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A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO2) into biomass. Using a microalgal photobioreactor as a CO2 mitigation system is a practical approach to the problem of CO2 emission from waste gas. In this study, a marine microalga, Chlorella sp. NCTU‐2, was applied to assess biomass production and CO2 removal. Three types of photobioreactors were designed and used: (i) without inner column (i.e. a bubble column), (ii) with a centric‐tube column and (iii) with a porous centric‐tube column. The specific growth rates (μ) of the batch cultures in the bubble column, the centric‐tube and the porous centric‐tube photobioreactor were 0.180, 0.226 and 0.252 day−1, respectively. The porous centric‐tube photobioreactor, operated in semicontinuous culture mode with 10% CO2 aeration, was evaluated. The results show that the maximum biomass productivity was 0.61 g/L when one fourth of the culture broth was recovered every 2 days. The CO2 removal efficiency was also determined by measuring the influent and effluent loads at different aeration rates and cell densities of Chlorella sp. NCTU‐2. The results show that the CO2 removal efficiency was related to biomass concentration and aeration rate. The maximum CO2 removal efficiency of the Chlorella sp. NCTU‐2 culture was 63% when the biomass was maintained at 5.15 g/L concentration and 0.125 vvm aeration (volume gas per volume broth per min; 10% CO2 in the aeration gas) in the porous centric‐tube photobioreactor.

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