Effect of daytime CO2 supplement on productivity and biochemical composition of Scenedesmus armatus under outdoor cultivation

The cultivation of Scenedesmus armatus was carried out under outdoor Thailand climate conditions. The highest actual growth rate occurred at around 9:00 a.m. to 3:00 p.m., with a wide pH range of 6.4 to 11. The supply of CO₂ had slight influence on growth characteristics but did exert some observable effects on nutritional accumulations. Adding CO₂ from 2 to 15% by volume in the aeration (0.2 vvm) caused an increase in lipid and protein from 19.8 to 25.6 and 37.8 to 48.2% w/w, respectively, whereas carbohydrate decreased from 42.5 to 26.2% w/w. Scenedesmus armatus cultivated with 2% CO₂-enriched air provided the highest the average of the average biomass productivity of 91.25 mg L^?1 d^?1, which corresponded to a CO₂ fixation of 165 mg CO₂ L^?1 d^?1 with the average lipid, protein, and carbohydrate productivities of 22.24, 38.34, and 30.67 mg L^?1 d^?1.