Enhanced remediation of a real HCH-polluted soil by the synergetic alkaline and ultrasonic activation of persulfate

Abstract

The desorption of hydrophobic organic compounds (HOCs) and limited mass transfer in soil systems is a significant challenge for efficient soil remediation by oxidation treatments. The utilization of sonochemistry is a promising technology to enhance the decontamination of HOCs-polluted soils. In this work, ultrasound (US) was coupled to NaOH for activating persulfate (PS) to enhance the remediation of a real soil polluted with hexachlorocyclohexanes (HCHs) (ΣHCHs = 404 mg kg−1). Batch experiments (mass aqueous/soil ratio, VL/WS = 2) were performed to evaluate the effect of US on HOCs desorption and oxidation. Moreover, the influence of US power (0–245 W, corresponding to 0–91 W L-1 of US power density) and the initial oxidant concentration (CPS = 10–60 g L-1) on pollutants abatement, dechlorination degree, and oxidant consumption have been studied. Scanning electron microscopy (SEM) images verified that the US facilitates the breakdown of soil aggregates, enhancing the desorption of trichlorobenzenes (TCBs) (generated from HCHs alkaline hydrolysis) from the soil. Moreover, their subsequent oxidation is favouring because of higher radical species concentrations and the temperature rise. An increase in the US power up to 165 W accelerates the production rate of radicals, improving the pollutants’ degradation. The difference between pollutant oxidation and dechlorination decreases with increasing US power, associated with a lower concentration of intermediate chlorinated compounds. In the same way, the initial oxidant concentration plays a fundamental role in the remediation treatment. At the selected operating conditions (CPS = 60 g L-1, NaOH/PS = 2, 165 W), a pollutants degradation and dechlorination of 0.94 and 0.74, respectively, were achieved in just 3 h of reaction time.