Among green, brown, and red algae types, green algae have the lowest resource
value, being restricted to estuaries and freshwater-influenced environments where
seawater and freshwater mix. Red algae exist in numerous varieties, but most of
these are small, and while there is strong demand for mucilaginous polysaccharides
such as agar and carrageenan as thickening agents in foods and daily essentials,
there is little hope for their use as an ethanol production source. In that sense, brown
algae are expected to serve as a source for ethanol, existing in numerous large
varieties such as kelp, sea mustard, sargassum, and giant kelp and having the largest
production yields of the three algae types. At the same time, they also contain a
complex mixture of sugars, with large quantities of mannitol and other sugar
alcohols in addition to fucoidans, alginic acid, laminaran, and cellulose polysaccharides, which poses a large obstacle to their use in whole form.
Also, algae have softer tissues and higher moisture content than land biomass,
making them prone to rotting and foul odors when removed from the ocean.
Measures to prevent this are therefore essential.
9.2.1 Algae-Based Ethanol Production Process
The process of producing ethanol from marine biomass follows a sequence of algae
drying, crushing, pulverization, liquefaction, saccharification, and other preliminary
processing before ethanol fermentation and refinement (concentration and isolation)
(Sato 2011).
A. Liquefaction
Liquefaction is necessary for simple enzyme treatment or microbial fermentation
once the algae’s ingredients have been extracted. Methods of algae liquefaction
include ① extracting sugars from dried powder, ② using enzymes on live algae to
break down the replenishing polysaccharides in the cell wall or between cells, and
③ liquefying live algae under conditions of intense heat and pressure.
Method ① is used with land biomass, but reduces the energy balance because of
the large energy amount needed for drying and pulverization.
The enzyme treatment in ② involves liquefaction through treatment of the
algae’s structural polysaccharides with cellulose or the digestive enzymes of
algivorous mollusks. Liquefaction under mild conditions is possible with enzymes
that are capable of breaking down structural polysaccharide bonds, but the acquisition and costs of suitable enzymes can be an issue.
Liquefaction into a kind of paste form is achieved by treating the dried, powdered form of kelp or other brown algae with enzymes that break down the fibrin in
the cell wall or alginic acid-degrading enzymes that reduce the molecular weight of
the mucopolysaccharides (Alginic acid) between cells and reduce their viscosity.
The red algae Gelidium amansii can be treated with sodium chlorite to remove its
lignin, after which b-galactosidase and xylanase are used for liquefaction and
saccharification.
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9 Marine Bioenergy Production
value, being restricted to estuaries and freshwater-influenced environments where
seawater and freshwater mix. Red algae exist in numerous varieties, but most of
these are small, and while there is strong demand for mucilaginous polysaccharides
such as agar and carrageenan as thickening agents in foods and daily essentials,
there is little hope for their use as an ethanol production source. In that sense, brown
algae are expected to serve as a source for ethanol, existing in numerous large
varieties such as kelp, sea mustard, sargassum, and giant kelp and having the largest
production yields of the three algae types. At the same time, they also contain a
complex mixture of sugars, with large quantities of mannitol and other sugar
alcohols in addition to fucoidans, alginic acid, laminaran, and cellulose polysaccharides, which poses a large obstacle to their use in whole form.
Also, algae have softer tissues and higher moisture content than land biomass,
making them prone to rotting and foul odors when removed from the ocean.
Measures to prevent this are therefore essential.
9.2.1 Algae-Based Ethanol Production Process
The process of producing ethanol from marine biomass follows a sequence of algae
drying, crushing, pulverization, liquefaction, saccharification, and other preliminary
processing before ethanol fermentation and refinement (concentration and isolation)
(Sato 2011).
A. Liquefaction
Liquefaction is necessary for simple enzyme treatment or microbial fermentation
once the algae’s ingredients have been extracted. Methods of algae liquefaction
include ① extracting sugars from dried powder, ② using enzymes on live algae to
break down the replenishing polysaccharides in the cell wall or between cells, and
③ liquefying live algae under conditions of intense heat and pressure.
Method ① is used with land biomass, but reduces the energy balance because of
the large energy amount needed for drying and pulverization.
The enzyme treatment in ② involves liquefaction through treatment of the
algae’s structural polysaccharides with cellulose or the digestive enzymes of
algivorous mollusks. Liquefaction under mild conditions is possible with enzymes
that are capable of breaking down structural polysaccharide bonds, but the acquisition and costs of suitable enzymes can be an issue.
Liquefaction into a kind of paste form is achieved by treating the dried, powdered form of kelp or other brown algae with enzymes that break down the fibrin in
the cell wall or alginic acid-degrading enzymes that reduce the molecular weight of
the mucopolysaccharides (Alginic acid) between cells and reduce their viscosity.
The red algae Gelidium amansii can be treated with sodium chlorite to remove its
lignin, after which b-galactosidase and xylanase are used for liquefaction and
saccharification.
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9 Marine Bioenergy Production