Abstract
Microalgal cultures are usually sparged with CO2-enriched air to preclude CO2 limitation during photoautotrophic growth. However, the CO2 vol% specifically required at operating conditions to meet the carbon requirement of algal cells in photobioreactor is never determined and 1–10% v/v CO2-enriched air is arbitrarily used. A scheme is proposed and experimentally validated for Chlorella vulgaris that allows computing CO2-saturated growth feasible at given CO2 vol% and volumetric O2 mass-transfer coefficient (kLa)O. CO2 sufficiency in an experiment can be theoretically established to adjust conditions for CO2-saturated growth. The methodology completely eliminates the requirement of CO2 electrode for online estimation of dissolved CO2 to determine critical CO2 concentration (Ccrit), specific CO2 uptake rate (SCUR), and volumetric CO2 mass-transfer coefficient (kLa)C required for the governing CO2 mass-transfer equation. Ccrit was estimated from specific O2 production rate (SOPR) measurements at different dissolved CO2 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.
Highlights
With the developments in microalgal biotechnology towards the production of sustainable and clean bioenergy, it is becoming increasingly important to improve the kinetics and yield of microalgal cultures
The methodology completely eliminates the requirement of CO2 electrode for online estimation of dissolved CO2 to determine critical CO2 concentration (Ccrit), specific CO2 uptake rate (SCUR), and volumetric CO2 mass-transfer coefficientC required for the governing CO2 mass-transfer equation
Mathematical models of photosynthesis–light relationship, description of light regime, and prediction of photosynthetic response to light regime are the cornerstones of photobioreactor engineering (Brindley et al 2011; Fernandez et al 1997; Molina-Grima et al 1999; Merchuk et al 2007; Pottier et al 2005; Pruvost et al 2008; Yun and Park 2003)
Summary
With the developments in microalgal biotechnology towards the production of sustainable and clean bioenergy, it is becoming increasingly important to improve the kinetics and yield of microalgal cultures. Light, which drives the photochemical reactions to produce usable energy for carbon fixation in algal photosynthesis, has been researched utmost to maximize the rate of photosynthesis in photobioreactors, where the cells are often light-limited due to self shading (Olivieri et al 2014). Mathematical models of photosynthesis–light relationship, description of light regime (periodic variations in light intensity experienced by individual cells as they traverse through light gradient inside culture), and prediction of photosynthetic response to light regime are the cornerstones of photobioreactor engineering (Brindley et al 2011; Fernandez et al 1997; Molina-Grima et al 1999; Merchuk et al 2007; Pottier et al 2005; Pruvost et al 2008; Yun and Park 2003). The effect of CO2 concentration on the rate of photosynthesis has been
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