Carbon dioxide uptake efficiency by outdoor microalgal cultures in tubular airlift photobioreactors

Abstract

The influence of solar irradiance and carbon dioxide molar fraction of injected CO2–air mixtures on the behavior of outdoor continuous cultures of the microalga Phaeodactylum tricornutum in tubular airlift photobioreactors was analyzed. Instantaneous solar irradiance, pH, dissolved oxygen, temperature, biomass concentration, and the mass flow rates of both the inlet and outlet oxygen and carbon with both the liquid and gas phases were measured. In addition, elemental analysis of the biomass and the cell‐free culture medium was performed. The oxygen production rate and carbon dioxide consumption rate increased hyperbolically with the incident solar irradiance on the reactor surface. Carbon losses showed a negative correlation with the daily variation of the carbon dioxide consumption rate. The maximum CO2 uptake efficiency was 63% of the CO2 supplied when the CO2 concentration in the gas supplied was 60% v/v. Carbon losses were >100% during the night, due to CO2 production by respiration, and hyperbolically decreased to values of 10% to 20% in the midday hours. An increase in the carbon fixed in the biomass with the solar cycle was observed. A slight daily decrease of carbon content of the cell‐free culture medium indicated the existence of carbon accumulation in the culture. A decrease in CO2 molar fraction in the injected gas had a double benefit: first, the biomass productivity of the system was enhanced from 2.05 to 2.47 g L−1 day−1 by reduction of CO2 inhibition and/or pH gradients; and second, the carbon losses during the daylight period were reduced by 60%. The fluid dynamics in the reactor also influenced the carbon losses: the higher the liquid flow rate the higher the carbon losses. By using a previous mass transfer model the experimental results were simulated and the usefulness of this method in the evaluation and scale‐up of tubular photobioreactors was established. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 67: 465–475, 2000.

Airlift-driven external-loop tubular photobioreactors for outdoor production of microalgae: assessment of design and performance

“…Because the k * a * value in the loop was low, pure carbon dioxide was indicated for injection to improve the gas}liquid mass transfer driving force and prevent carbon limitations (Camacho Rubio et al, 1999). However, injecting pure carbon dioxide can a!ect local pH values and culture productivity (Olaizola, Duerr, & Freeman, 1991;Mazzuca Sobczuk et al, 2000). This e!ect may be reduced by diluting the injected gas with air or nitrogen.…”

Effect of cooling in the night on the productivity and biochemical composition of Tetraselmis suecica

“…On average, the net amount of fixated CO 2 (in g CO 2 g − 1 Table 1 Average daily photon fluxes, net volumetric productivities, yields of biomass on light and CO 2 production at night for the 3 different night temperatures. a T night (°C) biomass) by T. suecica was 1.53 g g −1 , which is in accordance with the CO 2 requirement of the algal biomass [30]. The CO 2 uptake was actually expected to be higher.…”

Lipid Production From Microalgae as a Promising Candidate for Biodiesel Production

“…Effect of CO 2 concentration on growth Sobczuk et al [10] reported that the yield of biomass increased significantly when the CO 2 molar fraction in the injected gas was reduced. They also showed that with less CO 2 in the injected gas, the O 2 generation rate and the CO 2 consumption rate were greater.…”