9.7 Applications
203
and does not compete with land. Although several species of algae are used as food
in many Asian countries, in many other parts of the world they are not consumed as
food and therefore not likely to pose a threat to food security.
The limitation to the use of polysaccharides such as cellulose for ethanol production is that there are limited microbes which can break down cellulose into glucose.
Microbes such as Saccharomyces cerevisiae can break down sucrose, a much simpler
structure into glucose and metabolize this and produce ethanol as a by-product in a
single process. Inclusion of an additional stage in the production process for breaking
down the feedstock into glucose or simple sugars will significantly add to the cost
of production.
There are microbes which are capable of fermenting laminarin to produce ethanol
such as Pichia angophorae (Horn et al. 2000) yeast S. cerevisiae and bacterium Saccharophagus degradans (Motone et al. 2016). In an age, where fossil fuel depletion
is a major concern, new alternative ways to produce fuel are vital to the survival
of the modern world which is heavily dependent on fuel consumption. Production
of bioethanol from biomass depends on a carbon source and a microbe which synthesizes the enzyme to break down the carbon source for its metabolism and in
the process produces ethanol as a by-product. Laminarinase enzyme extracted from
organisms such as the baker’s yeast S. cerevisiae and bacterium S. degradans can
degrade laminarin into its sugar units. In a coculture of these two organisms with a
medium containing 20 g/L of laminarin, 5.2 g/L of ethanol is obtainable (Motone
et al. 2016). In a separate study in a batch fermentation process, a yield of 0.43 g
ethanol per g substrate was achieved at a pH of 4.5 and oxygen level of 5.8 mmol L
−1
h
−1 (Horn et al. 2000).
One of the limitations of bioethanol production from laminarin is the relatively
lower yield and preference of the microbe for batch systems (Horn et al. 2000). For
large scale and lower cost of production, scaled up continuous process is required by
the biorefineries. For the successful production of bioethanol from laminarin, the cost
of extraction of laminarin from brown algae needs to be minimized as bioethanol
is a high volume and low-cost commodity and feedstock production needs to be
as cheap as possible. Compared to, for example, sugar extraction from sugarcane
which mainly requires mechanical processes and thus less cost of chemicals for
extraction, extraction of laminarin requires additional cost of chemicals such as
sodium hydroxide or calcium carbonate for extraction. Additional unit operations
such as ultrafiltration also add to the cost of laminarin as a feedstock for ethanol
production. Therefore, although a one-step fermentation process to obtain ethanol
from laminarin is possible, the cost implications presently limit the commercial
application.
203
and does not compete with land. Although several species of algae are used as food
in many Asian countries, in many other parts of the world they are not consumed as
food and therefore not likely to pose a threat to food security.
The limitation to the use of polysaccharides such as cellulose for ethanol production is that there are limited microbes which can break down cellulose into glucose.
Microbes such as Saccharomyces cerevisiae can break down sucrose, a much simpler
structure into glucose and metabolize this and produce ethanol as a by-product in a
single process. Inclusion of an additional stage in the production process for breaking
down the feedstock into glucose or simple sugars will significantly add to the cost
of production.
There are microbes which are capable of fermenting laminarin to produce ethanol
such as Pichia angophorae (Horn et al. 2000) yeast S. cerevisiae and bacterium Saccharophagus degradans (Motone et al. 2016). In an age, where fossil fuel depletion
is a major concern, new alternative ways to produce fuel are vital to the survival
of the modern world which is heavily dependent on fuel consumption. Production
of bioethanol from biomass depends on a carbon source and a microbe which synthesizes the enzyme to break down the carbon source for its metabolism and in
the process produces ethanol as a by-product. Laminarinase enzyme extracted from
organisms such as the baker’s yeast S. cerevisiae and bacterium S. degradans can
degrade laminarin into its sugar units. In a coculture of these two organisms with a
medium containing 20 g/L of laminarin, 5.2 g/L of ethanol is obtainable (Motone
et al. 2016). In a separate study in a batch fermentation process, a yield of 0.43 g
ethanol per g substrate was achieved at a pH of 4.5 and oxygen level of 5.8 mmol L
−1
h
−1 (Horn et al. 2000).
One of the limitations of bioethanol production from laminarin is the relatively
lower yield and preference of the microbe for batch systems (Horn et al. 2000). For
large scale and lower cost of production, scaled up continuous process is required by
the biorefineries. For the successful production of bioethanol from laminarin, the cost
of extraction of laminarin from brown algae needs to be minimized as bioethanol
is a high volume and low-cost commodity and feedstock production needs to be
as cheap as possible. Compared to, for example, sugar extraction from sugarcane
which mainly requires mechanical processes and thus less cost of chemicals for
extraction, extraction of laminarin requires additional cost of chemicals such as
sodium hydroxide or calcium carbonate for extraction. Additional unit operations
such as ultrafiltration also add to the cost of laminarin as a feedstock for ethanol
production. Therefore, although a one-step fermentation process to obtain ethanol
from laminarin is possible, the cost implications presently limit the commercial
application.