Carbon dioxide consumption of the microalga Scenedesmus obtusiusculus under transient inlet CO₂ concentration...

The extensive microalgae diversity offers considerable versatility for a wide range of biotechnological applications in environmental and production processes. Microalgal cultivation is based on CO₂ fixation via photosynthesis and, consequently, it is necessary to evaluate, in a short time and reliable way, the effect of the CO₂ gas concentration on the consumption rate and establish the tolerance range of different strains and the amount of inorganic carbon that can be incorporated into biomass in order to establish the potential for industrial scale application. Dynamic experiments allow calculating the short-term microalgal photosynthetic activity of strains in photobioreactors. In this paper, the effect of step-changes in CO₂ concentration fed to a 20L bubble column photobioreactor on the CO₂ consumption rate of Scenedesmus obtusiusculus was evaluated at different operation times. The highest apparent CO₂ consumption rate (336μmolm^-2s^-1 and 5.6% of CO₂) was 6530mg_CO2g_b^-1d^-1 and it decreased to 222mg_CO2g_b^-1d^-1 when biomass concentration increased of 0.5 to 3.1g_bL^-1 and 5.6% of CO₂ was fed. For low CO₂ concentrations (<3.8%) the pH remained close to the optimal value (7.5 and 8). The CO₂ consumption rates show that S. obtusiusculus was not limited by CO₂ availability for concentrations above of 3.8%. The CO₂ mass balance showed that 90% of the C-CO₂ transferred was used for S. obtusiusculus growth.