| Landfill leachate is the wastewater produced by landfill which contains high concentrations of pollutants and is hard to deal with. Currently, common biological treatments for landfill leachate are no longer able to meet the rising discharge standard. Hence, advanced treatments for the effluent of biological treatment of landfill leachate become necessary. In this thesis, coagulation combined with ozone advanced oxidation was applied to treat the effluent of landfill leachate after biological treatment.In the coagulation experiments, we firstly conducted three orthogonal tests for PAC, PAFC and FeCl3, respectively. Results showed that FeCl3was much better in removing TOC from the landfill leachate than PAC and PAFC, thus FeCl3was chosen as the coagulant for the following experiments. Based on results of the orthogonal test, we then determined the optimum coagulation condition by conducting a series of single factor experiment in terms of the dosage of FeCl3, initial pH of the system, the dosage of PAM and the method of agitation, respectively, using the removal efficiency of TOC as the evaluation criterion. The optimum condition in this study was1400mg/L of FeCl3, initial pH6,8mg/L of PAM, and stirring at300r/min for1min and at80r/min for another10min. Under this condition, the removal efficiencies of TOC and UV254were67.7%and79.5%, respectively; TOC, CODCr, BOD5, UV254and colority of the effluent were92.1mg/L,314.4mg/L,5.5mg/L,2.24and16times, respectively.Three different ozone-based advanced oxidation methods, namely O3, H2O2/O3and UV/O3, were employed to treat the landfill leachate after enhanced coagulation process. Results showed that, under the dosage of O3of8.3mg/(min L), the optimized initial pH for all three oxidation methods was9, indicating that acid condition is not in favor of ozone-based advanced oxidation. The optimum mole ratio of H2O2/O3in this method was0.7. The performances of H2O2/O3and UV/O3were significantly better than O3oxidation. Given a long enough reaction time, all the three advanced oxidation methods could attain relatively high removal efficiency of organic matters. With an reaction of120min and under the optimum operational condition, the removal efficiency of TOC in the effluent reached73.6%for O3oxidation,83.0%for H2O2/O3oxidation and79.6%for UV/O3oxidation. Kinetic studies for each oxidation method under its corresponding optimum operational condition indicated that the pseudo-first-order model fitted all the three sets of TOC removal rate data, with the kinetic constant being0.0118min-1for O3oxidation,0.0220min-1for H2O2/O3and0.0149min-1for UV/O3oxidation The kinetic constants demonstrated that the reaction rates of H2O2/O3and UV/O3oxidation processes were faster than that of O3oxidation process. Considering the economic cost, to decrease the TOC concentration in the effluent to30mg/L, the cost would be14.4yuan/t,8.8yuan/t and16.1yuan/t for O3, H2O2/O3and UV/O3, respectively.Ozone-based advanced oxidation process could significantly improve the B/C ratio of the landfill leachate. In this study, O3, H2O2/O3and UV/O3advanced oxidation techniques were all able to improve the B/C ratio from almost0to about0.3.GC-MS was used to analysis the changes of organic constituent before and after the coagulation combined with ozone advanced oxidation process.The result shows that most unsaturated organic compounds was removed,and the remains are mostly alkanes, aromatic compounds and some easters,alcohols... |
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