Enhanced flashing light effect with up-down chute baffles to improve microalgal growth in a raceway pond

•An up-down chute baffle was developed to enhance flashing light in a raceway pond.•Liquid mixing time decreased and mass transfer coefficient increased with baffles.•Increased vertical liquid velocity resulted in a decreased dark–light cycle period.•Chute baffles enhanced flashing light effect and increased biomass yield by 32.6%.

Novel up-down chute baffles that sequentially generate clockwise and anticlockwise liquid vortexes were developed to increase vertical liquid velocity between the bottom dark area and the top light area in a raceway pond. The vertical liquid velocity, mixing time, and mass transfer coefficient were measured as functions of paddlewheel speed and air aeration rate by using a particle imaging velocimeter, pH probes, and dissolved oxygen probes. The up-down chute baffles decreased the liquid mixing time and increased the mass transfer coefficient by 41% and 25%, respectively. Besides, the vertical liquid velocity increased from ∼0.5 cm/s to ∼6.1 cm/s. As a result, the dark–light cycle period was reduced to 1/12. This enhanced flashing light effect with up-down chute baffles increased biomass yield by 32.6% in the same raceway pond.