Toward sustainable and cost-effective hydrocarbon remediation: Designing alcohol-efficient oil-in-water emulsions

Abstract

Diesel and other petroleum hydrocarbons contribute to long-term soil pollution, characterized by their environmental persistence, mobility, and risks to groundwater. Alcohol flooding has been investigated for decades as a remediation strategy and has shown promise for hydrocarbon recovery. However, it typically requires high alcohol concentrations (≥50% v/v) in flushing solutions, raising concerns over cost, toxicity, and volatilization. Its efficiency is further constrained in heterogeneous soils by preferential flow, and in unsaturated (vadose) zones, the interplay between gravitational and capillary forces complicates alcohol flooding, limiting its field applicability. This study explores alcohol-efficient oil-in-water emulsions prepared using 1-pentanol (6.25–25% v/v), sodium dodecyl sulfate (5000 ppm), and xanthan gum (1000–2000 ppm) for diesel-contaminated soil remediation. The emulsions were characterized for stability and rheology, and their remediation performance was assessed in one-dimensional sand columns and two-dimensional tanks across saturated and unsaturated conditions, simulating field conditions. A formulation with 2000 ppm xanthan enhanced stability and imparted shear-thinning rheology at low alcohol concentrations, enabling controlled injection. Complete (100%) diesel recovery was achieved using emulsions containing only 6.25% (v/v) 1-pentanol in both saturated and unsaturated 1D systems. In 2D tanks, bottom-center injection promoted uniform radial spreading and complete recovery, as confirmed by imaging and effluent analyses. In vadose zones, the emulsion’s viscosity overcame gravitational and capillary limitations, enabling complete recovery—a performance not attained with other fluids. These findings demonstrate, for the first time, that low-alcohol emulsions can achieve complete diesel recovery in both saturated and unsaturated conditions, providing a cost-effective and environmentally sustainable strategy for hydrocarbon remediation.

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