| Chongqing has a large number of landfills and occupies an important position in the way of waste disposal.Domestic garbage is often collected and transported to the landfill for stacking treatment.During the long-term stacking and squeezing process,the domestic garbage is easily leached by rainwater to produce high-concentration leachate.If abnormal working conditions occur,the landfill If the anti-seepage system of the site is damaged or fails,the groundwater environment downstream of the landfill will be seriously threatened.This article takes a domestic waste landfill in the mountainous area of Chongqing as an example to conduct a detailed hydrogeological survey in the study area and combine related hydrogeological experiments to clarify the geological structure and lithological characteristics of the study area.Monitor the water quality and water level in the two phases of dry and high in the study area to provide data support for the later water quality evaluation and the establishment of groundwater model.Select zero-valent iron,zeolite and a mixed medium（volume ratio of 1:1）for the PRB（Permeable Reactive Barrier）filling medium screening experiment.According to the removal effect of the reaction medium on the target pollutant NH3-N,it is the groundwater in the study area Rehabilitation provides a reliable experimental basis.By analyzing the hydrogeological conditions,groundwater simulation and experimental results in the study area,the following conclusions are finally drawn:（1）Hydrogeological survey was conducted in the study area,and the collected groundwater was analyzed for water quality.It was found that the chemical type of groundwater in the study area was mainly HCO3-Ca type.The standard indicates that the groundwater quality in the study area is good.There are three types of groundwater in the study area,which are loose rock pore water,clastic rock fissure water and carbonate karst fissure water.Among them,the carbonate karst fissure water aquifer group is distributed in most of the study area Within the scope,it is the main aquifer of groundwater.（2）Arcgis software was used to extract DEM digital elevation data in the study area,and Visual modflow software was used to visualize the mountainous valley landscape in the study area.Modeling the groundwater flow in the study area,it was found that the overall flow direction of groundwater in the study area was northeast-southwest,which was consistent with the surface water flow direction in the study area,and collected downstream through the valley area.（3）According to the main location of the landfill leachate leakage,the landfill area of the landfill and the area of the leachate adjustment tank are determined to be the main sources of pollution in the study area,under the most unfavorable conditions（Failure of anti-seepage membrane at the bottom of the landfill and 5%damage to the bottom of the leachate conditioning tank）The migration process of COD and NH3-N,the simulation results show that the pollutant leakage gradually diffuses to the downstream area of the valley over time,which is consistent with the direction of groundwater flow,the diffusion distance is getting farther and farther,and the diffusion area is also getting more and more.The bigger.At the end of the simulation time of 20 years,the pollution plume spread to the farthest point,the concentration of COD and NH3-N reached the maximum,the concentration of COD reached 600mg/L,30 times exceeded,and the concentration of NH3-N reached 60mg/L,120 times exceeded.The maximum COD exceeding standard distance is 1112m,and the maximum exceeding standard area is0.35km2.The maximum over-range distance of NH3-N is 1585m,and the maximum over-area area is 0.46km2.The diffusion of pollutants has an impact on the downstream groundwater environment,but since the farthest point is predicted to be still a certain distance away from the Yangtze River,it should not affect the water quality of the Yangtze River during the simulated forecast period.（4）Select NH3-N as the target pollutant,conduct laboratory preparation of an initial concentration of 6mg/L NH3-N solution,and design to use zero-valent iron,zeolite,and zero-valent iron+zeolite（volume ratio 1:1）as the reaction medium.PRB filled media screening experiment to calculate the removal rate of NH3-N in different reactors at different times.The experimental results show that:zeolite>zero-valent iron+zeolite>zero-valent iron,and the average removal rate of zeolite to NH3-N is 90.3%The average removal rate of zero-valent iron to NH3-N is 68.7%,and the removal rate of zero-valent iron+zeolite to NH3-N is between the two,80.8%.Comparing the experimental results,it is found that the removal effect of zeolite on NH3-N is better than that of zero-valent iron and the combination of both.This is because zeolite and zero-valent iron are also used as adsorption media,but zeolite has a larger specific surface area It makes the contact with NH4+in physical adsorption and exchange better,and the reaction is more thorough. |
