The optimal conditions for the growth of a diatom Entomoneis sp. were investigated in a 2.5 L bubble column. A modified standard F/2 medium was selected as a standard medium. Silicon was the limiting factor for the growth of this alga, and a periodic addition of Si (fixed 6.7 mg L[superscript -1]) at the cultivating Days 3, 4 and 5 could, to some extent, overcome this limitation. The light intensity for the best growth was found at around 270 mumol photons m[superscript -2]s-[superscript -1] at the aeration rate (in terms of superficial velocity) of 0.5 cm s[superscript -1]. At this condition, the alga exhibited the highest growth rate of 41.39 x10[superscript 4] cells mL-1 and a maximum specific growth rate of 0.48 d-1. The cultivation of Entomoneis sp. in the 17 L flat plate airlift photobioreactor was exposed to sunlight during the day time and fluorescent light during the night. The light intensity from fluorescent light was about 43 mumol photon m[superscript -2] s[superscript -1]. The aeration was supplied at usg of 0.5 cm s-1 and this obtained a maximum specific growth rate of 0.59 d[superscript -1] with a maximum cell concentration of 31.05×104 cells mL[superscript -1] in a batch culture. A semi-continuous culture could be achieved where the 3-day harvesting interval provided the maximum cell concentration of 37.49x10[superscript 4] cell mL[superscript -1]and the specific growth rate of 0.54 d[superscript -1]. Lastly, the pre-evaluation of the effect of CO[subscript 2] for the cultivation of Entomoneis sp. operated with CO[subscript 2] from 1 to 7% in 17 L flat plate airlift in semi-continuous mode demonstrated that the best growth occurred at 5% CO[subscript 2] where the maximum cell concentration and specific growth rate were 53.89x10[superscript 4] cell mL[superscript -1] and 0.68 d-1, respectively.