Optimization of lipopeptide biosurfactant production by Bacillus licheniformis L20 and performance evaluation of biosurfactant mixed system for enhanced oil recovery

Abstract Biosurfactant is an important amphiphilic microbial product, which plays an important role in microbial enhanced oil recovery (MEOR) by reducing crude oil-water interfacial tension (IFT), emulsification and wettability alternation. Compared with chemical surfactants, biosurfactants have the advantages of lower toxicity and higher biodegradability, but the relatively low yield also limits their applications. In this study, the influence of hydrocarbon carbon sources on the production of biosurfactants by Bacillus licheniformis L20 was investigated, and the variable of unit biosurfactant concentration was proposed to optimize the biosurfactant production medium. The highest concentration was obtained in LB/MSS-K medium, which was up to 1.225 g/L. The biosurfactant produced by Bacillus licheniformis L20 in that medium was characterized as lipopeptide via using FTIR. This biosurfactant shown stable emulsifying properties for different hydrocarbons and crude oils, but it can not reduce the oil-water IFT significantly. However, after mixed biosurfactant with chemical anionic surfactants (1,3-diacylglycerols-2-sulfate) and nonionic surfactant (fatty alcohol-polyoxyethylene ether), the anionic surfactant/biosurfactant mixed system can reduce the crude oil-water IFT to 0.109 mN/m. In addition, the emulsification stability of the biosurfactant mixed system were determined, the results shown that the emulsion formed by the nonionic surfactant/biosurfactant mixed system or the anionic surfactant/biosurfactant mixed system can remain stable under a wide range of temperature, pH and NaCl concentration, respectively. Furthermore, the performance of chemical surfactant/biosurfactant mixed system were evaluated, the results shown that anionic surfactant/biosurfactant mixed system and nonionic surfactant/biosurfactant mixed system can increase the oil recovery rate by 24.12% and 21.67% respectively after water flooding, while the biosurfactant used alone was only 19.58%. Thus, the results obtained from this work shown that anionic surfactant/biosurfactant mixed system have good prospect of application in ex-situ MEOR.