Complex treatment of wastewater and groundwater contaminated by halogenated organic compounds

This paper deals with the development and application of two methods for the de-contamination of waste and underground water polluted by a variety of hazardous halogenated organic substances, namely polychlorinated biphenyls, chlorophenols, perchlorates and especially their decomposition products dichloroethanes and vinyl chloride, and potentially also polybrominated diphenyl ethers. The decomposition of organic substances by active radicals (Fenton reaction under the action of UV-irradiation) and by reductive dehalogenation (dehalogenation of organics on metallic Pd deposited on different supports at the presence of zero-valent iron-Pd/Fe) has been studied. To test the efficiency of both methods, water spiked with contaminants in the laboratory and real contaminated water samples collected from the field were treated. The results presented document the feasibility of both methods, even though their efficiencies differ from those reported in the literature. The weak point of both methods is a tendency to gradual blocking of catalyst and UV lamp surfaces by inorganic precipitates when treating waters originating from polluted industrial sites.

We have shown that two methods can be considered fundamental for removing hazardous halogenated and poly-halogenated compounds from contaminated waters, including underground water. These methods are the decomposition of organic substances by active hydroxyl radicals (Fenton reaction under the action of UV irradiation) and the decomposition of organic substances by reductive dehalogenation on bimetallic, catalysts, namely with Pd deposited on different supports (such as particles of zero-valent Fe or organic and/or inorganic supports in the case of a dual system composed of separate zero-valent iron and palladized inert support). The latter process, which makes regeneration of the Pd-catalyst easier, is also potentially applicable in the so called underground barriers, preferably with co-action of active bio-films. The results presented in this contribution document the feasibility of both methods, even though their efficiencies differ from those reported in the literature, in particular as to the extent and reproducibility of the conversions, as demonstrated with re-used catalysts. In general, the rates of decontamination and efficiencies of dehalogenation of both methods substantially differ for water spiked with contaminants in the laboratory and real contaminated water collected from the field. It is evident that the choice of the decontamination method cannot be generalized and will depend on the type of contaminants, real conditions and process costs. The efficiency of decontamination of contaminated waste water is strongly influenced by the presence of impurities and inorganic compounds. Exploratory experiments showed a surprisingly high ability of degradation of the PDBE 209 congener on the Pd/Fe system. However, further study and optimization of both of these methods of decontamination of halogenated organic compounds in aqueous solutions are urgently needed.