The Cultivation And Biochemical Respond Of N. Oceanica To Natural Soda Lake Water

Due to their high growth rate, high-value products and no farmland occupation, marine microalgae are important resource in pharmaceutical, health care and fine chemicals as well as the most feasible raw stocks of the third generation biofuels. As a low-valued CO2 and inorganic nutrients source, natural crude soda has the similar compositions with seawater, and is always rich in those area with plenty solar energy and vast land, which is the key environment factor for the large scale cultivation of microalgae with low cost Cultivating microalgae with natural crude soda will not only obtain biofuels and high-value products, but also extend the culture range of Nannochloropsis oceanica, and provide a new feasible approach for utilizing natural crude soda.For the evaluation purposes, in this thesis, Nannochloropsis oceanica was taken as a model strain to investigate the effects of natural crude soda on the cell growth and biochemical compositions under nitrogen-repleted and nitrogen-limitation conditions. The main results are as follows:(1) Under nitrogen-repleted condition without CO2 enrichment, the growth was inhibited step by step with the consumption of HCO32- and increase of p H. While aerating with 2% CO2 enriched air, the yield of biomass reached the maximum of 1.95 g/L in the medium containing 12 g/L natural crude soda, while the protein and EPA content were up to38.79% of dry weight and 36.90% of total fatty acids in 24 g/L natural crude soda,respectively. The maximum total carbohydrate content and the total lipid content were achieved, 10.15% and 24.23% of dry weight respectively, in 18 g/L natural crude soda.There was little TAG accumulation in N.oceanica under nitrogen-repleted condition.(2) Under nitrogen-limitation condition with aeration of 90 mL/min, the total lipids of N.oceanica were 35.2% and 34.3% of dry weight in the mediums of 6 g/L and 12 g/L natural crude soda, respectively. As aeration decreased, the biomass, protein, the total carbohydrate, the total lipid accumulation and fatty acid profiles of N.oceanica showed no significant difference to the origin aeration. More than 20% of TAG(in DW) were obtained under nitrogen-limitation condition. These indicated that, as in natural sea water,nitrogen stress could significantly increase lipid accumulation. Nitrogen limitation was a possible approach to cultivate N. oceanica for biodiesel production in natural crude soda.(3) The biomass and fatty acid content of N. oceanica cultured in medium of 12 g/L natural crude soda were similar to those of N. oceanica cultured in seawater while the evaluations were carried out in 100 L photo-bioreactor outdoor cultivation. And the result indicates that culturing microalgae in natural crude soda to produce biodiesel has significant economic feasibility on the base of economic analysis.The above results provide foundational experiment data and referable process conditions for industrial production of biofuels.