Preliminary Studies On The Scale Cultivation And Harvest Technology Of The Three Marine Microalgae Production

Due to the severely situation of the shortages of fossil fuels and the production of greenhouse gas carbon dioxide on their combustion, finding the renewable energy is receiving considerable attention. Because of the cleaner-burning and renewable fuel, biodiesel can be a focus of the bio-energy. Microalgae biomass energy is to find high efficient microalgae resource for the preparation of biodiesel, and it has great exploitation and utilizing potential. However the raw materials supply and cost constraints are always important factors in development of biodiesel industry. Microalgae biomass productivity and its lipid content are the key factors of the biodiesel cost. Many investigations indicated that lipid content and the dry matter yield of microalgae could be influenced by environmental conditions. In the present experiment, the cultural conditions for optimizing lipids productivity in Dunaliella Salina, Isochrysis zhanjiangensis and Nannochloropsis oculata were studied, and a technical route of microalga oil production was built.(1) In the present study, the crude lipid of seven species of marine microalgae were extracted by ethyl ether using soxhlet extraction method, under a temperature of approximately 60⁸0℃. The soxhlet extraction method was improved by dipping the microalgae in ethyl ether for some time before leaching. The results show that the improved soxhlet extraction was more efficient, lower cost and more thoroughly extraction. What's more the pollution caused by ethyl ether was reduced due to a shorter extraction time.(2) In the present experiment, the effect of CO₂ on the growth and lipid content three marine microalgae in two kinds of aerobic culture medium, groupâ… aeration of pure air and groupâ…¡aeration of mixture with and CO₂ for experimental were studied. The results indicated that the logarithmic phase of growth of the three marine microalgae was reached quickly, with the special growth higher than 1, but the growth and lipid content in experimental groupâ… were significantly lower than that in experimental groupâ…¡. At the end of logarithmic phase, the maximum densities of the three marine microalgae were 3.33×10⁶, 9.20×10⁶ and 1.75×10⁷ cell/mL, respectively. The densities were more than 1.28, 6.23 and 3.09 times in the experimental groupâ…¡as that in the experimental groupâ… of the three marine microalgae. In addition, the lipid content of Isochrysis zhanjiangensis was the highest, and its content was significantly higher in groupâ…¡than that in groupâ… , which uped to 40% and adding to 122.8%, while the lipid contents of Dunaliella Salina and Nannochloropsis oculata rose to 69.5% and 49.6% respectively. (3) The influences of salinity on the biomass and the total lipid of D. Salina were studied by one-factor experimental design. The results showed that there were remarkably effects of different salinity on the biomass and lipid of D. Salina. The microalgae could grow normally in the scope salinity of 20 to 100 , in addition, the salinity of 40 made the highest biomass and the highest lipid content, they got to 1.19 g/L and percentage at 33.84, respectively.(4) Added different sodium silicate concentrations to culture I. zhanjiangensis. The result showed that thought the added sodium silicate was not the key role of the lipid productivity of I. zhanjiangensis, the maximum specific growth rate and biomass were in the treatment group with a sodium silicate concentration of 10 mg/L. Whereas, the highest lipid content and lipid productivity were observed in the treatment group with a sodium silicate of 5 mg/L, which were 63.93% (dry weight basis) and 71.056 mg/L·d, respectively. According to the results of the present experiment, the sodium silicate concentration in the culture medium of I. zhanjiangensis for oil production should be 5¹0 mg/L.(5) Standing polyethylene film bags were used to culture marine microalgae. The two marine microalgae grew to log phase directly without lag phase at the second day. The highest density and specific growth rate of I. zhanjiangensis could high to 2.99×10^<sup>6 cell/mL and 0.626, respectively at the 8th day;Whereas, Nannochloropsis oculata could high to 8.50×10⁶ cell/mL and 0.565, respectively in the 10th day, and it seen continue to rose. Results invented that standing polyethylene film bags were flexible enough for good condition for the algae culture and prevent the film bags from damage. It was cheap, occupied small space and easy to harvest.(6) The harvest of I. zhanjiangensis and N. oculata scale culture were studied. The results indicated that flocculants has significant effects on the two marine microalgae were significant. The condensational degree of aluminium sulfate on I. zhanjiangensis was higher than 70% in 80 minutes, and the condensational degree of the zinc sulfate on N. oculata was higher than 50% within 10 minutes.