Non-destructive oil extraction from Botryococcus braunii (Chlorophyta)

Abstract

Some of the key reasons for why the production of biofuels from microalgae have not yet succeeded as a source of sustainable transport fuel are the costs involved and the amount of energy needed to obtain the oils compared to the energy contained in the final fuel. The key energy costs are in the dewatering of biomass followed by extraction of the oil, disposal of biomass, and the energy content of the nutrient fertiliser needed for regrowing the algae. In this study, we bypass all of these barriers by using a different approach towards cutting energy and fertiliser costs in the production of biofuels from microalgae-rather than growing the algae in the presence of fertilisers such as N and P, followed by harvesting the whole algae cells, and the energetically costly drying of cells and extraction of the fuel from the cells, this process makes use of the natural tendency of the green alga, Botryococcus braunii to release oils from the cell into the extracellular matrix during and after growth. Here, we non-destructively and repeatedly harvest the external oil (hydrocarbons) from B.braunii CCAP 807/2. Extraction with several solvents showed that hexane was not compatible with B.braunii, but that heptane in contact with B. braunii for less than 20 min did not negatively affect this alga. As an alternative, solvent-free method, we tested physical methods of extracting the extracellular oil. Light and temperature did not affect the extraction of the external oil from Botryococcus, but gentle pressure (i.e. 'blotting') was an effective method for external oil recovery. Less than 1 h of blotting also did not affect the physiology of Botryococcus. Both the heptane extraction and the nondestructive 'blotting' methods had no significant effect on growth and photosynthesis (F v /F m , ETR max ) of B. braunii. Our results indicate that over a period of 6 days, we can repeatedly extract over 35 % (using heptane) and 1 % (using 'blotting') of the total oil, mainly in the form of external hydrocarbon in stationary phase cells without damage to the cells.

Developments of five selected microalgae companies developing 'closed' bioreactor biofuel production systems

“…Successfully competing commercially against conventional fossil fuels 18 and biofuels will require enormous further technical and economic developments (Brennan and 19 Owende, 2010; Kovacevic and Wesseler, 2010). For example the development of non-destructive 20 microalgae oil extraction in closed photobioreactors, or the immobilisation of cultures to reduce 21 fertiliser use, a major OPEX component with current systems at present (Moheimani et al, 2013a). 22…”

Extracellular Metabolites from Industrial Microalgae and Their Biotechnological Potential

“…For the study of the long-term reliability of this oil recovery process, an integrated reactor was designed. In the authors view, immobilized biofilms may be the most realistic method for future scaling up of continued Botryococcus oil harvesting; in this way the dewatering stage, which is an energy consuming process of algae-to-biofuel production, can potentially be avoided [116]. …”

Botryococcus braunii for biodiesel production

“…Lipid extraction methods, such as solvent extraction, SC fluid extraction, HTL, and milking in microalgal biodiesel production are worthy of mention [60,[89][90][91][92]. The advantages and disadvantages of different methods for lipid extraction have been widely studied [93,94].…”

“…However, in this research, the oil was not characterized, so it is questionable if it can be applied to biodiesel production. It is interesting to mention the milking of B. braunii Kütz (CCAP 807/2) cells in both solventbased and the solvent-free (blotting) forms, as they are non-destructive external oil extraction methods which cause no cell damage [90]. It means that after lipid extraction, the cells can be returned to the cultivation medium to continue synthesizing lipids.…”