Optimizing gas transfer to improve growth rate of Haematococcus pluvialis in a raceway pond with chute and oscillating baffles

•H. pluvialis flow field was optimized by up–down chute baffle and oscillating baffle.•Mixing time decreased by 33% when the baffles were used.•Mass transfer coefficient increased by 1.3 times when the baffles were used.•Optimized flow field increased biomass yield by 18%.

Up–down chute and oscillating (UCO) baffles were used to generate vortex and oscillating flow field to improve growth rate of Haematococcus pluvialis in a raceway pond. Effects of gas flow rate, solution velocity, and solution depth on solution mass transfer coefficient and mixing time were evaluated using online pH and dissolved oxygen probes. Mass transfer coefficient increased by 1.3 times and mixing time decreased by 33% when UCO baffles were used in the H. pluvialis solution, resulting in an 18% increase in biomass yield with 2% CO2. The H. pluvialis biomass yield further increased to 1.5 g/L, and astaxanthin composition accumulated to 29.7 mg/L under relatively higher light intensity and salinity.