methods will ensure the availability of the substrates and further increase the
hydrogen production and yield.
Various methods which can be employed are physical, physicochemical, chemical and biological processes. Common physical methods which are used are wet and
dry milling, however the processing cost is very high.
Chemical pretreatments include acid, alkali and organosolv solvents. Acid treatment is most commonly researched method and improves the accessibility of
enzymes for fermentation. Alkali treatment is done to remove lignin from the
lignocellulosic biomass. The main disadvantage of this method is of high
processing cost.
Steam explosion and carbon dioxide explosion is one of the most widely
researched physicochemical methods. It involves quick depressurization of pressure
steam which leads to breakdown of lignocellulosic material to cellulose, hemicellulose and lignin.
Certain unusual chemicals such as N-methylmorpholine-N-oxide and cholinium
taurate have also been used for pretreatment purposes (Veeravalli et al. 2019;
Srivastava et al. 2020a, b).
2.6.4 Dark Fermentation
Hydrogen is generated from electrons through fermentation via 2 stages (1) oxidation
of substrate to pyruvate and (2) pyruvate is converted to volatile fatty acids (VFAs)
and alcohols.
Organic mass after pretreatment contains glucose which yields two molecules of
pyruvate. This pyruvate moves into the acidogenic pathway that coupled with
hydrogen production. Other pathways which generate hydrogen are acetic acid
Table 2.3 Different biohydrogen processes with their advantages and disadvantages (Saratale et al.
2019)
Process
Microorganisms
Advantages
Disadvantages
Biophotolysis Blue green algae and
Cynaobacteria
• Cheap source
• Uses solar energy
• Oxygen inhibits the
hydrogen production
Photo
fermentation
Purple non-Sulphur photosynthetic bacteria
• Substrate is
completely utilized
• Waste effluents can
be used
• Low volumetric rates of
production
Dark
fermentation
Strict anaerobes and facultative anaerobes
• High volumetric
rates of production
• Different substrates
can be used
• Low yield of the
product
Microbial
electrolysis
Geobacter, Pseudomonas
and Shewanella
• Complete substrate
utilization
• Extra voltage needed
• Expensive
2 Application of Microorganisms for Biofuel Production
51
hydrogen production and yield.
Various methods which can be employed are physical, physicochemical, chemical and biological processes. Common physical methods which are used are wet and
dry milling, however the processing cost is very high.
Chemical pretreatments include acid, alkali and organosolv solvents. Acid treatment is most commonly researched method and improves the accessibility of
enzymes for fermentation. Alkali treatment is done to remove lignin from the
lignocellulosic biomass. The main disadvantage of this method is of high
processing cost.
Steam explosion and carbon dioxide explosion is one of the most widely
researched physicochemical methods. It involves quick depressurization of pressure
steam which leads to breakdown of lignocellulosic material to cellulose, hemicellulose and lignin.
Certain unusual chemicals such as N-methylmorpholine-N-oxide and cholinium
taurate have also been used for pretreatment purposes (Veeravalli et al. 2019;
Srivastava et al. 2020a, b).
2.6.4 Dark Fermentation
Hydrogen is generated from electrons through fermentation via 2 stages (1) oxidation
of substrate to pyruvate and (2) pyruvate is converted to volatile fatty acids (VFAs)
and alcohols.
Organic mass after pretreatment contains glucose which yields two molecules of
pyruvate. This pyruvate moves into the acidogenic pathway that coupled with
hydrogen production. Other pathways which generate hydrogen are acetic acid
Table 2.3 Different biohydrogen processes with their advantages and disadvantages (Saratale et al.
2019)
Process
Microorganisms
Advantages
Disadvantages
Biophotolysis Blue green algae and
Cynaobacteria
• Cheap source
• Uses solar energy
• Oxygen inhibits the
hydrogen production
Photo
fermentation
Purple non-Sulphur photosynthetic bacteria
• Substrate is
completely utilized
• Waste effluents can
be used
• Low volumetric rates of
production
Dark
fermentation
Strict anaerobes and facultative anaerobes
• High volumetric
rates of production
• Different substrates
can be used
• Low yield of the
product
Microbial
electrolysis
Geobacter, Pseudomonas
and Shewanella
• Complete substrate
utilization
• Extra voltage needed
• Expensive
2 Application of Microorganisms for Biofuel Production
51