Optimization of carbon dioxide fixation and starch accumulation by Tetraselmis subcordiformis in a rectangular airlift photobioreactor

Abstract

Culture conditions are very important to CO₂ bio-fixation and carbohydrate accumulation in microalgae. The objective of this study was to optimize semi-continuous culture conditions of Tetraselmis subcordiformis in a rectangular airlift photobioreactor for obtaining maximized carbon dioxide fixation rate and intracellular starch productivity. The effects of the initial biomass concentration (0.13, 0.8, 1.8, 2.8 and 3.47 g L^-1), the gas flow rate (0.03, 0.1, 0.2, 0.3 and 0.37 V V^-1 m^-1) and different carbon dioxide concentrations (1.63, 5, 10, 15 and 18.37%) were considered using a central composite design. By using response surface methodology and the desirability function approach, the optimal CO₂ fixation rate of 55.15 mg L^-1 h^-1 and the intracellular starch productivity of 10.66 mg L^-1 h^-1 occurred when the initial biomass concentration was 1120 mg L^-1 and the air supplemental CO₂ concentration was 6.9% with a gas flow rate of 0.35 V V^-1 m^-1. These results suggest the potential of applying T. subcordiform to CO₂ mitigation and starch production.

Key words: Photobioreactor, CO₂ fixation rate, starch productivity, response surface methodology, desirability function approach.