Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 346

plastocyanin (PC). This complex also provides additional pumping force for protons
across lipid bilayer. In addition, the proton gradient across the thylakoid membrane
drives adenosine triphosphate (ATP) production via the action of ATP-synthase. Via the
lumen, PC diffuses to P700 and releases the electrons which reduce the reaction center
and are transported to the electron carrier ferredoxin (Fd) after renewed light-induced
excitations. At last, nicotinamide adenine dinucleotide phosphate (NADP + ) is reduced
to NADPH via the action of ferredoxin-NADP reductase (FNR), and the protons in
stroma and the electrons transported are combined to generate hydrogen biocatalyzed
by hydrogenase. Hydrogen produced then moves out of the phototbioreactor.
11.2.1.2 Cyanobacteria
Unlike green algae, cyanobacteria are simple prokaryotes possessing photosynthetic
pigment. Many cyanobacteria are currently found to be capable of evolving hydrogen
from water, including Anabaena cylindrica (Weissman and Benemann, 1977), Nostoc
muscorum (Shah et al., 2003), Plectonema boryanum (Kashyap et al., 1996), Oscillo-
toria limnetica, Aphanothece halophytica (Belkin and Padan, 1978) and so on, which
are summarized in Table 11.2.1. Due to the presence of different enzymes, i.e. hydro-
genase and nitrogenase, cyanobacteria can further be divided into the non-nitrogen
fixing or nitrogen fixing cyanobacteria. Consequently, the photobiohydrogen produc-
tion pathways of cyanobacteria are noticeably different. However, the advantages of
simple nutritional requirements, inexpensive cultivation and separating hydrogen and
oxygen evolution are still offered by both types of cyanobacteria (Pinto et al., 2002).
Non-nitrogen fixing cyanobacteria also consist of PSI and PSII that are similar to
green algae, as shown in Figure 11.2.2. During the operation, both water and light
are transported to the reaction center of PSII in a reactor. After that, light is absorbed
by the light-harvesting pigment in the thylakoid membrane and water is decomposed
into protons, oxygen and electrons. Oxygen is consumed and high-energy electrons
produced by the PSII go into the PQ, and then electrons are transported to Fd after a
Figure 11.2.2 The photosynthetic system of non-nitrogen fixing cyanobacteria.