Experimental Study And Mechanism Analysis Of Oil-rich Microalgae Culture And Pyrolysis Of Microalgae Residue

The exhaustion of fossil fuels since its non-renewal,the problems of environmental pollution are promoting the development of renewable energy.Biodiesel could be used directly as a substitute for fossil energy.In recent years,oil-rich microalgae have been suggested as a very good candidate used for biodiesel production.But the high cost is the bottleneck of its industrialized production.Selection of excellent algae species,improvement of culture process and oil content in algae,and comprehensive utilization of algal residue are all key technical issues.In this paper,algal strains were selected with higher growth rate and higher lipid production.Separation,screen,identification and optimization conditions for growth were studied.The factors and mechanism of microalgae oil accumulation,the pyrolysis of algal slag after oil extraction were studied.The main conclusions of this paper can be drawn as follows:1.Two algae strains were obtained from water samples.With morphology and molecular biology identification,they were identified belonging to Scenedesmus sp.TD8 and Nannochloropsis sp.TD16 respectively.2.A single factor experiment and orthogonal experiment were conducted to study on the effect of nutrients.The best growth conditions of Nannochloropsis sp.TD16 were got.Under the optimum conditions TD16 biomass yield could reach1.55 which was 1.29-fold compared with that cultured with natural water.3.Biomass and oil content of Scenedesmus sp.TD8.were measured in the four kinds of photobioreactors.The race-way photobioreactor was the best photobioreactor.Waste water was used for culturing Scenedesmus sp.TD8.Five nutrients were added as follows:Na NO₃ 2.25g·L^-1,K₂HPO₄·3H₂O 40mg·L^-1,Mg SO₄·7H₂O 56.25mg·L^-1,Fe Cl₃·6H₂O 9mg·L^-1 and Na₂CO₃ 15mg·L^-1.TD8biomass yield could reach 1.62.4.The results show that TD16 biomass yield was the highest when the N/P was12:1,and the oil content was 23.43%when the N/P was 4:1,and the lipid accumulation was 5.8%higher compared with the conditions before optimization.When the concentration of citric acid and malic acid was 0.15 g·L^-1,the total lipid content was 1.85 and 1.34 folds higher than control group.The lipid content of Nannochloropsis oceanica increased when the concentration of cerium was 6.0 mg·L^-1.The low concentration of cerium promoted the increase of the content in chlorophyll a,while the high concentration inhibited.The activity of SOD,MDA and CAT all increased and the PIabs decreased after being treated by cerium.We found the acyl Co A oxidase was down-regulated by RNA-seq.5.Overexpression vector of acyl carrier protein ssl2084 was constructed.The mutant strains of ssl2084 gene overexpression were obtained by transforming cytoplasm 6803.The algae strains grow slowly.But the oil content increased by4.9%.Overexpression of ssl2084 gene promoted the enrichment of intracellular lipids.6.The pyrolysis of microalgal residue of TD16 has been performed in a fixed-bed reactor.The maximum yield of liquid product was determined.CO₂ and CO contents changed with pyrolysis temperature.The liquid product from microalgal residue contained more alkane/alkene and less aromatic than that from lignocellulose biomass.7.The pyrolysis process shown that the metal-modified ZSM-5 catalysts can enhance decomposition reaction,resulted the gas product increasing with the liquid product yield decreased.The CO₂ content were decreased as the Mg O promoter addition to Ni/ZSM-5 zeolites.Using the Ni（6%）-Mg（2%）/ZSM-5 catalyst with a Si/Al ratio of 50 for the catalytic pyrolysis,the bio-oil product contain the highest hydrocarbon compounds.In this paper,algae strains were selected with higher growth rate and lipid production,and its growth characteristics and mechanism of oil accumulation were preliminarily studied,and its low-cost industrial cultivation was discussed.These results support that the strain has potential as a raw material for biodiesel.