Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 352

hupL gene has to be conducted. Specially, for photosynthetic bacteria, the glnB-glnK
mutant can effectively resolve the problem of ammonium ion.
11.4 HIGH-PERFORMANCE PHOTOBIOREACTOR
The performance of a photobioreactor will directly determine the feasibility of large-
scale photobiohydrogen production. Therefore, how to develop a high-performance
photobioreactor is critically important and has received much attention from all
over the world. Various strategies for achieving a high-performance photobioreac-
tor, including modification of the photobioreactor configurations, optimization of the
operating parameters, and application of the cell immobilization, have been carried
out, which are discussed below.
11.4.1 Modification of photobioreactor configurations
As mentioned earlier, the mass transport and light transmission simultaneously occur in
the photobioreactor and are inherently coupled with the photobiochemical reaction. To
ensure the physiological activity and metabolic stability of microorganisms and thus
achieve continuous, stable and photobiohydrogen production performance, a high-
performance photobioreactor that enables efficient reactants transport and products
removal and light transmission with good uniformity, is required. Various enhancing
strategies have been proposed towards different types of photobioreactors shown in
Figure 11.4.1, including column photobioreactors, flat panel photobioreactors and
tubular photobioreactors, which are summarized in Table 11.4.1.
11.4.1.1 Column photobioreactor
A column photobioreactor (Figure 11.4.1a) usually consists of a vertically-oriented col-
umn made by transparent material with an external artificial light source. An inlet and
an outlet are set at the bottom and top of the column photobioreactor for supplying the
fresh medium and collecting the produced hydrogen, respectively. For green algae and
cyanobacteria, the bottom of the column photobioreactor also retains an inlet for the
gases such as argon and carbon dioxide to maintain anaerobic conditions and provide
carbon source. Such a design possesses several advantages of simple structure, excellent
liquid content and heat and mass transfer characteristics, high durability of the bioac-
tivity and packing material, low costs (Dasgupta et al., 2010; Miron et al., 2002). For
these reasons, extensive researches on the column photobioreactor have been reported.
However, the drawbacks of the column photobioreactor are also obvious, that is, small
illumination surface area and low surface-to-volume ratio for scaling up (Ugwa et al.,
2008). Various measures to improve the column photobioreactor configurations have
been proposed by changing the external light sources to the internal light sources and
increasing the surface-to-volume ratio. An annular triple jacketed photobioreactor
consisting of three coaxial glass cylinders with two closed chambers was developed by
Liu et al. (2006) for this purpose. In this design, the chamber formed between the outer
and middle cylinders was used for cultivation and fluorescent lamps were inserted in
the inner chamber as an internal light source, which increased the surface-to-volume
ratio, leading to a light conversion efficiency of approx. 1% and a photobiohydrogen