Study Of High-efficiency Fermentation Of Surfactin And Its Application In Waste Crude Oil Demulsification

Surfactin is one of the most powerful biosurfactants,presenting good biocompatibility,biodegradability,emulsifying and antibacterial activity.It has wide applications in petroleum,environmental remediation,food,cosmetics and biomedical industries.However,the high production as well as application costs is largely limited its practical applications in industry.In general,the low-yield and small-scale fermentation resulted in a high production costs,and then make surfactin present much poor competitive advantage compared with the conventional chemical surfactant.Therefore,this paper is aimed to improve t the surfactin production using high cell density strategy,and develop new applications of surfactin in demulsification.?1?Strain B.subtilis ATCC 21332 was selected for fermentative production of surfactin,and a series of identification of strain and fermentation product were carried out.The microscopic observation and a series of morphological identification confirmed that the strain we used was ATCC 21332 able to produce surfactin.The main product separated by acid precipitation and solvent extraction was confirmed by TLC,HPLC and HPLC-ESI-MS analysis.In addition,the obtained surfactin extract presented excellent surface activities with a CMC value as low as 13 mg/L,which reduced the surface tension of water to 27 mN/m,and had an emulsification index of over 95%against vegetable oil.?2?Surfactin production was then improved using high cell density strategy when Mn2+and Fe²⁺was added into the medium.It was found that Fe²⁺and EDTA^2-added at 1:1 was effective to improve the yield of surfactin.The 0.2 mmol/L EDTA-Fe obtained a high surfactin yield of 5.13 g/L,while surfactin yield was only 0.9 g/L in the absence of Fe²⁺.In addition,surfactin production was further improved during sequential fed-batch fermentation,reaching an extremely high value of 9.414 g/L during a batch fermentation,which is nearly 9 times higher than the initial batch fermentation surfactin yield of 0.95 g/L.?3?Finally,we developed a new application of surfactin in demulsification.Based on the pH-sensitive properties of surfactin,a two-step demulsification process was proposed.Firstly,surfactin was added into the emulsion severed as co-emulsifier,and then acid was added to induced surfactin precipitate from oil-water interface,and thus result in an efficient oil separation.As found,the two-step demulsification process efficiently demulsified standard O/W and W/O emulsions.An extremely high oil separation of over 98%was obtained when surfactin was firstly severed as co-emulsifier,and then 10 mM sulfuric acid was added when settled in the 50 ^oC water bath for 20 min.In addition,the reliability of this two-step demulsification process was also confirmed in the real waste crude oil.More than 95%of oil was separated,and the separated oil phase had a much low water content of less than 0.5%,which can be re-entered into the refinery for reuse.Hence,in consideration of high demulsification efficiency,environmental friendliness and low cost of demulsification,surfactin as a biodemulsifier has great application potential in treatment of waste crude oil which was the severe problem in many petroleum industries.