| Aiming to the national strategy of "carbon neutrality and carbon peaking",and following the academic frontier of CO2 reduction in flue gas by microalgae,we have conducted the research in the aspect of microalgae species,photobioreactors and carbon fixation process.We have revealed the first 3D subcellular architectures of C pyrenoidosa cell and provides a structural framework for unlocking the higher growth rate in microalgae relevant to a wide range of industrial applications.We have designed alternatively permutated conic baffles in the raceway pond to inprove the development of vortex field and flashing light eficiency of microalgae cells.We have propoesed a CO2 absorptive photobioreactor to efficiently convert gaseous CO2 molecules into liquid HCO3-ions for increasing the CO2 fixation rate and efficiency by Spirulina stainsIn order to unveil its full potential,it is necessary to characterize its subcellular architecture.We achieved 3D visualization of the architectures of C.pyrenoidosa cells,by combining focused ion beam scanning electron microscopy(FIB-SEM),cryo-FIB milling,and cryo-electron tomography(cryo-ET).These high-resolution images bring to light intricate features of intact organelles,including thylakoid membranes,pyrenoid,starch granules,mitochondria,nucleus,lipid droplets and vacuoles,as well as the fine architectures within the chloroplast,including the concave-convex pyrenoid,plastoglobules,thylakoid tips,and convergence zones.Significantly,comparative analysis of wild-type and nuclear-irradiated mutagenic strains determined that cell volume and surface area of mutant cells have increased substantially to 2.2-fold and 1.7-fold,respectively,consistent with up-regulation of the enzyme Rubisco and enhanced photosynthetic metabolic processesAlternatively permutated conic(APC)baffles were proposed to generate vertical and horizontal vortex flow to intensify mixing and mass transfer in a raceway pond Both clockwise vortexes were generated before and after conic baffles in the main stream to increase perpendicular velocity by 40%on vertical cross section.Self-rotary flow around conic baffles and vortex flow among conic baffles were generated to increase perpendicular velocity by 80%on horizontal cross section.The bubble generation time and diameter decreased by 26%and 39%,respectively,while bubble residence time increased by 84%.The solution mixing time decreased by 48%and mass transfer coefficient increased by 34%,the vorticity magnitude and turbulent kinetic energy increased by 6 and 14 times,respectively,and the flashing light frequency of microalgal cells increased by 1.0 times with optimized relative spacing(?)and height(?)of conic baffles.The biomass productivity of Spirulina increased by 40%under pure CO2 with APC baffles in a raceway pondIn order to solve problems of short residence time and low conversion efficiency of CO2 gas aerated directly to raceway ponds,a novel porous nickel-foam filled CO2 absorptive photobioreactor system was developed to strengthen CO2 conversion into NaHCO3 in a short time for improving photosynthesis of microalgae cells.The conversion efficiency from soluble NaHCO3 to microalgae biomass first increased and then decreased with increased pore diameter(peaked at 2 mm)and relative height(peaked at 0.24)of nickel-foam,and CO2 gas outflow rate(peaked at 2 L/min)Finally,we have applied our alternatively permutated conic baffles and CO2 absorptive photobioreactor system to Inner Mongolia Spirulina cultivation base wih a 660 m2 raceway pond.It was found that the CO2 fixation rate of Spirulina in the raceway pond with alternatively permutated conic baffles have increased by 42%,and the growth rate of Spirulina by the CO2 absorptive photobioreactor have increased by 25%.These two technologies have significantly contributed to the carbon fixation rate by microalgae,providing a technical accumulation for the large-scale application of microalgae CO2 emission reduction technology,which may help the national "carbon neutrality and carbon peaking" strategy. |
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