The establishment of a marine focused biorefinery for bioethanol production using seawater and a novel marine yeast strain

Abstract

Current technologies for bioethanol production rely on the use of freshwater for preparing the fermentation media and use yeasts of a terrestrial origin. Life cycle assessment has suggested that between 1,388 to 9,812 litres of freshwater are consumed for every litre of bioethanol produced. Hence, bioethanol is considered a product with a high-water footprint. This paper investigated the use of seawater-based media and a novel marine yeast strain ‘Saccharomyces cerevisiae AZ65’ to reduce the water footprint of bioethanol. Results revealed that S. cerevisiae AZ65 had a significantly higher osmotic tolerance when compared with the terrestrial reference strain. Using 15-L bioreactors, S. cerevisiae AZ65 produced 93.50 g/L ethanol with a yield of 83.33% (of the theoretical yield) and a maximum productivity of 2.49 g/L/h when using seawater-YPD media. This approach was successfully applied using an industrial fermentation substrate (sugarcane molasses). S. cerevisiae AZ65 produced 52.23 g/L ethanol using molasses media prepared in seawater with a yield of 73.80% (of the theoretical yield) and a maximum productivity of 1.43 g/L/h. These results demonstrated that seawater can substitute freshwater for bioethanol production without compromising production efficiency. Results also revealed that marine yeast is a potential candidate for use in the bioethanol industry especially when using seawater or high salt based fermentation media.

Exploring the tolerance of marine yeast to inhibitory compounds for improving bioethanol production

“…Yeasts, especially S. cerevisiae, are used for bioethanol production, but wild S. cerevisiae has been described as moderately osmotic and salt tolerant compared with other yeasts. 22,23 Marine yeasts have been reported as promising candidates for the production of bioethanol and other chemicals, as they possess high salt tolerance. 22 Previous studies have revealed that there is a wide range of phenotypic responses in the presence of these inhibitory compounds in yeasts and yeasts with a tolerant phenotype perform better in fermentation in the presence of these inhibitory compounds.…”

“…22,23 Marine yeasts have been reported as promising candidates for the production of bioethanol and other chemicals, as they possess high salt tolerance. 22 Previous studies have revealed that there is a wide range of phenotypic responses in the presence of these inhibitory compounds in yeasts and yeasts with a tolerant phenotype perform better in fermentation in the presence of these inhibitory compounds. 24 Research has revealed that marine yeast strains have the ability of converting monomeric hexose sugars into ethanol more efficiently than terrestrial yeast strains.…”

“…24 Research has revealed that marine yeast strains have the ability of converting monomeric hexose sugars into ethanol more efficiently than terrestrial yeast strains. 22,25 A marine yeast, Candida membranifaciens, has been shown to have xylose and arabinose utilising capabilities and whilst ethanol production was not determined using these sugars, this yeast did produce riboavins from these carbon sources and could ferment hexose sugars such as glucose, sucrose and maltose. 26 The ability of yeast to convert sugars present in marine biomass (seaweed) is restricted due to the low or no cellulosic content of this feedstock; however, yeasts with the capability of using sugars derived from seaweed (fucose, mannitol, rhamnose etc.)…”

Free Marine Natural Products Databases for Biotechnology and Bioengineering

“…Microalgae are particularly interesting as they may be farmed in saline water and wastewater streams . Other important developments are related to the production of bioethanol by marine yeast species, even though bioethanol is considered a product with a high‐water footprint …”

Processing watermelon waste using Saccharomyces cerevisiae yeast and the fermentation method for bioethanol production

“…Various filamentous fungi, such as certain Trichoderma and Aspergillus species, have been reported to produce bioethanol as the main fermentation product from lignocellulosic biomass, directly. These fungi are thought to contain two biological systems: one system produces cellulase enzyme for degradation of cellulose to fermentable sugars under aerobic conditions; the second system produces ethanol under anaerobic conditions (Greetham, Zaky, & Du, ; Greetham, Zaky, Makanjuola, & Du, ; Zaky, Greetham, Tucker, & Du, ). However, although Trichoderma and Aspergillus are able to utilize five of the lignocellulosic sugars (glucose, mannose, galactose, xylose, and arabinose) and the ability of direct fermentation of lignocellulose to bioethanol, they do not produce bioethanol with high yield and high rate.…”