Compatibility of surfactants with activated-persulfate for the selective oxidation of PAH in groundwater remediation

Abstract

Surfactants foam technology can improve the in situ remediation of hydrophobic organic contaminants by enhancing their solubility and the delivery of remediation chemicals. However, the presence of surfactants may impair the effectiveness of the selective oxidation of those contaminants. To tackle the issue, kinetics and selectivity of phenanthrene (PHE) oxidation in aqueous suspensions and its affecting factors including surfactant concentration (CS) and nature, temperature and persulfate (PS) concentration were studied. Significant differences in selectivity were observed between surfactants, reflecting Coulomb interactions with the anionic oxidizers. Lauryl Betaine (LB) stood out as the most compatible surfactant for PHE oxidation in presence of thermally activated PS. However, for PHE oxidation selectivity still dropped from 160 to 0.7 in the absence of LB and at 200 times its critical micellar concentration (CMC), respectively. Raising the reaction temperature accelerated significantly the PHE degradation. However, the selectivity for PHE degradation was minimal at 40°C, because of temperature-dependence of the CMC. Reaction by-products including phenanthrenequinone, diphenyl dicarboxylic acid and phthalic acid were observed. The degradation kinetics of 2–5 rings polycyclic aromatic hydrocarbons (PAH) was monitored in presence of micelles of LB. It revealed a slight increase of the rate constant with the molecular size. Oxidizer accessibility to protected PAH increases with the latter.