Date

April 1994

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Environmental Science and Engineering

Institution

Oregon Graduate Institute of Science & Technology

Abstract

Reductive dehalogenation is an important reaction that generally leads to detoxification of many halogenated methanes. Halogenated methanes are widely used in industrial and commercial applications and the inadvertent or deliberate release of these chemicals has caused contamination of the atmosphere, soil and groundwater. The research presented here details the study of several systems for reductive dehalogenation of chlorinated methanes. The first system described in this dissertation involves reductive dechlorination of chlorinated methanes by laboratory cultures of methanogens. A vessel was constructed that allowed maintenance of anaerobic conditions and minimized losses of the volatile chlorocarbons. Methylene chloride was not dechlorinated in the presence of pure cultures of methanogens. Similarly, dechlorination did not occur in enrichments made with samples from several different anaerobic digesters. Abiotic dehalogenation studies showed that cobalamins, cobalt-centered macrocyclic compounds, catalyzed the reductive dechlorination of several halomethanes in anaerobic, closed batch systems. These studies focused on immobilization of cobalamins to several types of supports for use in pollution remediation strategies. Cyanocobalamin bound to Epoxy-Activated Sepharose 6B and talc catalyzed the rapid reduction of carbon tetrachloride and methylene chloride to sequentially reduced products. Corroding iron metal was also studied as a reductant for halogenated methanes. Several chlorinated methanes were reductively dechlorinated in closed, anaerobic, laboratory-scale model systems containing granular iron. Carbon tetrachloride was sequentially dehalogenated, via chloroform, to methylene chloride. The initial rate of each reaction was pseudo-first order in substrate and declined substantially with each dehalogenation step. Trichloroethene was also dechlorinated by iron, although more slowly than carbon tetrachloride. The reaction of chlorinated methanes appears to involve a direct interaction between the substrate and the iron surface. When surface condition is constant, the rate of reaction is roughly first-order in iron surface area and the rate increases markedly with increasing iron surface area. Studies were also performed to determine the effects of microbial and geochemical processes that developed during a field demonstration in which iron metal had been buried in the path of a chlorinated-solvent contaminated plume. Two sets of cores were obtained and examined for microbial and geochemical developments one, and two, years after burial of the iron.

Identifier

doi:10.6083/M4J9649V

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