Characterization of biosurfactant from Bacillus sp. GY19 and formulation of dispersant for petroleum remediation in seawater

Abstract

Oil spills in seawater have resulted in significant contamination to the environment. This research aimed to formulate a solvent-free dispersant for crude oil spills based on the hydrophilic-lipophilic deviation (HLD) concept and using lipopeptides from Bacillus sp. GY19. The lipopeptides were recovered and concentrated from cell-free broth by foam fractionation and freeze-drying, respectively. They had good surface activity under varying temperatures, pH and NaCl levels. Moreover, the lipopeptides had low toxicity to copepods (LC50 2,609 mg/L) and whiteleg shrimp (LC50 1,050 mg/L). The characteristic curvature (Cc) of the lipopeptides showed that they were more hydrophobic (Cc 4.93) than sodium dihexyl sulfosuccinate (SDHS, Cc -0.92). The HLD equation was used to calculate the lipopeptide and the SDHS fractions in the dispersant formulations according to the equivalent alkane carbon number (EACN) of hydrocarbons and seawater salinity. The molar fraction of lipopeptides increased with increasing EACN. The lipopeptide-SDHS mixtures formed microemulsion Type III with specific hydrocarbons and crude oils, for example, a mixture of 0.025 M lipopeptide biosurfactant and 0.075 M sodium dihexyl sulfosuccinate in 3.4 % of NaCl was suitable for Bongkot light crude oil. Oil displacement and baffled flask tests showed that the formulations reduced the interfacial tension and solubilized crude oil in the water column at higher efficiency than commercial dispersants or lipopeptides alone. To complete the oil spill removal, Gordonia sp. JC11, a petroleum degrading-bacteria was applied to degrade the crude oil droplets that formed after applying the lipopeptide based dispersant. The 40 L and 160 L 3D-box mesocosm experiments confirmed the efficiency of lipopeptide based for remediation process in both synthetic seawater and natural seawater collecting from a port of Chonburi Province. In the mesocosm with both lipopeptide based dispersant and Gordonia sp. JC11, the concentration of crude oil decreased faster than that in the mesocosm with dispersant alone. The results were corresponded with the increasing number of oil degrading bacteria in seawater. In conclusion, the lipopeptide based dispersant should be applied followed by Gordonia sp. JC11 for oil spill remediation.