Thesis (M.Sc.)--Chulalongkorn University, 2013

This research aims to produce biosurfactant by using Gordonia sp. GY40 immobilized cells and to apply the biosurfactant for enhancing petroleum removal from seawater. Gordonia sp. GY40 was previously isolated from soil in Chonburi province, Thailand and found to efficiently produce biosurfactant. Firstly, immobilization technique and optimum biosurfactant production was studied. When using chitosan flakes as immobilizing matrix and 2% soy-bean oil as carbon source in basal medium, Gordonia sp. GY40 could reduce the surface tension of basal medium from 59.6 to 34.9 mN/m. The cell-free supernatant was able to emulsify diesel and slideway oil; as well as, disperse 100 and 97% of slideway oil and diesel in the oil displacement test, respectively. Biosurfactant with dispersion and emulsification activities could be used to enhance the biodegradation of petroleum in seawater. Furthermore, this biosurfactant was not toxic to lubricant-degrading bacteria, Gordonia sp. JC11 as well as indigenous seawater microorganisms. After that, biosurfactant was used together with polyurethane foam-immobilized Gordonia sp. JC11 to remove fuel oil in synthetic seawater. The system removed 81% of 1,000 ppm fuel oil within 6 day, while the immobilized cells alone removed 70% of the oil. The experiments were later tested with seawater samples from a port in Chonburi province, Mapthaphut, Rayong province, and Samed Island, Rayong province. The application of biosurfactant along with immobilized cells removed 60-70% of fuel oil, while the natural attenuation (control) removed only 26-35%.