Abstract
In this study, Scenedesmus almeriensis as green microalga was cultivated on bench-scale for carbon dioxide (CO2) capture and lutein production. The autotrophic cultivation of S. almeriensis was carried out by using a vertical bubble column photo-bioreactor (VBC-PBR) with a continuous flow of a gaseous mixture of oxygen (O2), nitrogen (N2), and CO2, the latter in content of 0.0–3.0 %v/v. The liquid phase was batch. S. almeriensis growth was optimized. In addition, lutein extraction was carried out by using accelerated solvent extraction with ethanol as Generally Recognized as Safe (GRAS) solvent at 67 °C and 10 MPa. Upon optimization of CO2 concentration, the maximum biomass productivity, equal to 129.24 mg·L−1·d−1, was achieved during the cultivation by using a content of CO2 equal to 3.0 %v/v and it allowed to obtain a lutein content of 8.54 mg·g−1, which was 5.6-fold higher in comparison to the analogous process carried out without CO2 addition. The ion chemical analysis in the growth medium showed that by gradually increasing CO2 content, the nutrient consumption during the growth phase also increased. This study may be of potential interest for lutein extraction at industrial scale, since it is focused on pigment production from a natural source with a concomitantly CO2 capture.
Highlights
Microalgae cultivation is widely accepted as a valid method for carbon dioxide (CO2 ) capture from industrial plants, and for the extraction of high-value products, such as carotenoids and fatty acids [1,2,3,4,5,6,7,8].Microalgae-based CO2 biofixation and biomass production are strongly dependent on the microalgae strain selection and the adopted growth conditions [5]
PH increased from the initial value of 7.5 at the beginning of the cultivation, to the final value of 8.5 at the end of the cultivation; for the CO2 concentration range investigated (0–3.0 %v/v), the pH of the culture medium was marginally affected by the CO2 content, as reported by several authors [44,45]
By increasing CO2 content, an increase of both biomass productivity, with the consequence reduction of the cultivation time required for the achievement of the maximum value, and of the concentration of the biomass were observed, despite the concentration of the microalgae fed with a gaseous mixture with a CO2 content of 1.5 %v/v and the one fed with a gaseous mixture with a CO2 content of 3.0 %v/v being comparable, even if the cultivation time decreased
Summary
Microalgae cultivation is widely accepted as a valid method for carbon dioxide (CO2 ) capture from industrial plants, and for the extraction of high-value products, such as carotenoids and fatty acids [1,2,3,4,5,6,7,8].Microalgae-based CO2 biofixation and biomass production are strongly dependent on the microalgae strain selection and the adopted growth conditions [5]. Scenedesmus almeriensis, being the highest lutein natural producer, has attracted growing interest and it represents the only commercialized microalgae for pigment extraction [9,10,11,12]. Lutein is classified as a primary xanthophyll because of the presence of two hydroxyl functional groups in the structure [13,14,15]. It acts as a light energy harvesting compound, which improves the photosynthesis efficiency and it prevents photodamage [16]. Lutein is accumulated in the macula of the human eye retina and it is able to prevent or ameliorate cardiovascular diseases [18]
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