Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 358

2010). The energy supply exceeded the metabolic capability of nitrogenase, leading to
low light conversion efficiency. Therefore, it is concluded that the incident light should
be shifted to the optimal light wavelength and intensity to enhance the performance
of photobiohydrogen production.
11.4.2.2 Temperature
The temperature is another critical factor affecting the performance of the photo-
biohydrogen production as the bioactivity of microorganisms highly depends on the
operating temperature. Carlozzi and Lambardi (2009) reported that the optimal tem-
perature to culture R. palustris was between 30 ◦ C and 35 ◦ C. Wang et al. (2010) studied
the photobiohydrogen production performance of Rhodopseudomonas palustris CQK
01 by varying temperatures from 15 to 40 ◦ C and found that the photobiohydro-
gen production rate, substrate utilization efficiency and hydrogen bioconversion yield
increased as the temperature increased from 15 to 30 ◦ C. With the temperature further
increasing to 40 ◦ C, the trends reversed, indicating the optimal temperature for the bio-
hydrogne production by Rhodopseudomonas palustris CQK 01 is 30 ◦ C. To attain an
excellent photobiohydrogen production rate, therefore, the optimal temperature con-
trol by using the circulated water via temperature controlled water in existing studies
was proposed (Hoekema et al., 2002). However, the resulting high energy consumption
limits the application of this technique for industrialization. Wang et al. (2010) then uti-
lized heaters arranged at the bottom of the photobioreactor and T-type thermocouples
distributed at the photobioreactor to control the temperature of the influent solu-
tion. This method can effectively avoid heat dissipation and achieve energy-savings.
In summary, for enhancing the performance of photobioreactors, the temperature
should be controlled to maximize the bioactivity in terms of used microorganisms
and but with low energy consumption.
11.4.2.3 pH value
It is well known that the pH value of the influent medium can affect the metabolic path-
ways and thus the performance of the photobiohydrogen production. The study with
respect to the effect of pH value on the photobiohydrogen production by Rhodobacter
sphaeroides O.U. 001 revealed that the optimum pH value leading to the maximum
photobiohydrogen production rate was found to be around 7 (Sasikala et al., 1995).
Studies by Tian et al. also (2010) showed that the optimum photobiohydrogen produc-
tion rate by Rhodopseudomonas palustris CQK-01 occurred at a pH of 7.0. Hence, it
can be found that the optimal pH value for photosynthetic bacteria is usually about 7.
For phototrophic bacteria, the optimal pH value is slightly changed with respect to
microorganisms. Works by Li et al. (2008) concluded the optimal photobiohydrogen
production rate was achieved at the pH of 7.0-7.5 with the acetate and butyrate as the
substrate. However, Fang et al. (2005) reported the optimal pH values were 8.0 and
9.0 with respect to acetate and butyrate in batch experiments, respectively. The perfor-
mance of photobiohydrogen production significantly dropped when the pH was not in
the optimum range because the activity of enzyme was inhibited. In some researches,
to obtain the optimal pH, HCl/NaOH was added into the solution to stimulate the
microorganisms for achieving high activity of enzyme (Skjanes et al., 2008). Therefore,