The investigation of fluorene removal with chemical oxidation after soil washing

Abstract

Soils contaminated by polycyclic aromatic hydrocarbons (PAHs) pose potential risks to human health and the environment. In this study a combined physical-chemical treatment involving soil washing and advanced oxidation was investigated. A fluorene contaminated loamy soil was treated with a washing solution containing a non-ionic surfactant polyoxyethylene 20 cetyl ether (Brij 58). The washing solution containing fluorene (48.5-54.3 mg/L) was afterwards treated with Fenton and electro-Fenton oxidation. The conventional Fenton oxidation results revealed a fast removal of fluorene (>84%) within the first 15 min. COD removal representing the general destruction of washing solution remained at about 10%, but increased to 81% when the reaction time was increased to 480 min using 2% hydrogen peroxide (H2O2). The corresponding fluorene removal was about 98%. The pseudo-second order rate constants observed for fluorene (0.0016 L/mg min) and COD (1.5 x 10(-6) L/mg min) oxidation supported these results by indicating to a faster oxidation of fluorene. Increase in the H2O2 concentration similarly influenced the oxidation of COD rather than fluorene. The COD removal efficiency increased from 43% to 97% when the H2O2 concentration was increased from 2% to 10% for a treatment time of 120 min. Electro-Fenton oxidation studies with a current density of 15 mA/cm(2) and an electrolyte conductivity of 2 mS/cm revealed even better results enabling a reduction in reaction time. 60 min of reaction time with 2% H2O2 represented removal efficiencies of 98% and 91% for fluorene and COD, respectively.