Preparation And Performance Evaluation Of Biosurfactants

Biosurfactant was a kind of surface active metabolite that produced by microorganisms,whose characteristic was lipophilic and hydrophilic. Compared with other surfactants,biosurfactants had the advantages that were acidproof, salt tolerance, biodegradable, lowtoxicity, antimicrobial resistance, not environmental pollution and good biocompatibility.Therefore, screening for high-yield biosurfactants producing strains and studying the optimalculture conditions of biosurfactants had a wide range of biological significance and economicvalue.Through three screening methods,15biosurfactants producing strains were screenedfrom the three plants oilfield water in Daqing oilfield. The biosurfactants producing strainsthrough the rapid screening method had the maximum diameter of the oil spreading and thehighest emulsification index. So the rapid screening method was the best method forscreening biosurfactants producing strains. Through the biosurfactant evaluation experimentssuch as the ability to reduce surface tension and the ability of acid, alkali, salt tolerance, theresults showed that S2strain had the lower critical micelle concentration (25mg/L), thehigher degree of salinity tolerance (20%NaCl), the wider pH range (pH3-11).The high-yield biosurfactant producing strain (S2) was identified through physiologicaland biochemical experiments and16S rDNA sequence analysis, which exhibitted the highestsimilarities to Bacillus subtilis strains CCTCC M201162. After extracted and purified, S2biosurfactant concentration was0.72g/L. Through the fourier transform infrared spectroscopyanalysis and chemical analysis, S2biosurfactant was identified as lipopeptide biosurfactant.The effect of single factor such as carbon, nitrogen and phosphorus sources on S2biosurfactant emulsifying activity and surface tension was studied. The results showed thatwhen the beer wastewater (40g/L) was carbon source and NH4H2PO4(4g/L) was nitrogenand phosphorus source, the S2biosurfactant had the highest surface active and emulsifyingactivity. Through response surface optimization method, the culture conditions (inoculationconcentration, pH, temperature and rotation speed) of the S2strain were optimized. On thebasis of response surface model, optimum pH value (7.2), optimum temperature (43.5℃),optimum inoculation concentration (5.2%), and optimum rotation speed (162r/min) wasobtained through the quadratic fit regression equation. The experimental level and significantfactor analysis showed pH, temperature, inoculation concentration had significant effect onemulsification index (E24) of S2strains fermentation broth, while the pH value was the mostsignificant factor. Under the optimum condition, the best E24of S2biosurfactant was81.20%,S2biosurfactant concentration was1.26g/L and surface tension of the fermentation brothreduced from72.0mN/m to25.8mN/m.The mechanism of biosurfactants and crude oil interaction was studied. The resultsshowed that S2biosurfactant could reduce crude oil viscosity and oil freezing point ofdifferent oil production plant (crude oil of three plants in Daqing oil wells No.3-264,3-265,crude oil of peripheral Yushulin well in Daqing oilfield No.32-31,312-JX-311). After S2 strain treatment, the maximum reduction rate of crude oil viscosity was45%, oil freezingpoint maximum reduced by4℃; the reduction rate of Pr/Ph was5%, the reduction rate ofC28+C29/C21+C22was66%. The results indicated that S2strain could increase the lightcomponent of crude oil and reduce the heavy components of crude oil effectively in order toincrease the mobility of crude oil.