Dielectric barrier discharge plasma used as a means for the remediation of soils contaminated by non-aqueous phase liquids

Abstract

A plane-to-grid dielectric barrier discharge (DBD) reactor operating with air at atmospheric pressure was used to investigate the removal of non-aqueous phase liquids (NAPLs) from soil layers. A mixture of n-C10, n-C12 and n-C16 was used as a model NAPL that polluted the soil at a very high initial concentration (100,000mg/kg-soil). The effect of treatment time, energy consumption, and soil thickness on the NAPL removal efficiency was investigated, the plasma active species were identified, and the macroscopic gas temperature was determined. The NAPL remediation efficiency found to be as high as 99.9% after 60–120s of plasma treatment, depending on soil thickness. The energy density required to remediate completely the NAPL was about 600J/g-soil and was practically independent of the soil thickness, indicating that the DBD-based plasma has the potential to become a highly cost-effective technology for the remediation of NAPL-contaminated soils. N2+, N2∗, NOx and O3 were identified as plasma-induced reactive species, a maximum gas temperature close to 300°C was recorded, and the total carbon detected in exhaust gases, in the form of CO and CO2, was ca 40% of that contained in the NAPL removed from the soil. The main mechanisms of NAPL removal by plasma found to be the evaporation of organic compounds coupled with their oxidation in liquid and gas phase. Using ATR-FTIR in combination with high-throughput organic profiling analysis by GC–MS, ketones and alcohols were identified as the main intermediate products of alkanes oxidation in soil matrix.