Improving Co₂ Fixation By Microalgae With A Jet-aerated Tangential Swirling-flow Plate Photobioreactor

Microalgae has become one of the most promising research hotspots in carbon emission reduction and new energy development due to their outstanding CO₂ fixation ability,light energy utilization efficiency and conversion into additional biomass.Therefore,it is crucial to develop a photobioreactor with superior performance.In this paper,two novel swirling-flow plate photobioreactors were developed,CFD numerical simulation,dissolved oxygen/p H online test system and high-speed camera system were used.The internal flow field,flashing effect,mixed mass transfer and aeration bubbles of the photobioreactors were studied.Developed a novel jet-aerated tangential swirling-flow plate photobioreactor.In this system,the circulating microalgal solution enters a jet aerator that takes up 15% CO₂ by vacuum suction and then injects into a plate photobioreactor through four centrally symmetric nozzles.Each jetflow is tangent to a tangential circle,driving vertical vortex movement of the surrounding microalgal solution.The vortex flow field in the JTSP photobioreactor was revealed by CFD numerical simulation,and its related structural parameters were optimized,which improved the photobioreactor turbulent kinetic energy?TKE?and light/dark circle frequency,and reduced the dead zone.Compared with the traditional airlift plate photobioreactor,the dead zone of the JTSP photobioreactor was reduced by 56.9%,whereas TKE increased by 35.5% to 18.2 cm²/s².Meanwhile,the motion frequency of microalgae cells between the light zone and dark zone of the photobioreactor was enhanced,which increased the light/dark circle frequency by 11.4-fold to 0.13 Hz,effectively promoting the growth and carbon fixation of microalgae.The mixing mass transfer performance of JTSP photobioreactor was tested by oxygen /pH on-line system and high-speed camera system.It was found that the JTSP photobioreactor can significantly reduce the bubble diameter and enhance the gas-liquid mixed mass transfer to improve the growth and CO₂ fixation rate of microalgae.The mass transfer coefficient was enhanced by decreasing the nozzle number?n?and increasing the ratio of tangential circle diameter to plate photobioreactor equivalent diameter?d/D?.Compared with the TAP photobioreactor,the average bubble diameter decreased by 80.2% to 0.37 mm and the mass transfer coefficient increased 4.6 times to 48.9 h^-1 when n was 4 and d/D was 0.34.Finally,the optimized system increased the biomass dry weight of microalgae by 49.4%.Developed a three-dimensional tangential swirling-flow plate?TTSP?photobioreactor,which could further enhance the mixed mass transfer and light/dark circle frequency of photobioreactor and promote the growth of microalgae and the fixation of CO₂.The microalgae liquid was pumped from the bottom of the photobioreactor through the pump into the jet aerator to take up 15% CO₂,and then injected into the photobioreactor through four symmetrically arranged nozzles.The nozzle axis had an angle with the center section of the photobioreactor and was tangent to an imaginary cylindrical surface located horizontally in the center of the photobioreactor,thereby driving the surrounding microalgae liquid to form staggered vortex of three-dimensional structures.When the angle between the nozzle axis and the central section of the photobioreactor was 22.1° and the ratio of the diameter of tangential cylinder to photobioreactor equivalent diameter?d/D?was 0.34,the light/dark circle frequency and the light time ratio in TTSP photobioreactor were increased by 90.9% and 36.3%,respectively,compared with those in JTSP photobioreactor,the mixing time was decreased by 48.4%,and the biomass dry weight of microalgae was increased by 28.9%.