The open raceway ponds are nowadays the most used large-scale reactors for microalgae culture. To... more The open raceway ponds are nowadays the most used large-scale reactors for microalgae culture. To avoid the stacking of microalgae, the paddle wheels are the most widely used to circulate and mix the culture medium. In this paper, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of open raceway ponds with different types of paddle wheels (the traditional paddle wheels and the novel paddle wheels with specially inclined angle of the blades). The particle image velocimetry (PIV) was used to validate the reliability of the CFD model. The CFD simulation results showed that the novel raceway pond with 15° inclined angle of the blades had the best mixing efficiency under the same power consumption. Lastly, the results of microalgae culture experiments showed that the growth rates of Chlorella pyrenoidosa in the novel raceway pond with 15° inclined angle of the blades were higher than those in the traditional reactor. The results of the culture experiments and CFD simulations were identical with each other. Therefore, a novel paddle wheel with 15° inclined angle of the blades was obtained for better microalgae cultivation.
The ability to rapidly switch the intracellular energy-storage form from starch to lipids is an a... more The ability to rapidly switch the intracellular energy-storage form from starch to lipids is an advantageous trait for microalgae feedstock. To probe this mechanism, we sequenced the 56.8 Mb genome of Chlorella pyrenoidosa FACHB-9, an industrial production strain for protein, starch and lipids. The genome exhibits positive selection and gene-family expansion in lipid and carbohydrate metabolism and genes related to cell cycle and stress response. Transcriptomic dynamics tracked via mRNA-Seq over six time points during metabolic switch from starch-rich heterotrophy to lipid-rich photoautotrophy revealed that under heterotrophy, genes most strongly expressed were from TCA cycle, respiratory chain, oxidative phosphorylation, gluconeogenesis, glyoxylate cycle and amino acid metabolisms, whereas those most down-regulated from fatty acid and oxidative pentose phosphate metabolism. The shift from heterotrophy into photoautotrophy highlights up-regulation of genes from carbon fixation, phot...
Bioprocess and biosystems engineering, Jan 14, 2015
In this study, a numerical simulation using computational fluid dynamics (CFD) was used to invest... more In this study, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of circular ponds with three different impellers (hydrofoil, four-pitched-blade turbine, and grid plate). The reliability of the CFD model was validated by particle image velocimetry (PIV). Hydrodynamic analyses were conducted to evaluate the average velocity magnitude along the light direction (U z), turbulence properties, average shear stress, pressure loss and the volume percentage of dead zone inside circular ponds. The simulation results showed that U z value of hydrofoil was 58.9, 40.3, and 28.8 % higher than those of grid plate with single arm, grid plate with double arms and four-pitched blade turbines in small-scale circular ponds, respectively. In addition, hydrofoil impeller with down-flow operation had outstanding mixing characteristics. Lastly, the results of Chlorella pyrenoidosa cultivation experiments indicated that the biomass conce...
Haematococcus pluvialis is the best source of natural astaxanthin known as "the king of anti... more Haematococcus pluvialis is the best source of natural astaxanthin known as "the king of antioxidants". The mass outdoor culture is the most workable strategy for astaxanthin production, but the effects of daytime and night temperatures on the biomass concentration and astaxanthin content of H. pluvialis have received little attention. This study indicated that, raising the daytime or night temperature could stimulate night accumulation of astaxanthin until temperature up to 28°C; the night biomass loss increased firstly and then decreased along with the daytime temperature reducing; decreasing the night temperature can lessen night biomass loss; the daytime temperature of 28°C and the night temperature below 28°C were optimal for achieving high biomass and astaxanthin content. Subsequently, the outdoor culture strategy has been improved and can increase the net biomass and astaxanthin productivities by 5 and 2.9-fold as compared to the former strategy.
A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The... more A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The effects of mixer were theoretically evaluated using computational fluid dynamics (CFD) according to radial velocity of fluid and light/dark cycles within reactors. The structure parameters, including the riser width, top clearance, clearance between the baffles and walls, and number of the chambers were further optimized. The microalgae culture test aiming at validating the simulated results was conducted indoor. The results showed the maximum biomass concentrations in the optimized and archetype reactors were 32.8% (0.89gL(-1)) and 19.4% (0.80gL(-1)) higher than that in the control reactor (0.67gL(-1)). Therefore, the novel mixer can significantly increase the fluid velocity along the light attenuation and light/dark cycles, thus further increased the maximum biomass concentration. The PBRs with novel mixers are greatly applicable for high-efficiency cultivation of microalgae.
