Stability test of biosurfactant produced by Bacillus licheniformis DS1 using experimental design and its application for MEOR

Microbial enhanced oil recovery (MEOR) is a proven tertiary recovery technique. Biosurfactant is a microbial bioproduct that plays an important role in MEOR applications. This study aimed to test biosurfactant stability using a design experiment based on response surface methodology. First, isolation and screening for potential biosurfactant-producing bacteria from crude oil samples was performed, followed by their characterization. A biosurfactant core flooding experiment was also conducted to examine bacterial activity on MEOR. Thirty-one sequential isolates of bacteria were screened based on qualitative and semi-qualitative parameters. One selected biosurfactant-producing bacterium was identified as Bacillus licheniformis DS1 based on phylogenetic analysis of the 16S rRNA gene. This bacterium had the highest emulsification activity (E_i24 = 65.19%) in light crude oil and could reduce the interfacial tension between oil and water with an effective critical-micelle concentration of 157.5 mg/L. The biosurfactant was observed as a growth-associated metabolite type and the Fourier transform infrared spectrum revealed that the biosurfactant produced belonged to a group of lipopeptides. The biosurfactant has good stability in maintaining emulsification activity at pH 4–10, high temperatures up to 120 °C, and with an NaCl concentration up to 10% (w/v). Based on response surface methodology using the Box–Behnken experimental design, the optimum condition for the most stable biosurfactant is pH 12, a 40 °C temperature and 10% salinity, with an E_i24 value of 94.28%. Core flooding experiments with biosurfactant resulted in 5.4% additional oil recovery. Therefore, this biosurfactant shows a high potential application for MEOR.