Experimental investigation of cosolvent flushing of DNAPL in double-porosity soil using light transmission visualization

This paper investigates the effect of cosolvent content and flushing velocity on the remediation of dense non-aqueous phase liquid (DNAPL) in double-porosity medium using light transmission visualization technique (LTV). Double-porosity was created using local silica sand and sintered spheres of kaolin, arranged in a periodic manner. The flushing solution consisted of ethanol-water mixtures with various ethanol concentrations ranging from 20% to 65% by volume. The effect of contact time was investigated by changing the flow rates of the flushing solution. The accuracy of the LTV technique was examined by comparing an actual injected volume of DNAPL with the calculated volumes generated from image analysis. The LTV results allowed for the visualization of the DNAPL enhanced dissolution as well as its mobilization. While the removal efficiency increased with the increase of the ethanol content, the removal efficiency was negatively affected by the velocity of flushing solution. Image analysis revealed that the highest DNAPL removal efficiency of 92% was obtained at 65% ethanol content and low flushing velocity. This efficiency decreased to 85%, in the case of high flushing velocity. Overall, this study demonstrated that the LTV technique is a viable laboratory tool that can accurately depict enhanced DNAPL dissolution and DNAPL mobilization due to cosolvent flushing.