136
O. Pulz and K. Scheibenbogen
- reproducible cultivation conditions
-
higher flexibility with regard to environmental influences,
-
significantly smaller space requirements.
The first item can constitute a rather significant cost factor. Soeder [86] has
calculated costs of US-$ 2000 for CO2 per ton algal dry mass produced at
optimum conditions. Weissman et al. [40] reported losses of more than 80% in
open systems, while in the tubular reactors for comparison the CO2 is better
utilized, independently of the pH-value and salinity. However, the authors
concluded that the tubular systems are not superior to raceway ponds because
of the reduced suitability to up-scaling, the high energy consumption and the
frequently observed hypercritical oxygen concentrations. Nevertheless, great
attention has been paid to tubular systems, during the last years.
5.2.1 Tubular Photobioreactors
The groups of Materassi and coworkers in Italy and Gudin and Chaumont in
the South of France have invested much effort in the development of outdoor
reactors. Generally these tubular systems are arranged in a horizontal serpentine form and made of glass or plastic tubes. The culture suspension was
recirculated either by a pump or - more preferably - by air-lift technology.
Temperature was controlled by floating or submerging the tubes on or in a pool
of water, oxygen degassing being guaranteed by flexible tube elements. With
a 100 m 2 culture unit (tube diameter 6 cm) and Porphyridium cruentum a productivity of 20-25 g d.wt. m - 2 d- 1 (corresponding to approx. 0.4 g d.wt. 1 - 1 d - t)
was achieved during 2 months of steady-state continuous culture. The company
Heliosynth~se SA in the south of France developed this type further and has
launched commercial production [13, 87-89]. A manifold tubular reactor was
established in Israel, using reduced diameters (32 ram) of polycarbonate tubes
for the cultivation of Spirulina and Anabaena [82]. In Italy, too, several attempts
were made to use closed tubular systems. Torzillo et al. [90] achieved a
maximum productivity of 25 g d.wt. m - 2 d - 1 (Spirulina) in a 10 m 3 serpentine
bioreactor with intermitted culture circulation and obtained further improvements by constructing a two-plane tubular photobioreactor with mean daylight
productivities of about 30 g d.wt. m- 2 d - ~ corresponding to 1.5 g d.wt. 1-1 d - 1
[91]. Using strongly curved outdoor tubular reactors with high flow rates
(0.97 m s - 1) generating Reynolds numbers above 4000 within the tubes (2.6 cm
inner diameter), the growth rate could be increased by about 17%, as against
straight tubes with 1.2 g d.wt. 1 - 1 d- 1, i.e: 23 g d.wt. m - 2 d - 1 areal productivity
[92]. For closed tubular reactors in Italy an overall mean volumetric productivity of 0.8 g d.wt. 1 - 1 d - t Spirulina per annum has been summarized [93].
Lee et al. [94] developed with their a-shaped 3001 tubular loop
reactor a similar approach to increase turbulences and yielded up to
72.5 g d.wt. m - 2 d - 1 Chlorella pyrenoidosa biomass (about 2.9 g d.wt. 1-1 d - 1).
O. Pulz and K. Scheibenbogen
- reproducible cultivation conditions
-
higher flexibility with regard to environmental influences,
-
significantly smaller space requirements.
The first item can constitute a rather significant cost factor. Soeder [86] has
calculated costs of US-$ 2000 for CO2 per ton algal dry mass produced at
optimum conditions. Weissman et al. [40] reported losses of more than 80% in
open systems, while in the tubular reactors for comparison the CO2 is better
utilized, independently of the pH-value and salinity. However, the authors
concluded that the tubular systems are not superior to raceway ponds because
of the reduced suitability to up-scaling, the high energy consumption and the
frequently observed hypercritical oxygen concentrations. Nevertheless, great
attention has been paid to tubular systems, during the last years.
5.2.1 Tubular Photobioreactors
The groups of Materassi and coworkers in Italy and Gudin and Chaumont in
the South of France have invested much effort in the development of outdoor
reactors. Generally these tubular systems are arranged in a horizontal serpentine form and made of glass or plastic tubes. The culture suspension was
recirculated either by a pump or - more preferably - by air-lift technology.
Temperature was controlled by floating or submerging the tubes on or in a pool
of water, oxygen degassing being guaranteed by flexible tube elements. With
a 100 m 2 culture unit (tube diameter 6 cm) and Porphyridium cruentum a productivity of 20-25 g d.wt. m - 2 d- 1 (corresponding to approx. 0.4 g d.wt. 1 - 1 d - t)
was achieved during 2 months of steady-state continuous culture. The company
Heliosynth~se SA in the south of France developed this type further and has
launched commercial production [13, 87-89]. A manifold tubular reactor was
established in Israel, using reduced diameters (32 ram) of polycarbonate tubes
for the cultivation of Spirulina and Anabaena [82]. In Italy, too, several attempts
were made to use closed tubular systems. Torzillo et al. [90] achieved a
maximum productivity of 25 g d.wt. m - 2 d - 1 (Spirulina) in a 10 m 3 serpentine
bioreactor with intermitted culture circulation and obtained further improvements by constructing a two-plane tubular photobioreactor with mean daylight
productivities of about 30 g d.wt. m- 2 d - ~ corresponding to 1.5 g d.wt. 1-1 d - 1
[91]. Using strongly curved outdoor tubular reactors with high flow rates
(0.97 m s - 1) generating Reynolds numbers above 4000 within the tubes (2.6 cm
inner diameter), the growth rate could be increased by about 17%, as against
straight tubes with 1.2 g d.wt. 1 - 1 d- 1, i.e: 23 g d.wt. m - 2 d - 1 areal productivity
[92]. For closed tubular reactors in Italy an overall mean volumetric productivity of 0.8 g d.wt. 1 - 1 d - t Spirulina per annum has been summarized [93].
Lee et al. [94] developed with their a-shaped 3001 tubular loop
reactor a similar approach to increase turbulences and yielded up to
72.5 g d.wt. m - 2 d - 1 Chlorella pyrenoidosa biomass (about 2.9 g d.wt. 1-1 d - 1).