Reduction of CO sub(2) by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor

The microalga incorporated photobioreactor is a highly efficient biological system for converting CO sub(2) into biomass. Using microalgal photobioreactor as CO sub(2) mitigation system is a practical approach for elimination of waste gas from the CO sub(2) emission. In this study, the marine microalga Chlorella sp. was cultured in a photobioreactor to assess biomass, lipid productivity and CO sub(2) reduction. We also determined the effects of cell density and CO sub(2) concentration on the growth of Chlorella sp. During an 8-day interval cultures in the semicontinuous cultivation, the specific growth rate and biomass of Chlorella sp. cultures in the conditions aerated 2-15% CO sub(2) were 0.58-0.66 d super(-1) and 0.76-0.87 g L super(-1), respectively. At CO sub(2) concentrations of 2%, 5%, 10% and 15%, the rate of CO sub(2) reduction was 0.261, 0.316, 0.466 and 0.573 g h super(-1), and efficiency of CO sub(2) removal was 58%, 27%, 20% and 16%, respectively. The efficiency of CO sub(2) removal was similar in the single photobioreactor and in the six-parallel photobioreactor. However, CO sub(2) reduction, production of biomass, and production of lipid were six times greater in the six-parallel photobioreactor than those in the single photobioreactor. In conclusion, inhibition of microalgal growth cultured in the system with high CO sub(2) (10-15%) aeration could be overcome via a high- density culture of microalgal inoculum that was adapted to 2% CO sub(2). Moreover, biological reduction of CO sub(2) in the established system could be parallely increased using the photobioreactor consisting of multiple units.