Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 366

Figure 11.4.10 Optical fiber with (a) smooth-surface, and; (b) additional rough surface (Guo et al.,
2011).
be obtained by controlling the proper size of bio-carrier. Moreover, three types of car-
riers, including activated carbon, silica gel, and expanded clay were also used to be
additives to the medium (Chen and Chang, 2006). It was indicated that the addition of
clay and silica gel provided extra surface area for attached cell growth to form biofilm,
resulting in better hydrogen yield, and light conversion efficiency than those obtained
from the carrier-free culture. However, the activated carbon-supplemented culture did
not show a significant improvement in the performance of the photobiohydrogen pro-
duction due to high cell density in the activated carbon-supplemented culture and
the tiny fragments flaking off the activated carbon carriers, which both resulted in
the blocking of light penetration from the external light sources and poor light con-
version efficiency in the activated carbon-supplemented culture. In order to enhance
the light conversion efficiency, therefore, some researchers utilized the materials with
high transparence as a carrier for the photobiohydrogen production. Tekucheva et al.
(2011) developed a novel photobioreactor using an inexpensive glass-fiber matrix to
accelerate the immobilization process and to enhance light penetration. Furthermore,
in order to enhance both the light penetration and the surface-to-volume ratio of the
carrier for the high biomass concentration in the photobioreactor, Tian et al. (2010)
designed a biofilm photobioreactor with packed glass beads on which Rhodopseu-
domonas palustris CQK 01 was immobilized on the surface of the transparent packed
materials to form a biofilm. In addition, they also developed a biofilm photobioreac-
tor with the external light source replaced by an internal light source of optical fibers
(Figure 11.4.10a). Particularly, an additional rough surface (Figure 11.4.10b) was cre-
ated to enhance the biofilm formation (Guo et al., 2011). The results showed that the
biofilm photobioreactor with the added rough-surface optical fibers exhibited higher
performance of photobiohydrogen production than did the biofilm photobioreactor
with the smooth-surface optical fiber and the optical fiber suspension photobioreactor
because it could furnish extra surface attachment sites, enhancing the biofilm formation
and enriching biomass in photobioreactor. In the wake of this photobioreactor design,