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Technical insight on the requirements for CO₂-saturated growth of microalgae in photobioreactors.

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 (k _L a)_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 (C_crit), specific CO₂ uptake rate (SCUR), and volumetric CO₂ mass-transfer coefficient (k _L a)_C required for the governing CO₂ mass-transfer equation. C_crit 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.

SUBMITTER: Yuvraj

PROVIDER: S-EPMC5451369 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Technical insight on the requirements for CO2-saturated growth of microalgae in photobioreactors.

Yuvraj Padmanabhan Padmini P

3 Biotech 20170531 2

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 fea ...[more]

PMID: 28567633

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Project description:The valorization of CO2 to produce high-value chemicals, such as methanol and hydrocarbons, represents key technology in the future net-zero society. Herein, we report further investigation of a PdZn/ZrO2 + SAPO-34 catalyst for conversion of CO2 and H2 into propane, already presented in a previous work. The focus of this contribution is on the scale up of this catalyst. In particular, we explored the effect of mixing (1:1 mass ratio) and shaping the two catalyst functions into tablets and extrudates using an alumina binder. Their catalytic performance was correlated with structural and spectroscopic characteristics using methods such as FT-IR and X-ray absorption spectroscopy. The two scaled-up bifunctional catalysts demonstrated worse performance than a 1:1 mass physical mixture of the two individual components. Indeed, we demonstrated that the preparation negatively affects the element distribution. The physical mixture is featured by the presence of a PdZn alloy, as demonstrated by our previous work on this sample and high hydrocarbon selectivity among products. For both tablets and extrudates, the characterization showed Zn migration to produce Zn aluminates from the alumina binder phase upon reduction. Moreover, the extrudates showed a remarkable higher amount of Zn aluminates before the activation rather than the tablets. Comparing tablets and extrudates with the physical mixture, no PdZn alloy was observed after activation and only the extrudates showed the presence of metallic Pd. Due to the Zn migration, SAPO-34 poisoning and subsequent deactivation of the catalyst could not be excluded. These findings corroborated the catalytic results: Zn aluminate formation and Pd0 separation could be responsible for the decrease of the catalytic activity of the extrudates, featured by high methane selectivity and unconverted methanol, while tablets displayed reduced methanol conversion to hydrocarbons mainly attributed to the partial deactivation of the SAPO-34.

Project description:BackgroundMicroalgae CO2 fixation results in the production of biomass rich in high-valuable products, such as fatty acids and carotenoids. Enhanced productivity of valuable compounds can be achieved through the microalgae's ability to capture CO2 efficiently from sources of high CO2 contents, but it depends on the species. Culture collections of microalgae offer a wide variety of defined strains. However, an inadequate understanding of which groups of microalgae and from which habitats they originate offer high productivity under increased CO2 concentrations hampers exploiting microalgae as a sustainable source in the bioeconomy.ResultsA large variety of 81 defined algal strains, including new green algal isolates from various terrestrial environments, were studied for their growth under atmospheres with CO2 levels of 5-25% in air. They were from a pool of 200 strains that had been pre-selected for phylogenetic diversity and high productivity under ambient CO2. Green algae from terrestrial environments exhibited enhanced growth up to 25% CO2. In contrast, in unicellular red algae and stramenopile algae, which originated through the endosymbiotic uptake of a red algal cell, growth at CO2 concentrations above 5% was suppressed. While terrestrial stramenopile algae generally tolerated such CO2 concentrations, their counterparts from marine phytoplankton did not. The tests of four new strains in liquid culture revealed enhanced biomass and chlorophyll production under elevated CO2 levels. The 15% CO2 aeration increased their total carotenoid and fatty acid contents, which were further stimulated when combined with the starvation of macronutrients, i.e., less with phosphate and more with nitrogen-depleted culture media.ConclusionGreen algae originating from terrestrial environments, Chlorophyceae and Trebouxiophyceae, exhibit enhanced productivity of carotenoids and fatty acids under elevated CO2 concentrations. This ability supports the economic and sustainable production of valuable compounds from these microalgae using inexpensive sources of high CO2 concentrations, such as industrial exhaust fumes.

Dataset Information

Technical insight on the requirements for CO₂-saturated growth of microalgae in photobioreactors.

Publications

Technical insight on the requirements for CO<sub>2</sub>-saturated growth of microalgae in photobioreactors.

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