0.1–7.0 g/L is typically used as the source of nitrogen
(Tapia-Venegas et al. 2015). In photo fermentation, nitrogenase activity is greatly influenced by the nitrogen, and it is
reported that among different amino acids, glutamate is the
most suitable nitrogen supplement for the photo fermentation. Ammonia, as a nitrogen source, affects hydrogen production as the high ammonia concentration inhibits the
nitrogenase activity. Rhodobacter capsulatus produced high
H 2 when glutamate as nitrogen source and acetate as carbon
source was supplied in the carbon: nitrogen ratio of >35
(Baskar et al. 2012; Kim et al. 2012). Similarly, phosphate is
essential for various cellular metabolic processes due to its
nutritious value and buffering capacity that enhances H 2
production. However, high phosphate concentration can
cause substrate inhibition (Brandt-Talbot et al. 2017; Datar
et al. 2007).
Metal Ion
The metallic cofactors, such as Mg, Fe, and Ni are vital
for the enzymes in H 2 production. These metallic
cofactors are essential for nitrogenase-catalyzed fermentation by easing the transport processes in the microorganisms. The presence of Fe
2+ is necessary for the
hydrogenase and other enzymes. The Fe embedded in
enzyme act as an electron carrier and facilitate pyruvate
oxidation to acetyl-CoA, CO 2 , and H 2 (Sinha and Pandey
2011; Cheng and He 2014; Wang and Wan 2008).
Similarly, nickel is a major constituent of [NiFe]-hydrogenase. The activity of [NiFe]-hydrogenase and H 2 yield
reduces when Ni present in high proportion. Mg
2+ can
stabilize nucleic acids, cell membranes, and ribosomes
and activate many kinases and synthetases in the cell.
Copper ions (Cu
2+ ) act as an inhibitor for FoF1-ATPase
and hydrogenase enzymes associated with the membrane
of E. coli (Kirakosyan et al. 2008). The other trace
metals, such as Cr and Zn, also affect the hydrogen
production rate (Ratti et al. 2015; Jiang et al. 2015).
Partial Pressure of Hydrogen
The development of partial pressure due to produced
hydrogen plays a substantial role in lowering the H 2 yields.
The hydrogenase enzyme is responsible for the oxidization
and reduction of ferredoxin. The activity of the hydrogenase
enzyme gets affected by a substantial build-up of H 2 produced as it alters the oxidizing capacity of hydrogenase. The
stirring rate, reduction of headspace pressure using a vacuum
pump, and biogas sparging methods are employed to reduce
partial H 2 pressure (Guo et al. 2010).
Light Intensity
Light intensity is a vital factor for photo fermentation,
whereas, it is insignificant for dark fermentation. The light
energy is essential to carry out the photon-induced reaction,
for transportation of electron, ATP synthesis, and hydrogen
production. The photo-bioreactor usually uses solar light
with a provision for artificial light (Lu et al. 2016). The high
concentration of ATP and high reductive power at the
optimal light intensity is essential for nitrogenase to produce
hydrogen (Li et al. 2011; Assawamongkholsiri et al. 2019).
The high light intensity than the optimum value produces
excess ATP and Fd red (ferredoxin reductase), which causes
the nitrogenase enzyme to have a photo-inhibition. The
combination of different types of light sources enhances the
H 2 production rate. For example, an internal illumination of
photo-bioreactor with solar energy excited optical fiber
coupled with external irradiation of tungsten filament lamp
(Li and Fang 2009; Kawagoshi et al. 2010).
Reactor Design
The proper fermentation reactor is the basic need to proceed
with any fermentation process, and the reactor’s configuration controls the operation and output of the fermentation
process (Kadier et al. 2016). Many studies used a batch
reactor on a laboratory scale for dark fermentation as it was
easy to operate. The batch reactors are very useful in optimizing operational parameters on the pilot-scale level;
however, for large production of H 2 on the industrial scale, a
continuous stirred tank reactor (CSTR) is utilized. The
photo-fermentative reactor requires additional configurations, such as incandescent lamps, a combination of light
receiving unit and reflection sheet, and, concentric glass
cylinders, etc. (Baskar et al. 2012).
6 Summary
Bioconversion of lignocellulose residue is an attractive
method for the production of hydrogen. However, most of
the research has been explored at the lab-scale and still
requires a comprehensive assessment before moving to pilot
or large-scale production. Future research could be in the
direction of using the lab data for large scale demonstrations.
