Enhanced in situ remediation of naphthalene-contaminated soil by alkaline activated persulfate using acetonitrile as assistant solvent

Abstract

Although the advanced oxidation process based on persulfate (PS) is an attractive approach due to its high efficiency and environmental friendliness, the difficult degradability and low solubility of naphthalene (NAP) hinder its practical application for in situ chemical remediation of contaminated sites. Herein, this study reported that alkaline activated PS with acetonitrile (ACN) as assistant solvent for in-situ remediation of NAP contaminated soils to improve the removal efficiency. The results showed that the degradation rate of NAP in contaminated soil was up to 36.7 % on the 1st day in the presence of C_PS = 382 mmol L^-1, and pH = 12, which was significantly higher than the NAP removal rate without the addition of ACN (8.6 %) under the same conditions. This indicated that the addition of ACN promoted the solubility of organic pollutants in the liquid phase and improved its degradation efficiency. The NAP removal rate (the 21st day) was up to 97.5 %. ESR tests and free radical quenching experiments indicated that SO₄^•−, ·OH and ¹O₂ were the dominant active species. The degradation mechanism of NAP mainly involved hydroxylation, decarboxylation, and ring opening reactions. The toxicity assessment using the Toxicity Estimation Software Tool (T.E.S.T.) and bioluminescent bacteria assays showed that NAP could eventually be degraded into less toxic degradation intermediates. In summary, this study confirmed the suitability of ACN enhanced alkaline activated PS system for the degradation of organic pollutants and provided some new ideas for the in situ large-scale remediation of organic contaminated sites.