Study On Improvement Of Biodiesel Production Capacity Of Nannochloris Oculata And Tetraselmis Sp.

Due to the depletion of fossil energy and the resulting environmental pollution,the global energy strategy has changed from the fossil energy to renewable bioenergy,among which biodiesel is believed as one of the potential substitutes for fossil fuels.As the third-generation raw material of biodiesel,microalgae not only have the characteristics of fast growth and high lipid content,but also can fix carbon dioxide in the air,and are also beneficial to alleviate the current global warming problem.Nannochloris oculata and Tetraselmis sp.have the fast growth,high lipid content and excellent diesel quality,so they were considered as potential biodiesel feedstocks.In this study,the culture conditions optimization to enhance their lipid production,diesel performance and production efficiency were examined,which will provide a theoretical basis for future commercial utilization.The main experimental results of the study are as follows:1.Optimizing of nutrition conditions for N.oculata.By the comparison of different culture media,it is proposed that nutrient-rich medium is beneficial to the growth of N.oculata,nutrient-poor one is beneficial to lipid content and to improve the combustion and oxidation stability of biodiesel.The medium of f/2 is the optimal one for lipid production of N.oculata.Based on the composition of f/2 medium,it was found that the addition of trace element of Zn can significantly improved the lipid content and oxidation stability of biodiesel for N.oculata.A decrease in the concentrations of macroelements of N and P will inhibit the growth of N.oculata,but promote its lipid contents.NaNO3 is more conducive to the growth and biodiesel performance of N.oculata,while NH4Cl and CH4N2O are more conducive to the lipid content for N.oculata.β-sodium glycerophosphate is more beneficial to both lipid content and biodiesel performance for N.oculata.2.Optimizing of nutrition and environmental conditions of Tetraselmis sp:The effects of nutrient elements,salinity and light on Tetraselmis sp were investigated.It is proposed that the decrease of N and P concentration inhibited the growth of Tetraselmis sp,but promoted the increase of its lipid proportion.The nitrogen and phosphorus sources that are beneficial to the growth of Tetraselmis sp and the improvement of biodiesel performance are NaNO3 and sodium dihydrogen phosphate,respectively.When the salinity was as high as 60‰,the dry weight of Tetraselmis sp.decreased significantly with the promoted lipid content;when the salinity is 30‰,its biodiesel has excellent combustion performance and oxidation stability.By examining the effects of photoperiod and light quality on the growth of Tetraselmis sp.,it is concluded that the biodiesel production capacity and performance of Tetraselmis sp.reached the optimal value when photoperiod was 16:8.The density and dry weight of Tetraselmis sp.treated with 2R5B(red:blue=2:5)were 4.7%and 16.0%higher than the control group,respectively.Light quality B(monochromatic blue light)and 2R5B are more conducive to increasing the lipid content of Tetraselmis sp.,while the combustion performance and oxidation stability of biodiesel are better under light quality R(monochromatic red light).The illumination strategy of using the combined monochromatic light does not require changes to the current composition and control system of the photosynthetic bioreactor,and only requires the replacement of appropriate LED light sources to enhance the ability of lipid production,therefore,is highly attractive.The above optimization of nutrition and environment conditions aiming on biodiesel production provides a certain reference for the selection of culture media and the cost control for the large-scale cultivation of microalgae.3.Screening of chemical regulators for N.oculata and Tetraselmis sp.The effects of MT,3-MA,and MT&3-MA on N.oculata and Tetraselmis sp.were studied.It is found for N.oculata that the cell density,dry weight,lipid content and lipid production in treatment of MT are higher,and the combustion performance and oxidation stability are better,but the fluidity at low-temperature is worse when compared to those in control and treatment of 3-MA.The cell density and dry weight of Tetraselmis sp.in treatment of MT&3-MA and the lipid content and lipid production in MT group are higher than the others treatments.Addition of these chemical regulators did not significantly improve the diesel performance of Tetraselmis sp.Treatment of 2.5μmol/L MT led lipid contetnt of N.oculata reaching 1.36 times that of the control.When the MT concentration was 20μmol/L,the lipid production was 1.24 times that of the control.The MT concentration of 10μmol/L made the lipid content and lipid production of Tetraselmis sp.reaching the highest value of 7.32%and 25.90 mg/L.Therefore,suitable chemical regulators like plant hormones can significantly improve the lipid production capacity of microalgae at very low concentrations,which is a strategy worth further exploration for microalgae cultivation.To investigate the mechanism of the influence of cultivation conditions on the biodiesel production capacity of microalgae,the effects of different MT concentrations on the photosynthetic activity of N.oculata and Tetraselmis sp.were examined.When the concentration of MT was 40μmol/L,the rETRmax of Tetraselmis sp.was significantly higher than those in other treatments,while the rETRmax of N.oculata were not significantly affected by concentration of MT.When the concentration of MT was 2.5 and 10μmol/L,the Fv/Fm and Fv/Fo of N.oculata and Tetraselmis sp.reached the respective highest values,indicating that MT was beneficial to alleviate abiotic stress.The PIABS and PICS of N.oculata and Tetraselmis sp.both reached the highest values in the control and 5 μmol/L treatment.There is a correlation between photosynthetic activity and lipid accumulation and diesel performance.Lipid accumulations of N.oculata and Tetraselmis sp.are moderately negatively correlated with rETRmax and Ik.However,the correlation between diesel performance and photosynthetic activity of two algae was different.Therefore,the relationship between the photosynthetic activity and substance production of these two microalgae strains still needs further clarification.By comparing the biodiesel production potential of the two algae strains,N.oculata showed greater potential for biodiesel production.4.Orthogonal experiment of nutritional conditions and chemical regulators.Based on the above experimental results,the orthogonal experiments on the comprehensive effects of N,P and MT concentrations on N.oculata and Tetraselmis sp.were conducted.The N and P had the greater impact on the growth and substance production of N.oculata and Tetraselmis sp.than MT did.In experimental group 9(N-0.88 mmol/L,P-0.04 mmol/L,MT-2.5μmol/L),the dry weight of N.oculata was the highest among all treatments.Lipid production in experimental group 2(nitrogen-0.176 mmol/L,phosphorus-0.024 mmol/L,MT-2.5μmol/L)was the highest,which was increased by 80.51%compared with the control group.The dry weight of Tetraselmis sp reached the maximum in experimental group 4(nitrogen-0.528 mmol/L,phosphorus-0.04 mmol/L,MT-10μmol/L).Lipid production in experimental group 5(nitrogen-0.528 mmol/L,phosphorus-0.024 mmol/L,MT-10μmol/L)was the highest,which was 2.26%higher than that in the control group.The comprehensive effects of the above conditions provide experimental basis for the process parameters of large-scale cultivation of these two microalgae.