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 (Ei24 = 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 Ei24 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. •Bacillus licheniformis was isolated successfully from oil reservoir.•Box-behnken experimental design was effective tool for biosurfactant stability test analysis.•Biosurfactant produced by B. licheniformis was stable at wide range of pH, high temperature and salinity.•The biosurfactant has potential to be applied for MEOR due to its stability at extreme environmental condition.