Research Subject: Nowadays, application of biosurfactants in microbial enhanced oil recovery (MEOR) have aroused much attention and several investigations have been conducted on this field. But their performance in comparison to synthetic surfactants in enhanced oil recovery has little been studied. Most of these researches are limited to comparison of one produced biosurfactant with only a chemical surfactant. To fill this gap, in this research, the potential use of a rhamnolipid type biosurfactant  in MEOR was compared to several conventional synthesized surfactants: SDS, SDBS, CTAB and DTAB.
Research Approach: Since the main goal of this research is the comparison between produced biosurfactant and conventional chemical surfactants in oil recovery, several flooding tests were conducted and involved mechanisms were investigated. All of tests were conducted in an oil wet glass micromodel saturated with heavy oil at ambient condition. Injected solutions were prepared at critical micelle concentration of surfactants. During the flooding tests, high quality pictures were taken with a camera connected to the computer to monitor the motion of injected solution in the micromodel.
 Main Results: 40% oil recovery was achieved after biosurfactant flooding while SDBS, SDS, CTAB and DTAB resulted 36%, 34%, 32% and 29% oil recovery, respectively. For mechanistic study, the surface tension (ST) and viscosity measurements were performed and contact angle was determined. The surface tension reduction, wettability alteration towards more water-wet condition and increasing the ratio of injected fluid viscosity to oil viscosity were dominant mechanisms. The rhamnolipid was more effective than other surfactants in reduction of surface tension and altering the wettability towards favorable water-wet conditions. It decreased the surface tension of water from 72 to 28 mN/m, which was the least comparing to other surfactants and increased the capillary number about 19.4 times greater than in water flooding. Additionally, it changed the contact angle from 106 to 6, 94.3%, the widest change among applied surfactants. 

Biosurfactants are metabolites produced by microorganisms which have potential capabilities in various industries due to abundant beneficial properties. In spite of great advantages, commercial utilization of biosurfactants especially in food industry and pharmaceuticals are limited for the reasons of technical and commercial such as low yield, high production cost, and the type of producing strain. Majority of biosurfactant producer microorganisms have ever evaluated, are pathogenic strains which are not acceptable in industrial and environmental utilization particularly in health and cosmetics, pharmaceuticals and food industries. However, the present study aims to investigate high production of cell-bound biosurfactant by lactic acid bacterium Lactobacillus plantarum through optimization of the main carbon source of specific culture medium. Therefore, three culture media with different amount of glucose were evaluated for biomass and biosurfactant (by surface tension reduction of phosphate buffered saline) production in shake flasks and bioreactor (controlled temperature, pH and agitating speed). The results from both shake flasks fermentation and bioreactor showed the maximum biomass concentration of 3.9 and 4.17 g/L, the minimum surface tension of 41.17 and 40.48 mN/m and subsequently the maximum biosurfactant production in culture medium including 30 g/L of glucose, respectively. Furthermore, fourier transform infrared spectroscopy analysis indicated the biosurfactants are structurally a mixture of protein, polysaccharide and possibly phosphate group, possessing glycoprotein structure.