Masters Theses

Zhou Shi

Date of Award

5-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

Kevin G. Robinson

Committee Members

Mriganka M. Ghosh, Gary S. Sayler

Abstract

Polychlorinated biphenyls (PCBs) are wildly distributed environmental contaminants which extensively bind to soil thereby limiting their bioavailability. Removal of sorbed PCBs is an essential step in enhancing the biodegradation potential of bound contaminants. Surfactants have been effectively used to desorb hydrophobic contaminants (including PCBs) from soils, however, the impact of surfactant washing on contaminant bioavailability remains unclear. The major purpose of this research is to study the treatment effectiveness of a microbially produced surfactant (biosurfactant) on the biological fate of selected PCBs. Batch treatments were used to evaluate the impact of biosurfactant (Rhamnolipid R1) on the solubilization of non-aqueous phase 4CB and 4,4'CB and the mobilization of soil-bound 4,4'CB. Microbial utilization of 4,4'CB in the presence of biosurfactant was then evaluated by monitoring production of 14CO2 after addition of an acclimated bacterial culture. Rhamnolipid R1, produced by P. aerugenosa (PRP652), linearly increased the apparent solubility of 4CB and 4,4'CB with increasing biosurfactant concentration (above the CMC) . At a biosurfactant concentration of 4 g/L, the enhanced solubilities of mutual solutes, 4CB and 4,4'CB, were 56 and 105 fold over their respective intrinsic solubilities. Biosurfactant R1 was also an effective agent in mobilization of 4,4'CB from contaminated soils. A 4.0 g/L biosurfactant solution desorbed greater than 47% of soil-bound 4,4'CB in the first wash and greater than 85% after three washes. Mineralization of 4,4'CB by Alcaligenes eutrophus (A5) was enhanced in the presence of biosurfactant. Both the mineralization rate and total amount of 4,4'CB mineralized were elevated through biosurfactant addition. For a biosurfactant concentration of 4.0 g/L, overall average mineralization rates were 1.07 and 4.43 times that measured in controls (no biosurfactant) for solutions with and without excess 4,4'CB crystals. Mineralization enhancements were more pronounced when biosurfactant concentrations above the CMC were utilized. The total mass of 4,4'CB mineralized in biosurfactant solutions (without excess 4,4'CB crystals) exceeded the total initial mass of 4,4'CB dissolved in biosurfactant free solutions, which confirmed that micellized 4,4'CB was biodegradable. Co-mineralization of biosurfactant was at a minimum during periods of high 4,4'CB mineralization. An enhanced mineralization of 4,4'CB in the biosurfactant soil wash fluids was also observed. In general, solubilization and mineralization of selected PCBs were more pronounced when biosurfactant concentrations above the CMC were utilized. This fact confirmed that micelles, which only form above the CMC, played an important role in PCB solubilization and mineralization enhancement. The results of this research provide clear evidence that biosurfactant soil washing followed by pure culture biological treatment of the wash fluid is a promising technology for PCB soil remediation.

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