Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 360

and so on, for the photobiohydrogen production by Synechocystis sp . PCC6803 and
obtained a 150-fold increase in the photobiohydrogen production rate. The effect
of the concentrations of molybdenum and iron on the photobiohydrogen production
by Rhodobacter sphaeroides O.U.001 was also investigated (Kars et al., 2006). The
results showed that 16.5

M sodium molybdate and 0.1 mM ferric citrate in nutrient
solution yielded the highest total hydrogen accumulation. In summary, an appropriate
nutrient composition is one of the keys to obtain a high photobiohydrogen production
performance and the respective optimal nutrients concentrations depends on the used
microorganism and other operating conditions.

µ

11.4.2.6 Operational modes

Existing studies indicate that the distributions of biomass, substrate and product con-
centrations in photobioreactors are also affected by the operational modes. Hence, the
effects of the operational modes, including batch, continuous and fed-batch modes, on
the mass transfer and biomass distribution have been investigated and enhancement
strategies have also been proposed (Argun and Kargi, 2011). Shi and Yu (2006) utilized
continuous operational mode for the photobiohydrogen production with Rhodopseu-
domonas capsulate , the maximum photobiohydrogen production rate of 37.8 ml/g
dry weight (dwt)/h, light conversion efficiency of 3.69% and substrate conversion effi-
ciency of 45% were achieved at a mixture of acetate 1.8 g/l, propionate of 0.2 g/l
and butyrate of 1.0 g/l. Ren et al. (2009) studied the photobiohydrogen production
by Rhodopseudomonas faecalis strain RLD-53 in fed-batch operational mode using
acetate as the sole carbon and the results demonstrated the fed-batch operational
mode obtained a high efficiency. Chen et al. (2006a) compared three different oper-
ational modes with the same initial substrate concentration and culture volume to
determine which operational mode was preferable in the photobiohydrogen produc-
tion by indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5.
It was suggested that the fed-batch operational mode was a good mode due to the
high cell concentration and adjustable substrate loading under similar culture condi-
tions. Conclusions drew from previous studies are different may be due to the design
of the photobioreactor. Recently, an enhancement method with the ultra-sonication
pretreatment was proposed to improve the batch operational mode by increasing the
mass transport and permeability of the cell membrane so that the performance of the
photobiohydrogen production was greatly improved (Zhu et al., 2011). In summary,
to improve the photobiohydrogen production rate, the enhancement strategies need
to be incorporated into these operational modes to increase the mass transfer rate and
biomass as well as their uniform distributions.

11.4.2.7 Anaerobic condition

In a photobiohydrogen production system, maintaining good anaerobic condition is
critically important to prevent the toxic effect from the oxygen evolution, allowing
for the activation of the enzymes involved in hydrogen metabolism (Melis, 2002).
For instance, continuous sparging of inert gas into the photobiohydrogen production
system can maintain a low partial pressure of oxygen (Hallenbeck and Benemann,
2002). However, the hydrogen content obtained is very low in such a system, which
increases the difficulties in the separation and purification of hydrogen. The addition