Research On Pretreatment By Fenton--reinjection Into The Landfill Of Concentrated Leachate

The concentrated leachate can be purified by direct reinjection to landfills, which can be used as a "biofilter", but the macromolecular organics in the concentrated leachate are difficultly degraded and then they will be remained in the landfilled waste and leachate. This not only enhances the difficulty of leachate treatment, but also the pollutants in the concentrated leachate are toxic to the microorganisms in landfills, which inhibite the degradation of landfilled waste and delay the stabilization of landfilled waste. Based on the analysis of pollutants in the concentrated leachate, the optimistic condition of Fenton process, the variation in biotoxicity of pollutants before and after Fenton process and effects of Fenton+leachate recirculation on the stabilization of landfilled waste were investigated in the study. These findings would provide theoretical basis for the economical and effective treatment of the concentrated leachate. The main results are as follows.(1) The composition of landfill leachate and concentrated leachate varied with landfills. Metals, C1-and SO42-were diffcultly removed during the process of landfill leachate treatment and accumulated in the concentrated leachate. Single stage anaerobic-aerobic treatment process mainly transformed the leachate NH4+-N into NO3--N, which was accumulated in the concentrated leachate. The biodegradability of concentrated leachate was lower, compared with the landfill leachate, owing to its high concentrations of refractory organic matters including aromatic compounds, long-chain hydrocarbons and halohydrocarbons, as well as its high toxicity with the presence of toluene, ethylbenzene, dibutyl phthalate and chlorobenzene, which have been identified as USEPA priority environmental pollutants.(2) Considering the cost and biodegradability, the optimistic condition of Fenton reaction for promoting the biodegradability of the concentrated leachate used in this study was:Fe2+dosage,400mg/L; H2O2/Te2+,9; initial pH value,3.0; reaction time,2h. Hydrophobic organic compound (HOCs) including toluene, ethylbenzene, chlorobenzene, DMP, DEP, DBP and DOP, metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb, Mo and Cd) and As were remarkably removed by Fenton proces. After treated by Fenton process, the precent of HOCs and metal in humus by adsorption or complex decreased. Since the concentrations of HOCs were low and a part of HOCs was bonded with humus, the contribution of HOCs to toxicity to Photobacterium phosphoreum (T3variant) of concentrated leachate was negligible before and after Fenton treatment. Metal is the main source of toxicity to Photobacterium phosphoreum (T3variant) of concentrated leachate before and after Fenton treatment.(3) During the experiment of simulated landfills, among the low carbon fatty acids of acetic, propanoic, butyric and valeric acids, butyric and propanoic acids were highest, followed by valeric and acetic acids. Leachate recirculation could effectively reduce the emitted amounts. The cumulative COD amounts in leachate from landfills with concentrated leachate or the concentrated leachate wre only20-22%of that without leachate recirculation.