Laboratory and Field Evaluation of Upward Mobilization and Photodegradation of Polychlorinated Aromatics in Soil

Principal Investigators
S. Kapila, D. Forciniti, and D.W. Armstrong, University of Missouri

Abstract

Goal: The overall objective of this research is to evaluate the effectiveness of solvent-mediated mobilization and photodegradation of chlorinated dioxins and furans as a means of soil decontamination. In order to meet this objective, a series of laboratory and field experiments have been planned.

Rationale: Many sites in the United States and abroad hav e become contaminated with polychlorinated dibenzodioxins and related polychlorinated aromatics, either as a result of accident or industrial activities. The only proven technology for decontaminating the soil at such sites is high-temperature incineration, which is extremely expensive. Destruction of dioxins and furans by natural or artificial sunlight is known to occur and has been shown to be highly efficient under certain conditions in the laboratory. This process, photodegradation, has not been regarded as promising for decontamination of soil, however, due to the sharp attenuation of light beyond a fraction of a millimeter in soil. If the substances to be photodegraded could be brought to the soil surface, the efficiency of the process could be dramatically improved and might provide an option less expensive than incineration.

Approach: Experiments will be conducted to study the following: (1) partition behavior of hepta and octachloro dibenzo-p-dioxins in soil and solvent systems which are environmentally acceptable and amenable to photodegradation. Emphasis will be placed on use of complexing agents such as sulfoxides; (2) effects of co-contaminants on dechlorination mechanisms of polychlorinated dibenzo-p-dioxins (PCDDs); (3) photo degradation rate of chlorinated dioxins and furans in suitable solvent systems; (4) quenching effect of co-contaminants on photodegradation; and (5) optimization of carbon adsorption/regeneration for recycling of solvents. Field trials will evaluate the efficacy of an optimized mobilization-photodegradation process on a pilot scale at contaminated sites in California and Missouri.

Status: Partition experiments have been carried out to study distribution of dioxins in soils and selected solvent systems. Solution phase photodegradation experiments have been carried out under natural and simulated sunlight conditions. Phototransformation rates were highest when both heterogeneous and homogeneous photocatalysts were used simultaneously. Experim ents to monitor degradation of PCDDs which might escape into the atmosphere revealed no measurable release of PCDDs; however, this is still being monitored. Irradiation experiments revealed that different dioxin congeners degrade at different rates. The data revealed an inverse relationship between degree of chlorination and rate of disappearance. The data also indicated that more toxic laterally substituted congeners degrade at a slower rate than perisubstituted congeners, in contrast to degradation observed in the solution phase. Field experiments have been initiated in California. Studies in the area of chemical dehalogenation have resulted in development of an innovative chemical dehalogenation process designated "CDP." Work with counterflow oxidative regeneration showed that photodegradation and chemical dehalogenation processes are efficient in degrading organic wood preservation chemicals. However, use of the processes over long periods can lead to build-up of residual contaminants and reaction byproducts. To maintain high extraction efficiency, these byproducts and constituents must be removed. Removal can be achieved through adsorption. This project is in its final year.

Clients/Users: Results of this project will be of interest to those in wood-treatment and agriculture industries, as well as to government agencies such as U.S. Environmental Protection Agency and U.S. Department of Defense.

Key words: photodegradation, mobilization, polychlorinated dibenz o-p-dioxins, furans, soil.

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