4.12 Challenges
The molar yields of hydrogen and feedstock costs are typically the two major
obstacles in fermentation technology. The key problem in hydrogen fermentation
is that it is usually possible to produce less than 15% of the energy from the organic
source in the form of hydrogen (Logan 2004). Therefore, it is not shocking that
major efforts seek to dramatically increase the hydrogen yield. The US DOE
fermentation development plan aims to achieve yields of 4 and 6 mol of hydrogen
per glucose mole, respectively, by 2013 and 2020, as well as 3 and 6 months of
continuous operation over the same years. In addition, some integrated strategies,
such as the two-stage fermentation cycle (acid-genic photobiological or acid-genic
methanogenic processes) or the use of modified microbial fuel cells, have been
created (Vrije and Claasen 2003; Ueno et al. 2007). In the second stage, additional
energy or hydrogen per feed mole can be obtained via the conjugated processes.
Appropriate bacterial strain, process adaptation, adequate bioreactor design, and
even molecular engineering and genetic technique can be used to change the
metabolic pathway to increase the hydrogen yield. The adoption of genetically
modified microbes remains a concern because of the apprehension of horizontal
gene transference. However, chromosomal integration and the removal of plasmids
containing antibiotic markers using available molecular tools may rule out horizontal
transference of the gene substance (Datsenko and Wanner 2000). In addition, the use
of genetic engineering to improve the development of hydrogen is mainly aimed at
breaking up endogenous genes, rather than initiating new microbe activities. Novel
mechanisms need to be investigated to maximize the possible 12 mol of hydrogen
present in a hexose mole. Indeed, hydrogen is more costly than other alternatives like
gasoline. Ultimately, hydrogen can only play an important role in the economy if
innovations and developments can be successful in cost reduction. The use of green
biomass for the manufacture of hydrogen may be a way to address some of the
economic constraints. Effluent from distillery, sugarcane juice, or molasses can be
used as feedstocks. These substrates produce large amounts of sugar, thereby
considerably decreasing the cost of production as well as the unit energy cost of
hydrogen. A detailed techno-economic analysis is important to demonstrate a costeffective assessment of hydrogen produced biologically and from various fossils.
4.13 Conclusion
Hydrogen is known as one of the energy carriers with the most potential in the future.
In the past few decades, several studies have been carried out into various methods of
processing hydrogen. Biomass is theoretically a dependable energy tool for the
production of hydrogen. The biomass is sustainable, abundant, and easy to use.
Due to the photosynthesis of green plants, net CO 2 emissions are almost nil over the
life cycle. The methods of development of thermochemical pyrolysis and
98
L. Gangadhar et al.
The molar yields of hydrogen and feedstock costs are typically the two major
obstacles in fermentation technology. The key problem in hydrogen fermentation
is that it is usually possible to produce less than 15% of the energy from the organic
source in the form of hydrogen (Logan 2004). Therefore, it is not shocking that
major efforts seek to dramatically increase the hydrogen yield. The US DOE
fermentation development plan aims to achieve yields of 4 and 6 mol of hydrogen
per glucose mole, respectively, by 2013 and 2020, as well as 3 and 6 months of
continuous operation over the same years. In addition, some integrated strategies,
such as the two-stage fermentation cycle (acid-genic photobiological or acid-genic
methanogenic processes) or the use of modified microbial fuel cells, have been
created (Vrije and Claasen 2003; Ueno et al. 2007). In the second stage, additional
energy or hydrogen per feed mole can be obtained via the conjugated processes.
Appropriate bacterial strain, process adaptation, adequate bioreactor design, and
even molecular engineering and genetic technique can be used to change the
metabolic pathway to increase the hydrogen yield. The adoption of genetically
modified microbes remains a concern because of the apprehension of horizontal
gene transference. However, chromosomal integration and the removal of plasmids
containing antibiotic markers using available molecular tools may rule out horizontal
transference of the gene substance (Datsenko and Wanner 2000). In addition, the use
of genetic engineering to improve the development of hydrogen is mainly aimed at
breaking up endogenous genes, rather than initiating new microbe activities. Novel
mechanisms need to be investigated to maximize the possible 12 mol of hydrogen
present in a hexose mole. Indeed, hydrogen is more costly than other alternatives like
gasoline. Ultimately, hydrogen can only play an important role in the economy if
innovations and developments can be successful in cost reduction. The use of green
biomass for the manufacture of hydrogen may be a way to address some of the
economic constraints. Effluent from distillery, sugarcane juice, or molasses can be
used as feedstocks. These substrates produce large amounts of sugar, thereby
considerably decreasing the cost of production as well as the unit energy cost of
hydrogen. A detailed techno-economic analysis is important to demonstrate a costeffective assessment of hydrogen produced biologically and from various fossils.
4.13 Conclusion
Hydrogen is known as one of the energy carriers with the most potential in the future.
In the past few decades, several studies have been carried out into various methods of
processing hydrogen. Biomass is theoretically a dependable energy tool for the
production of hydrogen. The biomass is sustainable, abundant, and easy to use.
Due to the photosynthesis of green plants, net CO 2 emissions are almost nil over the
life cycle. The methods of development of thermochemical pyrolysis and
98
L. Gangadhar et al.