Thinning of Botryococcus braunii Colony Sheath by Pretreatment Enhances Solvent-Based Hydrocarbon Recovery

Abstract

Botryococcus braunii is a green microalga that is attracting attention as an alternative aviation fuel owing to its hydrocarbon production. In this study, we investigated two approaches to reducing the energy required by pretreatment for hydrocarbon recovery by solvent extraction. Saltwater culture has been reported previously only for the B race of Botryococcus braunii; it improved hydrocarbon recovery from the A race too. We developed a hot water rinsing method that reduced the temperature requirement from the 85 °C which was previously reported for the B race. As the salt concentration in the medium increased, the colony sheath that covered the entire colony surface of the Yamanaka strain (race A) became thinner and the hydrocarbon recovery increased. Saltwater culture can be applied to race A without any energy input. Hydrocarbon recovery from the Showa strain (race B) exceeded 90% after nine rinses with 70 °C hot water while maintaining this temperature. Thus, both pretreatments lowered the treatment temperature by at least 15 °C compared to previously reported methods. Both treatments improved hydrocarbon recovery by thinning the colony sheaths.