556 / 2018-09-30 11:20:59

Developing double paddlewheels in a flat plate photo-bioreactor to generate cycle flow between dark and light zones for the improvement of microalgal CO2 fixation

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Double paddlewheels were proposed to generate cycle flow for increasing horizontal fluid velocity between dark and light zones in a flat plate photo-bioreactor, which strengthened the mass transfer and the mixing effect to improve microalgal growth with 15% CO2. Numerical fluid dynamics were used to simulate the cycle flow field with double paddlewheels. The local flow field measured with particle image velocimetry fitted well with the numerical simulation results. DPM analysis were employed to systemic analysis the movement of microalgae cells in the cycle flow that generated by the double paddlewheels. The average cell light/dark (L/D) cycle and time ratio of microalgae between light area were investigated with different gas aeration rate and paddlewheels rotation speed. Results showed that the double paddlewheels could decreased the light/dark cycle time of microalgae and thereby improve microalgal growth rate. The horizontal fluid velocity in the photo-bioreactor was markedly increased from 5.8×10-5 m/s to 0.45 m/s with the rotation of double paddlewheels, resulting in a decreased dark/light cycle period. When the gas aeration rate was 0.06vvm, the average cell light/dark cycle decrease by 51% with the double paddlewheels. Therefore, bubble formation time and diameter reduced by 24.4% and 27.4%, respectively. Meanwhile, solution mixing time reduced by 31.3% and mass transfer coefficient increased by 41.2%. The biomass yield of microalgae Nannochloropsis Oceanic increased by 127.1% with double paddlewheels under 15% CO2 condition. The peak CO2 fixation rate increased from 0.08 to 0.29 g/L/d。