| The landfill is one of the main ways of harmless disposal of domestic waste in China,and it is also the most important pollution site in human society.Except for chlorine ion(Cl-),ammonia nitrogen(NH4+-N)and other conventional detection indexes exceeding the standard,a variety of emerging organic pollutants(EOCs)were found in the landfill leachatecontaminated groundwater.EOCs usually have a stable chemical structure,are difficult to biodegrade,and are easy to bioaccumulate and so on.So EOCs still pose a potential threat to ecological environment security at very low concentrations.In China,remediation technologies for contaminated groundwater from landfill sites are insufficient to remove EOCs.Therefore,it is urgent to develop the remediation technology of EOCs which can adapt to the special environment of landfill leachate-contaminated groundwater.This paper removes EOCs from landfill leachate-contaminated groundwater by using the technology that combines Advanced Oxidation Processes(AOPs)and Permeable Reactive Barrier(PRB).The main research contents and conclusions are as follows:(1)This research systematically studied the efficiency and mechanism of pyrite activated peroxysulfate(PDS)system,pyrite activated peroxysulphate(PMS)system and pyrite activated hydrogen peroxide(H2O2)system for Ibuprofen(IBU)degradation.Pyrite can activate PMS,PDS and H2O2 to the reactive oxygen species(ROS),which has high oxidation potential and can degrade IBU efficiently.The dosage of oxidizer and pyrite,initial p H and temperature are important factors affecting the oxidation efficiency of the AOPs.Under the same dosage of oxidant,the oxidation efficiency of pyrite activated PMS system is the highest and the p H range of the system is wide.By comparing the characterization results of pyrite before and after reaction,we found that the reductive sulfur in pyrite can promote the reduction of Fe(II)/Fe(III)in the system,thus improving the activation efficiency of oxidant.(2)The effect of Cl-and NH4+-N on the degradation of IBU by pyrite activated PMS system was studied.Cl-can react with SO4·-、HO· and PMS to form reactive chlorine species(RCS),while NH4+-N can react with RCS quickly,thus indirectly consuming PMS and reducing the degradation efficiency of IBU.The time of pyrite participating in the activation reaction is an important control condition for the degradation of EOCs by pyrite activated PMS system.Increasing the time of pyrite participating in the activation reaction can reduce the concentration of RCS,and can reduce the consumption of NH4+-N to oxidizer,and then can improve the degradation effect of AOPs on IBU.However,if the time is too long,the effective utilization of oxidant will be reduced,and the degradation of IBU will be decreased too.(3)The mechanism of convective migration of IBU in a one-dimensional PRB reactor filled with pyrite was analyzed.The migration of IBU can be retarded by the characteristics of porous media and fluid,such as the distribution of seepage channels,surface adsorption of pyrite,surface oxidation of pyrites,seepage velocity,and co-existing pollutants.Furthermore,the numerical model inversion shows that there are flow regions with connected pores and non-flow regions without connected pores in the reaction column of the permeable reaction wall.The migration of IBU in the column is affected by convection,mechanical dispersion and molecular diffusion.The adsorption saturation of IBU in the reaction column cannot be achieved instantaneously under various retardation.IBU is adsorbed on the surface of pyrite in the main flow channel in porous media at first.Then,under the diffusion driven by concentration gradients,IBU is replaced and transferred in the pores of the local low flow velocity region and the non-flow region,and finally slowly reaches adsorption saturation.(4)The removal efficiency of EOCs from groundwater by heterogeneous advanced oxidation coupled with PRB was studied based on a one-dimensional PRB reactor.The ROS produced by PMS will attack IBU in the flowing region first,then the non-activated PMS will enter the non-flowing region by diffusion,and oxidize the IBU immediately after activation.The increase in oxidant dosage and Hydraulic Retention Time(HRT)will also affect the utilization of oxidants.Because porous media can block the migration of PMS and ROS,the increase in oxidant dosage and Hydraulic Retention Time(HRT)will also affect the oxidant utilization.Without changing the value of HRT,the time of pyrite participating in the activation reaction can be controlled by adjusting the proportion of pyrites in the fillers,thus controlling the negative effect of co-existing Cl-and NH4+-N on the removal of EOCs.In addition,the coupling system has a good mineralizing effect on EOCs such as diclofenac acid(DCF),bisphenol A(BPA)and ciprofloxacin(CIP).The intermediate products produced by the coupling system for degrading DCF,BPA and CIP have high biodegradability.The coupling system is universal for the removal of EOCs.(5)The TOC in landfill leachate-contaminated groundwater was treated by the coupling system,of the Pyrite/PMS and PRB.At the same time,the change in the concentration of NH4+-N and other anions in contaminated groundwater was analyzed to control the risk of secondary pollution after the oxidation reaction.The results show that pyrite/PMS coupled with PRB technology can effectively remove TOC from groundwater polluted by leachate.And the three-dimensional fluorescence analysis showed that the coupling system has degraded most of the refractory organic compounds into small molecules,which can effectively improve the biodegradation potential of organic compounds in the effluent.HRT,pyrite ratio and PMS dosage are the factors influencing the removal of TOC from the landfill leachate-contaminated groundwater.When the HRT was 15 min,the proportion of pyrite VPy:VQs=2:8,and the dosage of PMS was 10 g/L,the coupling system could remove TOC effectively and reduce the negative effects of the oxidation reaction. |
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