Complex treatment of soils, waste water and groundwater contaminated by halogenated organic compounds

This paper deal with the development and application of the technologies for the decontamination of solid wastes (soils, sediments, inorganic adsorbents, used activated carbon) polluted by variety of hazardous halogenated organic substances, namely by polychlorinated biphenyls, perchlorates and especially dichlorethanes and vinyl chloride as their decomposition products, chlorophenols and prospectively also polybrominated diphenyl ethers. This project has focused on the development of a complex assembly of technological decontamination units:- a low temperature indirectly heated thermal batch process for the desorption of volatile and semivolatile organics from soils and other contaminated solid wastes, with batch capacity of about 20 metric tones/week, - the extraction of organics from solid supports by an aqueous solution of selected surfactants, - the treatment of separated liquids by adsorption and/or chemical decontamination. The separation efficiency of the batch low temperature thermal desorption is over 99.9% and by incorporating reductive dechlorination reaction within the process (mixing contaminated solids with caustic) a regulatory level for unrestricted disposal of treated solids of less of 0.05 mg organics/kg can be comfortably achieved, independently on the original concentration in treated solid wastes. The efficiency of extraction of organics from sandy loam type soils by aqueous solvents (aloxylates of fatty alcohols) is in the order of about 80% and the washing process has been consequently retained for cleaning of screened oversize material and the debris separated from the incoming feed to the thermal desorption. The results show that the method of thermal desorption does not have weak points as far as the effective separation of pollutants from solid supports, but problems are posed by the removal of organic substances from the aqueous solutions that are produced by the separation technologies applied (oil-in-water condensates from thermal desorption and aqueous extracts respectively). The principal effort has therefore focused on the treatments of waste waters contaminated with mentioned pollutants. Their efficient cleaning constitutes substantial part of the total costs of the complex decontamination process. We have shown that as to the treatment of contaminated water, inclusive underground ones, the two methods can be considered as fundamental for solving the problem at real conditions, namely the decomposition of organic substances by active radicals (Fenton reaction under the action of UV irradiation-UV/OX) and the decomposition of organics on catalyst with Pd deposited on different supports at the presence of zero-valent Fe. To test the efficiency of the proposed methods simulated and real water samples were chosen and were treated at laboratory (Pd/Fe) and pilot-plant (UV/OX) conditions. The results presented made evidence of the feasibility of both methods. The weak point of both methods is a tendency to gradual blocking of catalyst and UV lamp surfaces by inorganic precipitates.