A Two-Dimensional Experimental Study Of DNAPL And Water Interfacial Area In Porous Media

The dense nonaqueous-phase liquid(DNAPL)-water interfacial area in porous media is a key parameter for DNAPL dissolution and interfacial adsorption processes.It is important for the organic contaminant in-situ remediation and pollution risk assessment in groundwater.In the present study,two types of partitioning tracer methods(interfacial partitioning and bulk partitioning)were used in two-dimensional flow cell experiments on the basis of previous one dimensional experiment research.The media was silica sand,and Trichloroethylene was used as representative DNAPL.The primary research content were:(1)comparison and analysis of measured DNAPL-water interfacial areass at DNAPL residual saturation of different experimental dimensions;(2)the relationship between interfacial area with DNAPL saturation,DNAPL mass transfer rates and grain diameter;(3)the effect of conservative tracer(taking Br-as an example)on interfacial area measurement.The results showed that:(1)The measured interfacial area values obtained from the three sets of experiments at residual NAPL saturation of the same kind of sand were 201±14 cm-1,which were 2～3 times of the colume experimental results in literatures.This reflected the influence of the vertical distribution of DNAPL on the interfacial area.Compared with the colume experimental results in literatures,the measured maximum specific interfacial area values from the flow cell experiments were closer to the values obtained in previous field experiments;(2)With in-situ chemical oxidation remediation of Fe2+-activated persulfate,the interfacial area decreased from 206 cm-1 to 37 cm-1,the DNAPL saturation decreased from 1.34%to 0.33%,and the DNAPL mass transfer rates decreased from 0.42 g/PV to 0.05 g/PV.Within the scope of this experiment,a good linear relationship was observed between interfacial areas with DNAPL saturation and mass transfer rates.The linear relations can be used as a simple method for interfacial area estimation and used to perfect the existing forecast model.(3)A total of four silica sands were used in this study:20/30,30/40,40/50 and 80/100.The results showed that the interfacial area,maximum mterfacial area and DNAPL morphology index decreased with the increase of grain sizes,and showed linear relationship with inverse median diameter.Due to the influence of DNAPL vertical distribution,the measured maximum mterfacial areas and DNAPL morphology index for different grain sizes in the flow cell were approximately two orders of magnitude of the values in column experiments of literatures.This reflected the impact degree of the system dimension increase;(4)Based on the analysis of the influence of conservative tracer,the presence of Br-increased the adsorbtion of meida and interfacial area,and the interfacial area increased 10%as a result.The results provided a reference for the study of the effects of other tracer ions.The relationship between aqueous phase-solid phase distribution coefficient Kd value and Br-concentration was Kd=0.00032CBr+0.0798(CBr≤200 mg/L),which can be used for measured Kd value validation.