Technical insight on the requirements for CO-saturated growth of microalgae in photobioreactors.

Microalgal cultures are usually sparged with CO-enriched air to preclude CO limitation during photoautotrophic growth. However, the CO vol% specifically required at operating conditions to meet the carbon requirement of algal cells in photobioreactor is never determined and 1-10% v/v CO-enriched air is arbitrarily used. A scheme is proposed and experimentally validated for Chlorella vulgaris that allows computing CO-saturated growth feasible at given CO vol% and volumetric O mass-transfer coefficient (k a). CO sufficiency in an experiment can be theoretically established to adjust conditions for CO-saturated growth. The methodology completely eliminates the requirement of CO electrode for online estimation of dissolved CO to determine critical CO concentration (C), specific CO uptake rate (SCUR), and volumetric CO mass-transfer coefficient (k a) required for the governing CO mass-transfer equation. C was estimated from specific O production rate (SOPR) measurements at different dissolved CO concentrations. SCUR was calculated from SOPR and photosynthetic quotient (PQ) determined from the balanced stoichiometric equation of growth. Effect of light attenuation and nutrient depletion on biomass estimate is also discussed. Furthermore, a simple design of photosynthetic activity measurement system was used, which minimizes light attenuation by hanging a low depth (ca. 10 mm) culture over the light source.