Remediation of HCHs-contaminated sediments by chemical oxidation treatments

The intensive use of organochlorine pesticides, such as lindane (gamma-HCH), and the inadequate management of their wastes, is a huge environmental problem. The lindane production during the last century has generated huge volumes of solid wastes of other HCH isomers, causing hot points of soil and groundwater contamination. The soil treated in this work was obtained from a landfill located in the nearby of an old lindane factory, containing alpha HCH and beta-HCH as main contaminants. This study addresses for the first time the application of different chemical oxidation treatments, viz. Fenton process (H2O2 + Fe), persulfate (PS) activated by temperature (20 and 40 degrees C), by alkali (NaOH) and by the combination of alkali and temperature (NaOH, 40 degrees C) for the remediation of HCH-polluted soils (C-HCHs = 155 mg kg(-1)). The intrinsic characteristics of the soil (high carbonate content) led to high consumption of H2O2 (X-H2O2 approximate to 100% at 24 h) and complete iron precipitation, making unappropriated the application of the Fenton process. The efficiency of thermal PS was limited by the low solubility of HCH isomers in the aqueous phase, the high refractoriness of these compounds towards oxidation, and the presence of the contaminants in the form of particulate matter. After 25 days of treatment, a conversion of chlorinated organic compounds (COCs) of 50% was achieved (V-L/W-soil = 2, C-PS = 40 g L-1, 40 degrees C), whereas the application of PS activated by alkali and temperature (40 degrees C) led to promising results. At pH above 12, HCHs were dehydrochlorinated to trichlorobenzenes, which were further oxidized by hydroxyl radicals. The hydrolysis rate of beta-HCH was the limiting step of the process, and it was favored by increasing the reaction temperature. At 40 degrees C, a conversion of COCs above 95% was achieved (V-L/W-soil = 2, CPS = 40 g L-1, C-NaOH = 13.5 g L-1, 14 days) with low oxidant consumption (X-PS = 30%). (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The intensive use of organochlorine pesticides and inadequate waste management pose a huge environmental problem. This study addressed the application of different chemical oxidation treatments for the remediation of HCH-polluted soils. Results showed that the combination of hydrogen peroxide and persulfate activated by alkali showed promising results in purifying contaminated soil.