| Microalgae fix CO2 through photosynthesis,produce organic carbon and divert it into biomass such as lipids,proteins,and carbohydrates.Dunaliella is a halophilic single-celled alga without a cell wall.It grows rapidly and is easy to cultivate.It has high biomass productivity and high lipid content,and has the potential for bioenergy development.It is also rich in protein,polysaccharide,glycerin,β-carotene and other nutrients,so is also good raw material for feed,fine chemicals and other industries.In this thesis,Dunaliella salina UTEX-LB-1644 and Dunaliella bardawil FACHB-847 were taken as the research objects,and the most suitable nutritional conditions,light conditions and salinity of the two strains were studied.The optimization of culture conditions based on the improvement of biomass and lipid production,and preliminary research on the photosynthetic performance were conducted to further improve the economic value and commercial potential of the algal large-scale production.The specific research results are as follows:Effect of salinity.Both strains grew vigorously in the salinity range of 15-30g/L.When the salinity exceeded 30g/L,the biomass and lipid production decrease with the increase of salinity.Both D.bardawil and D.salina obtained the maximum dry weight at a salinity of 15g/L,which were 1716.67mg/L and 494.85mg/L,and the maximum lipid production was 344.75mg/L and 107.75mg/L,respectively.The highest content of lipid was around 21%.Further studies have found that the salinity range of D.bardawil could be expanded to 5g/L-200g/L,and the protein and glycerol content had significant advantages when the salinity was 200 g/L,and the extremely low salinity(5 g/L)and extremely high salinity(150 g/L and 200 g/L)increased the lipid content.When the salinity was 5 g/L,the lipid content was the highest and the maximum lipid production was obtained.Effect of nitrogen concentration and the interaction between nitrogen concentration and salinity.In the range of 0 g/L-0.84 g/L for final concentration of NaNO3,the maximum production performance,including all production indicators except for the lipid content,of D.bardawil was achieved at a NaNO3 concentration of 0.42 g/L.When concentrations of NaNO3 were very low(0 and 0.021 g/L),the lipid contents were increased.Two-factors experiment on salinity and nitrogen concentration found that nitrogen concentration-salinity of 0.42g/L-S35 was beneficial to D.Bardawil for increasing dry weight,protein,chlorophyll a and b production;that of 0.42g/L-S5,0.42g/L-S80,and 0.021g/L-S35 helped increase carotenoid and lipid production,polysaccharide production,and lipid content,respectively.Effect of light.When the long-period photoperiod(light:dark)was 24:0,D.Salina reached the highest dry weight,polysaccharide,and pigment production,while the lipid content and production reached the maximum at the photoperiod of 12:12.In the frequency photoperiod experiment based on long-period photoperiod of 16:8,it was found that D.salina has the highest dry weight at a frequency photoperiod of 1 and the highest lipid production at a frequency photoperiod of 25.Monochrome red light of 7R0B,monochromatic blue light of 0R7B and six combinations of red-blue light with different proportions were used for the culture of D.bardawil.It was found that white light only had advantages in pigment concentrations among all treatments.The content of lipid and polysaccharid as well as the prodcutions of chlorophyll a,chlorophyll b,carotenoids,biomass,protein,polysaccharide,and lipid under red light 7R0B was much lower than white light.The effect of 6R1B was similar to red light.The production and content of polysaccharide under 0R7B reached the respective highest value,and the production and content of lipid under 3R4B reached the highest values.Comparison of fatty acid composition and biodiesel performance of two algae.The highest fatty acids in D.bardawil and D.salina were both C18:3(n-3),accounting for more than 50%and 40%,respectively.And CN values of biodiesel from D.bardawil ranged from 5.73 to 8.97,CFPP values ranged from-10℃ to-12℃.CN values of biodiesel from D.salina ranged from 13.08 to 22.42,CFPP values ranged from-6℃to-10℃.For both D.bardawil and D.salina in the salinity range of 15-30g/l,CN and CFPP were higher than other treatments significantly,while DU and IV lower significantly.In comparison,D.bardawil had faster growth and higher biomass production.Its dry weight and lipid production were more than 3 times that of D.salina.The combustion performance and stability of D.salina biodiesel were better than those of D.bardawil biodiesel,and D.bardawil biodiesel had better low-temperature fluidity than D.salina.Photosynthetic activity of D.bardawil.Salinity,nitrogen concentration and light quality affected the photosynthetic activity of PSII.The salinity except 80g/L and low nitrogen concentration(0,0.021,and 0.0525 g/L)all increased VJ and VI,the OEC center was damaged,and the electron receptor pool at the end of PSI receptor side was reduced.The quantum yield of electron transport between PSⅡ components increased with salinity increase,decreased φDo,the energy flux per reaction center decreased with salinity increase.The three performances indices of PIABS,PICS,and PITOTAL increased with salinity increase within the salinity range of 5-100 g/L.When the nitrogen concentration was low(0,0.021,and 0.0525g/L),decreased φDo,the quantum yield of electron transport decreased,but the energy flux per reaction center increased,the energy flux per cross-sectional area decreased,and the performance indices generally decreased.Non-white light quality increased rETRmax,Ik and QYss,and reduced NPQ.Light quality of 7R0B and 6R1B increased VJ,but also increased the activity of the OEC center.Light quality of 0R7B slightly impaire the OEC center and reduced the terminal electron acceptor pool on the PSI receptor side.Light quality of 0R7B and 1R6B increased the probability of electron transfer from the reduced intersystem electron acceptor to the final electron acceptor of PSI.Non-white light quality reduced VI,increased quantum yield of electron transport between PSⅡcomponents,decreased φDo,and increased performance indices of PIABS,PITOTAL,and PICS.Analyzing the relationship between the photosynthetic activity of D.bardawil and its substance production,it was found that the relationship between PSⅡ parameters and substance production would also change due to the different effects of nitrogen concentration and light quality treatment on the photosynthetic activity of algae,but VJ and VI were always negatively correlated with production performance,and φPo,Ψo,φEo,φRo,PIABS,and PITOTAL were always positively correlated with production performance. |
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