Combined alkaline-activated persulfate and surfactant for remediation of diesel-contaminated soil in permafrost environments: laboratory study

Abstract

Diesel is the primary energy supply source and the main source of contamination in the Arctic and sub-Arctic, posing challenges for remediation due to the permafrost presence, limited operational time window, lack of treatment facilities, and a sensitive ecosystem. This research aimed to develop a remediation technology applicable to a permafrost environment. Two remediation methods were evaluated: in-situ chemical oxidation (ISCO) using persulfate (PS) and calcium peroxide (CP), and surfactant-assisted in-situ chemical oxidation (S-ISCO), which combines the oxidants with a surfactant mixture. The inclusion of surfactant in the oxidant solution led to a consistent and steady decomposition of PS, a gradual and a progressive non-exothermic oxidation reaction, and enhanced the diesel transfer from soil to the aqueous phase. However, it can react with the oxidant, reducing the likelihood of the oxidant-diesel reaction. The evaluation of diesel concentration indicated that the surfactant presence could enhance the total diesel removal efficiency (in comparison to oxidant alone), although excessive surfactant reduced the oxidant’s effectiveness. A challenge in activation of PS by CP was generation of cement-like byproducts of CP hydration that could potentially restrict the diesel-oxidant interaction. However, insoluble byproducts elimination (by filtration), and solution adjustments (pH, PS, and CP concentration) proceeded with ˃ 99% and 90.8% diesel removal (initial concentration of 5000 mg/kg) after 8 weeks of ISCO and S-ISCO at ambient temperature. In the sub-Arctic soil treatment at 4.2 °C, 89.4 and 88.3% of diesel mass removal resulted in ISCO and SISCO, respectively, which are about 2 times higher than natural attenuation (41.6%).