| Landfill is one of the best ways to waste final disposal, and leachate generated in this process would cause harm to the environment. Leachate composition is very complex, which contains a variety of refractory organic matter. Advanced oxidation processes were effective to degrade refractory organics. In this paper, based on the electro-Fenton treatment, Research on optimization of operating conditions and enhanced technology were expanded. In-depth study of oxidation and coagulation removal of COD from landfill leachate by E-Fenton. Factorial design analysis to screen the significant factors which influenced photoelectro-Fenton process. And the biodegradability of leachate during E-Fenton process was discussed. As SBR adapt to changes in leachate quality and effective removal of ammonia, studies of optimization of SBR process were conducted. And then the combination of SBR with E-Fenton related technologies were investigated.(1) COD removal by oxidation as well as by coagulation during Fered-Fenton treatment of landfill leachate was quantitatively determined in this study. The effects of operating conditions such as H2O2to Fe2+mole ratio, Fenton's reagent dosage, initial pH, current density, inter-electrode gap and hydrogen peroxide feeding mode on COD removal was investigated. The results showed that COD removal by oxidation is dominant due to the high H2O2/Fe2+mole ratio employed and the overall COD removal showed the same behavior as oxidation removal. The coagulation removal of COD increased with initial pH and ferrous iron dosage, but it was independent of current density and the inter-electrode gap at a fixed initial pH value and ferrous iron dose. Increasing Fenton's reagent dosage or decreasing the initial pH is likely to promote COD removal by oxidation. There existed an optimal H2O2/Fe2+mole ratio, current density or inter-electrode gap to reach the highest COD removal efficiency by oxidation. The stepwise or continuous addition of hydrogen peroxide was more effective to oxidize organics than a single dose of hydrogen peroxide. Nearly all the organic compounds (>4kDa) were degraded into smaller ones after Fered-Fenton treatment. GC-MS analysis was used to determine the organic compounds before and after the treatment.(2) PE-Fenton process induces the production of hydroxyl radicals from the regeneration of ferrous ions and the reaction of hydrogen peroxide with UV light. As there are so many operating parameters in the PE-Fenton process, it is necessary to develop a mathematical model in order to produce the most economical process. In the present study a factorial design was carried out to evaluate leachate treatment by the photoelectro-Fenton process. The influence of the variables:initial H2O2concentration, initial Fe2+concentration, current and pH in the PE-Fenton process was investigated by measuring COD removal efficiencies after60min of reaction time. The relationship between the COD removal and the most significant independent variables was established by means of an experimental design. The H2O2concentration and initial Fe2+concentration, the pH and the interaction effect between current density and initial pH were all significant factors. The factorial design models were derived based on the COD removal efficiency results and the models fit the data well.(3) A basic study to investigate the variety of water quality associated with biodegradability during E-Fenton process. The rate of MWCO less than4k Da would be obviously shifted from70.2%to92.5%after E-Fenton. FTIR observations reveal the decrease of aromatic organic compounds and the increase of the aliphatic ones. The removal of ammonium was less than the removal of COD at the experimental conditions, heavy metal ions As, Pb, Hg and Cr was nearly all removed. The biodegradability was improved (BOD5/COD from0.09to0.21, BOD5/TOC from0.27to0.29), although the value of BOD5is reduced.(4) Leachate treatment using the sequencing batch reactor with different operation mode and volume load, and membrane bioreactor are trial operated. The research results show that the removal of COD and TN is better in the condition of anoxic/aerobic/anoxic/aerobic (A/O/A/O) than that of anoxic/aerobic (A/O) process. During the treatment with SBR of A/O/A/O, The volume loading around0.5-0.55kgCOD/m3·d has got better results. The COD removal rates of45.9%?49.1%and NH4+-N removal rates of72.2%?77.3%were achieved. The particial nitrification is achieved in the reactor with more than92.1%of the nitrite accumulation ratio with volume loading around0.54kgCOD/m3·d. SBR-membrane bioreactor treatment of landfill leachate was investigated, average removal rates of COD and NH+-N were87.3%and91.2%.(5)The integration of SBR and E-Fenton or SBR and electrochemical oxidation technologies to deal with landfill leachates have been investigated. The raw leachate, with average values of COD6325mg/L and NH4+1269.1mg/L, was first treated by SBR reducing the former parameters to797mg/L of average COD and101.5mg/L of average NH4+. Next, the effluent was treated using electrochemical oxidation technologies or E-Fenton method. After the treatment of E-Fenton, COD and NH4+-N were reduced to187.3mg/L and56.1mg/L respectively. The increase of ammonium removal was34.3%by three-dimensional electrodes compared to two-dimensional electrodes. COD and NH4+removal rate is higher in40mA/cm2than that of30mA/cm2, and93.5%of ammonium nitrogen removal efficiency and66.9%of COD removal efficiency could be achieved at40mA/cm2in3hour. Ammonium was degraded to lower25mg/L by three-dimensional electrode method, below the disposal limit of chinese pollution control standards. The integration of SBR and E-Fenton were prefered to COD removal, while the integration of SBR and electrochemical oxidation technologies were prefered to ammonium removal. |
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