Short CommunicationStress-induced lipids are unsuitable as a direct biodiesel feedstock: A case study with Chlorella pyrenoidosa
Introduction
Microalgae are an attractive choice for a sustainable and environmentally-friendly alternative to petrodiesel. Usually, high lipid content of the microalgae is considered as the major screening criteria for selecting the species for biodiesel production (Francisco et al., 2010). This has led to an upsurge in research for enhancing microalgal lipid production through manipulation of cultivation conditions. Many a researcher investigated the effect of nutritional stress, photo-oxidative stress, and other undesirable environmental stress on microalgal lipid production (Dayananda et al., 2007, Converti et al., 2009 Nigam et al., 2011, Ruangsomboon, 2012). However, unlike thorough characterization of fuel properties (cetane number, oxidative stability, iodine number and cold filter plugging point) of lipids obtained from the plant and vegetable sources (Santoria et al., 2012, Ramos et al., 2009, Knothe, 2009), studies on fuel characterization of microalgal lipid are scarce (Francisco et al., 2010). Surprisingly, while the concept of employing various stresses on microalgae for enhanced production of lipid-rich feedstock for biodiesel has been explored continuously, the investigations on the suitability of lipid synthesized at various cultivation conditions (including stress conditions) as a biodiesel feedstock have been grossly overlooked. Fundamental question such as whether stress induced lipids are suitable as biodiesel feedstock still remains unanswered and hence the need to find the most suitable cultivation which compromises neither fuel quality nor quantity is pertinent. Therefore, we investigated for the first time, the effect of various cultivation conditions on the suitability of microalgae synthesized-lipid for biodiesel production. Chlorella pyrenoidosa (C. pyrenoidosa) was taken as a model microalga to study biodiesel quality at different nutritional, environmental, and physiological cultivation conditions. Important fuel properties of synthesized-lipids were characterized through detail fatty acid methyl esters (FAMEs) profiling.
Section snippets
Microalgal strain
The microalgal specie C. pyrenoidosa was procured from National Collection of Industrial Microorganisms (NCIM), CSIR-National Chemical Laboratories (NCL), Pune; Maharashtra, India.
Culture media and growth conditions and biomass quantification
Bold’s Basal Medium (Dayananda et al., 2007) was used to subculture, maintain and acclimatize the microalgal species to laboratory conditions prior to using it for experimental purpose. Sodium bicarbonate (4.5 g L−1) was used as the sole source of inorganic carbon except for the cultures grown at ambient CO2
Biomass production, lipid content, and CO2 biofixation
Nitrate depletion at indoor and outdoor condition has resulted in 7.62% and 17% enhanced lipid accumulation. However, at the same conditions; biomass productivity was decreased by 19% and 18%, respectively (Fig. 1., Table 1). Similarly, as compared to nitrate sufficient indoor culture, decrease of 23.23%, 13.84%, and 18.41% lipid accumulation was observed at 0.03% CO2, 16:8 h L: D photoperiod and at pH 10–12. In spite of 24.50% increase in biomass production at pH 6–8, lipid content was
Conclusion
To the best of our knowledge, we for the first time evaluated the suitability of the lipid synthesized under stress as a direct biodiesel fuel feedstock. Maximum biomass productivity (106.63 mg L−1 d−1) and lipid content (29.68%) was observed at pH 8–10 (indoor, nitrate sufficient, 24 h illumination). FAMEs and biodiesel quality properties revealed it as the best condition for biodiesel production. Lipid synthesized under various stress conditions was marked with two-fold increase in PUFA content;
Acknowledgements
The first author is thankful to the Council of scientific and industrial research (CSIR), New Delhi, India for the award of senior research fellowship (CSIR–SRF). Department of Biotechnology (DBT), Government of India, New Delhi has been acknowledged for financial assistance towards the microalgae biofuel production related projects. First author is also grateful to the Director and The Academy of Scientific and Innovative Research – National Environmental Engineering Research Institute
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