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Poor light utilization efficiency and large occupied area of traditional raceway pond photobioreactors result in low areal microalgal biomass yield in industrial applications. In this study, a pond-tubular hybrid photobioreactor (PTH-PBR) comprising raceway ponds and horizontal tubes was developed to strengthen flash light effect and improve areal microalgal biomass yield. The highest flash cycle frequency (0.63 Hz) of microalgae cells along flow pathway was obtained in the raceway pond of PTH-PBR when shaded area percentage was 20% and ratio of adjacent tube interval to tube diameter was 1, which enhanced microalgal biomass yield by 31.2% than traditional raceway pond. Meanwhile, intracellular chlorophyll content increased by 33.6% and PSII maximum quantum yield (F v /F m ) increased by 8.1% due to decreased photoinhibition stress. The areal microalgal biomass yield of PTH-PBR was 54.7% higher than that of traditional raceway pond without horizontal tubes., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

To reduce bubble diameter and enhance mass transfer, a novel jet-aerated tangential swirling-flow plate photobioreactor was developed that improves the growth rate of microalgae. In this system, the circulating microalgal solution enters a jet aerator that takes up 15% CO 2 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, which markedly reduced the bubble diameter and enhanced mass transfer. 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). 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%., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Computational fluid dynamics were employed to simulate microalgal cells movement with enhanced flash-light effects in a gaslift loop-current column photobioreactor (GLCP) with serial lantern-shaped draft tube (LDT). Clockwise and anticlockwise vortexes were formed in outer down-flow region of GLCP with LDT. The radial velocity, axial velocity, and turbulent kinetic energy of microalgal solution appeared periodical change around the lanterns. The average radial velocity showed a sixfold improvement from 0.003 m/s to 0.021 m/s, and average turbulent kinetic energy was enhanced by 18.2% from 22.5 × 10 -4  m 2 /s 2 to 26.6 × 10 -4  m 2 /s 2 , thus increasing light/dark cycle frequency by 54%. The light/dark cycle frequency increased first and then decreased with an increase of individual lantern height. The increased lantern number promoted the light/dark cycle frequency and light time ratio. Microalgal biomass yield in the GLCP with LDT was improved by 30%, and CO 2 fixation peak rate was promoted by 35%., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A novel serial lantern-shaped draft tube (LDT) that generates vortices is proposed to increase radial velocity between dark and light regions for improving CO 2 fixation with microalgae in a gas-lift circumflux column (GCC) photobioreactor. Clockwise vortices are generated in the downflow outerloop of the GCC photobioreactor with LDT. Radial velocity was improved from 1.50 to 4.35 × 10 -2  m/s, thereby decreased liquid cycle period between dark and light regions by 1.9 times. Mixing time decreased by 21%, and mass transfer coefficient increased by 26% with LDT. Liquid radial velocity in the downflow outerloop and mass transfer coefficient in the GCC photobioreactor both first increased and then decreased when single-lantern height was increased. Peak CO 2 fixation rate increased from 0.62 to 0.87 g/L/d, microalgal biomass yield increased by 50%. Removal efficiencies of pollutants (chemical oxygen demand, ammonium, tilmicosin, and ethinylestradiol) in wastewater were 62-90% with microalgae growth in GCC photobioreactor with LDT., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Highlights • A CO 2 microbubbles dissolver promoted dissolving carbon in a photo-bioreactor. • The influence of pump power was more obvious than that of gas flow rate. • Ceramic shell aerator was more effective at increasing mass transfer coefficient. • Biomass yield was increased by 30% with ceramic shell aerator in dissolver. Abstract A CO 2 microbubbles dissolver (CMD) was developed to facilitate dissolving inorganic carbon and strengthening mass transfer in a horizontal tubular photo-bioreactor system (HTPBRS), which enhanced microalgae biomass productivity with flue gas containing 15% CO 2. The influence of pump power on the bubble formation and mixing effect was found to be more obvious than that of gas flow rate. Ceramic shell aerator was more favorable for reducing bubble diameter and enhancing mass transfer than traditional rubber strip aerator. Bubble formation time decreased by 53.4% and mixing time decreased by 68.9% in response to the increased pump power. When the base area ratio of ceramic shell aerator to dissolver in the HTPBRS increased, bubble formation time decreased by 19.6% and mass transfer coefficient increased by 80.9%. The biomass yield of microalgae Chlorella PY-ZU1 with ceramic shell aerator was 30% higher than that with rubber strip aerator in the HTPBRS. [ABSTRACT FROM AUTHOR]

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% CO 2 . 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. 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. 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% CO 2 condition. [ABSTRACT FROM AUTHOR]