The helix pitch and trichome length of Spirulina sp. were promoted to improve the biomass harvesting efficiency and CO2 fixation rate in 660m(2) 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 mu m, and CO2 fixation rate has increased by 42.3% and peaked to 51.3 g/m(2)/d in a DBA raceway pond. Biomass harvesting efficiency was increased with increased helix pitch. When the day-average greenhouse temperature was 33 degrees C and day-average sunlight intensity was 72,100 lux, the helix pitch of Spirulina sp. was increased to 56.2 mu m. 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.