Novel Bioreactors for Culturing Marine Organisms 12.3 Airlift Bioreactors (ALBR) and Bubble Column Bioreactors (BCBR) 345
Part B | 12.3
small diameter of the loop and the low biomass concentration involved, the laboratory-scale tubular loop PBR
performance data could be considered free of the effect
of self-shading, and in this regard, the TL-PBR could be
considered a thin-film photobioreactor. The larger column reactors were used to examine the effect of mixing
under conditions of high optical density, where selfshading and fluid dynamics were responsible for the
periodicity of exposure to light.
The tubular loop reactor (volume 0:43 L) consisted
of a series of glass tubes (I.D. 0:007 m) connected to
a small vessel into which air containing 3% CO 2 was
bubbled (to supply a carbon-source and remove O 2 ); the
loop was closed through a peristaltic pump. The ratio of
illuminated/dark zones was controlled by darkening different lengths of the tube. The ventilation vessel, which
was always covered, formed part of the dark zone. Illumination was provided from a bank of fluorescent
lamps.
The column reactors (both 2 m high, column diameter 0:180 m) were also supplied with air containing
3% CO 2 and were housed in a temperature-controlled
room at 25
ı C. The difference in construction between
the AL-PBR and the BC-PBR was that a draft tube
(height 1:5 m, diameter 0:09 m) was installed coaxially in the AL-PBR. The draft tube plays a pivotal
role in transforming the flow of the liquid, which
is approximately random in the bubble column, into
more ordered patterns in the ALR. The liquid rises
through the central riser due to the difference in hydrostatic pressure, and descends through the annular downcomer, engaging part of the gas. The extent of this gas carryover depends on the operating
conditions.
Krichnavaruk et al. [12.35] used a small-scale glass
BC-PBR (2:5 L) as well as an AL-PBR and a BCPBR (both 17 L volume) to investigate the growth
of the chlorophyll containing marine diatom Chaetoceros calcitrans which is commonly used as feed for
shrimp larvae. For the large-scale column reactors, run
in batch mode, both maximum specific growth rate
and maximum cell concentration were higher in the
AL-PBR by about 18 and 16%, respectively. For the
AL-PBR operated in semicontinuous mode, maximum
specific growth rate increased further by 30%. Experiments to determine the optimal growth conditions of
C. calcitrans were performed in a small-scale glass
bubble column (volume 2:5 L). Compressed air (flowing 3:8 L min
1 ) entered the bottom of the column.
Illumination was provided through 250 W lamps, and
incident light intensity was controlled by varying the
distance between the lamps and the column. Both largescale bioreactors were acrylic-made (diameter 15 cm)
but the AL-PBR was equipped with a draft tube installed centrally in the column. The ratio between the
cross-sectional areas of downcomer and riser was 2:63.
Compressed air was supplied at the bottom of the draft
tube and a 5 cm gap was left between the bottom of the
draft tube and the column to allow liquid circulation.
Aeration was controlled by a calibrated rotameter –
superficial gas velocity in the riser was controlled in
a range of 25 cm s
1 . Light was supplied through 12
fluorescent lamps placed at the side, along the length of
the columns and temperature was controlled 30
ı C
(˙2
ı C).
The superior performance of the ALBR vis-a-vis the
BCBR may be attributed to a well-defined flow pattern
in the ALBR that allows more effective light utilization
by the diatom. In the BCBR, proper recirculation of
cells is not possible since aeration only superimposes
random motion with no net liquid movement – whereas
some cells are exposed to high light intensity in close
proximity of the illuminated column walls, those centrally positioned in the column are exposed to much
lower light intensity causing ineffective photosynthesis
and consequently low biomass growth. However, uneven fluid density in the riser and downcomer sections
of the ALBR, induces a well-defined flow pattern – upward liquid movement in the riser and downward in the
downcomer. Consequently diatoms in the riser, would,
after lapse of a certain time, flow to the downcomer
where light is directly incident, implying exposure to
more uniform light density than in the BC. Furthermore,
liquid movement in the ALR prevents cell accumulation at the bottom of the column (and an uneven cell
density along the length of the column arising therefrom) by facilitating cell circulation even at high cell
density. Cell accumulation at the bottom of the column may potentially cause starvation, death, and even
culture contamination, thereby resulting in an overall
reduced growth rate.
