Environmental Engineering Reference
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Figure 11.4.11 Scanning electron microscopy images of the surface of spherical glass bead: (a) before
biofilm, and; (b) after biofilm (Zhu et al., 2012).
an unsaturated flow bioreactor consisted of a reaction bed packed with spherical glass
beads and an internal optical fiber was also developed by this team to promote the
rates of substrate and products transfer, to achieve efficient gas-liquid separation and
to enhance the biofilm formation (Figure 11.4.11) through utilizing the three-phase
interfaces (Zhu et al., 2012). Unfortunately, the surface of glass bead carriers in these
studies is smooth, leading to difficulty in the bacterial adhesion and biofilm formation.
Therefore, surface treatment is needed to improve this design of the photobioreactor.
In summary, the cell immobilization technique can greatly increase the biomass
concentration in the photobioreactor, which is beneficial for the improvement in
the photobiohydrogen production performance. However, the problems of low light
penetration and mass transfer inside of the entrapment and biofilm still exist. To
industrialize the cell immobilization technique for the large-scale photobiohydrogen
production, the cell immobilization with high surface-to-volume ratio, mass transfer
rate, light penetration and good mechanical strength and biocompatibility is needed.
11.5 CHALLENGES AND FUTURE DIRECTIONS
In the process of photobiohydrogen production, the coupling of the photosynthesis
and mass transport and light transmission occurs. The photobiohydrogen production
performance highly depends on the microorganisms used and their bioactivity as well
as the optimizations of the photobioreactor design and operational conditions. There
has been a substantial improvement in the hydrogen yield, photobiohydrogen produc-
tion rate and light efficiency. This chapter gives an overview of past studies on the
high-performance microorganisms, photobioreactor design and effect of the opera-
tional conditions. The past experimental data show that although the improvement
has been achieved, the photobiohydrogen production performance still has to con-
siderably surpass the present achievement. To attain a high and stable performance,
therefore, future research into photobiohydrogen production should be directed to
addressing the following critical issues for the widespread commercialization.
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