Non-aqueous phase liquid-contaminated soil remediation by ex situ dielectric barrier discharge plasma

Non-thermal dielectric barrier discharge plasma is examined as a method for the ex situ remediation of non-aqueous phase liquid (NAPL)-contaminated soils. A mixture of equal mass concentrations (w/w) of n-decane, n-dodecane and n-hexadecane was used as model NAPL. Two soil types differing with respect to the degree of micro-heterogeneity were artificially polluted by NAPL: a homogeneous silicate sand and a moderately heterogeneous loamy sand. The effect of soil heterogeneity, NAPL concentration and energy density on soil remediation efficiency was investigated by treating NAPL-polluted samples for various treatment times and three NAPL concentrations. The concentration and composition of the residual NAPL in soil were determined with NAPL extraction in dichloromethane and GC-FID analysis, while new oxidized products were identified with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The experimental results indicated that the overall NAPL removal efficiency increases rapidly in early times reaching a plateau at late times, where NAPL is removed almost completely. The overall NAPL removal efficiency decreases with its concentration increasing and soil heterogeneity strengthening. The removal efficiency of each NAPL compound is inversely proportional to the number of carbon atoms and consistent with alkane volatility. A potential NAPL degradation mechanism is suggested by accounting for intermediates and final products as quantified by GC-FID and identified by ATR-FTIR.