Background: Microalgae have been extensively investigated and exploited because of their competit... more Background: Microalgae have been extensively investigated and exploited because of their competitive nutritive bioproducts and biofuel production ability. Chlorella are green algae that can grow well heterotrophically and photoautotrophically. Previous studies proved that shifting from heterotrophy to photoautotrophy in light-induced environments causes photooxidative damage as well as distinct physiologic features that lead to dynamic changes in Chlorella intracellular components, which have great potential in algal health food and biofuel production. However, the molecular mechanisms underlying the trophic transition remain unclear.
Novel flat plate PBRs with special mixers were designed for microalgae cultivation. The mixers si... more Novel flat plate PBRs with special mixers were designed for microalgae cultivation. The mixers significantly promote the fluid mixing along the light gradient. The special mixers increased the performance of PBRs for microalgae cultivation. Key factors for algal growth are fluid velocity along light gradient and L/D cycles.
Using CO 2 to regulating pH at 7 can enhance cells growth in the batch mode. Cells cultured in ni... more Using CO 2 to regulating pH at 7 can enhance cells growth in the batch mode. Cells cultured in nitrogen-limitation condition had high lipid content. A semi-cont inuous culture with pH control and nitrogen limitation was developed. The above culture strategy can greatly improve lipid productivity.
A novel cultivation strategy called ''sequential heterotrophy-dilution-photoinduction'' was devel... more A novel cultivation strategy called ''sequential heterotrophy-dilution-photoinduction'' was developed for efficient algal biomass and lipid production. Three Chlorella species were first cultivated heterotrophically to achieve high cell density, then the broth was diluted to suitable concentration (2-5 g/L) and transferred to light environment for photoinduction. With this strategy, the Chlorella intracellular protein and chlorophyll increased rapidly to 50.87% and 32.97 mg/g by a 12-h illumination, which were close to the level of cells cultivated photoautotrophically. Moreover, the lipid contents were increased by 84.57%, 70.65% and 121.59% within 24-h photoinduction for C. vulgaris, C. pyrenoidosa and C. ellipsoidea, respectively. Maximum lipid content as 26.11% of biomass and maximum lipid productivity of 89.89 mg/L/d was both accomplished by C. pyrenoidosa. Further outdoor experiments showed consistent patterns. Therefore, the proposed strategy provided an effective approach for microalgal biomass production to meet the urgent need for both health food and biodiesel.
The open raceway ponds are nowadays the most used large-scale reactors for microalgae culture. To... more The open raceway ponds are nowadays the most used large-scale reactors for microalgae culture. To avoid the stacking of microalgae, the paddle wheels are the most widely used to circulate and mix the culture medium. In this paper, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of open raceway ponds with different types of paddle wheels (the traditional paddle wheels and the novel paddle wheels with specially inclined angle of the blades). The particle image velocimetry (PIV) was used to validate the reliability of the CFD model. The CFD simulation results showed that the novel raceway pond with 15° inclined angle of the blades had the best mixing efficiency under the same power consumption. Lastly, the results of microalgae culture experiments showed that the growth rates of Chlorella pyrenoidosa in the novel raceway pond with 15° inclined angle of the blades were higher than those in the traditional reactor. The results of the culture experiments and CFD simulations were identical with each other. Therefore, a novel paddle wheel with 15° inclined angle of the blades was obtained for better microalgae cultivation.
The ability to rapidly switch the intracellular energy-storage form from starch to lipids is an a... more The ability to rapidly switch the intracellular energy-storage form from starch to lipids is an advantageous trait for microalgae feedstock. To probe this mechanism, we sequenced the 56.8 Mb genome of Chlorella pyrenoidosa FACHB-9, an industrial production strain for protein, starch and lipids. The genome exhibits positive selection and gene-family expansion in lipid and carbohydrate metabolism and genes related to cell cycle and stress response. Transcriptomic dynamics tracked via mRNA-Seq over six time points during metabolic switch from starch-rich heterotrophy to lipid-rich photoautotrophy revealed that under heterotrophy, genes most strongly expressed were from TCA cycle, respiratory chain, oxidative phosphorylation, gluconeogenesis, glyoxylate cycle and amino acid metabolisms, whereas those most down-regulated from fatty acid and oxidative pentose phosphate metabolism. The shift from heterotrophy into photoautotrophy highlights up-regulation of genes from carbon fixation, phot...
