** Corresponding author: ccardonaal@unal.edu.co
Chlorella vulgaris is an eukaryotic microalgae from the Chlorellaceae family which can be cultivated under three different metabolic routes: autotrophic, heterotrophic and mixotrophic [1]–[3]. In the autotrophic metabolic route the microalgae catches the CO2 and solar luminosity, using them as carbon and energy sources through photosynthesis for cell growth. These autotrophic microalgae cultures can be located near industries or CO2 and NOx sources [4]. On the other hand, heterotrophic growth involves higher production costs due to the use of an external carbon source as substrate without CO2 consumption. Therefore, the interest in the use of industrial, agricultural and domestic wastes are prospective alternative substrates for microalgae culture [5], [6]. And the last metabolic route is the mixotrophic culture. This culture involves the use of inorganic and organic carbon sources [7], [8].
This work presents an analysis about the production costs of microalgae C. vulgaris through heterotropic and autotrophic growth. Additionally, C. vulgaris growth was experimentally evaluated using dairy waste as substrate. The total content of lipids, carbohydrates and proteins of the collected and dried C. vulgaris biomass were determined through Methanol-Chloroform method [9], [10], Phenol-Sulfuric method [11] and Kjeldahl digestion method respectively [12].
With the aim of using some of the molecules produced inside by the microalgae (lipids and carbohydrates from C. vulgaris cake) were evaluate the bioethanol and biodiesel production based on kinetics and yields reported in the literature [13], [14], [15], [16]. The simulation procedure was developed using the commercial software Aspen Plus V8.2 (ASPEN TECHNOLOGY INC). The economic evaluation was performed using the software commercial Aspen Process Economic Analyzer V8.2 (ASPEN TECHNOLOGY INC) taking into account the Colombian context. It was possible to compare 3 cases for the microalgae growth: i) biodiesel and bioethanol production for autotrophic microalgae growth, ii) Biodiesel and bioethanol for heterotrophic growth using a conventional substrate, and iii) Biodiesel and bioethanol production for heterotrophic growth using milk whey as substrate. Finally, considering the share represented by raw materials was probed the sensitivity of microalgae production costs to the substrate source and price. Other important identified issue is related to the microalgae yields which represent the main drawback for profitable biofuels production.
References
[1] F. J. Choix, L. E. de-Bashan, and Y. Bashan, “Enhanced accumulation of starch and total carbohydrates in alginate-immobilized Chlorella spp. induced by Azospirillum brasilense: II. Heterotrophic conditions,” Enzyme Microb. Technol., vol. 51, no. 5, pp. 300–309, 2012.
[2] M. F. Blair, B. Kokabian, and V. G. Gude, “Light and growth medium effect on Chlorella vulgaris biomass production,” J. Environ. Chem. Eng., vol. 2, no. 1, pp. 665–674, 2014.
[3] C. H. Liu, C. Y. Chang, Q. Liao, X. Zhu, and J. S. Chang, “Photoheterotrophic growth of Chlorella vulgaris ESP6 on organic acids from dark hydrogen fermentation effluents,” Bioresour. Technol., vol. 145, pp. 331–336, 2013.
[4] J. Kim, J.-Y. Lee, and T. Lu, “Effects of dissolved inorganic carbon and mixing on autotrophic growth of Chlorella vulgaris,” Biochem. Eng. J., vol. 82, pp. 34–40, Jan. 2014.
[5] M. M. El-Sheekh, R. a. Hamouda, and A. a. Nizam, “Biodegradation of crude oil by Scenedesmus obliquus and Chlorella vulgaris growing under heterotrophic conditions,” Int. Biodeterior. Biodegradation, vol. 82, pp. 67–72, Aug. 2013.
[6] D. Mitra, J. (Hans) van Leeuwen, and B. Lamsal, “Heterotrophic/mixotrophic cultivation of oleaginous Chlorella vulgaris on industrial co-products,” Algal Res., vol. 1, no. 1, pp. 40–48, May 2012.
[7] A. P. Abreu, B. Fernandes, A. a Vicente, J. Teixeira, and G. Dragone, “Mixotrophic cultivation of Chlorella vulgaris using industrial dairy waste as organic carbon source.,” Bioresour. Technol., vol. 118, pp. 61–6, Aug. 2012.
[8] A. Ebrahimian, H.-R. Kariminia, and M. Vosoughi, “Lipid production in mixotrophic cultivation of Chlorella vulgaris in a mixture of primary and secondary municipal wastewater,” Renew. Energy, vol. 71, pp. 502–508, Nov. 2014.
[9] E. G. Bligh and W. J. Dyer, “Extraction of Lipids in Solution by the Method of Bligh & Dyer,” Can. J. Biochem. Physiol, vol. 37, pp. 911–917, 1959.
[10] J. Folch, M. Lees, and G. H. Sloane Stanley, “A Simple Method for the Isolation and Purification of Total Lipides from Animal Tissues,” J. Biol. Chem, vol. 226, pp. 497–509, 1957.
[11] M. Dubois, K. a Gilles, J. K. H. Ton, P. a Rebers, and F. Smith, “Colorimetric Method for Determination of Sugars and Related Substances,” Anal. Chem., vol. 28, pp. 350–356, 1956.
[12] J. Lynch and D. M. Barbano, “Kjeldahl Nitrogen Analysis as a Reference Method for Protein Determination in Dairy Products.,” J. AOAC Int., vol. 82, pp. 1289–1398, 1999.
[13] J. Moncada, J. a. Tamayo, and C. a. Cardona, “Integrating first, second, and third generation biorefineries: Incorporating microalgae into the sugarcane biorefinery,” Chem. Eng. Sci., vol. 118, pp. 126–140, 2014.
[14] L. E. Rincon, J. Moncada Botero, and C. A. Cardona Alzate, Catalytic Systems for Integral Transformations of Oil Plants through Biorefinery concept., First Edit. Manizales, Colombia: Universidad Nacional de Colombia sede Manizales, 2013.
[15] J. a. Quintero and C. a. Cardona, “Process simulation of fuel ethanol production from lignocellulosics using aspen plus,” Ind. Eng. Chem. Res., vol. 50, pp. 6205–6212, 2011.
[16] J. J. Jaramillo, J. M. Naranjo, and C. a. Cardona, “Growth and oil extraction from Chlorella vulgaris: A techno-economic and environmental assessment,” Ind. Eng. Chem. Res., vol. 51, pp. 10503–10508, 2012.