Biodiesel yields and fuel quality as criteria for algal-feedstock selection: Effects of CO 2 -supplementation and nutrient levels in cultures Iracema Andrade Nascimento a, ⁎, Iago Teles Dominguez Cabanelas a , Jacson Nunes dos Santos b , Mauricio A. Nascimento b , Leandro Sousa a , Giovanni Sansone c a Institute of Biology, Federal University of Bahia, Campus Ondina, CEP 40, 170-290 Salvador, Bahia, Brazil b Polytechnic Institute, Federal University of Bahia, CEP 40, 210-630 Salvador, Bahia, Brazil c Università degli studi di Napoli Federico II, via Mezzocannone 16, 80134 Napoli, Italy abstract article info Article history: Received 9 September 2014 Received in revised form 2 December 2014 Accepted 4 January 2015 Available online xxxx Keywords: Microalgae CO 2 -ﬁxation rates Lipid productivity FA proﬁles Biodiesel quality Biodiesel yields Microalgae-oil yields and quality, associated with CO 2 -ﬁxation rates, are able to enhance the feasibility of algal- biodiesel production and economics. Those issues were used as selective criteria applied to Trebouxiophyceae strains. Chlorella vulgaris and two Botryococcus strains were conﬁrmed to grow and to produce high quality biodiesels at distinct levels (2.5 to 20%) of CO 2 -supplementation. Nevertheless, under nutrient-sufﬁcient conditions, C. vulgaris showed the highest CO 2 -ﬁxation rate (0.611 g L -1 d -1 ) and biomass production at 5% CO 2 - supplementation, while for Botryococcus terribilis and Botryococcus braunii, the maximum rates (0.614 and 0.555 g L -1 d -1 CO 2 ) were obtained at 10%-supplementation. Under nutrient-deﬁcient conditions lipids have increased to be above the contents found during the exponential growth-phase, by a maximum of 43%. The fatty-acid proﬁles varied according to strains and CO 2 -levels in cultures. Despite variation, palmitic, oleic and linoleic acids predominated. The higher percentage of oleic and palmitic acids over stearic acid, tended to bal- ance the excess of the long chain-size and saturation effects on algal biodiesels' ignition and cold-ﬂow properties . Thus, CO 2 -supplemented levels from 2.5 to 10.0% made biodiesels compliant with fuel-quality standards. Based on the obtained CO 2 -ﬁxation rates biodiesels were projected to minimum yields of 42 to 46 L ha -1 d -1 . © 2015 Elsevier B.V. All rights reserved. 1. Introduction Increasing the supply of clean energy, becoming independent of fossil fuel and reducing greenhouse gases (GHG) emissions are inter-connected challenges to be overcome in the immediate future. Concerns about global warming have accelerated the development of technologies aimed at coupling carbon sequestration and increasing the availability and use of renewable energy, to avoid most of the envi- ronmental problems due to the use of fossil fuels [1]. These efforts have led to the recognition that biological CO 2 -ﬁxation is the only process that can address clean energy production associated with the reduction of atmospheric GHG [2,3]. However, biofuel production is currently based on ﬁrst-generation technologies that rely mostly on CO 2 bio- ﬁxation by land-crop feedstocks [3]. They currently require large quan- tities of arable land, deforestation, fertilizers and changes in land use, which may generate higher GHG emissions than the biofuels' market would offset [4]. Moreover, largely due to the slow growth rates of conventional land crops, terrestrial plants' potential for increasing CO 2 capture has been estimated to contribute a reduction of only 3–6% of fossil fuel emissions [5]. Most recent studies [1,6] have noted that photosynthetic microbes, such as microalgae, are capable of generating various types of biofuels, including biodiesel, while simultaneously promoting CO 2 ﬁxation during their photosynthetic growth. Moreover, microalgae can have a very short production cycle in salt- or sewage water without competi- tion from land crops for food production and can be harvested for a con- tinuous supply of oil throughout the year [3]. The major constraint on the commercialization of algal biodiesel is its high cost [7]. Nevertheless, because microalgae offer a CO 2 ﬁxation efﬁciency that is approximately 10–50 times greater than that of terrestrial plants [5], this capacity for reducing CO 2 emissions may enhance the economic feasibility of using algal oil for biodiesel production [7]. Presently, microalgae are garnering interest as feedstock for biodiesel production, a process in which they can simultaneously use waste as a source of nutrients [8] and ﬁx indus- trial CO 2 to generate biomass and a higher quantity of renewable oil compared with oleaginous land crops [9]. This type of integrative pro- duction process will contribute to sustainability efforts, by turning waste and greenhouse gases into business opportunities. Therefore, integrative industrial approaches may potentially lower the costs of algal biofuel production, which has been previously reported to be 2.3 Algal Research 8 (2015) 53–60 ⁎ Corresponding author at: Av Oceanica, 2353/403 Ondina, 40170-010 Salvador, Bahia, Brazil. http://dx.doi.org/10.1016/j.algal.2015.01.001 2211-9264/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal