Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 348

Figure 11.2.3 The photosynthetic system of photosynthetic bacteria (Akkerman et al., 2002).
2002; Keskin et al., 2011). The produced hydrogen ultimately transports out of the
photobioreactor.
11.2.3 Critical issues in photobiohydrogen production
Although photobiohydrogen production is encouraging, there are still some major
challenges that should be resolved. Firstly, the characteristics of microorganisms
clearly play important roles in the photobiohydrogen production processes, which
directly affect the rate of the photobiochemical reactions. Thus breeding microorgan-
isms with high photobiohydrogen production performance is one of the critical issues
in photobiohydrogen production. In addition to the microorganisms themselves, the
photobiohydrogen production performances are also inherently related to the design
of the photobioreactor and operating conditions. Basically, the photobioreactor design
and operating conditions affect the mass transport that is coupled with the photobio-
chemical reaction during the photobiohydrogen production process. Too low reactant
concentrations or too high hydrogen concentration can cause a low reaction rate and
thus poor photobiohydrogen production performance. In addition to mass transport,
inefficient light transport and non-uniform light distribution can also decrease the
light utilization and the photobiohydrogen production rate. Therefore, efficient reac-
tants transport and products removal along with high light transport and uniform
distribution are keys to maintaining the physiological activity and metabolic stabil-
ity of microorganisms and achieve continuous, stable and good photobiohydrogen
production performance, which highly depends on the photobioreactor design and
operating conditions. Besides, other operating conditions, such as temperature, pH
value and so on, also significantly affect the photobiohydrogen production perfor-
mance. As a result, the improvement in photobioreactor design together with the