Remediation of Diesel-Contaminated Aquifers Using Thermal Conductive Heating Coupled With Thermally Activated Persulfate

Diesel fuel contamination of aquifers is a global environmental problem. In recent years, in situ thermal remediation (ISTR) has attracted much attention owing to its advantages of high removal rate and rapid remediation. In this study, the treatment of a diesel-contaminated aquifer with thermal conduction heating (TCH) was studied. And for the purpose of making full use of the TCH residual heat, its combination with in situ chemical oxidation (ISCO) was also investigated. Results show that a maximum total petroleum hydrocarbon (TPH) removal of 70.3% or 81.73% was observed for the TCH treatment of the solid or water phase, respectively, highlighting the possibility of successfully and simultaneously remediating both aquifer phases. The effect of evaporation/boiling plays a major role in final contaminant removal processes. And the water-diesel mixture started co-boiling at 100.3℃ theoretically according to Antoine equation and Raoult’s law. The higher the temperature is, the higher the initial TPH concentration and the larger the removal rate of pollutants. The dosage of persulfate (PS) required by the system became lower with the temperature increasing, and the contribution of oxidation to the pollutant removal became greater, with the proportion of oxidation increasing from 29.05 to 66.87% from 40 to 80 °C. In the 2-D remediation experiment, the area of the heated zone above 80℃ accounted for 71.0% of the whole tank. At the heating time of 180 min, the average aqueous TPH concentration in the tank was about 248.7 mg/L and a lowest concentration of 73.1 mg/L was found around the heating resistance. During the cooling process after TCH, 97.9% of the heated area of the tank was above 30 °C when the heating resistance was turned off for 6 h, which was sufficient to activate PS for removing pollutants. Hence, TCH treatment could be an optimal method for the rapid remediation of diesel-contaminated aquifers, and the combination of TCH and ISCO can not only expand the treatment zone, but also reduce the cost of remediation.