The current processes for hydrogen production suffer several
shortcomings, including a lower yield of hydrogen due to the
use of energy-intensive and inefficient pretreatment methods,
low activity of microbes, and inhibition of the products. The
development of an energy-efficient, economically viable
74
P. D. Patil et al.
(Tapia-Venegas et al. 2015). In photo fermentation, nitrogenase activity is greatly influenced by the nitrogen, and it is
reported that among different amino acids, glutamate is the
most suitable nitrogen supplement for the photo fermentation. Ammonia, as a nitrogen source, affects hydrogen production as the high ammonia concentration inhibits the
nitrogenase activity. Rhodobacter capsulatus produced high
H 2 when glutamate as nitrogen source and acetate as carbon
source was supplied in the carbon: nitrogen ratio of >35
(Baskar et al. 2012; Kim et al. 2012). Similarly, phosphate is
essential for various cellular metabolic processes due to its
nutritious value and buffering capacity that enhances H 2
production. However, high phosphate concentration can
cause substrate inhibition (Brandt-Talbot et al. 2017; Datar
et al. 2007).
Metal Ion
The metallic cofactors, such as Mg, Fe, and Ni are vital
for the enzymes in H 2 production. These metallic
cofactors are essential for nitrogenase-catalyzed fermentation by easing the transport processes in the microorganisms. The presence of Fe
2+ is necessary for the
hydrogenase and other enzymes. The Fe embedded in
enzyme act as an electron carrier and facilitate pyruvate
oxidation to acetyl-CoA, CO 2 , and H 2 (Sinha and Pandey
2011; Cheng and He 2014; Wang and Wan 2008).
Similarly, nickel is a major constituent of [NiFe]-hydrogenase. The activity of [NiFe]-hydrogenase and H 2 yield
reduces when Ni present in high proportion. Mg
2+ can
stabilize nucleic acids, cell membranes, and ribosomes
and activate many kinases and synthetases in the cell.
Copper ions (Cu
2+ ) act as an inhibitor for FoF1-ATPase
and hydrogenase enzymes associated with the membrane
of E. coli (Kirakosyan et al. 2008). The other trace
metals, such as Cr and Zn, also affect the hydrogen
production rate (Ratti et al. 2015; Jiang et al. 2015).
Partial Pressure of Hydrogen
The development of partial pressure due to produced
hydrogen plays a substantial role in lowering the H 2 yields.
The hydrogenase enzyme is responsible for the oxidization
and reduction of ferredoxin. The activity of the hydrogenase
enzyme gets affected by a substantial build-up of H 2 produced as it alters the oxidizing capacity of hydrogenase. The
stirring rate, reduction of headspace pressure using a vacuum
pump, and biogas sparging methods are employed to reduce
partial H 2 pressure (Guo et al. 2010).
Light Intensity
Light intensity is a vital factor for photo fermentation,
whereas, it is insignificant for dark fermentation. The light
energy is essential to carry out the photon-induced reaction,
for transportation of electron, ATP synthesis, and hydrogen
production. The photo-bioreactor usually uses solar light
with a provision for artificial light (Lu et al. 2016). The high
concentration of ATP and high reductive power at the
optimal light intensity is essential for nitrogenase to produce
hydrogen (Li et al. 2011; Assawamongkholsiri et al. 2019).
The high light intensity than the optimum value produces
excess ATP and Fd red (ferredoxin reductase), which causes
the nitrogenase enzyme to have a photo-inhibition. The
combination of different types of light sources enhances the
H 2 production rate. For example, an internal illumination of
photo-bioreactor with solar energy excited optical fiber
coupled with external irradiation of tungsten filament lamp
(Li and Fang 2009; Kawagoshi et al. 2010).
Reactor Design
The proper fermentation reactor is the basic need to proceed
with any fermentation process, and the reactor’s configuration controls the operation and output of the fermentation
process (Kadier et al. 2016). Many studies used a batch
reactor on a laboratory scale for dark fermentation as it was
easy to operate. The batch reactors are very useful in optimizing operational parameters on the pilot-scale level;
however, for large production of H 2 on the industrial scale, a
continuous stirred tank reactor (CSTR) is utilized. The
photo-fermentative reactor requires additional configurations, such as incandescent lamps, a combination of light
receiving unit and reflection sheet, and, concentric glass
cylinders, etc. (Baskar et al. 2012).
6 Summary
Bioconversion of lignocellulose residue is an attractive
method for the production of hydrogen. However, most of
the research has been explored at the lab-scale and still
requires a comprehensive assessment before moving to pilot
or large-scale production. Future research could be in the
direction of using the lab data for large scale demonstrations.
The current processes for hydrogen production suffer several
shortcomings, including a lower yield of hydrogen due to the
use of energy-intensive and inefficient pretreatment methods,
low activity of microbes, and inhibition of the products. The
development of an energy-efficient, economically viable
74
P. D. Patil et al.