Cobalamin-Enhanced Anaerobic Biotransformation of Carbon Tetrachloride

Hashsham, Syed Anwar

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Description

Title

Cobalamin-Enhanced Anaerobic Biotransformation of Carbon Tetrachloride

Author(s)

Hashsham, Syed Anwar

Issue Date

1996

Doctoral Committee Chair(s)

Freedman, David L.

Department of Study

Civil Engineering

Discipline

Environmental Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Engineering, Environmental

Language

eng

Abstract

• Anaerobic microbial transformation for the bioremediation of groundwaters contaminated with carbon tetrachloride (CT) is a promising alternative, but accumulation of hazardous metabolites and the inhibition of biotransformation when CT is present in the milligram per liter range has limited its application. The purpose of this study was to evaluate the potential of improving the product distribution and rate of biotransformation at high CT concentrations by supplementing cultures with cobalamins. Three different cultures; an acetogenic pure culture-Acetobacterium woodii (ATCC-29683), a dichloromethane degrading enrichment culture, and a methanol enrichment culture were studied for this purpose.
• With A. woodii, complete transformation of 470 $\mu$M CT was achieved within 2.5 days when 10 $\mu$M hydroxocobalamin (OH-Cbl) was added along with fructose. The transformation was at least 25 times faster compared to A. woodii with no added OH-Cbl. Nonenzymatic transformations were also significant, as indicated by increased transformation rates in autoclaved cultures with added OH-Cbl. Studies with ($\sp $C) CT revealed that adding OH-Cbl to live cultures also resulted in an increased percentage of CT transformed to CO$\sb2$ and soluble materials including acetate, butyrate, and L-lactate, and decreased percentage of CT reduced to chloroform (CF) and abiotically transformed to CS$\sb2$.
• A dichloromethane (DCM) degrading enrichment culture showed similar enhancement effects with cyanocobalamin (CN-Cbl). The culture by itself transformed ($\sp $C) CT to chloroform, CS$\sb2$, and CO$\sb2$. When CN-Cbl was added along with CT, the percentage converted to CO$\sb2$ increased almost 3-fold, while CS$\sb2$ decreased somewhat, and virtually none of the CT was reduced to CF. Adding CN-Cbl also increased the rate of CT transformation in live cultures by at least 10-fold. Accelerated rates of transformation by live cultures were sustained for as long as 200 days, with hydrogen serving as the electron donor. Besides CN-Cbl, OH-Cbl, and methylcobalamin (MeCbl) were found to be equally effective, while a 3-week lag period was required before adenosylcobalamin (AdoCbl) started to enhance CT transformation.
• To demonstrate the applicability of this approach in bioremediation, an enrichment culture grown on methanol was also studied. The results were similar to those with the DCM enrichment culture. Addition of at least 0.1 $\mu$M CN-Cbl was required to observe a measurable enhancement in rate, with no optimum up to 10 $\mu$M CN-Cbl. Products formed from ($\sp $C) CT confirmed the previous findings of increased CO$\sb2$ and soluble materials formation. Long term biotransformation studies with added hydrogen also revealed that CS$\sb2$ production was related to the concentration of sulfides.
• Studies with alumina, clay, a sand with low organic carbon content, and a sandy soil with high organic carbon content gave retardation factors in the range of 1.9-3.0. This indicated that the adsorption of CN-Cbl to aquifer materials was marginal. The effect of organic matter present in the groundwater was also small.
• This study demonstrated that adding catalytic amounts of cobalamins improves biotransformation of high concentrations of CT by increasing the rate and minimizing the accumulation of hazardous products. Relatively low adsorption of CN-Cbl in sand indicated that adding cobalamins to groundwater for in situ bioremediation may be a feasible option. The high cost of cobalamins for remediating CT contaminated aquifers may be offset by a decrease in total remediation time and reduction in hazardous product accumulation.

Graduation Semester

1996

Type of Resource

text

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