4 Cases and Outlook for Commercial Production
It is broadly accepted that microalgal-based biofuels’ economics would be largely
improved if obtained in the frame of biomass biorefineries for the production of
multiple commodities and higher value products. According to the US Energy
Information Administration (EIA 2017), world biofuel production will increase
from approximately 1.3 million barrels per day in 2010 to approximately
3.0 million barrels per day in 2040 (Kim et al. 2017). Fermentations run in study of
(Rizza et al. 2017) yielded as coproducts 0.06 kg dry edible yeast S. cerevisiae per
1 kg dry Desmodesmus sp. biomass and the spent fermentation broth that would be
used as animal feed supplements or other biotechnological applications. It is presumed that CO 2 produced as a fermentation product (at least 0.22 kg/kg of dry
Desmodesmus biomass) could be recycled into microalgae to increase productivity
and reduce the C footprint of bioethanol production, as previously reported in the
literature (Stewart and Hessami 2005).
Moreover, sufficient carbohydrate content and efficient biomass harvest are
required for economical bioethanol production from microalgae. Kim et al. (2017)
studied the red algae P. cruentum, which is one of the most promising candidate
organisms for producing fatty acids, lipids, carbohydrates, and pigments, from
seawater and freshwater. In this, research was compared to the separate hydrolysis
and fermentation, and simultaneous saccharification and fermentation methods.
After optimizing each process, these authors designed an overall mass balance for
bioethanol production: 100 g of seawater microalgae consists of 16.9 g glucose,
5.3 g of galactose, and 4.7 g of xylose, whereas 100 g of freshwater microalgae
consists of 16.6 g glucose, 5.5 g galactose, and 6.4 g xylose. Saccharification and
fermentation processing (5% substrate loading, w/v) of microalgae was conducted
with pectinase (4.8 mg/g), cellulase (7.2 mg/g), and S. cerevisiae at 37 °C for 12 h,
resulting in ethanol production of 5.58 and 5.90 g, respectively (Fig. 5). These
results suggest that freshwater is a more efficient candidate for bioethanol production than seawater biomass.
Algenol is an American company owner of the first industrial plant for bioethanol production from engineered microorganisms. Cyanobacterium sp. with
plasmids of a heterologous alcohol dehydrogenase gene (from Synechocystis) and
pyruvate decarboxylase gene (from Zymomonas) (Piven et al. 2015). These high
photosynthetic efficiency values can be ascribed not only to the species used but
also to the geometrical characteristics of the photobioreactors (vertical bags) and to
the cultivation under continuous conditions. The main limitations reported about
this process are the fixed carbon/ethanol ratio, incidence of light, contaminants, and
CO 2 supply time.
Other companies have been research of bioethanol production from microalgae,
according to review (de Farias Silva and Bertucco 2016). In 2011, Joule Unlimited
started a project to build an industrial plant using an engineered cyanobacterium
from light, carbonic gas, water, and salts, with authorization of the Environmental
Protection Agency (EPA) in 2014. This company claims to have an efficient system
11 Biofuels from Microalgae: Bioethanol
243
It is broadly accepted that microalgal-based biofuels’ economics would be largely
improved if obtained in the frame of biomass biorefineries for the production of
multiple commodities and higher value products. According to the US Energy
Information Administration (EIA 2017), world biofuel production will increase
from approximately 1.3 million barrels per day in 2010 to approximately
3.0 million barrels per day in 2040 (Kim et al. 2017). Fermentations run in study of
(Rizza et al. 2017) yielded as coproducts 0.06 kg dry edible yeast S. cerevisiae per
1 kg dry Desmodesmus sp. biomass and the spent fermentation broth that would be
used as animal feed supplements or other biotechnological applications. It is presumed that CO 2 produced as a fermentation product (at least 0.22 kg/kg of dry
Desmodesmus biomass) could be recycled into microalgae to increase productivity
and reduce the C footprint of bioethanol production, as previously reported in the
literature (Stewart and Hessami 2005).
Moreover, sufficient carbohydrate content and efficient biomass harvest are
required for economical bioethanol production from microalgae. Kim et al. (2017)
studied the red algae P. cruentum, which is one of the most promising candidate
organisms for producing fatty acids, lipids, carbohydrates, and pigments, from
seawater and freshwater. In this, research was compared to the separate hydrolysis
and fermentation, and simultaneous saccharification and fermentation methods.
After optimizing each process, these authors designed an overall mass balance for
bioethanol production: 100 g of seawater microalgae consists of 16.9 g glucose,
5.3 g of galactose, and 4.7 g of xylose, whereas 100 g of freshwater microalgae
consists of 16.6 g glucose, 5.5 g galactose, and 6.4 g xylose. Saccharification and
fermentation processing (5% substrate loading, w/v) of microalgae was conducted
with pectinase (4.8 mg/g), cellulase (7.2 mg/g), and S. cerevisiae at 37 °C for 12 h,
resulting in ethanol production of 5.58 and 5.90 g, respectively (Fig. 5). These
results suggest that freshwater is a more efficient candidate for bioethanol production than seawater biomass.
Algenol is an American company owner of the first industrial plant for bioethanol production from engineered microorganisms. Cyanobacterium sp. with
plasmids of a heterologous alcohol dehydrogenase gene (from Synechocystis) and
pyruvate decarboxylase gene (from Zymomonas) (Piven et al. 2015). These high
photosynthetic efficiency values can be ascribed not only to the species used but
also to the geometrical characteristics of the photobioreactors (vertical bags) and to
the cultivation under continuous conditions. The main limitations reported about
this process are the fixed carbon/ethanol ratio, incidence of light, contaminants, and
CO 2 supply time.
Other companies have been research of bioethanol production from microalgae,
according to review (de Farias Silva and Bertucco 2016). In 2011, Joule Unlimited
started a project to build an industrial plant using an engineered cyanobacterium
from light, carbonic gas, water, and salts, with authorization of the Environmental
Protection Agency (EPA) in 2014. This company claims to have an efficient system
11 Biofuels from Microalgae: Bioethanol
243