Combined chemical and biological process for the remediation of soils polluted with organochlorinated pesticides

Abstract

The invention relates to a process for the remediation of soils polluted with organochlorinated pesticides from the category of persistent organic pollutants of the type of hexachlorocyclohexane (HCH) isomers, dichlorodiphenyltrichloroethane (DDT) and derivatives thereof, dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE). According to the invention, the process consists in treating the soils contaminated with organochlorinated pesticides, in stages, ex­situ or on­site, by combining the process of chemical oxidation with hydrogen peroxide consisting of a 5...20 % solution, depending on the contamination degree, or hydrogen peroxide in combination with calcium peroxide, in case of acid soils, in variable doses in the range of 30...1 00 x stoichiometric need, periodically introduced in 1 2 portions, at an interval of 2 hours, in the presence of a catalyst based on bivalent iron in doses of 1 0...50 mg Fe2+/kg of dry soil, introduced in two portions at an interval of 1 2 hours, followed by a sequential biological remediation, with addition of carbon supplemental source, of molasses type, in doses of 1 0...50 g/kg of dry soil, depending on the pollution degree, in successive bioremediation cycles, for maximum 5 months, obtaining global pesticide removal efficiency of more than 90%, each bioremediation cycle comprising a succession of phases with aerobic or anaerobic conditions, the duration of the aerobic phase varying between 3 and 10 days, and the duration of the anaerobic phase varying between 6 and 20 days, depending on the type and degree of contamination and also on the intensity of the chemical oxidation stage.