Pretreatment of diesel-contaminated hydrophobic soil using surfactant and sodium hexa-metaphosphate (Na-HMP) to improve infiltration of aqueous phase remedial agents in unsaturated soil

Abstract

The remediation of diesel-contaminated hydrophobic soil is difficult due to the inability of aqueous phase remedial agents to infiltrate the soil. This novel laboratory study enhanced the gravity-driven infiltration of water and oxidant solution into the hydrophobic soil by pretreatment. For this purpose, the hydrophobic soil was pretreated (partially liquid saturating) using 0.1% sodium hexa-metaphosphate (Na-HMP) and 0.5% alpha olefin sulfonate (AOS). The diesel-contaminated soil (34,167 ± 560 mg TPH/kg) was partially saturated with 0.5 pore volumes of Na-HMP and surfactant mixture solution. The infiltration experiment of the pretreated soil was conducted by pouring a solution (water/oxidant) provided from the Marriott reservoir over the digital balance. This study did not observe any natural infiltration of water or oxidant reagent into the diesel-contaminated soil. After the pretreatment, the cumulative infiltration of water to the pretreated soil increased to 5.17 cm after 40 min. The natural infiltration occurred due to the dispersion of soil particles and reduction of hydrophobicity by the Na-HMP and AOS, respectively. Widened soil pores were observed after pretreatment using the scanning electron microscopy (SEM) analysis. The infiltration of 5% Na2S2O8 solution was 5.80 cm after 40 min when the diesel-contaminated soil was pretreated with 0.1% Na-HMP and 0.5% AOS. Pretreatment using Na-HMP and AOS can enhance the remediation of highly hydrophobic and low-permeability soils. This finding can provide an insight into enhancing the soil remediation efficiency by increasing the gravity-driven uniform delivery of the remediation agent into the undisturbed soil. Graphical abstract