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 CO(2)-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 CO(2) uptake efficiency was 63% of the CO(2) supplied when the CO(2) concentration in the gas supplied was 60% v/v. Carbon losses were >100% during the night, due to CO(2) 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 CO(2) 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 CO(2) 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.
Article: A review of carbon dioxide capture and utilization by membrane integrated microalgal cultivation processes[show abstract] [hide abstract]
ABSTRACT: a b s t r a c t The capture of carbon dioxide (CO 2) from the air for microalgal cultivation has received increasing interest since it allows advantages that do not only reduce the amount of CO 2 already added to the air, but it is also more economical due to the accessibility of air, there are no regeneration requirements and it is a safe method that can help enhance microalgal growth. In order to capture CO 2 from the air, it is necessary to deal with CO 2 emissions from all sources in an atmosphere. Interestingly, the capture unit and microalgal culture can be located at any favorable site. Although a number of photobioreactors have been proposed with a CO 2 distribution system, the consequence of CO 2 losses is still being ignored. Thus, capturing CO 2 from the air via an integrated separation process in a photobioreactor is required for microalgal cultivation. Among the four available separation technologies, the membrane separation process would offer a safe, reliable and low cost method for CO 2 capture. Thus, this method of separation can be considered as a key factor in accelerating the development of a CO 2 enrichment process from the air for microalgal cultivation.Renewable and Sustainable Energy Reviews 01/2011; 15:4002-4012. · 6.02 Impact Factor
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ABSTRACT: The objective of this work was to evaluate different operational strategies for photobioreactors to remove carbon dioxide using the cyanobacteria, Aphanothece microscopica Nägeli. Two types of reactor configuration, bubble column and airlift were evaluated under three different operational conditions to treat air containing 15% carbon dioxide: simple operation, air recirculation and two sequential reactors. The results obtained showed that the reactor configuration and the operational mode were both determinant criteria for the performance of photobioreactors in the biological conversion of carbon dioxide. Operations with air recirculation showed possibilities for use in small-scale operations, but two-stage sequential photobioreactors (elimination capacity and removal efficiency of 12,217 gcarbon/m3reactor day and 52.5%, respectively) were shown to be the operational mode with greatest potential for application on an industrial scale by the increased removal efficiency.Chemical Engineering Journal.