Photobioreactors
141
4.9gd.wt. 1- ~d-1, and with slow growing Dunaliella a rate of
2 g d.wt. 1- ~ d- 1 was attained. The cell concentrations achieved in batch cultivation are also rather high; at approx. 12 g Chlorella or Spirulina dry mass per
litre effective cell density growth inhibition was already reached. The results
were determined in a 10-1 reactor. Due to the fact that the algal suspension as
a whole has to be brought into rotation, the energy input is increasing significantly with increasing volume, so that with the planned 25-1 fermenter the limit
of technical usefulness will be practically reached.
Even higher cell concentrations were achieved by Lee and Palsson 1-64] in
a 100-ml reactor and an ultrafiltration unit. Intensive illumination was realized
by an array of LEDs with monochromatic light at 680 nm. This thin layer
system is best suited to studies on mass transfer processes in microalgal cultures
[127] as well as on photosynthetic efficiency and the flash-light effect 1,128].
The transfer of light from external sources to the reactor chamber was also
subject to research over the last few years. The patent of Meyer et al. 1-129]
covers a plate-type acryl-glass unit which, as immersion block, distributes the
light in the suspension at mathematically defined conditions. At the Facult6
Polytechnique in Mons, Belgium, small quantities of isotopically labelled organic compounds are produced from Spirulina in this type of reactor. The trend
to use light guiding systems for photobioreactors has led to the development of
fibre optic arrangements.
5.3.2 Fibre Optic Reactors
Javanmardian and Palsson [63] have solved the problem of uniform light
dissipation by using the inner walls of the medium vessel itself as dissipation
unit. The 0.6-1 acryl-glass fermenter consists of concentrically fitted cylinders
which are supplied with light from the exterior via fibre optics. The fibres have
their ends in channels with wedge-shaped notches which distribute the incoming
light over the whole surface of the cylinder. In this reactor, the light dissipation
system takes approx. 40% of the reactor volume but a rather high O/V-ratio of
320 m- 1 is reached. At a PAR luminance of 30-60 ~tE m- 2 s- 1 and with a strain
of Chlorella vulgaris the maximum productivity amounted to 1.5 g d.wt. 1- ~ d- 1
which approaches the value of 1.9 g d.wt. 1-1 d- ~ at approx. 30 laE m- 2 s- 1
theoretically calculated by Javanmardian. Regarding the growth rates of other
reactors of up to 5 g d.wt. 1- a d- a and the relatively low PAR-intensities, this
system has the disadvantage of rather low light input. Nevertheless, dry masses
of more than 20 g d.wt. 1-1 result from batch cultivation with an ultrafiltration
unit.
Concepts such as the reactor designed by Mori [130] make use of the idea to
use fibres directly as radiation surface because, due to their small diameter, they
produce a very high O/V-ratio. This system, which may also be used for solar
radiation, consists of a light collecting unit, a Fresnel lens, which filters out IR
and UV-radiation by aberration and supplies the residual light into a fibre
141
4.9gd.wt. 1- ~d-1, and with slow growing Dunaliella a rate of
2 g d.wt. 1- ~ d- 1 was attained. The cell concentrations achieved in batch cultivation are also rather high; at approx. 12 g Chlorella or Spirulina dry mass per
litre effective cell density growth inhibition was already reached. The results
were determined in a 10-1 reactor. Due to the fact that the algal suspension as
a whole has to be brought into rotation, the energy input is increasing significantly with increasing volume, so that with the planned 25-1 fermenter the limit
of technical usefulness will be practically reached.
Even higher cell concentrations were achieved by Lee and Palsson 1-64] in
a 100-ml reactor and an ultrafiltration unit. Intensive illumination was realized
by an array of LEDs with monochromatic light at 680 nm. This thin layer
system is best suited to studies on mass transfer processes in microalgal cultures
[127] as well as on photosynthetic efficiency and the flash-light effect 1,128].
The transfer of light from external sources to the reactor chamber was also
subject to research over the last few years. The patent of Meyer et al. 1-129]
covers a plate-type acryl-glass unit which, as immersion block, distributes the
light in the suspension at mathematically defined conditions. At the Facult6
Polytechnique in Mons, Belgium, small quantities of isotopically labelled organic compounds are produced from Spirulina in this type of reactor. The trend
to use light guiding systems for photobioreactors has led to the development of
fibre optic arrangements.
5.3.2 Fibre Optic Reactors
Javanmardian and Palsson [63] have solved the problem of uniform light
dissipation by using the inner walls of the medium vessel itself as dissipation
unit. The 0.6-1 acryl-glass fermenter consists of concentrically fitted cylinders
which are supplied with light from the exterior via fibre optics. The fibres have
their ends in channels with wedge-shaped notches which distribute the incoming
light over the whole surface of the cylinder. In this reactor, the light dissipation
system takes approx. 40% of the reactor volume but a rather high O/V-ratio of
320 m- 1 is reached. At a PAR luminance of 30-60 ~tE m- 2 s- 1 and with a strain
of Chlorella vulgaris the maximum productivity amounted to 1.5 g d.wt. 1- ~ d- 1
which approaches the value of 1.9 g d.wt. 1-1 d- ~ at approx. 30 laE m- 2 s- 1
theoretically calculated by Javanmardian. Regarding the growth rates of other
reactors of up to 5 g d.wt. 1- a d- a and the relatively low PAR-intensities, this
system has the disadvantage of rather low light input. Nevertheless, dry masses
of more than 20 g d.wt. 1-1 result from batch cultivation with an ultrafiltration
unit.
Concepts such as the reactor designed by Mori [130] make use of the idea to
use fibres directly as radiation surface because, due to their small diameter, they
produce a very high O/V-ratio. This system, which may also be used for solar
radiation, consists of a light collecting unit, a Fresnel lens, which filters out IR
and UV-radiation by aberration and supplies the residual light into a fibre