Hydrocarbon production in high density Botryococcus braunii race B continuous culture

Abstract

Continuous cultures of Botryococcus braunii race B were maintained at photosynthetic cell densities as high as 20 g dry weight per liter for up to 3 months. Growth associated triterpene hydrocarbon accumulation was nearly constant at 22.5% of dry weight for a range of growth rates maintained by daily replacement of 5-15% of the respective cultures. The ability to achieve high cell concentrations and oil levels of roughly 5 g triterpene oil/L resulted from a combination of high light (∼ 1/4 full sun for 15 h/day) and replenishing stoichiometrically balanced growth medium. Due to light-limited growth conditions, cell concentration dropped nearly linearly with increased dilution rate. This reduction in cell number resulted in increased productivity per cell at higher dilution rates and was accompanied by a dramatic increase in algae colony size from 0.09 to 0.343 mm at high dilution rate. This change in colony size resulted in an equally dramatic change in optical density (OD) per gram dry weight, which precluded use of simple correlations of OD and cell concentration. A trickle-film photobioreactor was also demonstrated as a scalable approach to achieving these ultra-high cell concentrations. Additional media analysis revealed a steady increase in photobioreactor conductivity suggesting an accumulation of ions may be the reason for rapid culture crash and washout observed at all dilution rates after several months of continuous operation. The volumetric productivity of 22.5 mg oil/L/photo-h reported here is more than an order of magnitude higher than previous reports for B. braunii race B, reflecting the high cell densities used in this work and substantiating a higher metabolic rate for B. braunii race B than previously surmised from its relatively long doubling times.

Influence of limiting factors on biomass and lipid productivities of axenic Chlorella vulgaris in photobioreactor under chemostat cultivation

“…Hence, improvements to existing PBRs or optimization of culture conditions in PBRs are essential steps to take algal biofuels closer to commercial reality. Furthermore, such studies would enable understanding of basic algal biology, and effects of various culture factors (e.g., light intensity, light cycle, temperature, nutrient concentration, CO 2 , pH) on microalgal biomass and production other bioproducts (Khatri et al, 2014). …”

“…Currently, the understanding of 4 process parameters and limiting conditions on microalgal biomass and lipid productivity is scarce especially in chemostat cultivation (Khatri et al, 2014). A model algae used thus far for studying continuous culture, Chlorella, which was isolated from environmental samples, was selected in this study .…”

A process economic assessment of hydrocarbon biofuels production using chemoautotrophic organisms

“…Ancestors of this alga have been implicated in producing up to 1.4% of the total hydrocarbon in maar-type oil shales based on the unique carbon footprint of C 34 botryococcene oil (Derenne et al, 1997). They have properties similar to crude oil (Hillen et al, 1982), a higher energy density than ethanol (38.1 vs. 23.5 kJ/L) (Tuerk, 2011) and can be easily separated from an aqueous phase by decantation (Khatri et al, 2014). Given these advantages, it was anticipated that the production of botryococcenes could yield higher EROI than ethanol.…”

“…braunii (Khatri et al, 2014) and the associated discovery of the enzymes responsible for the synthesis of C 30 squalene and botryococcene (Okada et al, 2004). C 30+ triterpenes include methylated botryococcenes and squalenes, and are produced by B. braunii race B, a colonial green algae that accumulates these hydrocarbon oils up to 30% of its dry weight composition (Metzger and Largeau, 2005).…”

Botryococcus braunii for the production of hydrocarbons and exopolysaccharides and the role of associated bacteria

“…braunii can produce hydrocarbons with different chemical structures. These hydrocarbons play a role in the natural growth cycle of B. braunii (Khatri et al 2014). Depending on what type of hydrocarbons are produced, B. braunii is subclassified into four chemical races, designated A, B and L (Metzger and Largeau 2005), and S, a recent assignment (Kawachi et al 2012).…”