Study On Migration And Transformation Law Of Toluene In Vadose Zone And Numerical Simulation

Petroleum is the main energy source for the development of today’s society,and the petroleum industry is also the core industry of my country’s social and economic development.Refining and chemical companies play an important role in crude oil refining.For historical reasons,some of my country’s refining and chemical companies built their plants earlier,and the anti-seepage facilities and control measures of underground structures(sewage pipes,sewage tanks,accident pools,etc.)in the plant areas are not as complete as the new refineries at this stage.Affected by time and external corrosion,the buried facilities in the plant itself are at risk of leakage.Because the leakage of buried facilities is concealed,once a leak occurs and is not repaired in time,the leaked pollutants will pollute the vadose zone and groundwater of the plant.Vadose zone is an important channel for pollutants to enter aquifers.At present,in the domestic groundwater environmental assessment project,the role of vadose zone is mostly ignored,and pollutants enter the groundwater aquifer directly,and pollutant components are rarely considered in the aquifer.The migration and transformation process in the belt.Therefore,studying the migration and transformation process of toluene in the vadose zone is of great significance for protecting the groundwater environment.This thesis takes the site of a refining and chemical company in Northwest China as the research area,and selects the characteristic pollutant toluene of the petrochemical company as the research object.Based on the comprehensive analysis of existing materials,the parameters required by the numerical model are obtained through indoor experiments,combined with the Hydrus software for toluene The migration and transformation process in the vadose zone is predicted.This research not only provides data support for the migration and transformation of toluene in the vadose zone,but also provides a theoretical basis for the protection and treatment of groundwater pollution.Through indoor experiments and numerical simulations,this article mainly obtains the following research results:(1)The adsorption experiment shows that the adsorption process of the two soils is instantaneous adsorption.The adsorption equilibrium time of toluene by sandy miscellaneous fill and silty clay is about 240 min and 150 min,respectively,and the maximum adsorption capacity is 11.82mg/Kg and 17.54mg/Kg respectively.The isothermal fitting curve of sandy soil conforms to the Langmuir model Cs=2.42Cw/(1+0.166Cw),and the isothermal fitting curve of silty clay conforms to the Freundlich model Cs=0.824Cw0.633.When other conditions are the same,the adsorption capacity: silty clay> sandy mixed fill.(2)Toluene is mainly volatilized in the sandy layer,and microbial degradation is weak;toluene is mainly degraded by microorganisms in the silty clay layer.(3)Use the Hydrus software to construct a solute transport model,correct the experimental parameters through the indoor leaching experiment,and verify the model with the indoor soil column test data.The model prediction results and the experimental data have a high degree of fit,indicating that the established The model can better describe the on-site situation.(4)Use Hydrus-1D and 2D software to predict the downward migration of toluene at the leak point.The simulation results show that when there is accumulated water in the vadose zone due to leakage,whether it is continuous pollution or short-term pollution,toluene will quickly enter the aquifer and pollute the groundwater;toluene migrates vertically in the vadose zone.Mainly,the lateral migration is weak;under the conditions of rainfall and evaporation,toluene is mainly trapped in the sandy soil layer,and it is difficult to enter the silty clay layer.Under the action of microbial degradation and volatilization,the concentration of toluene will gradually decrease,so aeration The migration of pollutants in the belt is greatly affected by the local climatic conditions.Therefore,the relevant departments of refining and chemical enterprises still need to increase the maintenance of buried sewage facilities to reduce the risk of pollutant leakage and prevent harm to the site medium and groundwater environment.This article provides a scientific basis for the protection of soil and groundwater resources in the study area.