Degradation Of Refractory Organics In Landfill Leachate By Advanced Oxidation Technology Based On Fenton Reaction

Landfill leachate is a strongly polluted wastewater and contains high concentration of refractory organic compounds. Conventional biological treatment methods are difficult to obtain satisfactory removal of pollutants. In the effluent of membrane bioreactor (MBR) in landfill leachate treatment plants, the chemical oxygen demand (COD) concentration is always higher than the limits of discharge regulated by GB16889-2008. Many leachate treatment plants have adopted advanced membrane processes, such as nanofiltration (NF) or reverse osmosis (RO), to polish the residual refractory organics. However, NF and RO units do not degrade these refractory organic pollutants, but derive them into the reject concentrates of these membrane processes. In the present thesis, the degradation and mineralization of the refractory organics present in both MBR effluent and NF reject concentrates was carried out by using advanced oxidation processes based on the principle of Fenton reaction. The aims are twofold, i.e. to develop a single-step oxidation process to decrease COD in MBE effluent to a level less than100mg/L in order to comply to the discharge requirement; and to cost-effectively remove the biodegradable organic matters in NF reject concentrates by combining Fenton and photo-Fenton processes. The main conclusions are drawn as follows:1) For a leachate MBR effluent COD=590mg/L of raw water, Fenton, UV-assisted Fenton, microwave discharge electrodeless lamp (MDEL)-assisted Fenton can effectively remove the refractory organics. Leachate organic contents, in terms of COD, TOC, UV254, and color, were diminished significantly after the treatment. More than80%organic macromolecules in leachate were converted into small molecules with a molecular weight less than1K Da. The effluent COD ranged130-150mg/L after Fenton and UV-assisted Fenton process; while a COD less than100mg/L could be obtained by MDEL-Fenton treatment and the color also meet the discharge requirement. MDEL-Fenton provides a single-step treatment option for polishment of biologically treated leachate treatment. More importantly, MDEL-Fenton does not produce concentrated water that needs further treatment.2) The combination of Fenton and UV-Fenton processes was conducted to remove the refractory organic matters present in two different NF reject leachates with COD of1300and3000mg/L, respectively. COD removal efficiency of90%were achieved and effluent COD values were between100-200mg/L. Moreover, the ratio of biochemical oxygen demand to chemical oxygen demand increased from less than0.05to around0.3.3) High concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were detected in both MBR effluent and NF concentrates. After MDEL-Fenton process,5PAHs and15PCBs in MBR effluent were decreased, while2PAHs and9PCBs decreased in NF A.4PAHs and13PCBs in NF B water were removed.