Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6e. Surfactant-Enhanced Remediation

Formatted Title:

Enhanced Remediation of LNAPL-Contaminated Heterogeneous Aquifers Using Polymer-Alcohol Emulsions

Background/Objectives:

Environmental pollution, notably soil contamination, is one of the urgent problems at present. Light refined petroleum products (gasoline, diesel, engine oil, etc.) which represent light non-aqueous phase liquids (LNAPL) are among the most widespread environmental pollutants. Injecting non-Newtonian fluids such as aqueous polymers presents a significant industrial application interest for in situ remediation of contaminated soil, especially for aquifers with significantly high permeability and strong heterogeneity. However, after flushing with the polymer solution, there will still remain some LNAPL ganglia trapped in pore space that cannot be mobilized anymore. In addition, there are some limitations on the use of high-viscosity fluids. For instance, injecting a high-viscosity polymer solution during soil remediation may increase the injection pressure, leading to injection difficulties or soil uplift. Consequently, developing eco-friendly, sufficiently viscous, and biodegradable fluid is highly in demand. Therefore, in this study, we show how the injection of polymer-surfactant-alcohol emulsion can improve the recovery of residual LNAPL (here diesel fuel) in porous media.

Approach/Activities:

In this study, we prepared a new formulation using biopolymer xanthan gum (XG), an eco-friendly surfactant sodium dodecyl sulfate (SDS), and water-insoluble biodegradable alcohol “1-pentanol”. This mixture forms a stable emulsion in which the alcohol is dispersed in an aqueous solution. Batch experiments were conducted in small glass vials to test the mechanisms of alcohol partitioning in the presence of aqueous and diesel phases. To evaluate the performance of the emulsion, the recovery of diesel was tested in one-dimensional 30 cm long silica sand-pack columns (with low and high permeabilities). The 1D column experiments consider different fluid injection methods such as direct and post-injection. The concentration of diesel fuel in the effluent was measured using refractive index analysis. Furthermore, the effectiveness of this emulsion will be assessed using a confined 2D tank at the decimeter scale to test diesel recovery in multilayer systems (i.e., heterogeneous media).

Results/Lessons Learned:

Batch experiment results demonstrated that water-insoluble 1-pentanol in the presence of aqueous and diesel phases promotes partitioning into the diesel phase. As a result, swelling in the volume of the diesel phase was noted, which is typical for the LNAPL mobilization mechanism. Moreover, when 1-pentanol was mixed with XG-SDS solution, it formed stable cloudy emulsions. Further, we studied the direct injection of XG-SDS-1-pentanol emulsion (at 50% alcohol content in the mixture) for diesel removal in the 1D column experiments. The results showed a 99.9% removal of diesel for a high-permeable sand-pack column. Conversely, the recovery efficiency from post-injection of XG-SDS-1-pentanol emulsion improved from 80% to 93.8% after primary flushing with only XG solution. To achieve higher diesel removal during post-treatment, it is important to inject an emulsion with a higher viscosity than the XG solution used in the primary flushing to ensure a stable displacement. Experiments on low-permeability 1D columns are still in progress to evaluate the diesel removal efficiency of the XG-SDS-1-pentanol emulsion. Further, the performance of this emulsion will be evaluated in a heterogeneous 2D tank consisting of both high and low permeability layers.

In conclusion, utilizing a mixture of swelling alcohols and a polymer solution is an effective approach to enhance the recovery of residual diesel in heterogeneous porous media. The combination of a viscous shear-thinning emulsion and a “swelling” mechanism improves the flushing process.

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