Doctoral Dissertations

Date of Award

5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Frank E. Löeffler

Committee Members

Steve Wilhelm, Karen Lloyd, Claudia Rawn, Mircea Podar

Abstract

Trichlorofluoromethane (CFC-11), dichlorofluoromethane (CFC-12), and tetrachloromethane (CT) are fully halogenated methanes that were produced as refrigerants in the early part of the 1900s and later used in many industrial processes. They are ozone-depleting agents and common groundwater contaminants. They are volatile chemicals that are moderately soluble in water. Due to their volatility when released to the environment, they are predominantly found in the atmosphere, though they also dissolve into the groundwater. In anaerobic environments, they can undergo dehalogenation reactions with several redox-active compounds. This dissertation presents results from two treatability studies from sites contaminated with CFC-11, CFC-12, and CT. Additionally, the effect of pH on the dehalogenation of CFC-11, CFC-12, and CT is examined, and a sulfidogenic enrichment culture grown in the presence of CT is characterized. The first treatability study indicates that the addition of reactive iron species (i.e., zero-valent iron or ferrous sulfide) combined with the bioaugmentation culture KB-1 Plus and lactate can facilitate the transformation of CT into non-halogenated end products. The most effective remediation strategy for CT observed during the treatability study for the second contaminated site was the addition of zero-valent iron; this facilitated the transformation of CT to chloroform (CF). CF is a non-desirable end product, and additional remediation efforts are recommended for the second contaminated site. A shift in the type of transformation products formed during the reduction of CFC-11, CFC-12, or CT by super-nucleophilic cobalamin was observed as pH increased. Mackinawite and vivianite were identified as the two precipitate phases formed in the presence of the sulfidogenic enrichment culture. Vivianite formation likely occurs via precipitation with the phosphate present in the medium, and that mackinawite forms via precipitation with hydrogen sulfide produced by the sulfidogenic bacteria present in the enrichment. Additionally, a greater decline in CT was observed in microcosms that contained active enrichment culture than in heat-killed controls, suggesting that the consortium aids in the degradation of CT, probably via mackinawite formation, as it is a reactive iron species.

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