Fermentation of pigment-extracted microalgal residue using yeast cell-surface display: direct high-density ethanol production with competitive life cycle impacts. Issue 1 (4th December 2019)

• Record Type: Journal Article
• Authors: Huang, Xiaochen; Bai, Shunwen; Liu, Zhuo; Hasunuma, Tomohisa; Kondo, Akihiko; Ho, Shih-Hsin
• Is Part Of: Green chemistry. Volume 22:Issue 1(2020)
• Page Start: 153
• Page End: 162
• Publication Date: 2019-12-04
• Subjects: Environmental chemistry -- Industrial applications -- Periodicals; Environmental management -- Periodicals; 660
• DOI: 10.1039/c9gc02634g
• Languages: English
• ISSNs: 1463-9262

Abstract

Abstract : This study attempts to optimize the use of microalgal biomass for direct high-density ethanol production instead of conventional pretreatments, combining with comprehensive evaluation of environmental impact by life cycle assessment (LCA). Abstract : Microalgae have attracted increasing attention as a potential feedstock for biofuel production. However, direct high-density ethanol production from microalgae is not commercially feasible due to the requirement for complex pre-treatments and insufficient enzymatic hydrolysis. In this study, we successfully developed a consolidated bioprocessing (CBP) system using recombinant Saccharomyces cerevisiae displaying synergistic cellulases/amylases on cell surfaces to overcome energy-conversion limitations. As Chlamydomonas sp. JSC4 can accumulate considerable amounts of carbohydrates and pigments ( i.e., lutein), performing four rounds of pigment extraction from wet microalgal biomass using acetone was found to significantly eliminate the need for biomass pre-treatment and increase commercial viability. The pigment-extracted JSC4 residues increased ethanol production by 10.7% and 31.6% compared to raw starch and whole JSC4 cells, respectively. The theoretical ethanol production mass and yield from 300 g L −1 of JSC4 material were 73 g L −1 and 64%, respectively, after fermentation for 72 h in the presence of amylase- and cellulase-displaying yeasts, which are dramatically higher than those reported previously. Life cycle assessment (LCA) further revealed that this CBP system has 2.7- to 10.7-fold lower total environmental impact compared to alternative ethanol production methods using microalgal biomass. 2.43 kg ethanol and additional products of 5 g lutein from 1 kg microalgal biomass significantly increased the total economic output to $60.875. Overall, this study successfully demonstrates a feasible cell-surface display fermentation system for use in direct high-density ethanol production from pigment-extracted microalgal material.