Date of Award

8-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Dr. David L. Freedman

Committee Member

Dr. Cindy M. Lee

Committee Member

Dr. Kevin T. Finneran

Abstract

Oil spills are a recurring issue associated with fossil fuel consumption. The largest accidental oil spill in the history of the petroleum industry was the Deepwater Horizon explosion and seafloor well blowout, where the Deepwater Horizon oil rig exploded and sank, allowing the well to gush uncontrolled from April 20, 2010, until it was capped on July 15, 2010, releasing an estimated 210,000,000 gallons of oil. Oil dispersants were used in unprecedented quantities during the cleanup response to the spill with a total of 1,840,000 gallons of the dispersant COREXIT being applied. The goal of this research was to evaluate the biodegradation of the oil dispersant components 1,2-propanediol (1,2-PD) and 2-butoxyethanol (2-BE) in seawater and under anaerobic conditions, such as those found in near-shore estuarine environments of the Gulf of Mexico. Relatively little is known about the biodegradability of these two compounds in seawater. The specific research objectives were: 1) to evaluate the terminal electron acceptor (TEA) conditions under which 2-BE was biodegraded in microcosms and enrichment cultures based on the stoichiometry of electron acceptor and 2-BE utilization; and 2) to develop enrichment cultures capable of using 2-BE as a growth substrate under anaerobic and aerobic conditions and evaluate the role of sulfate-reducing bacteria through the use of molybdate as an inhibitor. The work conducted and described herein showed that: 1) Analytical methods were successfully developed for quantification of 1,2-PD, 2-BE, nitrate, ferrous iron, and sulfide in the high ionic strength matrix of seawater; 2) 1,2-PD biodegraded in seawater under both aerobic and anaerobic conditions in microcosms constructed with seawater and sediment from Bay Jimmy, Louisiana, which appears to be the first report of 1,2-PD biodegradation in a high salt environment. Because of the high level of biodegradable organic matter in the microcosms, it was not possible to associate the anaerobic consumption of 1,2-PD to a specific terminal electron acceptor; 3) 2-BE biodegraded in seawater under both aerobic and anaerobic conditions in microcosms constructed with seawater and sediment from Bay Jimmy, Louisiana, which appears to be the first report of 2-BE biodegradation in a high salt environment. Because of the high level of biodegradable organic matter in the microcosms, it was not possible to associate the anaerobic consumption of 2-BE to a specific terminal electron acceptor; and 4) Biodegradation of 2-BE was sustained in aerobic and anaerobic enrichment cultures, through two transfers (1% v/v). Nitrate, Fe(III) and sulfate did not appear to be used as the TEAs under anaerobic conditions. Molybdate slowed but did not stop consumption of 2-BE. Sulfide was detected, but at levels well below the amount expected if complete mineralization occurred with sulfate as the TEA. Based on these results, the presumptive pathway for anaerobic biodegradation of 2-BE in the study was via fermentation. Products were not measured, although 2-butoxy acetic acid and hydrogen are likely intermediates. The results of the study definitively show that 1,2-PD and 2-BE biodegraded in microcosms constructed using Bay Jimmy sediment and transfer enrichment cultures. Analytical methods for the measurement of 1,2-PD, 2-BE, Fe(II), nitrate, and sulfide were developed, which has laid the foundation from which future students will investigate the biodegradation of 1,2-PD, 2-BE, and other COREXIT compounds in seawater and in the presence of petroleum hydrocarbons.

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