Promoting helix pitch and trichome length to improve biomass harvesting efficiency and carbon dioxide fixation rate by Spirulina sp. in 660 m2 raceway ponds under purified carbon dioxide from a coal chemical flue gas

The helix pitch and trichome length of Spirulina sp. were promoted to improve the biomass harvesting efficiency and CO2 fixation rate in 660 m2 raceway ponds aerated with food-grade CO2 purified from a coal chemical flue gas. The CO2 fixation rate was improved with increased trichome length of the Spirulina sp. in a raceway pond with double paddlewheels, baffles, and CO2 aerators (DBA raceway pond). The trichome length has increased by 33.3 μm, and CO2 fixation rate has increased by 42.3% and peaked to 51.3 g/m2/d in a DBA raceway pond. Biomass harvesting efficiency was increased with increased helix pitch. When the day-average greenhouse temperature was 33 °C and day-average sunlight intensity was 72,100 lu×, the helix pitch of Spirulina sp. was increased to 56.2 μm. Hence the biomass harvesting efficiency was maximized to 75.6% and biomass actual yield was increased to 35.9 kg in a DBA raceway pond.