Vortex Flow Strengthened Flashing-light In Column Bioreactors To Promote CO₂ Fixation And Wastewater Purification

Microalgae have been a research hotspot in the field of carbon fixation,renewable energy,and environmental remediation because of their high light energy utilization efficiency,great growth and CO₂ fixation rate,and strong wastewater purification ability.Efficient photobioreactor is a key technology for CO₂ sequestration with microalgae.CFD simulation,particle image velocity measurement,and miniatur Doppler velocimeter were used to invent and develop column photobioreactor with vortex flow and enhanced flashing-light effect,such as tangential spiral-flow column photobioreactor and serial lantern-shaped draft tube column photobioreactors,improve the turbulence intensity of microalgal solution,decrease the bubble diameters,strengthen the mixing and mass transfer,and reveal the cellular responses of microstructure and antioxidant capacity during CO₂ fixation and wastewater purification with microalgae.Novel tangential spiral-flow column photobioreactor?TSCP?,which generated spiral-flow field,was designed and invented.The radial velocity of microalgal solution was increased by 59 times to enhance the radial flashing-light effect and improve the microalgal growth and CO₂ fixation.The turbulent kinetic energy of microalgal solution was enhanced by 15%,the mixting time was decreased by 64%,and the mass transfer coefficient was improved by 1.9 times.Thus,the actual photochemical efficiency of microalgal cells was increased by 19%,the biomass yield was increased by 1.4 times.When the optimal structural and operational parameters?number of the nozzles = 4,injected velocity of microalgal solution = 1.33 m/s and relative diameter of imaginary tangential circle = 0.3?were used,the mixing time and mass transfer coefficient in TSCP were 32.9 s and 125.6 h-1,respectively.A novel serial lantern-shaped draft tube?LDT?was developed to improve radial disturbance and enhance vortex flow in a column photoreactor.The radial velocity,axial velocity and turbulent kinetic energy of microalgal solution appeared periodical change around the lanterns.The radial velocity increased by 6 times,the turbulent kinetic energy increased by 18.2%,and the light-dark cycle frequency of microalgal cells increased by 54%.The light/dark cycle frequency increased first and then decreased with the increase of individual lantern height.The increased lantern number promoted the light/dark cycle frequency.The experimental results shown that LDT decreased bubble diameter by 37%,increased bubble residence time by 74%,decreased mixing time by 21%,and improved mass transfer coefficient by 26%.As a result,the biomass yield of microalgae was increased by 50%.The microalgae cellular microstructure and antioxidant capacity response when purified flue gas CO₂ and removed organic pollutants in wastewater were revealed.Under 15% CO₂,the removal efficiencies of micropollutants tilmicosin and ethinylestradiol in wastewater reached 99.8% and 94.0%,respectively.When the initial concentrations of tilmicosin and ethinylestradiol increased,the fractal dimension of microalgae cells increased monotonously,and the cell size shrank monotonically.The activities of SOD and CAT,which represented the antioxidant capacity of microalgal cells,increased first and then decreased.Ozone pretreatment broke C=C bonds and benzene rings of refractory organics in the effluent and degraded them into lowmolecular-weight organics,thereby improving microalgae growth and promoting the removal efficiencies of ammonia nitrogen,total phosphorus and COD to 99%,99% and 68%.Pilot scale tests of TSCP with a volume of 1000 L were established.The operational parameters of CO₂ aeration rate,CO₂ volume concentration and cycle pump power were optimized to obtain the influence and regulate law of promoting microalgal growth and photosynthetic pigment synthesis.The chlorophyll a and carotenoid contents of microalgal solution in TSCP were increased by 6% and 41%,respectively.The CO₂ fixation rate was increased by 59%.