Characterization and optimization of biosurfactants produced by Acinetobacter baylyi ZJ2 isolated from crude oil-contaminated soil sample toward microbial enhanced oil recovery applications

• Surface activities of biosurfactants produced by Acinetobacter baylyi ZJ2 were studied.
• Biosurfactant was identified as lipopeptide based on TLC, FT-IR and NMR.
• Biosurfactant reduced the ST from 65 mN/m to 35 mN/m and the IFT from 45 mN/m to 15 mN/m.
• Biosurfactant was most effective when the salinity was below 4% and the pH was 6–7.
• Biosurfactant was efficient for crude oil degradation and oil displacement process.

The present work aims to investigate the surface activity of the biosurfactant produced by Acinetobacter baylyi ZJ2 isolated from crude oil-contaminated soil sample in China and evaluate its potential application in microbial enhanced oil recovery. The biosurfactant produced by A. baylyi ZJ2 was identified as lipopeptide based on thin-layer chromatography, Fourier transform infrared spectroscopy and nuclear magnetic resonance techniques. This biosurfactant could reduce the surface tension of water from 65 mN/m to 35 mN/m, and interfacial tension against oil from 45 mN/m to 15 mN/m. Moreover, surface activity stability results showed that this biosurfactant was effective when the salinity was lower than 8% and the pH value was 4–9, and it was especially stable when the salinity was lower than 4% and pH was 6–7. Based on the result of gas chromatography, there was a decrease in heavy components and an increase in light components, which indicated that A. baylyi ZJ2 exhibited the biodegradability on the heavy components of crude oil. Furthermore, the ability of recovering oil from oil-saturated core showed that nearly 28% additional residual oil was displaced after water flooding. The lipopeptide biosurfactant produced by A. baylyi ZJ2 presented a great potential application in microbial enhanced oil recovery process, owing its good surface activity and satisfying degradation ability to crude oil.