Cyclodextrin effects on the ex-situ bioremediation of a chronically polychlorobiphenyl-contaminated soil

Abstract

The possibility of enhancing the intrinsic ex-situ bioremediation of a chronically polychlorinated biphenyl-contaminated soil by using cyclodextrins was studied in this work. The soil, contaminated with a large array of polychlorinated biphenyls and deriving from a dump site where it has been stored for about 10 years, was found to contain indigenous cultivable aerobic bacteria capable of utilising biphenyl and chlorobenzoic acids. The soil was amended with inorganic nutrients and biphenyl, saturated with water, and treated in aerobic batch slurry- and fixed-phase reactors. Hydroxypropyl-beta-cyclodextrin and gamma-cyclodextrin, added to both reactor systems at the concentration of 10 g/L at the 39th and 100th days of treatment, were found to generally enhance the depletion rate and extent of the soil polychlorobiphenyls. Despite some abiotic losses could have affected the depletion data, experimental evidence, such as the production of metabolites tentatively characterized as chlorobenzoic acids and chloride ion accumulation in the reactors, indicated that cyclodextrins significantly enhanced the biological degradation of the soil polychlorobiphenyls. This result has been ascribed to the capability of cyclodextrins of enhancing the availability of polychlorobiphenyls in the hydrophilic soil environment populated by immobilised and suspended indigenous soil microorganisms. Both cyclodextrins were metabolised by the indigenous soil microorganisms at the concentration at which they were used. Therefore, cyclodextrins, both for their capability of enhancing the biodegradation of soil polychlorobiphenyls and for their biodegradability, can have the potential of being successfully used in the bioremediation of chronically polychlorinated biphenyl-contaminated soils. Copyright 1998 John Wiley & Sons, Inc.