Electrokinetic delivery of anodic in situ generated active chlorine to remediate diesel-contaminated sand

Abstract

Electrokinetic in situ chemical oxidation (EK-ISCO) is an innovative and effective method for removing petroleum contaminants from soil. However, the high cost of exogenous oxidants is one of the main drawbacks of this technology. In this research, a new approach for the electrokinetic (EK) delivery anodic in situ generation of an oxidant was designed with the aim of solving this problem. Six EK experiments lasting 15 d with different electrolytes (NaCl or NaNO3) and different voltage potentials were performed in order to evaluate the feasibility of this approach. It was found that active chlorine was produced by a dimensionally stable anode and a NaCl solution, and can contribute to remediate sand spiked with diesel fuel (10 g/kg) during EK-ISCO. The obtained results showed that an increase in NaCl electrolyte concentration (from 10 to 40 g/L) increases the maximum concentration of active chlorine in the aqueous sand matrix (from 12.5 to 30 mmol/L). The diesel removal efficiencies were increased from 33% to 44% for 1 V/cm and from 43% to 67% for 2 V/cm, respectively, by using 20 g/L NaCl compared to using 20 g/L NaNO3. Vial tests also confirmed that the anodic in situ generated active chlorine in the electrolyte solution had the effect of oxidizing alkanes of diesel. The products had a higher solubility due to the inclusion of polar functional groups. Under optimal conditions, the energy consumption for removing 1% of contaminants was approximately 2 k Wh/ton. Consequently, the EK delivery of anodic in situ generated active chlorine can be considered as a new cost-effective method for removing organic contaminants from porous media.