Study On The Effect Of Layered Heterogeneous Stratum Interface On The Remediation Of Benzene-contaminated Aquifers By In-situ Air Sparging

With the rapid development of the social economy,the problem of organic contaminant in soil and groundwater is becoming more and more serious.Air sparging?AS?is considered to be one of the most effective methods for removing volatile organic contaminant?VOCs?from aquifers as an in-situ remediation technique.Air sparging has been widely used due to its low cost,easy operation,short remediation time and high efficiency.Based on the research status at home and abroad,layered heterogeneity is a common stratigraphic structure in the actual site.But the research about the influence of aeration parameters on the air sparging and the removal efficiency of contaminant in the layered heterogeneity formation is weak.And there is not enough experimental theory research and analysis,therefore,this article is mainly studying the effects of different media combinations on the aeration parameters and the removal efficiency of contaminant in the layered heterogeneous formation.Benzene was taken as the research object in this experiment and layering simulation by one-dimensional sand column in laboratory,the grain size of the lower medium increases gradually while the sand in the upper layer remains unchanged,studying on the variation of aeration pressure,air saturation and pollutant removal efficiency.The grain size of the upper medium increases gradually with the same sand content in the lower layer,studying on the variation of aeration pressure,air saturation and pollutant removal efficiency.And sudy the influence on removal efficiency of benzene in homogeneous formation compared to the heterogeneo formation to provide a theoretical basis for the application of air sparging technology.The main research results obtained in this study are as follows:1.For layered heterogeneity,the permeability coefficient of the lower medium where the aeration head is located is set to be K₂,the permeability coefficient of the upper medium is K₁,R=K₂/K₁.When R<1,the stratified interface includes upper coarse sand 1,coarse sand 2,coarse sand 3,gravel and lower medium sand.Definition of non-blocking interface based on experimental results.When R>1,the stratified interface includes middle sand in the upper layer and lower coarse sand 1,coarse sand2,coarse sand 3,gravel.Definition of the blocking interface based on experimental results.2.For R<1 non-blocking interface,when the permeability coefficient of layered heterogeneous media is not of the same order of magnitude,there is little difference in removal efficiency of pollutants between upper and lower sand columns.On the premise of the same hydrostatic pressure and aeration flow rate,the initial aeration pressure and stable aeration pressure of layered heterogeneous aquifer mainly depend on the layered heterogeneous underlying media.3.For R>1 blocking interface,when the permeability coefficient of layered heterogeneous media is not of the same order of magnitude,the change of the permeability coefficient of the lower layer will make the concentration of pollutants in the upper part of the sand column increase first and then decrease more obviously.On the premise of the same hydrostatic pressure and aeration flow rate,when the upper medium is medium sand,the initial aeration pressure and the stable aeration pressure gradually decrease with the increase of the size of the lower medium.4.When the permeability coefficient of layered heterogeneous media is in the same order of magnitude,the change of layered condition has little effect on pollutant removal efficiency.5.Under the condition of layered heterogeneity,the airflow enters the high permeability medium from the low permeability medium,and the pollutant removal rate is relatively faster.