Photobioreactors
137
Dvorin [95] reported about a plant of 130 m 3 size in Tadshikistan (Fa. Sagdiana
PGT Javan) which operated with a hydrodynamic regime generating Reynolds
numbers over 8000 for efficient mass transfer. In 1991, productivity of green
algal biomass however was far below 0.1 gd.wt.1-1 d-1. Another plant to
produce Chlorella biomass commercially was established in Turkmenistan in
1978. With a 10m 3 tubular device an annual capacity of 1 tonne, i.e.
1 g d.wt. 1-1 d- 1 and 0.7 g d.wt. 1-1 d- ~ Spirulina was achieved [96, 97]. Tredici
and Zitelli [98] investigated the scale-up of photobioreactors to commercial
size. They stated that incorrect evaluation of the efficiencies can lead to economic disaster. In case of PhotoBioreactors Ltd. (PBL, Spain) an inclined and
near horizontal tubular system, according to full-scale design patented by Pirt
et al. [99], was built in 1990, using 200 km of polyethylene tubing (12 mm in
diameter). However, incorrect management of the system led to poor growth
and PBL was shut before starting operations.
The helical tubular system commonly called Biocoil seems to be a promising
method. The idea was set up in the U.K. [100] and is based on an arrangement
of coiled polyethylene tubes (30-60 mm in diameter) around an open circular
framework. Algal suspension is recirculated either by pumps or according to the
air-lift principle. In Australia, 40-1001 laboratory reactors have been intensively
studied and successfully scaled up to i m 3 outdoor pilot plants [101, 102].
Laboratory scale reactors still are subject to intensive microalgal research [ 103].
Productivities are comparable to other tubular systems, but the completely
closed Biocoil could be continuously operated for several months with high
service ability and simple maintenance occupying less space than traditional
tubular configurations. Several 5 m 3 reactors are planned to be established in
the U.S.A. for aquaculture purposes [104]. Thus, the Biocoil has to be considered as one of the few commercially available outdoor photobioreactors.
There are several further approaches in small-scale tubular technology.
Anderson and Eakin [105] experimented with a highly sophisticated angular
adjustment of solar collector module to produce polysaccharides
(20-26 g d.wt. m- 2 d- 1) from Porphyridium. At the end of the 1980s, James and
A1-Kahrs [106] have designed for aquaculture applications a 200 1 turbidostatic
system with transparent vertically arranged tubes (diameter 30 cm) where the
algal suspension is aerated by an air stream and illuminated by fluorescent
lamps at a maximum of 330gEm-2s -1. The productivity achieved with
Chlorella amounted to 0.26 g d.wt. 1- ~ d- 1 (20-26 g d.wt. m- 2 d- 1). Similar results were achieved by Pulz [59] in a tubular fermenter (diameter of the glass
tubes 2.5 cm) where the algal suspension (501) is pumped around the light source
by a radial centrifugal pump (Fig. 3). Taking the glass tube surface as the basis of
calculation the surface-related growth rates of 14 g d.wt. m- 2 d- 1 do not exceed
the productivities of open systems.
The fundamental role of the ratio of illuminatable surface and suspension
volume was described by Myers and Graham in 1961 [107]. They cultivated in
a simple cylinder which was illuminated only from above by focused light of
1750 gEm -2 s -1. The surface/volume ratio (d/r 2 ratio of tubes) was increased
137
Dvorin [95] reported about a plant of 130 m 3 size in Tadshikistan (Fa. Sagdiana
PGT Javan) which operated with a hydrodynamic regime generating Reynolds
numbers over 8000 for efficient mass transfer. In 1991, productivity of green
algal biomass however was far below 0.1 gd.wt.1-1 d-1. Another plant to
produce Chlorella biomass commercially was established in Turkmenistan in
1978. With a 10m 3 tubular device an annual capacity of 1 tonne, i.e.
1 g d.wt. 1-1 d- 1 and 0.7 g d.wt. 1-1 d- ~ Spirulina was achieved [96, 97]. Tredici
and Zitelli [98] investigated the scale-up of photobioreactors to commercial
size. They stated that incorrect evaluation of the efficiencies can lead to economic disaster. In case of PhotoBioreactors Ltd. (PBL, Spain) an inclined and
near horizontal tubular system, according to full-scale design patented by Pirt
et al. [99], was built in 1990, using 200 km of polyethylene tubing (12 mm in
diameter). However, incorrect management of the system led to poor growth
and PBL was shut before starting operations.
The helical tubular system commonly called Biocoil seems to be a promising
method. The idea was set up in the U.K. [100] and is based on an arrangement
of coiled polyethylene tubes (30-60 mm in diameter) around an open circular
framework. Algal suspension is recirculated either by pumps or according to the
air-lift principle. In Australia, 40-1001 laboratory reactors have been intensively
studied and successfully scaled up to i m 3 outdoor pilot plants [101, 102].
Laboratory scale reactors still are subject to intensive microalgal research [ 103].
Productivities are comparable to other tubular systems, but the completely
closed Biocoil could be continuously operated for several months with high
service ability and simple maintenance occupying less space than traditional
tubular configurations. Several 5 m 3 reactors are planned to be established in
the U.S.A. for aquaculture purposes [104]. Thus, the Biocoil has to be considered as one of the few commercially available outdoor photobioreactors.
There are several further approaches in small-scale tubular technology.
Anderson and Eakin [105] experimented with a highly sophisticated angular
adjustment of solar collector module to produce polysaccharides
(20-26 g d.wt. m- 2 d- 1) from Porphyridium. At the end of the 1980s, James and
A1-Kahrs [106] have designed for aquaculture applications a 200 1 turbidostatic
system with transparent vertically arranged tubes (diameter 30 cm) where the
algal suspension is aerated by an air stream and illuminated by fluorescent
lamps at a maximum of 330gEm-2s -1. The productivity achieved with
Chlorella amounted to 0.26 g d.wt. 1- ~ d- 1 (20-26 g d.wt. m- 2 d- 1). Similar results were achieved by Pulz [59] in a tubular fermenter (diameter of the glass
tubes 2.5 cm) where the algal suspension (501) is pumped around the light source
by a radial centrifugal pump (Fig. 3). Taking the glass tube surface as the basis of
calculation the surface-related growth rates of 14 g d.wt. m- 2 d- 1 do not exceed
the productivities of open systems.
The fundamental role of the ratio of illuminatable surface and suspension
volume was described by Myers and Graham in 1961 [107]. They cultivated in
a simple cylinder which was illuminated only from above by focused light of
1750 gEm -2 s -1. The surface/volume ratio (d/r 2 ratio of tubes) was increased