Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 344

of researches for improving the hydrogen-producing microorganisms by genetic and
metabolic engineering are provided in Section 11.3. In the following, Section 11.4
presents the high-performance photobioreactor designs and operating parameters opti-
mization. Particular attention will be paid to the cell immobilization technique for the
improvement in the biomass concentration. Finally, challenges and future directions
on the photobiohydrogen production technology will be addressed in Section 11.5.
11.2 GENERAL DESCRIPTION OF PHOTOBIOHYDROGEN
PRODUCTION
In general, two types of photosynthetic microorganisms can be used to produce
hydrogen. One is photoautotrophic microorganisms mainly including green algae
and cyanobacteria, which decompose water into hydrogen and oxygen using light
as the energy source, so-called water photolysis, and carbon dioxide as the carbon
source for microorganism growth. Another one is photoheterotrophic microorganisms
(photosynthetic bacteria) that separate hydrogen atom from the organic compounds
to produce hydrogen. Their respective photobiohydrogen production processes are
described below.
11.2.1 Photoautotrophic hydrogen production
11.2.1.1 Green algae
Green algae with both the oxygenic photosynthesis and hydrogen metabolism are the
only known eukaryotes that can produce hydrogen through water photolysis (Happe
et al., 2002). Since Gaffron (1939) firstly found that Scenedesmus obliguus with
oxygen-free cultivation could utilize hydrogen as a reductant and Gaffron and Rubin
(1942) then revealed that unicellular algae could liberate hydrogen slowly in the dark if
the surrounding air was replaced by nitrogen, after more than 70 years' development it
has been found that over 1000 microorganisms among about 30 green algae genera are
able to produce hydrogen by water photolysis (Kruse et al., 2005), including Chlamy-
domonas reinhardti (Happe and Kaminski, 2002), Scenedesmus obliquus (Wunschiers
et al., 2001), Platymonas subcordiformis (Guan et al., 2004) and others, as summa-
rized in Table 11.2.1. Photobiohydrogen production by green algae can provide many
features of higher light efficiency than agricultural plants, short growth, automatic
collection of light energy and cleanness (Das and Veziroglu, 2008). Besides, supplied
carbon dioxide is for the microorganism growth so that it is carbon-free hydrogen
production and enables carbon dioxide capture (Levin et al., 2004).
As illustrated in Figure 11.2.1, green algae contain two photosynthetic systems,
photosystem I (PSI) and photosystem II (PSII) which are inserted in the thylakoid mem-
brane with an enclosed inner space called lumen and operate in series (Akkerman et al.,
2002; Allakhverdiev et al., 2010; Miyake et al., 1999; Srirangan et al., 2011). The reac-
tion centre of PSII shows the strongest adsorption at 680 nm and thus is called P680,
while the reaction center of PSI, P700, shows the strongest absorption at 700 nm. In the
photobiohydrogen production process, water is transported from the bulk into green
algae through the cell membrane and light is transmitted through the medium solution