Part B | 9.3
276 Part B Tools and Methods in Marine Biotechnology
Air in
Tubular
section
Change in
fluid height
Air out
Pump
Culture
upflow
Tubular
section
Air out
Degasser
Culture
downflow
Culture
upflow
Air
injection
a)
b)
Fig. 9.14a,b
Tubular photobioreactors: (a)
mechanical versus (b) airlift
pumping
tubular section. In both configurations, the culture recirculation system must compensate for pressure drop
due to friction of the culture with the tubing walls and
the difference in elevation between the tubular section
entrance and exit points. The airlift system is relatively
gentle on the cells and has no moving parts, but cannot
accommodate high flow rates or pump against high fluid
heads. The mechanically pumped system can provide
high flow rates against high pressure drops. However,
Air out
Air in
Riser section
(large bubbles
in tube)
Illumination source
Culture downflow
Fig. 9.15 The inclined tubular airlift photobioreactor
the pump can potentially damage the culture if the cells
are fragile towards hydrodynamic or mechanical shear
forces. In this context, volumetric pumps, where the
pump rotor speed is proportional to flow rate, are preferred over centrifugal pumps, where the rotor speed
is fixed independently of culture flow rate. Diaphragm
pumps also provide relatively low shear.
A variant of the airlift pumping system for the tubular photobioreactor is the airlift tubular photobioreactor.
It combines the elements of an airlift and tubular bioreactors into one system, as illustrated in Fig. 9.15. In
the airlift tubular photobioreactor, the tube is inclined
upward at an angle. Air is injected into the bottom of
the tube to provide gas exchange and to move the suspension culture up the tube. Since the aeration gas is
inside the tube, the tubing diameter is larger than that
for conventional tubular reactors. Furthermore, the reactor volume must be increased to compensate for the
space occupied by the bubbles. At the top of the tube is
a degassing vessel where the aeration gas exits the system, and the culture flows back down to the bottom of
the tube.
Tubular Recycle Photobioreactors
The tubular photobioreactors described above are designed for batch operation. Even though the culture is
continuously flowing in and out of the tubing bank,
it is still recirculating between the tubular section and
276 Part B Tools and Methods in Marine Biotechnology
Air in
Tubular
section
Change in
fluid height
Air out
Pump
Culture
upflow
Tubular
section
Air out
Degasser
Culture
downflow
Culture
upflow
Air
injection
a)
b)
Fig. 9.14a,b
Tubular photobioreactors: (a)
mechanical versus (b) airlift
pumping
tubular section. In both configurations, the culture recirculation system must compensate for pressure drop
due to friction of the culture with the tubing walls and
the difference in elevation between the tubular section
entrance and exit points. The airlift system is relatively
gentle on the cells and has no moving parts, but cannot
accommodate high flow rates or pump against high fluid
heads. The mechanically pumped system can provide
high flow rates against high pressure drops. However,
Air out
Air in
Riser section
(large bubbles
in tube)
Illumination source
Culture downflow
Fig. 9.15 The inclined tubular airlift photobioreactor
the pump can potentially damage the culture if the cells
are fragile towards hydrodynamic or mechanical shear
forces. In this context, volumetric pumps, where the
pump rotor speed is proportional to flow rate, are preferred over centrifugal pumps, where the rotor speed
is fixed independently of culture flow rate. Diaphragm
pumps also provide relatively low shear.
A variant of the airlift pumping system for the tubular photobioreactor is the airlift tubular photobioreactor.
It combines the elements of an airlift and tubular bioreactors into one system, as illustrated in Fig. 9.15. In
the airlift tubular photobioreactor, the tube is inclined
upward at an angle. Air is injected into the bottom of
the tube to provide gas exchange and to move the suspension culture up the tube. Since the aeration gas is
inside the tube, the tubing diameter is larger than that
for conventional tubular reactors. Furthermore, the reactor volume must be increased to compensate for the
space occupied by the bubbles. At the top of the tube is
a degassing vessel where the aeration gas exits the system, and the culture flows back down to the bottom of
the tube.
Tubular Recycle Photobioreactors
The tubular photobioreactors described above are designed for batch operation. Even though the culture is
continuously flowing in and out of the tubing bank,
it is still recirculating between the tubular section and