The High Density Culture Of Nitzschia Closterium

In order to overcome some problems such as low-density, easy to pollute and the complex operating process during the culture of Nitzschia closterium, the growth characteristics of this microalga was researched in the flate plate bioreactors by the methods of fed-bath and semi-continuous cultures with the optimization cultural medium, and the biomass, polysaccharides and protein content in the cells also inspected under different culture modles. The results are summarized as follows:1. Major macroelement factors and trace metal ions were optimized by means of orthogonal tests. The optimum medium was NaNO₃ 300mg/L,NaH₂PO₄ 25 mg/L,NaHCO₃ 500 mg/L,Na₂SiO₃ 100 mg/L,Mn²⁺ 0.80μmol·L^-1,Cu²⁺ 0.08μmol·L^-1,Zn²⁺ 0.10μmol·L^-1,Mo⁶⁺ 0.02μmol·L^-1,Co²⁺ 0.004μmol·L^-1, by which the growth and cell biomass productivity of Nitzschia closterium was increased about 200% comparing with the medium f/2.2. To investigate the growth characteristics of Nitzschia closteriu, the cultures were carried out in the flat plate photobioreactors. The light attenuation equation and the average light intensity equation of Nitzschia closterium was established in the flat plate photobioreactor. The results showed that 30 mm light-path flat plate photobioreactor could effectively improve the optical efficiency by comparing Eavg/E of the flat plate photobioreactors with the differient light-path of 30 mm, 50 mm and 100 mm. And, the biomass in the 30 mm light-path flat plate photobioreactor was 2 times higher than that in 100 mm light-path flat plate photobioreactor.3. In order to investigate the relationships between renewal rate, renewal period and growth, metabolite and the utilization of nitrogen and phosphorous, the semi-continuous cultures of Nitzschia closterium were carried out in the flat plate photobioreactors. The results showed that the recovery yield followed a parabolic distribution with the increasing of the renewal rates, and the maximum biomass was 2.11×10¹² cell by 33% renewal rate. And by 33% renewal rate, the maximum of biomass recovery yield arrived to 3.12×10¹² cell with the 1 day renewal period. The contents of PO₄-P and NO₃-N in the culture media were increased with a progressive of the renewal rate. When the renewal rate was 10%, the average content of the protein in the cells raised to the maximum, while the average content of polysaccharides in the cells arrived to the maximum by the renewal rate of 23%. In banlance, the better pattern for the semi-continuous culture of Nitzschia closterium in the plate flat photobioreactor was 33% renewal rate and 1 d renewal period.4. To investigate the effects of culture mode on the growth of Nitzschia closterium, the methods of the batch and fed-batch culture were employed. The results showed that different fashions of the fed-batch cultures had distinct affects on the growth and production of protein and polysaccharide in the cells of Nitzschia closterium. The cell density, the content of protein and polysaccharides at the 10th day were 1.901×107cell·mL^-1, 42.82 mg·L^-1 and 95.68 mg·L^-1 when the cultures were fed-cultured with a invariable fed-velocity, which were 2.29 times,1.60 times and 2.15 times as much as that of in the batch cultures, respectively. Under the feeding rate of 0.167, the biomass, the content of protein and polysaccharide in the cells of Nitzschia closterium was 3.83, 5.23 and 5.12 times higher than that of the batch cultures, respectively.