denticulatum, Gracilaria verrucosa, and Kappaphycus alvarezii, with very high
annual production of 8.98 million metric ton/year (Lee and Lee 2016). The major
carbohydrate polymers obtained from red algae are carrageenan, apart from agar and
cellulose which can be used as bioethanol feedstock. Several reports suggest
bioethanol yield of 45–236 mg/g of dry biomass with 0.5–4.72 g/L high titer
(Meinita et al. 2013;Wu et al. 2014). The major species of brown algae are Laminaria japonica, Sargassum fusiforme, and Undaria pinnatifida with estimated
production of nearly 0.68 million metric ton per year (Lee and Lee 2016). The
major carbohydrate polymers for brown algae are cellulose, fucoidan, mannitol,
alginate, and laminarin. Different biotransformation procedures are developed for
utilization of alginate and mannitol for generation of ethanol. The bioethanol yield
obtained from different brown algae varies from 152 mg up to 362 mg per gram of
dry biomass with 0.196–37.8 g/L titer (Wargacki et al. 2012; Kim et al. 2013;
Enquist-Newman et al. 2014). The major green algae strains used for bioethanol
production are Caulerpa sp., Codium fragile, Enteromorpha clathrata, Monostroma
nitidum, and Ulva fasciata with starch and cellulose as major polysaccharide content. Among different macroalgal groups, the annual production of green algae is
minimum, i.e., 21.5 thousand metric ton per year (Lee and Lee 2016). The ethanol
yield for the green algae is also very low, i.e., 0.09 with comparable titer of 9.31 for
Ulva fasciata (Trivedi et al. 2013). Due to high photosynthetic efficiency,
macroalgae generate huge carbohydrate polymers with no or less lignin and
hemicelluloses. Therefore, the carbohydrate polymers are readily available can be
subjected to hydrolysis without any prior pretreatment (John et al. 2011). Also, the
short growth time, that can be one added advantage for making the large biomass
available in short time.
7.2.4 Fourth-Generation Feedstock for Bioethanol Production
Fourth-generation feedstocks are bio-oils, genetically modified microbes, and plants
with high carbon capture and sequestration efficiency. These feedstocks are
engineered to capture more CO 2 during the growth of the feedstock. The processing
of this feedstock also involves processes which can enhance carbon capture which
can be stored in geological formations (e.g., exhausted oil fields) or as mineral
storage in the form of carbonates. Therefore, fourth-generation feedstock-based
bioethanol generation technology is often termed as “bioenergy with carbon storage”
or carbon negative techniques (CBU 2007; Rubens 2008).
Fourth-generation feedstocks are used in different approaches such as (i) petroleumlike hydroprocessing and advanced biochemistry approach of conversion of bio-oils to
bioethanol, (ii) innovative processes of Joule’s “solar-to-fuel” method, (iii) genetic modification of feedstock with the ability to increase carbon capture capacity, and (iv) synthetic
biology approach for genomically synthesized microbes (algae and cyanobacteria). Fourth
generation defies any other category of biofuel (Kagan 2015; Aro 2016). The schematic
representation of different steps involved in fourth-generation feedstock-based bioethanol
generation is shown in Fig. 7.2
7 Bioethanol Production: Generation-Based Comparative Status Measurements
167
annual production of 8.98 million metric ton/year (Lee and Lee 2016). The major
carbohydrate polymers obtained from red algae are carrageenan, apart from agar and
cellulose which can be used as bioethanol feedstock. Several reports suggest
bioethanol yield of 45–236 mg/g of dry biomass with 0.5–4.72 g/L high titer
(Meinita et al. 2013;Wu et al. 2014). The major species of brown algae are Laminaria japonica, Sargassum fusiforme, and Undaria pinnatifida with estimated
production of nearly 0.68 million metric ton per year (Lee and Lee 2016). The
major carbohydrate polymers for brown algae are cellulose, fucoidan, mannitol,
alginate, and laminarin. Different biotransformation procedures are developed for
utilization of alginate and mannitol for generation of ethanol. The bioethanol yield
obtained from different brown algae varies from 152 mg up to 362 mg per gram of
dry biomass with 0.196–37.8 g/L titer (Wargacki et al. 2012; Kim et al. 2013;
Enquist-Newman et al. 2014). The major green algae strains used for bioethanol
production are Caulerpa sp., Codium fragile, Enteromorpha clathrata, Monostroma
nitidum, and Ulva fasciata with starch and cellulose as major polysaccharide content. Among different macroalgal groups, the annual production of green algae is
minimum, i.e., 21.5 thousand metric ton per year (Lee and Lee 2016). The ethanol
yield for the green algae is also very low, i.e., 0.09 with comparable titer of 9.31 for
Ulva fasciata (Trivedi et al. 2013). Due to high photosynthetic efficiency,
macroalgae generate huge carbohydrate polymers with no or less lignin and
hemicelluloses. Therefore, the carbohydrate polymers are readily available can be
subjected to hydrolysis without any prior pretreatment (John et al. 2011). Also, the
short growth time, that can be one added advantage for making the large biomass
available in short time.
7.2.4 Fourth-Generation Feedstock for Bioethanol Production
Fourth-generation feedstocks are bio-oils, genetically modified microbes, and plants
with high carbon capture and sequestration efficiency. These feedstocks are
engineered to capture more CO 2 during the growth of the feedstock. The processing
of this feedstock also involves processes which can enhance carbon capture which
can be stored in geological formations (e.g., exhausted oil fields) or as mineral
storage in the form of carbonates. Therefore, fourth-generation feedstock-based
bioethanol generation technology is often termed as “bioenergy with carbon storage”
or carbon negative techniques (CBU 2007; Rubens 2008).
Fourth-generation feedstocks are used in different approaches such as (i) petroleumlike hydroprocessing and advanced biochemistry approach of conversion of bio-oils to
bioethanol, (ii) innovative processes of Joule’s “solar-to-fuel” method, (iii) genetic modification of feedstock with the ability to increase carbon capture capacity, and (iv) synthetic
biology approach for genomically synthesized microbes (algae and cyanobacteria). Fourth
generation defies any other category of biofuel (Kagan 2015; Aro 2016). The schematic
representation of different steps involved in fourth-generation feedstock-based bioethanol
generation is shown in Fig. 7.2
7 Bioethanol Production: Generation-Based Comparative Status Measurements
167