gained attention (Roy et al. 2014; Batista et al. 2014; Ortigueira et al. 2015). In
comparison with other biomass, microalgae present several advantages to be used
as feedstock for biohydrogen production: (1) they have higher growth rate with
superior photosynthetic efficiency; (2) they can grow on non-arable land; (3) they
can grow in wide variety of water sources (fresh, salt, brackish and wastewater);
(4) they do not contain lignin, so no rigorous pretreatment is required (Sambusiti
et al. 2015).
This chapter is aimed to describe about biohydrogen production from microalgae
both by biophotolysis as well as dark fermentation. The barriers in biohydrogen
production from microalgae and the molecular approaches to enhance the hydrogen
production are taken into consideration.
2 Microalgal Hydrogen Production Processes
Microalgae can participate for hydrogen production mainly by two processes:
(1) photolysis of water, which requires light and is closely related to the process of
photosynthesis; (2) light-independent process in which microalgal biomass, rich in
carbohydrate and protein, is used up as a feedstock for dark fermentation.
2.1 Biophotolysis
Biophotolysis is the action of light energy on the biological systems that results in
the dissociation of substrate, usually water molecule, into hydrogen and oxygen.
Unicellular green algae and cyanobacteria are organisms known to perform both
oxygenic photosynthesis and biohydrogen production (Happe et al. 2000). In
microalgae, the process of photolysis is closely related to the process of photosynthesis. Unlike photosynthesis, where the reductants released by the dissociation
of water are consumed in the Calvin cycle or pentose phosphate pathway to reduce
CO 2 for cell growth, in biophotolysis the reductants are directed for hydrogen
evolution. The photosynthetic machinery of eukaryotic green algae and prokaryotic
blue-green algae is similar to higher terrestrial plants. In eukaryotic microalgae, the
photosynthetic machinery is embedded in the thylakoid membranes present inside
an intracellular organelle, the chloroplast. In contrast, the photosynthetic apparatus
of cyanobacteria lacks compartmentalization and the thylakoid membranes are
present in the cytoplasm, adjacent to the plasma membrane. The thylakoid membranes contain several light-absorbing pigments such as chlorophyll a, antenna
chlorophylls, carotenoid and phycobiliproteins which are arranged in two different
kinds of functional arrays called photosystems (PSI and PSII). Photosystem I and
photosystem II consist of distinct photochemical reaction centre, P700 and P680
respectively. Absorption of photons by the chlorophyll molecules of P700 and P680
causes their excitations and drives the electrons through thylakoid membrane to
10 Biofuels from Microalgae: Biohydrogen
203
comparison with other biomass, microalgae present several advantages to be used
as feedstock for biohydrogen production: (1) they have higher growth rate with
superior photosynthetic efficiency; (2) they can grow on non-arable land; (3) they
can grow in wide variety of water sources (fresh, salt, brackish and wastewater);
(4) they do not contain lignin, so no rigorous pretreatment is required (Sambusiti
et al. 2015).
This chapter is aimed to describe about biohydrogen production from microalgae
both by biophotolysis as well as dark fermentation. The barriers in biohydrogen
production from microalgae and the molecular approaches to enhance the hydrogen
production are taken into consideration.
2 Microalgal Hydrogen Production Processes
Microalgae can participate for hydrogen production mainly by two processes:
(1) photolysis of water, which requires light and is closely related to the process of
photosynthesis; (2) light-independent process in which microalgal biomass, rich in
carbohydrate and protein, is used up as a feedstock for dark fermentation.
2.1 Biophotolysis
Biophotolysis is the action of light energy on the biological systems that results in
the dissociation of substrate, usually water molecule, into hydrogen and oxygen.
Unicellular green algae and cyanobacteria are organisms known to perform both
oxygenic photosynthesis and biohydrogen production (Happe et al. 2000). In
microalgae, the process of photolysis is closely related to the process of photosynthesis. Unlike photosynthesis, where the reductants released by the dissociation
of water are consumed in the Calvin cycle or pentose phosphate pathway to reduce
CO 2 for cell growth, in biophotolysis the reductants are directed for hydrogen
evolution. The photosynthetic machinery of eukaryotic green algae and prokaryotic
blue-green algae is similar to higher terrestrial plants. In eukaryotic microalgae, the
photosynthetic machinery is embedded in the thylakoid membranes present inside
an intracellular organelle, the chloroplast. In contrast, the photosynthetic apparatus
of cyanobacteria lacks compartmentalization and the thylakoid membranes are
present in the cytoplasm, adjacent to the plasma membrane. The thylakoid membranes contain several light-absorbing pigments such as chlorophyll a, antenna
chlorophylls, carotenoid and phycobiliproteins which are arranged in two different
kinds of functional arrays called photosystems (PSI and PSII). Photosystem I and
photosystem II consist of distinct photochemical reaction centre, P700 and P680
respectively. Absorption of photons by the chlorophyll molecules of P700 and P680
causes their excitations and drives the electrons through thylakoid membrane to
10 Biofuels from Microalgae: Biohydrogen
203