Elsevier

Bioresource Technology

Volume 138, June 2013, Pages 382-386
Bioresource Technology

Short Communication
Stress-induced lipids are unsuitable as a direct biodiesel feedstock: A case study with Chlorella pyrenoidosa

https://doi.org/10.1016/j.biortech.2013.04.010Get rights and content

Highlights

  • pH 8–10 (nitrate sufficient, indoor) yielded best lipid as a biodiesel feedstock.

  • C16:0, C18:1, C18:2 and C18:3 were found to be the major FAMEs.

  • Stress caused enhanced PUFA rich lipid accumulation.

  • Biodiesel fuel properties were determined using FAME profile.

  • Biodiesel fuel of stress-induced lipid did not comply with worldwide standards.

Abstract

The effects of various stresses on the suitability of lipid synthesized by Chlorella pyrenoidosa for biodiesel production were investigated. Lipids were characterized for detailed fatty acid methyl ester profiling and biodiesel properties like cetane number (CN), iodine value, cold filter plugging point (CFPP). Maximum biomass productivity (106.63 mg L−1 d−1) and lipid content (29.68%) were obtained at indoor cultivation (nitrate sufficient, pH 8–10, 24 h illumination). However, compared to this condition, other nitrate sufficient cultures [pH 6–8 and 10–12 (24 h illumination), and at ambient CO2 and 16:8 h light:dark photoperiod (pH unadjusted)] showed ∼12–14% lower lipid productivity. Upon 50% nitrate depletion (at indoor and outdoor; pH unadjusted) lipid content has increased by 7.62% and 17%, respectively. Though stress conditions helped enhancing lipid accumulation, there was two-fold increase in PUFA content compared to that observed at pH 8–10. This resulted in fuel properties which did not comply with the biodiesel standards.

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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