Improving CO2 fixation with microalgae by bubble breakage in raceway ponds with up-down chute baffles.

The aeration gas was broken into smaller bubbles with enhanced local solution velocity to improve CO2 fixation with microalgae in raceway ponds with up-down chute baffles. A high-speed photography system and online precise pH probes were used to measure bubble generation and residence times, which were affected by paddlewheel speed, aerator orifice diameter, gas flow rate, and solution depth. Bubble generation time (from gas reaching aerator orifice surface to completely escaping from the aerator) decreased because of the enhanced local solution velocity, whereas bubble residence time increased because of the vortex flow field produced by up-down chute baffles. Bubble generation time decreased by 27% and bubble residence time increased by 27% when paddlewheel speed was 10r/min with an aeration gas rate of 0.03vvm. The decreased generation time and increased residence time of aeration bubbles promoted microalgae biomass yield by 29% in optimized flow fields in raceway ponds.