Microbial enhanced oil recovery method (MEOR) refers to all processes thatuse the capabilitie of various microorganisms to produce microbial metabolites to improve the efficiency of oil extraction. One of this metabolites, isbiosurfactant. Biosurfactants are surface active compounds that dissolve organic compounds in inorganic compounds by reduction the surface tension. In this paper will have an overview on methods and the advantages of using biosurfactants and effective factors in production and the impact of environmental condition on biosurfactantperformancein microbial enhanced oil recovery.

For the first time in this study, the effect of ionic liquids in different concentrations and properties on the growth and performance of microorganisms capable to be used for MEOR, biodegradation and bioremediation purposes has been investigated. In this regard, two ionic liquids with different characteristics and chain lengths, namely,1-octadecyl-3-methylimidozalium chloride and 2-decyl-3-methylimidozalium chloride were synthesized in the laboratory and their effects were investigated in different concentrations (0, 10, 25, 50, 100, 200 ppm) on 5 different bacterial species (including Enterobacter and Bacillus families), isolated from oil or oil-contaminated soil. The results show an optimum amount of concentration on the top-down curve of the growth and performance of microorganisms in most cases. The maximum the growth rate was obtained for the most species, ranges between 10 and 25PPM and the antibacterial concentration of studied ionic liquids for all species was achieved in 50 ppm. Also, in most cases, 1-octadecyl-3-methylimidozalium chloride was shown to have a greater effect on the growth and yield of all microorganisms.

A bacterial strain (designated as Alcaligenes sp. MS-103) isolated from oil sample of the Aghajari oilfield in the south of Iran, was able to produce an effective extracellular lipopolysaccharide biosurfactant (1.2±0.05 g/l) on molasses as a sole carbon source. The highest surface tension reduction to level 20 mN/m was achieved by biosurfactant produced by cells grown on molasses under optimum conditions. The optimum values of carbon to nitrogen ratio (C/N), salinity, pH and temperature for biosurfactant production were determined as 60:1, 7.5%, 7.0 and 50oC, respectively. Biosurfactant flooding experiments were carried out on both fractured and unfractured carbonate cores. The highest recovery of residual oil among different experiments was about 10.7% in the unfractured cores. Oil displacement indicates that recovery of crude oil can be increased by 9.2% from fractured core with a permeability of 12 mD. The results showed that the biosurfactant produced by Alcaligenes sp. MS- 103 has the potential for industrial applications and may be used in microbial enhanced oil recovery (MEOR).

In recent years, micromodels have been used to investigate and understand the mechanisms of oil recovery. Micromodels provide the opportunity to observe fluid flow and investigate displacement efficiency on the pore scale. In this work, the ability of Pseudomonas aeruginosa HATH to grow and produce rhamnolipid biosur-factant on sunflower as a carbon source is shown. The produced rhamnolipid can reduce the surface tension from 70 mNm/ to 28 mN/m and interfacial tension from 36 mN/m to 4 mN/m at the CMC concentration. These characteristics show that the produced rhamnolipid has a great potential for the oil recovery, especially in microbial enhanced oil recovery. Furthermore, the effect of produced rhamnolipid on enhanced oil recovery has been studied using a micromodel. The results of the experiments show that after rhamnolipid flooding at the CMC concentration (120 mg/l), about 5% of crude oil is recovered from a micromodel.

Microbially produced lipopeptide have been isolated and studied for microbial enhanced oil recovery. About 60 gram positive bacteria isolated from soil contaminated with crude oil, near the crude oil storage tank in Tehran Refinery, Tehran, Iran. However, most of these studies have produced lipopeptide by one of the pure-culture microbes isolated in a laboratory. Among the isolates, heamolytic tests revealed two biosurfactant producers. The isolated strains were designated as C2, E1. By using morphological, biochemical and molecular biology tests (16 SrRNA), the strains identified as Bacillus licheniformis and Bacillus subtitlis, respectively. Emulsification activity and measurement of surface tension indicated that, the isolates were high producers of biosurfactant. The product of C2 and E1 is mainly lipopeptide. This product reduce surface tension from 65 to 30 mN/m. Emulsified activity of crude oil was 92% for C2 and 90 % in case of E1. This is the first report of indigenous Bacillus licheniformis and Bacillus subtilis from a soil contaminated with oil in an Iranian refinery with ability to produce biosurfactant.

Biosurfactants or surface-active compounds are produced by microoaganisms. These molecules reduce surface tension both aqueous solutions and hydrocarbon mixtures. In this study, isolation and identification of biosurfactant producing bacteria were assessed. The potential application of these bacteria in petroleum industry was investigated. Samples (crude oil) were collected from oil wells and 45 strains were isolated. To confirm the ability of isolates in biosurfactant production, haemolysis test, emulsification test and measurement of surface tension were conducted. We also evaluated the effect of different pH, salinity concentrations, and temperatures on biosurfactant production. Among importance features of the isolated strains, one of the strains (NO.4: Bacillus.sp) showed high salt tolerance and their successful production of biosurfactant in a vast pH and temperature domain and reduced surface tension to value below 40 mN/m. This strain is potential candidate for microbial enhanced oil recovery. The strain4 biosurfactant component was mainly glycolipid in nature.