| Microalgae is one of the most promising raw material of biodiesel owing to its fast growth, high photosynthesis efficiency, robust to entironment conditions and growing in places away from the farmlands. How to increase both biomass producitivy and oil content is important for the microalgal biofuel technology. However, cell growth and lipid accumulation are influenced greatly by the cultural conditions.This paper focused on the cell growth and lipid induction under different culture medium composition and areaotion conditions for Chlorella (Chlorella sp.), hoping such investigatng results would help the determination of culture method of it to appraches higher biomass prroducity and lipid content.Firstly, Nile red staining method detecting the relative content of neutral lipid of Chlorella was setup and the measurement conditions were optimized. The measurement conditions of the Nile red staining method detecting the relative content of neutral lipid of Chlorella were:excitation wavelength 527nm, emission wavelength 569nm, detecting the fluorescence intensity after staining at 4℃ice bath for 90 seconds, the OD540 between 0.20 and 0.30, DMSO concentration 5%. And then observation of Nile red staining-fluorescence under microscopy was dfeveloped and sucessfully detected the formation of oil droplets of Chlorella cells during culturing.The concentrations of nitrogen and phosphorus in culture medium are important for the growth and lipid accumulation of Chlorella sp. The influces of initial concentrations of nitrogen and phorphos in culture medium on Chlorella sp.growth and lipid content were investigated in conventional flasks. It can be found that the cell growth cannot be significantly improved by increasing the nitrogen and phosphorus concentrations. The nutrient, especially the concentration of nitrogen and phosphos in f/2 medium is enough to maintain cell growth of Chlorella in the flask. However, as the flask was aerated with air/corbon dioxide, higher nitrogen and phosphorus concentration in BG11-S medium comparaed with f/2 medium would promote the cell growth and obtain high biomass yield, but the accumulation of lipid is inhibited.Under aeration culture, comparaed with nitrogen and phorphos, other nutritions of BG11-S medium such as Ca2+, Mg2+, Na2EDTA, citric acid, trace elements etc. made little effects on the cell growth and the accumulation of lipid. As the results, a optimized nutrient composition of culture medium based BG11 medium in aerated column photobioreactor was determined as nitrogen(8.80mmol/L), phosphorus(0.115mmol/L), CaCl2, MgSO4,citric acid, citric acid iron ammonium, trace elements, Na2EDTA.The cell growth, lipid content and lipid yield of Chlorella can be increased by aerobic culture. The cell density of aerobic condition is about 2-3 times to static flask conditions. In both BG11-S and f/2 medium, the total lipid under aerobic condition is higher than that of static condition. Even in aerobic condition in flask, BG11-S medium has a higher lipid producity of about 2.64mg·L-1·d-1 than that of in f/2 medium. In BG11-S medium, aerobic condition has a higher lipid producity of about 10.18mg·L-1·d-1 than that of static condition.A preliminary experiment of two-satge method, in which Chlorella sp. was first cultured in rich f/2 medium or BG11-S medium for cell proliferation and than transferred into nutrition-deplete culture medium (especially nitrogen or phorphos deprovision) for lipid induction in second satge was carried out in aerated column photobioreactor. The results shew that the lipid content would increase but the amount of biomass decreased. It means that such two-stage method would not help to enhance the producity of lipid for Chlorella sp. However, only on the view of lipid induction, sea water was good enough to instead the nutrition-deplete culture medium. |
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