The air‐lift photobioreactors with flow patterning for high‐density cultures of microalgae and carbon dioxide removal

A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO 2 ) into biomass. Using a microalgal photobioreactor as a CO 2 mitigation system is a practical approach to the problem of CO 2 emission from waste gas. In this study, a marine microalga, Chlorella sp . NCTU‐2, was applied to assess biomass production and CO 2 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% CO 2 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 CO 2 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 CO 2 removal efficiency was related to biomass concentration and aeration rate. The maximum CO 2 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% CO 2 in the aeration gas) in the porous centric‐tube photobioreactor.