Treatment Of Stabilized Landfill Leachate By The Combination Of Coagulation-catalytic Ozonation-sequencing Batch Reactor Processes

A series of M/ACF catalysts supported by active carbon fiber were prepared where M presents Fe, Mn, Co, Pd, Cu oxides. Laboratory experiments are conducted to compare the efficacy using these five catalysts to treat stabilized landfill leachate. Raw leachate was initially coagulated by ferric chloride at the experimental-determined optimum condition. Catalytic ozonation processes were subsequently applied. Results indicated that coagulation process and catalytic ozonation process were found to remove 41% and 69.5% of COD respectively, and all catalytic ozonation processes would result in a significant increase on the ratio of BOD₅/COD from 0.15 to about 0.5 with 1.26g/L ozone dose, UV₄₁₀ represents color and UV₂₅₄ were removed by 90.1% and 65.9% respectively. Ultrafiltartion indicated that predominate distribution of COD would be obviously shifted to the MWCO (molecular weight cutoffs) less than 1kDa over the other MWCO ranges. Fe/ACF was found to be the most effective approach among these M/ACF catalysts to enhance the biodegradability and remove COD of leachate.Effcts of gas feed rate, catalyst dose, times of catalyst reuse, pH value, system temperature were examined. Reuslt indicated that the optimum gas feed rate was 600mL/min, optimum catalyst dose was 5g/L, optimum system temperature was 25℃. The catalyst reused seven times with no significant change of its activity and no dissolution was observed. pH value had a significant impact on the process.The removal of COD by catalystic ozonation can be represented as a pseudo-first-order kinetic in assessed oxidation times. The deduced decay rate constants of Fe/ACF, Pd/ACF, Mn/ACF, Cu/ACF, Co/ACF catalystic system were 0.01741min^-1,0.01478min^-1,0.01102min^-1,0.01024 min^-1,0.00796 min^-1 respectively. The catalytic activity order of metals supported on ACF was found to be: Fe/ACF>Pd/ACF>Mn/ACF>Cu/ACF>Co/ACF, Co/ACF showed low activity under the reaction conditions.The possible function mechanism of M/ACF catalytic ozonation isdecomposition of ozone to produce hydroxyl radical or enhancement oxidation ability of ozone by forming electrophilic center.Active sludge was acclimated by raw leachate and effluent of catalytic ozonation process. Microscopic observations showed that the quality of sludge acclimated with effluent of catalytic ozonation process was better than that with raw leachat.Kinetic analysis of SBR treatment was carried out. The maximum specific decomposition rate of sbustrate and the saturation constant of Contois model of SBRprocess were deduced as q_max =0.139gCODgMLVSS^-1h^-1, K₁=2.83gCODgMLVSS^-1 respectively.Multi-stage catalytic ozonation-SBR treatment process was evaluated to apply for stabilized landfill leachate. Result indicated that three stage treatment(total ozone feed dose: 0.63g/L) showed a little bit higher removal of COD and higher removal of ammonia nitrogen than sighle stage treatment(total ozone feed dose: 1.26g/L). Moreover, effluent of multi-stage treatment can be compliant to the second class of State Standard GB16889-1997 by considering the concentration of COD and ammonia nitrogen in the effluent.A rough economy estimation of the ecomony of the catalytic ozonation process was carried out. The EE/O(Electrical energy per order ) value and the stoichiometric coefficient of process were 57.44 kW.h/Order/m³ and 0.761 gO₃/gCOD respectively.