Photobioreactors
143
source which can produce light energy quantities up to 400 J s-1 [137], but no
data of microalgal growth are published yet.
5.3.3 Immobilized Cell Systems and Hydrogen Production
In their review, Robinson et al. [138] stated the reasons for immobilizing algae:
-
use as biocatalysts and biotransformations,
- production of energy (hydrogen, electricity) and polysaccharides,
- for co-immobilized systems,
-
bioaccumulation of waste material,
-
towards prolonging longevity of cultures.
Immobilization techniques range from different matrices - agar, alginate or
carrageenan - to carrier material like polyurethane foam blocks or glass beads.
The design of immobilized cell photobioreactors depends on the purpose for
which organisms are employed. Packed-bed and fluidized-bed reactors as well
as air-lift systems are mentioned in the literature, but parallel plate types are
preferred for effective utilization of sunlight. However, growth rates of immobilized phototrophs are generally lower than those of free cells. The authors
emphasize that contents of pigments and storage substances, as well as production of extracellular products, especially hydrogen, could be improved remarkably in most cases.
During the last few years, hollow fibre bioreactors have aroused considerable interest in the fixation of phototrophic organisms because of the very high
surface/volume ratios obtainable. The product potentials from immobilized
cyanobacteria were summarized by Hall et al. [139], ranging from fine chemicals and fuels to water purification. The photosynthetic production of ammonia
and hydrogen with Anabaena fixed in hollow fibre systems and good carbon
dioxide uptake rates are described in detail [140, 141], though effective light
distribution is still a problem. Optical guiding systems could present solutions.
Applications on the basis of side light optical fibres for glutamate secretion with
Synechococcus [133] or of composite agar layer/microporous membrane structures for hydrogen photoproduction with Rhodospirillum [142] were examined.
For the illumination of the included organisms the gel plates are shielded to the
side of the nutrient solution by a microporous membrane and to the other side
by a steel plate. Small boreholes hold the ends of the fibers by which the
immobilisate is evenly illuminated.
Planar systems, such as the plate loop reactor proposed by Tramm-Werner
et al. [143] are suited very well to self-immobilization. With purple bacteria
Rhodobacter capsulatus a biofilm dry weight of over 20 g d.wt.m -2 could
be achieved in a 20-1 system. Depending on light intensity and quality, a
H2-production rate of 2 1 m- 2 h- 1 seems to be possible. Light penetration into
cultures of Rhodobacter sphaeroides was examined by Miyake [144]. He reports
a maximum conversion of light energy into photobacterially produced
143
source which can produce light energy quantities up to 400 J s-1 [137], but no
data of microalgal growth are published yet.
5.3.3 Immobilized Cell Systems and Hydrogen Production
In their review, Robinson et al. [138] stated the reasons for immobilizing algae:
-
use as biocatalysts and biotransformations,
- production of energy (hydrogen, electricity) and polysaccharides,
- for co-immobilized systems,
-
bioaccumulation of waste material,
-
towards prolonging longevity of cultures.
Immobilization techniques range from different matrices - agar, alginate or
carrageenan - to carrier material like polyurethane foam blocks or glass beads.
The design of immobilized cell photobioreactors depends on the purpose for
which organisms are employed. Packed-bed and fluidized-bed reactors as well
as air-lift systems are mentioned in the literature, but parallel plate types are
preferred for effective utilization of sunlight. However, growth rates of immobilized phototrophs are generally lower than those of free cells. The authors
emphasize that contents of pigments and storage substances, as well as production of extracellular products, especially hydrogen, could be improved remarkably in most cases.
During the last few years, hollow fibre bioreactors have aroused considerable interest in the fixation of phototrophic organisms because of the very high
surface/volume ratios obtainable. The product potentials from immobilized
cyanobacteria were summarized by Hall et al. [139], ranging from fine chemicals and fuels to water purification. The photosynthetic production of ammonia
and hydrogen with Anabaena fixed in hollow fibre systems and good carbon
dioxide uptake rates are described in detail [140, 141], though effective light
distribution is still a problem. Optical guiding systems could present solutions.
Applications on the basis of side light optical fibres for glutamate secretion with
Synechococcus [133] or of composite agar layer/microporous membrane structures for hydrogen photoproduction with Rhodospirillum [142] were examined.
For the illumination of the included organisms the gel plates are shielded to the
side of the nutrient solution by a microporous membrane and to the other side
by a steel plate. Small boreholes hold the ends of the fibers by which the
immobilisate is evenly illuminated.
Planar systems, such as the plate loop reactor proposed by Tramm-Werner
et al. [143] are suited very well to self-immobilization. With purple bacteria
Rhodobacter capsulatus a biofilm dry weight of over 20 g d.wt.m -2 could
be achieved in a 20-1 system. Depending on light intensity and quality, a
H2-production rate of 2 1 m- 2 h- 1 seems to be possible. Light penetration into
cultures of Rhodobacter sphaeroides was examined by Miyake [144]. He reports
a maximum conversion of light energy into photobacterially produced