Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 359

a high performance photobioreactor requires to be operated at the optimal pH value
that changes with the microorganism and substrate.
11.4.2.4 Substrate
Previous studies show that the performance of the photobiohydrogen production also
depends on the type of substrate as the composition of the organic compounds is dif-
ferent, affecting the biodegradation reaction (Chen et al., 2008; Kapdan and Kargi,
2006). Barbosa et al. (2001) chose four substrates, i.e. lactate, malate, acetate and
butyrate, for the photobiohydrogen production using the photosynthetic bacteria as
the producers and the results showed that the highest photobiohydrogen production
rate and light efficiency were achieved with acetate as the substrate. In addition to
the substrate type, the concentration of the substrate also affects the photobiohydro-
gen production performance, whose optimal value depends on the photobioreactor
design. Zhu et al. (2012) found that the photobiohydrogen production performance
of a column photobioreactor with transparent packed materials increased with increas-
ing glucose concentration from 0.02 to 0.1 M at a flow rate of 500 ml/h. For a flat panel
photobioreactor, Liao et al. (2010) studied the photobiohydrogen production perfor-
mance at a flow rate of 70 ml/h and found that the photobiohydrogen production rate
increased with an increase in the glucose concentration from 0.02 to 0.06 mM as a
result of enhanced mass transport, and then decreased gradually as the glucose con-
centration was further increased. The reason is that too high glucose concentration
results in the substrate inhibition, lowering the photobiohydrogen production rate.
However, Zhang et al. (2010) reported that the optimal substrate concentration of a
groove-type flat panel photobioreactor was obtained at glucose concentration of 10 g/l
due to the discrepancy of organic load carrying capacity for different photobioreactors.
From these studies, it is revealed that the photobiohydrogen production performance is
affected not only by the substrate type but also by the substrate concentration. Too low
or too high concentration can cause the mass transfer limitation or the substrate inhi-
bition, thereby lowering the performance of photobioreactor. It is essential to control
the substrate conditions according to the photobioreactor design in real applications.
11.4.2.5 Nutrients
In addition to the organic compounds, nutrients, such as nitrogen, phosphate and other
inorganic trace minerals, are also necessary for maintaining the cell cultivation and
hydrogen production in the photobiohydrogen production process (Chen et al., 2010;
Eroglu and Melis, 2011; Hakobyan, 2012). The appropriate nutrients can enhance the
performance of the photobiohydrogen production through changing the metabolism
of microorganisms. Tao et al. (2008) used L-glutamate, (NH 4 ) 2 SO 4 or ethanolamine
as nitrogen source for the photobiohydrogen production by a photosynthetic non-
sulfur strain named ZX-5 and found that 7-mM L-glutamate was the best nitrogen
source for photobiohydrogen production. Besides the selection of nitrogen source, the
carbon to nitrogen ratio in the medium is also of importance in the photobiohydrogen
production. Eroglu et al. (1999) used malic acid and glutamic acid as the carbon
and nitrogen sources, respectively, and the results showed that a carbon to nitrogen
ratio of 15:2 exhibited the highest photobiohydrogen production rate. Burrows et al.
(2008) also optimized the concentrations of nutrients including nitrogen, phosphate