Solubilization of petroleum hydrocarbons using biosurfactants

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.Low solubility of petroleum hydrocarbons in water is the major factor limiting the degradation rates of these compounds (Zhang and Miller, 1994). The fraction that is more soluble in the aqueous phase is degraded at higher rates, while less soluble or insoluble compounds have lower degradation rates due to limited bioavailability to the microbial community. A recent study in our lab found no significant degradation of weathered petroleum at a Texas petrochemical plant site. It was concluded that bioavailability of the crude oil to the microorganisms limited the degradation rates (Mills, 1994). Preliminary experiments at our laboratories have also indicated enhanced solubilities of petroleum hydrocarbons due to the effects of biosurfactants (Kanga et al., 1994). This research focused on biosurfactants because they have been shown to be as effective as chemical surfactants and, most importantly, they enhance biodegradation. Glycolipid biosurfactants are produced by Rhodococcus species HI 3-A to enhance substrate solubility and promote bioavailability for degradation. The work proceeded in two stages. The initial stage involved production and characterization of extracellular biosurfactants by HI 3-A when grown on minimal salts media with hexadecane as the carbon source. The second stage evaluated the performance of the biosurfactants in enhancing the aqueous solubility of weathered West Texas Crude. Initial results indicated production of the biosurfactants by Rhodococcus species H13-A during the stationary growth stage. Biosurfactants lowered the surface tension from 72 to-30 dynes/cm and interfacial tension to below 5 dynes/cm. The two-, three-, and four-ring aromatic compounds showed substantial increase in their aqueous phase concentrations in the presence of biosurfactants. The enhancement was more dramatic with the larger aromatics and also the highly substituted-compounds. Preliminary experiments on toxicity and biodegradation indicated higher levels of toxicity in the surfactant/aqueous mixtures due to increased PAH partitioning (Lambert, 1995), and increased degradation rates for the target PAH compounds