were the easiest to manage. The most important factor which needs to be
understood is the productivity factor of the feedstock. More productive algal
strains would require less space, and this is one of the best ways of mitigating the
space constraints (Pate et al. 2011).
4. Reducing capital and production costs: Neda Fakhimi et al. (2019) were able to
enhance the hydrogen production by combining mixotrophic combination of
algae with bacterial cultures. The amount of hydrogen production was found to
increase by 60% when Chlamydomonas reinhardtii along with the bacterium
Escherichia coli was used. Sewage water can be employed for hydrogen generation and simultaneous bioremediation which makes the process sustainable and
economically viable. Tools such as computational fluid dynamics (CFD) may be
used to design better bioreactors which can be used for efficient scale up of the
process. Modularization is one of the approaches which is a better option for
scaling up the process. In this method, small bioreactors are used. Intensity of the
light, nutrient supply, and carbon dioxide can be effectively managed. If any
problem arises in any of the module, it can be detached. The problem of
contamination of the system can be handled. The capital costs can be reduced if
the production of hydrogen is lined to sequestration of carbon dioxide. To
establish a viable process, techno-economic analysis and life cycle analysis are
presently needed.
5. Controlling cultivation conditions: This is one of the major challenges which
need to be addressed for generating biohydrogen. During the process, evaporation
of water is a major constraint which needs to be addressed. In open ponds, large
amounts of water are evaporated, and salt levels increase (Yang and Wang 2018).
Unless this is not addressed, the cultivating conditions cannot be controlled in a
bioprocess (Harto et al. 2010). The management of water and salt is the essential
areas which have to be addressed (Gerbens-Leenes et al. 2009). Darzins et al.
(2010) suggested that coastal regions are suitable if freshwater is not available for
salt water algal production (Darzins et al. 2010). Water requirements for cultivation of algae are comparatively higher when compared to that of other petroleumbased fuels (NRC 2011). Pate et al. (2011) opined that marine water, wastewater,
and water from other industrial wastes should be used to make the cultivation
process viable in place of freshwater.
6. Future Perspectives: The choice of pretreatment technology for biohydrogen
production method depends on substrate composition. The development of different pretreatment technologies will result in enhancements of hydrogen production and by effective solubilization of the substrate. Lee (2016a) opined that
biohydrogen is economically possible and may be commercialized with success.
A study by Lee (2016b) reported that biohydrogen will replace fossil fuels with
less economic burden. Ogden et al. (2004) suggested that the use of generated
algal hydrogen in hydrogen electric vehicles will be a major interesting application of hydrogen production using biomass. Stanislaus et al. (2017) investigated
hydrogen production from Ipomoea aquatica using digested sludge as inoculums
and reported that the energy consumed was lesser than energy produced in the
process, which shows a positive energy balance. Unless a process is less energy
7 Sustainable Production of Hydrogen by Algae: Current Status and Future. . .
207
understood is the productivity factor of the feedstock. More productive algal
strains would require less space, and this is one of the best ways of mitigating the
space constraints (Pate et al. 2011).
4. Reducing capital and production costs: Neda Fakhimi et al. (2019) were able to
enhance the hydrogen production by combining mixotrophic combination of
algae with bacterial cultures. The amount of hydrogen production was found to
increase by 60% when Chlamydomonas reinhardtii along with the bacterium
Escherichia coli was used. Sewage water can be employed for hydrogen generation and simultaneous bioremediation which makes the process sustainable and
economically viable. Tools such as computational fluid dynamics (CFD) may be
used to design better bioreactors which can be used for efficient scale up of the
process. Modularization is one of the approaches which is a better option for
scaling up the process. In this method, small bioreactors are used. Intensity of the
light, nutrient supply, and carbon dioxide can be effectively managed. If any
problem arises in any of the module, it can be detached. The problem of
contamination of the system can be handled. The capital costs can be reduced if
the production of hydrogen is lined to sequestration of carbon dioxide. To
establish a viable process, techno-economic analysis and life cycle analysis are
presently needed.
5. Controlling cultivation conditions: This is one of the major challenges which
need to be addressed for generating biohydrogen. During the process, evaporation
of water is a major constraint which needs to be addressed. In open ponds, large
amounts of water are evaporated, and salt levels increase (Yang and Wang 2018).
Unless this is not addressed, the cultivating conditions cannot be controlled in a
bioprocess (Harto et al. 2010). The management of water and salt is the essential
areas which have to be addressed (Gerbens-Leenes et al. 2009). Darzins et al.
(2010) suggested that coastal regions are suitable if freshwater is not available for
salt water algal production (Darzins et al. 2010). Water requirements for cultivation of algae are comparatively higher when compared to that of other petroleumbased fuels (NRC 2011). Pate et al. (2011) opined that marine water, wastewater,
and water from other industrial wastes should be used to make the cultivation
process viable in place of freshwater.
6. Future Perspectives: The choice of pretreatment technology for biohydrogen
production method depends on substrate composition. The development of different pretreatment technologies will result in enhancements of hydrogen production and by effective solubilization of the substrate. Lee (2016a) opined that
biohydrogen is economically possible and may be commercialized with success.
A study by Lee (2016b) reported that biohydrogen will replace fossil fuels with
less economic burden. Ogden et al. (2004) suggested that the use of generated
algal hydrogen in hydrogen electric vehicles will be a major interesting application of hydrogen production using biomass. Stanislaus et al. (2017) investigated
hydrogen production from Ipomoea aquatica using digested sludge as inoculums
and reported that the energy consumed was lesser than energy produced in the
process, which shows a positive energy balance. Unless a process is less energy
7 Sustainable Production of Hydrogen by Algae: Current Status and Future. . .
207