In-Situ Control of DNAPL Density Using Polyaphrons

Abstract

Once spilled into soils, dense nonaqueous phase liquids (DNAPLs) such as chlorinated solvents migrate deep into the subsurface because of their high density. Their downward migration typically continues until capillary forces balance gravitational forces or until essentially impermeable strata are reached. Efforts to mobilize the DNAPL for remediation purposes risks driving the contaminants deeper, which has spurred research for modifying buoyancy forces in situ. In this paper, a novel means of controlling the density of a DNAPL phase using polyaphrons is presented. Polyaphrons are a class of high internal phase ratio emulsions (HIPREs) that have unusual properties such as indefinite stability and flow properties through porous media. They provide a means of selectively delivering a light organic phase liquid to the vicinity of the DNAPL phase. Upon destabilization of the polyaphron by a polyvalent cation, the light internal phase mixes with the DNAPL to produce a nonaqueous phase of lower density than the original contaminant. The negative buoyancy of the DNAPL can thus be reversed. This approach holds great promise for manipulating DNAPL densities prior to or during remediation treatments.

A numerical study on the coalescence of emulsion droplets in a constricted capillary tube

“…8, whereas droplet coalescence is observed when C 1:1 is increased to 1 M. More importantly, a steep change in h is observed as it approaches the critical value, most likely due to the dominance of the van der Waals force in the absence of strong repulsive forces. The profile of h is also shown for the case where the added electrolyte is assumed to be a 3:3 type and its concentration is 10 −5 M. The curve basically coincides with that where the exterior phase contains 1 M 1:1 electrolyte, indicating that the electrostatic surface force is completely suppressed at such a low concentration of multivalent ions, which qualitatively agrees with the experimental results of Yan et al [20].…”

“…The parameters used in our simulations are different from those in our previous experimental work [20]. The droplet to pore-size ratio in the simulations is relatively large compared to that in the experimental work, which enhances coalescence; on the other hand, the capillary number in simulations is larger by approximately one order of magnitude, which prohibits coalescence.…”

“…To determine the dynamics of the droplets in a constricted capillary tube, one only needs to solve the linearized Stokes equation (19) and (20) along with the ODE (18). Once the boundary values are obtained, the velocity field in the flow domain can be readily calculated.…”

“…Recently, the application of polyaphrons has been extended to subsurface environmental remediation [20], in which case they are used to deliver light hydrocarbon species to manipulate the density of dense nonaqueous phase liquid (DNAPL) contaminants. In this procedure, the coalescence of polyaphrons induced by multivalent counterions appears to be a crucial step before the light hydrocarbon phase can mix with the contaminants and reduce their density.…”

Coupling Aggressive Mass Removal with Microbial Reductive Dechlorination for Remediation of DNAPL Source Zones: A Review and Assessment

“…Plume plunging behavior, however, may be mitigated through the addition of alcohols to the surfactant solution (Kostarelos et al 1998) and careful design of the hydraulic flow regime/control system (Abriola et al 2005). Concerns over downward migration of mobilized DNAPL may be alleviated by using SEAR technologies that reduce DNAPL density in situ before mobilization (Ramsburg et al 2003; Ramsburg and Pennell 2002; Yan et al 2003)…”