12H 2 O þ 6CO 2 ! C 6 H 12 O 6 þ 6O 2
ð1Þ
C 6 H 12 O 6 þ 12H 2 O ! 12H 2 þ 6CO 2
ð2Þ
In comparison with green microalgae, H 2 production via indirect photolysis from
cyanobacteria is more attractive (Yu and Takahashi 2007). In this process, the
problem of H 2 -producing enzyme sensitivity to O 2 is solved by the temporal or
spatial separation of H 2 and O 2 evolving reactions. In spatial separation, the
apparatus for photosynthesis and H 2 production is present at different locations.
Temporal separation involves the reactions of O 2 and H 2 evolution to occur at
different time by using light/dark cycles. In this process, during the daytime carbohydrate accumulation takes place via photosynthesis and during the night-time
H 2 production occurs via fermentation of stored sugar (Miura et al. 1997).
Cyanobacteria are capable of carrying out the both, CO 2 as well as nitrogen
fixation. In these organisms, nitrogen fixation occurs under anoxic conditions inside
the specialized cells known as heterocysts whereas oxygenic photosynthesis and
CO 2 fixation take place in the vegetative cells. Inside the heterocysts, anaerobic
environment is maintained due to the absence of the O 2 -evolving PSII. In addition,
the O 2 impermeable cell walls of heterocysts do not allow the oxygen diffusion
from the nearby vegetative cells thus helping further in creating anaerobiosis,
required for the nitrogen fixation and H 2 generation by the O 2 -sensitive nitrogenases (Das et al. 2014).
Nitrogen-fixing cyanobacteria known for H 2 production mostly include the
genus Anabaena, Nostoc, Calothrix and Oscillatoria. In these organisms, nitrogen
fixation and hydrogen evolution catalysed by the nitrogenase enzyme are described
according to Eq. 3 (Eroglu and Melis 2011):
Fig. 2 Biohydrogen production via indirect biophotolysis carried out by cyanobacteria
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H. Singh and D. Das
ð1Þ
C 6 H 12 O 6 þ 12H 2 O ! 12H 2 þ 6CO 2
ð2Þ
In comparison with green microalgae, H 2 production via indirect photolysis from
cyanobacteria is more attractive (Yu and Takahashi 2007). In this process, the
problem of H 2 -producing enzyme sensitivity to O 2 is solved by the temporal or
spatial separation of H 2 and O 2 evolving reactions. In spatial separation, the
apparatus for photosynthesis and H 2 production is present at different locations.
Temporal separation involves the reactions of O 2 and H 2 evolution to occur at
different time by using light/dark cycles. In this process, during the daytime carbohydrate accumulation takes place via photosynthesis and during the night-time
H 2 production occurs via fermentation of stored sugar (Miura et al. 1997).
Cyanobacteria are capable of carrying out the both, CO 2 as well as nitrogen
fixation. In these organisms, nitrogen fixation occurs under anoxic conditions inside
the specialized cells known as heterocysts whereas oxygenic photosynthesis and
CO 2 fixation take place in the vegetative cells. Inside the heterocysts, anaerobic
environment is maintained due to the absence of the O 2 -evolving PSII. In addition,
the O 2 impermeable cell walls of heterocysts do not allow the oxygen diffusion
from the nearby vegetative cells thus helping further in creating anaerobiosis,
required for the nitrogen fixation and H 2 generation by the O 2 -sensitive nitrogenases (Das et al. 2014).
Nitrogen-fixing cyanobacteria known for H 2 production mostly include the
genus Anabaena, Nostoc, Calothrix and Oscillatoria. In these organisms, nitrogen
fixation and hydrogen evolution catalysed by the nitrogenase enzyme are described
according to Eq. 3 (Eroglu and Melis 2011):
Fig. 2 Biohydrogen production via indirect biophotolysis carried out by cyanobacteria
206
H. Singh and D. Das