Gravity-driven remediation of DNAPL polluted aquifers using densified biopolymer brine solution

Abstract

Polymer solutions aid DNAPL (Dense Non Aqueous Phase Liquid)-contaminated soil remediation but are impacted by gravity and viscous forces. This study assesses the interplay between buoyancy and viscous forces in influencing the distribution of DNAPL and the invading phase, by introducing a densified brine (NaI) biopolymer (xanthan) solution as remediation fluid. A matrix of experiments was conducted, encompassing rheological measurements, multiphase flow tests in 1D-columns and 2D-tanks. Numerical modeling was used to assess polymer and DNAPL propagation under different conditions. NaI addition maintains xanthan's shear-thinning yet lowers mid-range shear viscosity 2.6 times. Confined column tests show similar 89 % performance for viscous polymer solutions regardless of density. Unconfined tests mimicking real sites reveal non-densified viscous polymer solution yield mere 0.09 recovery due to density-driven flow. Densified polymer attains radial invasion, boosting recovery to 0.46 with 1.21 aspect ratio. Numerical simulations aligned with experiments, suggesting a near-zero gravity number is necessary to prevent density-driven flow problems. The multiphase flow experiments in confined multilayer system are performed and using the numerical modeling the effects of the permeability contrast and dimensions of the layers on the shape of front are analyzed.