Remediation of real soils polluted with pesticides by activated persulfate and surfactant addition

Abstract

The existence of soils contaminated with organochlorine pesticides represents a serious environmental problem. In this work, a real soil contaminated with hexachlorocyclohexanes (ΣHCH = 373 mg kg−1), persistent organic pollutants included in the Stockholm Convention, was remediated. Surfactants were used to enhance the pollutants solubilization and activated persulfate (PS) oxidation to degrade the pollutants. Solubilization experiments were performed to evaluate the effect of surfactant (sodium dodecyl sulfate (SDS), Emulse-3® (E3) and Tween-80® (T80)), pH, reagents addition order and concentration (Csurfactant = 0–10 g L−1, CNaOH = 0–13.5 g L−1). Surfactants selection was performed attending to their ability to solubilize chlorinated organic compounds (COCs). The use of surfactants improved COCs solubilization, especially at pH > 12; conditions at which HCHs hydrolyze to trichlorobenzenes (TCBs), with higher solubility. The higher the surfactant concentration, the higher the COCs concentration in the emulsion. COCs solubilization of 83 % and 89 % were achieved in three surfactant consecutive cycles at highly alkaline conditions using SDS and E3, respectively (T80 was unstable). The resulting emulsions were treated by PS activated by alkali and intensified by temperature. COCs conversion of 30 % and 96 % were achieved when treating E3 and SDS-emulsions (72 h), respectively, highlighting the suitability of SDS for the integrated process.