Bioprocess and biosystems engineering, Jan 14, 2015
In this study, a numerical simulation using computational fluid dynamics (CFD) was used to invest... more In this study, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of circular ponds with three different impellers (hydrofoil, four-pitched-blade turbine, and grid plate). The reliability of the CFD model was validated by particle image velocimetry (PIV). Hydrodynamic analyses were conducted to evaluate the average velocity magnitude along the light direction (U z), turbulence properties, average shear stress, pressure loss and the volume percentage of dead zone inside circular ponds. The simulation results showed that U z value of hydrofoil was 58.9, 40.3, and 28.8 % higher than those of grid plate with single arm, grid plate with double arms and four-pitched blade turbines in small-scale circular ponds, respectively. In addition, hydrofoil impeller with down-flow operation had outstanding mixing characteristics. Lastly, the results of Chlorella pyrenoidosa cultivation experiments indicated that the biomass conce...
Haematococcus pluvialis is the best source of natural astaxanthin known as "the king of anti... more Haematococcus pluvialis is the best source of natural astaxanthin known as "the king of antioxidants". The mass outdoor culture is the most workable strategy for astaxanthin production, but the effects of daytime and night temperatures on the biomass concentration and astaxanthin content of H. pluvialis have received little attention. This study indicated that, raising the daytime or night temperature could stimulate night accumulation of astaxanthin until temperature up to 28°C; the night biomass loss increased firstly and then decreased along with the daytime temperature reducing; decreasing the night temperature can lessen night biomass loss; the daytime temperature of 28°C and the night temperature below 28°C were optimal for achieving high biomass and astaxanthin content. Subsequently, the outdoor culture strategy has been improved and can increase the net biomass and astaxanthin productivities by 5 and 2.9-fold as compared to the former strategy.
A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The... more A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The effects of mixer were theoretically evaluated using computational fluid dynamics (CFD) according to radial velocity of fluid and light/dark cycles within reactors. The structure parameters, including the riser width, top clearance, clearance between the baffles and walls, and number of the chambers were further optimized. The microalgae culture test aiming at validating the simulated results was conducted indoor. The results showed the maximum biomass concentrations in the optimized and archetype reactors were 32.8% (0.89gL(-1)) and 19.4% (0.80gL(-1)) higher than that in the control reactor (0.67gL(-1)). Therefore, the novel mixer can significantly increase the fluid velocity along the light attenuation and light/dark cycles, thus further increased the maximum biomass concentration. The PBRs with novel mixers are greatly applicable for high-efficiency cultivation of microalgae.
Background: Microalgae have been extensively investigated and exploited because of their competit... more Background: Microalgae have been extensively investigated and exploited because of their competitive nutritive bioproducts and biofuel production ability. Chlorella are green algae that can grow well heterotrophically and photoautotrophically. Previous studies proved that shifting from heterotrophy to photoautotrophy in light-induced environments causes photooxidative damage as well as distinct physiologic features that lead to dynamic changes in Chlorella intracellular components, which have great potential in algal health food and biofuel production. However, the molecular mechanisms underlying the trophic transition remain unclear.
Novel flat plate PBRs with special mixers were designed for microalgae cultivation. The mixers si... more Novel flat plate PBRs with special mixers were designed for microalgae cultivation. The mixers significantly promote the fluid mixing along the light gradient. The special mixers increased the performance of PBRs for microalgae cultivation. Key factors for algal growth are fluid velocity along light gradient and L/D cycles.
Using CO 2 to regulating pH at 7 can enhance cells growth in the batch mode. Cells cultured in ni... more Using CO 2 to regulating pH at 7 can enhance cells growth in the batch mode. Cells cultured in nitrogen-limitation condition had high lipid content. A semi-cont inuous culture with pH control and nitrogen limitation was developed. The above culture strategy can greatly improve lipid productivity.
A novel cultivation strategy called ''sequential heterotrophy-dilution-photoinduction'' was devel... more A novel cultivation strategy called ''sequential heterotrophy-dilution-photoinduction'' was developed for efficient algal biomass and lipid production. Three Chlorella species were first cultivated heterotrophically to achieve high cell density, then the broth was diluted to suitable concentration (2-5 g/L) and transferred to light environment for photoinduction. With this strategy, the Chlorella intracellular protein and chlorophyll increased rapidly to 50.87% and 32.97 mg/g by a 12-h illumination, which were close to the level of cells cultivated photoautotrophically. Moreover, the lipid contents were increased by 84.57%, 70.65% and 121.59% within 24-h photoinduction for C. vulgaris, C. pyrenoidosa and C. ellipsoidea, respectively. Maximum lipid content as 26.11% of biomass and maximum lipid productivity of 89.89 mg/L/d was both accomplished by C. pyrenoidosa. Further outdoor experiments showed consistent patterns. Therefore, the proposed strategy provided an effective approach for microalgal biomass production to meet the urgent need for both health food and biodiesel.
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