Oxidative degradation of polycyclic aromatic hydrocarbons in contaminated industrial soil using chlorine dioxide

Abstract

In situ chemical oxidation can be used to remediate soils contaminated with polycyclic aromatic hydrocarbons (PAHs). However, typical oxidation systems are limited by the acidic environment needed for Fenton reactions, cost and soil effects of activated persulfate, and large pores required for ozone or selected oxidation by permanganate. Chlorine dioxide (ClO2) is an environmentally friendly strong oxidant that is highly reactive with PAHs and produces limited halogenated byproducts. In this study, the kinetics, products, and mechanisms of PAH degradation in industrial soil using ClO2 were investigated. The degradation rate was approximately 84.24% for 0.90 mol kg−1 of ClO2; it increased with ClO2 concentration and temperature had little effect. The degradation process was divided into quick (<1h) and slow (1–48 h) reaction stages. PAH removal was significantly inhibited at higher pH levels, but > 70% of the PAHs were degraded at a typical soil pH of 5.0–7.0. Chemical pretreatment is favorable for PAH removal during ClO2 oxidation and the degradation rate was passively correlated with the desorbing fraction of the PAHs in the soil. Quenching experiments indicated that HOCl was the most important active species responsible for degradation. Among five representative PAH congeners, the degradation products of anthracene, phenanthrene, and benzo[a]pyrene were all oxygenated products. However, the degradation product of pyrene was the Cl substitution product and fluoranthene oxidation produced ring rupture oxygenated transformation and Cl substitution products. The mechanisms of PAH degradation by ClO2 oxidation include one-electron transfer, HOCl as a second oxidant, and •OH participation.