Author

Onofre Ortiz

Date of Award

5-1997

Degree Type

Thesis

University or Center

Clark Atlanta University(CAU)

Degree Name

M.S.

Department

Chemistry

Abstract

Microbial mats are natural heterotrophic and autotrophic communities dominated by cyanobacteria (blue-green algae). These constructed mats are durable, tolerant to a variety of toxins and resilient under changing environmental conditions. This research demonstrates that microbial mats provide an effective remediation treatment for 2,4,6 Trinitrotoluene (TNT) in water and soil. It showed that TNT is removed to undetectable limits after 5 days of treatment under any of the following conditions: light/dark; total light; total dark. This work also shows that in the presence of an inorganic material (lead), mats were able to remove both contaminants efficiently, thus making the microbial mat a good choice for mixed waste remediation. Kinetic studies performed during the first five hours of microbial treatment showed a pseudo first order reaction indicating that TNT removal is initially proportional to the concentration of TNT. The major metabolites detected after 24 hour of treatment were 4-amino-2,6- dinitrotoluene, 2-amino-4,6-dinitrotoluene, and 2,4-diamine-6-nitrotoluene. These metabolites have a toxicity level similar to TNT. However, mat extracts and growth medium concentrates taken after 24 hours treatment of TNT showed little or no toxicity. The lack of toxicity demonstrated by treated mat extracts and media concentrates suggest that these metabolites are not the final metabolic products. The chemical nature of these metabolites suggests that the chemical mechanism of biotransformation involves reduction of the nitro groups at the ortho and para position of the TNT structure. Results obtained from light and dark experiment suggest that photooxidation or photodegradation is not an important mechanism for degradation of TNT by mats. Results show that live mats likely degrade TNT via a biotransformation process. In comparison, heat killed mats show a much slower removal of TNT than live mats. TNT was the only species found in the water column and extracts of heat killed mats, which indicates that TNT is removed by a passive absorption process, but no evidence of biodegradation was observed.

Comments

Signature pages are on file with graduate school. An archival copy of the document is available in the Archives Research Center.

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Chemistry Commons

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