Sanchez-Miron et al. [12.36] undertook a comparative evaluation (mainly in terms of hydrodynamics
and transport phenomena) of three air-agitated photobioreactors, viz., a bubble column, a split-cylinder or
split-column ALR and a concentric draft-tube sparged
ALR (Fig. 12.17). Their focus was on fractional gas
holdup, liquid circulation velocity, and the overall gas–
liquid oxygen mass transfer coefficient and the interdependence of these variables in regimes relevant to
microalgal cultures. Comparative evaluation of reactor
performance was presented for the culture of the photo-
Part B | 12.3
small diameter of the loop and the low biomass concentration involved, the laboratory-scale tubular loop PBR
performance data could be considered free of the effect
of self-shading, and in this regard, the TL-PBR could be
considered a thin-film photobioreactor. The larger column reactors were used to examine the effect of mixing
under conditions of high optical density, where selfshading and fluid dynamics were responsible for the
periodicity of exposure to light.
The tubular loop reactor (volume 0:43 L) consisted
of a series of glass tubes (I.D. 0:007 m) connected to
a small vessel into which air containing 3% CO 2 was
bubbled (to supply a carbon-source and remove O 2 ); the
loop was closed through a peristaltic pump. The ratio of
illuminated/dark zones was controlled by darkening different lengths of the tube. The ventilation vessel, which
was always covered, formed part of the dark zone. Illumination was provided from a bank of fluorescent
lamps.
The column reactors (both 2 m high, column diameter 0:180 m) were also supplied with air containing
3% CO 2 and were housed in a temperature-controlled
room at 25
ı C. The difference in construction between
the AL-PBR and the BC-PBR was that a draft tube
(height 1:5 m, diameter 0:09 m) was installed coaxially in the AL-PBR. The draft tube plays a pivotal
role in transforming the flow of the liquid, which
is approximately random in the bubble column, into
more ordered patterns in the ALR. The liquid rises
through the central riser due to the difference in hydrostatic pressure, and descends through the annular downcomer, engaging part of the gas. The extent of this gas carryover depends on the operating
conditions.
Krichnavaruk et al. [12.35] used a small-scale glass
BC-PBR (2:5 L) as well as an AL-PBR and a BCPBR (both 17 L volume) to investigate the growth
of the chlorophyll containing marine diatom Chaetoceros calcitrans which is commonly used as feed for
shrimp larvae. For the large-scale column reactors, run
in batch mode, both maximum specific growth rate
and maximum cell concentration were higher in the
AL-PBR by about 18 and 16%, respectively. For the
AL-PBR operated in semicontinuous mode, maximum
specific growth rate increased further by 30%. Experiments to determine the optimal growth conditions of
C. calcitrans were performed in a small-scale glass
bubble column (volume 2:5 L). Compressed air (flowing 3:8 L min
1 ) entered the bottom of the column.
Illumination was provided through 250 W lamps, and
incident light intensity was controlled by varying the
distance between the lamps and the column. Both largescale bioreactors were acrylic-made (diameter 15 cm)
but the AL-PBR was equipped with a draft tube installed centrally in the column. The ratio between the
cross-sectional areas of downcomer and riser was 2:63.
Compressed air was supplied at the bottom of the draft
tube and a 5 cm gap was left between the bottom of the
draft tube and the column to allow liquid circulation.
Aeration was controlled by a calibrated rotameter –
superficial gas velocity in the riser was controlled in
a range of 25 cm s
1 . Light was supplied through 12
fluorescent lamps placed at the side, along the length of
the columns and temperature was controlled 30
ı C
(˙2
ı C).
The superior performance of the ALBR vis-a-vis the
BCBR may be attributed to a well-defined flow pattern
in the ALBR that allows more effective light utilization
by the diatom. In the BCBR, proper recirculation of
cells is not possible since aeration only superimposes
random motion with no net liquid movement – whereas
some cells are exposed to high light intensity in close
proximity of the illuminated column walls, those centrally positioned in the column are exposed to much
lower light intensity causing ineffective photosynthesis
and consequently low biomass growth. However, uneven fluid density in the riser and downcomer sections
of the ALBR, induces a well-defined flow pattern – upward liquid movement in the riser and downward in the
downcomer. Consequently diatoms in the riser, would,
after lapse of a certain time, flow to the downcomer
where light is directly incident, implying exposure to
more uniform light density than in the BC. Furthermore,
liquid movement in the ALR prevents cell accumulation at the bottom of the column (and an uneven cell
density along the length of the column arising therefrom) by facilitating cell circulation even at high cell
density. Cell accumulation at the bottom of the column may potentially cause starvation, death, and even
culture contamination, thereby resulting in an overall
reduced growth rate.
Sanchez-Miron et al. [12.36] undertook a comparative evaluation (mainly in terms of hydrodynamics
and transport phenomena) of three air-agitated photobioreactors, viz., a bubble column, a split-cylinder or
split-column ALR and a concentric draft-tube sparged
ALR (Fig. 12.17). Their focus was on fractional gas
holdup, liquid circulation velocity, and the overall gas–
liquid oxygen mass transfer coefficient and the interdependence of these variables in regimes relevant to
microalgal cultures. Comparative evaluation of reactor
performance was presented for the culture of the photo-