Remediation of Coal Tar–Contaminated Soil by Smoldering Combustion Using Vegetable Oils as Supplemental Fuel

Abstract

This study explored the remediation of coal tar–contaminated sand with smoldering combustion using vegetable oil as supplemental fuel. In this work, bench-scale column experiments were conducted one factor at a time to identify the minimum concentration limit of coal tar and the feasibility of vegetable oil as supplemental fuel. A range of key parameters including various concentrations of vegetable oil (10,000–50,000 mg/kg), types of vegetable oil (sunflower, soybean, and corn oils), and oil to coal tar mass ratios that affect smoldering combustion were examined in detail. Results demonstrated that exceeding 80,000 mg coal tar in 1 kg sand caused smoldering exceeding 630°C. The posttreatment coal tar concentration in treated sand was 648 mg/kg, indicating more than 99% initial coal tar was destroyed. Further, corn oil was a relative suitable supplemental fuel, which possessed higher average peak temperature and removal efficiency. To be specific, the sum of the concentration of corn oil and coal tar reaching 50,000 mg/kg was found to be a necessary requirement to determine whether smoldering combustion occurred or not; in addition, the content of coal tar was not less than 20,000 mg/kg. Overall, this study indicated that smoldering with injection of vegetable oil has potential to be effective in situ remediation application for low-concentration coal tar–impacted sand (<80,000 mg/kg).