyst under these conditions had more specific surface area and higher catalytic activity. The results indicated that metal ratio and calcination temperature have notable effect on catalytic activity (p=99% and p=95%, respective), while calcination time have no notable effect. The calcination temperature and metal ratio had notable interaction (p=99%). Therefore, this interaction between calcination temperature and metal ratio should be considered during the catalyst preparation. The best catalyst preparation conditions of interactive orthogonal design were superior to those of intuitionistic analysis. Interactive orthogonal design remedied the drawback of the orthogonal design while optimizing the preparation conditions of citric complex method, the catalytic activity of the optimized catalyst was promoted and exceeded that of the Co/Bi catalyst for the catalytic wet air oxidation of n-butyric acid. The pH of the solution during CWAO over interactive orthogonal design catalyst became higher, which reduced the corruption of the catalyst and the equipment, and the catalyst stability was also superior to the intuitionistic analysis catalyst.The parameters of BET indicate that the specific area and pore volume of Mn/Ce catalysts were higher than those of Co/Bi catalysts, meaning that the contact chance of Mn/Ce catalysts with organic matter were more than that of Co/Bi catalysts during CWAO. The reactivity of Mn/Ce catalysts superior to Co/Bi catalysts over the carboxylic acids oxidation., while the TOC removal rate of landfill leachate over Co/Bi catalyst were higher than that over Mn/Ce catalysts. This accounted for that the reactivity of Mn/Ce catalysts was affected by Ni2+ and NH3-N, and that Co/Bi catalysts could resist the effect definitely. The addition of NH3-N could increase the pH of the solution, and a significant decrease in the rate of oxidation when the pH of the carboxylic acid solution was increased. On the surface of Co/Bi and Mn/Ce catalyst hydrogen atom substitution react of carboxylic function could carried out, so the TOC removal rate didn't drop notably over Co/Bi catalyst.With 0.5g Mn/Ce catalyst at 200℃and 1Mpa oxygen partial pressure, acetic acid, n-butyric acid and n-hexanoic acid were degraded by CWAO. The results showed the TOC removal rates of n-butyric acid and n-hexanoic acid were higher than that of acetic acid, the TOC removal rates of n-butyric acid and n-hexanoic acid had no notable difference. The mixed solution between acetic acid, n-butyric acid and n-hexanoic acid with 0.5g Mn/Ce catalyst at 200℃and 1Mpa oxygen partial pressure by CWAO. The TOC removal rate of the mixed acid solution (the TOC ratio = 1) was lower than the single carboxylic acid solution for"0"min sample, this indicated there was interaction that inhibit the TOC degradation, and the TOC difference of the mixed acid reduced after 0 min. NH3-N had two kinds of effect on the organic acid degradation, NH3-N could make the solution pH value higher and promoted organic acid ionized, ionized organic acid was refractory, so the TOC removal rate of the solution became lower. On the other hand, the substitution react could carried out that the one hydrogen atom of carboxylic function was substituted with a NH2, the molecule was then oxidized very rapidly. N-butyric acid and NH3-N maybe had same adsorption site on the catalyst surface, the pollutant degradation was inhibited by the other when the competitive adsorption of n-butyric acid and NH3-N happened. The one hydrogen atom of carboxylic function was substituted with a NH2-, the n-butyric acid was oxidized rapidly whereafter NH2- was reproduced, so the NH3-N removal rate was slow.The TOC removal rate became higher while the temperature, oxygen partial pressure and the Mn/Ce catalyst dosage increased. The TOC abatement rate increased due to the organic matter concentration increased, but the TOC removal rate dropped. When the initial pH increased ,the TOC removal rate dropped significantly. Allometric function was used to well fitted the reaction kinetics process of different temperature, catalyst dosage, oxygen partial pressure and initial TOC concentration in CWAO of n-butyric acid (α=0.01, n=6, r>0.8343). The uniform design was employed to investigate TOC conversion during the heating process of catalytic wet air oxidation. The correlation analysis shows that the heating process expected model was notable under the notability level of 95%, the multiple correlation coefficient r reached 0.997, and the model could expect the residual TOC of heating process, this make the process control easily. The temperature, oxygen partial pressure, catalyst dosage and initial TOC concentration were the main effect factors with CWAO of landfill leachate. The kinetic exponential experience model was applied to investigated the process of the butyric acid degradation, the orders with respect to the main effect factors were calculated based upon linear regression. The kinetic exponential experience model was applied to forecasted the process of the butyric acid degradation, the values of r and NSC was 0.9015 and 0.9214 respective both of which were higher than 0.80, this indicated the model could forecast the residual TOC better. GC-MS was applied to detect the organic matter and the intermediate of landfill leachate during the CWAO, the content of organic acid was 88%. Finally, the degradation mechanism of landfill leachate by CWAO was analyzed.
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