non-reacting residue, but for materials with a high moisture content, biochemical
conversion can be used for more efficient fuel conversion.
Algae inhabit the sea and have high moisture content (around 90%), which
means that the biochemical approach is better for fuel conversion. With biochemical conversion, biodegradability is often an issue. Algae do not contain lignocellulose, which is difficult to degrade; microorganism decomposition is achieved
relatively easily, and algae provide one of the best-suited materials for fermentation
treatment.
One of the methods commonly used for biochemical conversion today is
methane fermentation. In methane fermentation, organic components of biomass
are broken down through various microorganism actions, resulting in its ultimate
conversion to biogas consisting of methane and carbon dioxide. Biogas (methane
gas) production is achieved through various reactions. The carbohydrates (sugars),
proteins, and lipids that make up the organic components of biomass are broken
down into low-molecular weight monosugars, amino acids, and fatty acids through
the actions of hydrolyzing bacteria. Next, low-molecular-weight organic acids such
as acetic acid are produced through the actions of acid fermentation bacteria.
Through the use of methane-producing bacteria, the resulting acetic acid can be
used to produce biogas containing methane and carbon dioxide. Methane gas is also
formed from the carbon dioxide and hydrogen released in the acid production
process.
The biogas produced from methane fermentation consists of roughly 60%
methane and 40% carbon dioxide and may be used as a fuel for boilers, gas engines,
and other gas devices. Biogas also contains trace quantities of hydrogen sulfide, and
iron oxides and activated carbon are used as desulfurizing agents for gas refinement.
In methane fermentation, it is impossible to convert all of the organic components of the biomass into biogas, and some are emitted as residues. These residues
contain undegraded organic components and the microbes responsible for methane
fermentation. Typically, the waste liquid produced in methane fermentation tanks is
used as liquid fertilizer or dehydrated and drained of moisture to produce a solid
mass that can also be used for fertilizer.
Other forms of biochemical conversion besides methane fermentation include
alcohol and hydrogen fermentation. Whereas only the carbohydrate (sugar) organic
components are converted in hydrogen and alcohol fermentation, lipids and proteins can also be used in methane fermentation, resulting in greater fuel conversion
efficiency. Another advantage is that the fuels obtained from methane and hydrogen
fermentation are gases and do not require isolation from the fermentation solution,
which means there is no energy loss due to distillation. Conversely, methane fermentation requires longer retention periods, which translates into larger fermentation tanks and equipment areas than the other approaches. Because methane and
hydrogen are gases with low energy density, they are more difficult to store and
transport than liquid alcohol. Each method has its pros and cons, and the choice of
conversion methods must take into account not only conversion efficiency but also
the installation site and the form of energy usage (Hossain et al. 2008).
9.3 Methane Production from Algae
305
conversion can be used for more efficient fuel conversion.
Algae inhabit the sea and have high moisture content (around 90%), which
means that the biochemical approach is better for fuel conversion. With biochemical conversion, biodegradability is often an issue. Algae do not contain lignocellulose, which is difficult to degrade; microorganism decomposition is achieved
relatively easily, and algae provide one of the best-suited materials for fermentation
treatment.
One of the methods commonly used for biochemical conversion today is
methane fermentation. In methane fermentation, organic components of biomass
are broken down through various microorganism actions, resulting in its ultimate
conversion to biogas consisting of methane and carbon dioxide. Biogas (methane
gas) production is achieved through various reactions. The carbohydrates (sugars),
proteins, and lipids that make up the organic components of biomass are broken
down into low-molecular weight monosugars, amino acids, and fatty acids through
the actions of hydrolyzing bacteria. Next, low-molecular-weight organic acids such
as acetic acid are produced through the actions of acid fermentation bacteria.
Through the use of methane-producing bacteria, the resulting acetic acid can be
used to produce biogas containing methane and carbon dioxide. Methane gas is also
formed from the carbon dioxide and hydrogen released in the acid production
process.
The biogas produced from methane fermentation consists of roughly 60%
methane and 40% carbon dioxide and may be used as a fuel for boilers, gas engines,
and other gas devices. Biogas also contains trace quantities of hydrogen sulfide, and
iron oxides and activated carbon are used as desulfurizing agents for gas refinement.
In methane fermentation, it is impossible to convert all of the organic components of the biomass into biogas, and some are emitted as residues. These residues
contain undegraded organic components and the microbes responsible for methane
fermentation. Typically, the waste liquid produced in methane fermentation tanks is
used as liquid fertilizer or dehydrated and drained of moisture to produce a solid
mass that can also be used for fertilizer.
Other forms of biochemical conversion besides methane fermentation include
alcohol and hydrogen fermentation. Whereas only the carbohydrate (sugar) organic
components are converted in hydrogen and alcohol fermentation, lipids and proteins can also be used in methane fermentation, resulting in greater fuel conversion
efficiency. Another advantage is that the fuels obtained from methane and hydrogen
fermentation are gases and do not require isolation from the fermentation solution,
which means there is no energy loss due to distillation. Conversely, methane fermentation requires longer retention periods, which translates into larger fermentation tanks and equipment areas than the other approaches. Because methane and
hydrogen are gases with low energy density, they are more difficult to store and
transport than liquid alcohol. Each method has its pros and cons, and the choice of
conversion methods must take into account not only conversion efficiency but also
the installation site and the form of energy usage (Hossain et al. 2008).
9.3 Methane Production from Algae
305