Photobiohydrogen production and high-performance photobioreactor - Solar Energy Sciences and Engineering Applications - page 361

of 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea (DCMU) that is a potent inhibitor of
the direct PSII-dependent photobiohydrogen production pathway can lead to a com-
plete anaerobiosis (Fouchard et al., 2005). Besides, the adsorbent and reductant of
oxygen can also make the photobiohydrogen production system to be operated under
anaerobic conditions by consuming the oxygen in the solution (Hansel and Lindblad,
1998). Unfortunately, these techniques do not possess practical value because of the
high processing cost. In 2000, Melis et al. (2000) and his colleagues developed a novel
two-stage hydrogen production method for sustaining photobiohydrogen production
using the green alga of Chlamydomonas reinhardtii as the photobiohydrogen pro-
duction microorganism. In this method, photosynthetic oxygen evolution and carbon
accumulation (stage 1) and concomitant hydrogen production (stage 2) were tempo-
rally separated to circumvent the severe oxygen sensitivity of the reversible hydrogenase
by the sulfur deprivation in culture, which can reversibly inactivate PSII and oxygen
evolution to ensure a transition from stage 1 to stage 2 (Melis et al. 2000). Although
this technique is effective, the system becomes complex. As a result, more cost-effective
and simple methods are needed for industrialization.

11.4.2.8 Hydrogen partial pressure

As the photobiohydrogen production proceeds, hydrogen produced in the photobiore-
actor is accumulated, causing an increase of the hydrogen partial pressure and thereby
lowering the photobiohydrogen production performance. Thus, reducing the hydrogen
partial pressure by efficiently removing hydrogen produced from the system to facili-
tate the photobiochemical reaction is of importance to improve the performance of the
photobioreactor. Currently, many strategies of removing or separating the produced
hydrogen have been developed to weaken the negative effect of the hydrogen accumu-
lation. Liao et al. (2012) found that feeding the sparging gas at 10 ml/min led to the
increase of the photobiohydrogen production rate, hydrogen yield and light conversion
efficiency by 2.2, 3.1 and 2.2 times than the case without gas sparging, respectively.
But this method increases the cost of the hydrogen separation. Furthermore, they
reported an ultrasonic treatment method that enabled the hydrogen concentration in
the solution to be decreased from 300

mol/L due to the disturbance
from the acoustic streaming (Wang et al., 2012). However, this technique can result in
an increase in the operation cost. As a consequence, it is essential to develop a simple
technique that can lower the hydrogen partial pressure with low operation cost.
In summary, to obtain a high photobiohydrogen production performance, the
operating conditions need to be optimized. The optimal combination of the illumina-
tion conditions, temperature, pH value, nutrients, substrate concentration as well as
operational modes in terms of both the photobioreactor design and the used microor-
ganism can maximize the photobiohydrogen production rate. Besides, careful selection
of substrate type along with the maintenance of good anaerobic condition and low
hydrogen partial pressure also benefits for the photobiohydrogen production.

µ mol/L to 50 µ

11.4.3 Application of cell immobilization
In an existing photobioreactor, microorganisms are usually suspended in culture solu-
tion. Although such operation can provide the advantage of good mass transfer