In Vitro Analysis of Enhanced Phenanthrene Emulsification and Biodegradation Using Rhamnolipid Biosurfactants and Acinetobacter calcoaceticus
The ability of biosurfactants and Acinetobacter calcoaceticus to enhance the emulsification and biodegradation of phenanthrene was investigated. Phenanthrene is a polycyclic aromatic hydrocarbon (PAH) that may be derived from various sources, for example incomplete combustion of petroleum fuel, thus it occurs ubiquitously throughout the environment. Phenanthrene biodegradation has been reported to be greatly enhanced in the presence of surfactants (Cuny et al. 1999; Chen et al. 2001). It is weakly soluble in water (1.2 mg L−1, 1 atm, 25°C); therefore, its’ biodegradation is strictly limited by its bioavailability (Chen et al. 2001). Emulsification assays were carried out to assess the stability of emulsions formed between phenanthrene and water in the presence of rhamnolipid biosurfactants. An increase in emulsion stability has been shown to equal an increase in bioavailability of a hydrophobic PAH (Dean et al. 2001). Emulsion stability was determined by height of emulsion layer and optical density measurements. Results show phenanthrene and water emulsifications were stabilized for a period up to 10 days at levels ranging from 70–80% with the use of un-encapsulated biosurfactants. Microencapsulated biosurfactants stabilized the emulsion up to 89% for 15 days. Experimental microcosm studies to assess biodegradation rates were carried out over 15 days in 40-mL bioreactors. The reactors were sampled at t = 0, 3, 6, 9, 12, 15 days. Biodegradation rates were determined from measurements of carbon dioxide respiration and phenanthrene concentrations. Results show that on average, more phenanthrene was mineralized (96.4% over 15 days) by bacteria amended with non-encapsulated rhamnolipid biosurfactant (NERhBS).
KeywordsBioremediation biosurfactants phenanthrene microencapsulation
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