Study On Glycerol Fermentation Rhamnolipid And Product Recovery Processes

Rhamnolipid produced by Pseudomonas aeruginosa is a biosurfactant with excellent surface performance, and it based on the many excellent characteristics is widely used in petroleum, pharmaceutical and food industries. However, in recent years, rhamnolipid is difficult for industrial application because of the high production cost and low production, especially the cost of raw materials, which holds almost half of total production costs. The large number of glycerin abandoned derived from biodiesel industrial can be used as a cheap carbon source to produce rhamnolipid. Therefore, the breeding of high-yielding strain with glycerol as carbon source, fermentation and separation processes of rhamnolipid were studied in this work, which aimed to reduce production costs and increase production of rhamnolipid.Firstly, the Pseudomonas aeruginosa FMO-H-1 stored in our laboratory was mutagenized with ultraviolet. The optimal radiation time is of 100s. Then it was cultured in the medium of glycerol-rhamnolipid for induction. Subsequently, then the mutant strains were screened by the combination of the blue gel plate method, anthrone-sulfuric acid method and surface tension method. Ultimately a high-yielding mutant strain named Pseudomonas aeruginosa ZGR6 was obtained which was of genetic stability. And the rhamnolipid production of strain ZGR6 reached 7.96g/L, increased nearly 1.33 times than the original strain FMO-H-1.Secondly, the effect of carbon sources, nitrogen sources and inorganic salt on production of rhamnolipid by Pseudomonas aeruginosa ZGR6 were investigated and analyzed through the orthogonal optimization experiment and single factor method. Meanwhile the dynamic process of rhamnolipid fermentation were also studied. Finally the optimal culture medium for rhamnolipid production were determined as follows (g/L):glycerol 22.0, glucose 2.0, dried corn steep liquor powder 10.0, K2HPO41.0, NaH2PO40.6, NaNO31.8, MgSO40.5, CaCl20.06, NaCl 1.0. And the rhamnolipid yield of strain ZGR6 could increased to 12.30g/L, while fermentation time was shortened to 55 h.At last, rhamnolipid was separated and extracted using the method of activated carbon adsorption-acidic precipitation from fermentation broth pretreated by ammonium sulfate. The thermodynamics and kinetics rules of rhamnolipid adsorbed onto activated carbon were discussed. The effect of pH on adsorption and the selection of eluent and desorption time were also investigated. The results indicated that the equilibrium time of the adsorption of shell activated carbon was cut down from 140 to 60 minutes with the temperature rising from 40 to 80? at pH 7.0. The maximum adsorption capacity is 103.5 mg/g at 80?. The acidic precipitation can obviously improve the capacity of adsorption. The equilibrium adsorption capacity of shell activated carbon was increased via three times reaching to 310.9mg/g at pH 2.0. In addition, the first yield of rhamnolipid could reach to 75.8%. The appropriate eluent and the time of desorption were 95% ethanol and 2 hours, and first desorption yield of rhamnolipid was 41.8%. The purity of the rhamnolipid crude product was determined about 90.6% and the main components was di-rhamnolipid after analyzed. The value of critical micelle concentration (CMC) was measured about 45 mg/L.