Graduate Thesis Or Dissertation
 

Measurement of the rates of reductive dechlorination of chlorinated phenols

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  • Knowledge of a compound's degradation pathway is crucial to the assessment of risk at contaminated sites. Pentachlorophenol and its metabolic products can serve as model compounds to study the fate and transport of halogenated aromatic compounds in the environment. Acclimation of anaerobic sewage sludge to pentachlorophenol produced a microbial consortium with the ability to remove chlorines from all three positions on the chlorophenol molecule. A series of split degradation pathways were observed in batch experiments of the reductive dechlorination of pentachlorophenol and its metabolites. Pentachlorophenol was rapidly degraded to 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, and 2,3,5,6-tetrachlorophenol. Experiments conducted with each metabolite revealed the complete pathways for the degradation of pentachlorophenol. Dechlorination of 2,3,4,5-tetrachlorophenol produced 3,4,5- trichlorophenol which was subsequently degraded to both 3,4-dichlorophenol and 3,5- dichlorophenol. 2,3,4,6-tetrachlorophenol was dechlorinated at both ortho and meta positions to produce 2,4,6-trichlorophenol and 2,4,5-trichlorophenol. 2,3,5,6- tetrachlorophenol was degraded to 2,3,5-trichlorophenol. Reductive dechlorination of 2,3,5-trichlorophenol produced 3,5-dichlorophenol. 2,4,6-trichlorophenol was degraded to 2,4-dichlorophenol and 2,4,5-trichlorophenol was dechlorinated at two positions to form 2,4-dichlorophenol and 3,4-dichlorophenol. Of the three dichlorophenols produced, only 2,4-dichlorophenol was degraded significantly within the time of the study (3 weeks), producing 4-chlorophenol. The sequence of metabolic products produced bypentachlorophenol-acclimated anaerobic sewage sludge during this study is identical to that observed during a previous study of reductive dechlorination of pentachlorophenol by a mixture of three sludges acclimated to 2-chlorophenol, 3-chlorophenol, and 4-chlorophenol respectively. These results suggest that separate groups of organisms or enzyme systems are responsible for the removal of ortho, meta, and parachlorines.
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