Photobioreactors
139
the algal cells in and out of the photic volume at as high a frequency as possible
[114]. Despite some light limitation caused by self-shading of the plates, even
under the rather unfavourable climatic conditions of Germany, maximum
biomass productivity (Chlorella) of 1.3 g d.wt. 1- i d- 1 was obtained. This corresponds to an areal growth of 130 g d.wt. m -2 d-1, which is considerably higher
as reported for raceway ponds and conventional tubular reactors [ 115]. Beside
the Biocoil reactor, this plate type photobioreactor, available as PBR-series
(B. Braun Biotech Int.) from 10 1 up to a capacity of 60001, is the only system
which is sold commercially [116]. With vertical alveolar panels the O/V-ratio
may be increased to 80 m-1, the productivities related to the thin artificially
illuminated plates of a surface of 0.3 m 2 amounting to 20-30 g d.wt. m- 2 d- 1
(Spirulina), 3 g d.wt. 1-1 d- l(Tetraselmis) respectively [117].
The latest development in the field of sloped photobioreactor systems was
presented by Doucha et al. [118] who proposed optimized large-scale modules
of 1000 m 2. The culture area is made of several 50 m long and 5-10 m wide
meandering sloped glass lanes (inclination 1.6%) which produce a layer thickness of just 6 mm. Though productivity dropped to 14.5 gd.wt.m-2d -1, the
increase of the volume productivity to 3 g d.wt. 1-1 d- 1 seems to be very high,
and the harvesting density of 30 g d.wt. 1-1 achieved - one of the highest cell
concentration ever reported - allows for effective downstream processing.
5.3 Experimental Photobioreactors
5.3.1 Laboratory-Scale Reactors
On the basis of numerous research works in the field of the preparation of
valuable substances from phototrophic microorganisms, Lee [75] has summarized the development of closed photobioreactors. Therefore, mainly the
trends of the last ten years will be considered.
The design of the 0.5 m 2 serpentine tubular system of Pirt et al. [991 though
known for more than ten years, now as before belongs to the most frequently
cited developments in the field of photobioreactor construction. It consists of 52
glass tubes, 1 m length with a 1 cm bore, connected in series by silicone rubber
U-bends, and an air-lift system generating an effective surface/volume ratio of
127 m- i. Biomass concentrations in excess of 20 g d.wt. 1-1 could be maintained
in continuous flow cultures and very high maximum productivities over
50 g d.wt.m- 2 d - 1 (about 5 g d.wt. 1-1 d- 1) could be achieved representing a PE
of 40% with respect to Chlorella growth. Both theory of design and performance
was described and discussed in full detail, and thus the patent, still representing
one of the best analyses of fundamental engineering of tubular reactors, also
covers the design of a full-scale system.
A number of further tubular laboratory systems was described. The superiority of helical air-lift systems as against stirred reactors was demonstrated
with a maximum biomass yield (Porphyridium cruentum) of 1.7 g d.wt. 1- i d- 1
139
the algal cells in and out of the photic volume at as high a frequency as possible
[114]. Despite some light limitation caused by self-shading of the plates, even
under the rather unfavourable climatic conditions of Germany, maximum
biomass productivity (Chlorella) of 1.3 g d.wt. 1- i d- 1 was obtained. This corresponds to an areal growth of 130 g d.wt. m -2 d-1, which is considerably higher
as reported for raceway ponds and conventional tubular reactors [ 115]. Beside
the Biocoil reactor, this plate type photobioreactor, available as PBR-series
(B. Braun Biotech Int.) from 10 1 up to a capacity of 60001, is the only system
which is sold commercially [116]. With vertical alveolar panels the O/V-ratio
may be increased to 80 m-1, the productivities related to the thin artificially
illuminated plates of a surface of 0.3 m 2 amounting to 20-30 g d.wt. m- 2 d- 1
(Spirulina), 3 g d.wt. 1-1 d- l(Tetraselmis) respectively [117].
The latest development in the field of sloped photobioreactor systems was
presented by Doucha et al. [118] who proposed optimized large-scale modules
of 1000 m 2. The culture area is made of several 50 m long and 5-10 m wide
meandering sloped glass lanes (inclination 1.6%) which produce a layer thickness of just 6 mm. Though productivity dropped to 14.5 gd.wt.m-2d -1, the
increase of the volume productivity to 3 g d.wt. 1-1 d- 1 seems to be very high,
and the harvesting density of 30 g d.wt. 1-1 achieved - one of the highest cell
concentration ever reported - allows for effective downstream processing.
5.3 Experimental Photobioreactors
5.3.1 Laboratory-Scale Reactors
On the basis of numerous research works in the field of the preparation of
valuable substances from phototrophic microorganisms, Lee [75] has summarized the development of closed photobioreactors. Therefore, mainly the
trends of the last ten years will be considered.
The design of the 0.5 m 2 serpentine tubular system of Pirt et al. [991 though
known for more than ten years, now as before belongs to the most frequently
cited developments in the field of photobioreactor construction. It consists of 52
glass tubes, 1 m length with a 1 cm bore, connected in series by silicone rubber
U-bends, and an air-lift system generating an effective surface/volume ratio of
127 m- i. Biomass concentrations in excess of 20 g d.wt. 1-1 could be maintained
in continuous flow cultures and very high maximum productivities over
50 g d.wt.m- 2 d - 1 (about 5 g d.wt. 1-1 d- 1) could be achieved representing a PE
of 40% with respect to Chlorella growth. Both theory of design and performance
was described and discussed in full detail, and thus the patent, still representing
one of the best analyses of fundamental engineering of tubular reactors, also
covers the design of a full-scale system.
A number of further tubular laboratory systems was described. The superiority of helical air-lift systems as against stirred reactors was demonstrated
with a maximum biomass yield (Porphyridium cruentum) of 1.7 g d.wt. 1- i d- 1