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2010-11-01 - Colloque/Article dans les actes avec comité de lecture - Anglais - 11 page(s)

Massart Amaury, Hantson Anne-Lise , "Optimization of the medium composition of the microalga « Dunaliella tertiolecta butcher” in order to combine high cell density and accumulation of lipids for biodiesel production" in 3rd International Symposium on Energy from Biomass and Waste, Venise, Italie, 2010

  • Codes CREF : Bio-énergétique (DI311B), Biotechnologie (DI3800)
  • Unités de recherche UMONS : Chimie et Biochimie appliquées (F504)
  • Instituts UMONS : Institut des Biosciences (Biosciences), Institut de Recherche en Energétique (Energie)
  • Centres UMONS : Biosys (BIOSYS)

Abstract(s) :

(Anglais) The inexorable depletion of petroleum combined with the contribution of fossil fuels to an increase in atmospheric carbon dioxide, has led scientists to develop alternative, renewable and carbon neutral fuels. One promising line of research is to produce biodiesel from microalgae. Microalgae are photosynthetic unicellular microorganisms present on Earth for more than 2 billion years. They use sunlight as an energy source to capture carbon dioxide, part of which is converted into triglycerides, a raw material in the production of biodiesel. Generally, during the experimental phase, these microorganisms are grown in batch (Erlenmeyer flasks) or in small photobioreactors (PBR). The parameters of the culture (pH, temperature, light) are regulated to increase the growth rate and obtain high cell densities. To grow, microalgae require a specific light intensity and a significant contribution in carbon dioxide. For cultures in small volumes (batch < 500 ml), supplementation in carbon dioxide is unnecessary, the surface of the culture medium is sufficient to ensure adequate gas exchange. A potentially interesting strain for producing biodiesel should have 2 important properties : a fast growth rate and a significant lipid content. Based on these criteria, the microalga Dunaliella Tertiolecta Butcher (ATCC 30923) was chosen for this study. It has an average doubling time of 4h and the lipid ratio reached 25% under certain conditions. The standard culture medium of this strain is the modified NORO medium which has the following composition : NaCl 10g/L, MgCl2.6H2O 1,5g/L, KNO3 1g/L, MgSO4.7H2O 0,5g/L, KCl 0,2g/L, CaCl2.2H2O 0,2g/L, K2HPO4 45mg/L. The objective of this study is to optimize the composition of the culture medium for rapid microalgal growth and an important lipid content in the culture. To do this, we use a design of experiments (3 factors and 2 levels) where the variable parameters are the concentration in nitrates, the light intensity and the salinity (concentration in sodium chloride) of the culture medium. Table 1. Levels of the 3 factors for the design of experiments Factor Low level High level Potassium nitrate 1 g/L 3 g/L Sodium chloride 10 g/L 50 g/L Light intensity 100 µmol.m-2.s-1 300 µmol.m-2.s-1 For each culture, two responses will be analyzed : the growth of algal biomass by visible spectrophotometry at 680 nm and the lipid content of microalgae by fluorescence spectroscopy. The fluorescence spectroscopy allows the quantification of lipids by microalgae through a fat-soluble dye (Nile Red, CAS number 7385-67-3) which makes lipid vesicles fluorescent. The first experiments have highlighted the difficulty of obtaining both a high growth rate and significant lipid content. Indeed, an antagonistic phenomenon occurs : cultures with a rapid growth rate have a low lipid content and vice versa. Moreover, we note that preliminary experiments show that culture media with high nitrate concentration promote growth while an increase in salinity promotes lipid storage. The analysis of the results of the design of experiments will determine the conditions leading to rapid growth coupled with a commercially exploitable lipid content.