Parametric analysis of the operation of a non-thermal plasma reactor for the remediation of NAPL-polluted soils

• NAPL degradation by DBD plasma depends on air flow rate and applied voltage.
• NAPL oxidation products in soil are independent of air flow rate and applied voltage.
• NOx and O3 are the main gaseous plasma active molecules.
• NOx concentration increases with air flow rate and applied voltage.
• NAPL is completely oxidized to COx at low air flow rate, minimizing VOCs’ release.

A new metallic plane-to-grid dielectric barrier discharge (DBD) reactor was designed for the efficient remediation of polluted soils at atmospheric pressure. A synthetic NAPL composed of equal mass fractions of n-C10, n-C12 and n-C16 was mixed with soil at a high initial NAPL concentration equal to 100 g/kg-soil. The NAPL was removed after a few minutes of plasma treatment, depending on NAPL composition, air flow rate and applied voltage. At 28 kV peak-to-peak, the NAPL was completely removed from soil very fast (1–3 min) for a flow rate ranging from 1.0 to 4.0 L min−1. At a constant flow rate (i.e. 2.0 L min−1) the NAPL removal efficiency was 99%, 61.4% and 18.8% for applied voltage 28, 25 and 22 kV, respectively, after 2 min of plasma treatment. NOx and O3 were detected as the main gaseous plasma active molecules, with the NOx concentration being an increasing function of the applied voltage and air flow rate. The intermediates of the NAPL oxidation in soil were identified as ketones and alcohols regardless of the experimental conditions (i.e. air flow rate and applied voltage). The temperature in the vicinity of the soil found to be varied in the range 285–340 °C stimulating the evaporation of NAPL. The total carbon content of initial NAPL detected in exhaust gas in the form of COx increased from 25.5% to 99% when the air flow rate decreased from 4.0 to 0.15 L min−1, minimizing the release of VOCs and environmental fingerprint. Except of the pollutant remediation efficiency and electric energy consumption, the process sustainability associated with the composition of exhaust gases should be taken into account when designing DBD plasma reactors and determining the optimal operational window.

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