Bioprocess Engineering of Phototrophic Marine Organisms 9.3 Basic Elements of Photobioreactor Design and Operation 267
Part B | 9.3
Table 9.4 Common light-saturation growth models for phototrophic marine organisms
Light-saturation growth
model
Equation
Adjustable parameters Limiting cases
Monod model (Model 1)
0 D
max I
IkCI
max , I k
I I k , 0 D max
I
Ik ; I D I k ; ; 0 D
0:5 max ; I ! 1, 0 ! max
Exponential model (Model 2)
0 D max
1 e
I
I k
Á
max , I k
I I k , 0 D max
I
Ik ; I D I k ; 0 D
0:632 max ; I ! 1, 0 ! max
Monod model with photoinhibition (Model 3)
0 D
max I
IkCICKiI 2
max , I k , K i
I I k , 0 D max
I
Ik ; I ! 1, 0 ! 0
Bannister–Monod model
(Model 4)
0 D
max I
.I
m
k CI m /
1=m
max , I k , m
m D 1, Monod model; I ! 1, 0 ! max
are usually dependent on the conditions under which
the organism is maintained. Specific factors include the
cell line of the organism, maintenance conditions for
pH, temperature, salinity, and light intensity, and finally the particular constituents of the liquid medium
formulation.
Phototrophic marine organisms are often subjected
to an illumination cycle, commonly known as a photoperiod. Usually, the photoperiod is referenced with
respect to a 24 h day and abbreviated as, for example,
16 W 8 LD, which refers to 16 h of light to 8 h of dark
for one cycle on a 24 h photoperiod. During the dark
phase of the photoperiod, it is assumed that no photosynthetic biomass production occurs. Therefore, the net
specific growth rate over the entire photoperiod can be
estimated by
photoperiod D continuous light f ;
(9.14)
where f is the fractional photoperiod, defined as the
time of culture illumination divided by the total time
of the photoperiod, e.g., for a 16 W 8 LD photoperiod, f
is equal to 0:67.
9.3 Basic Elements of Photobioreactor Design and Operation
Photobioreactors can assume many configurations. The
common requirements and process material balances
for well-mixed and tubular photobioreactors in batch
and continuous operation are described below.
9.3.1 Common Requirements
A photobioreactor is an enclosed, illuminated culture
vessel designed for the controlled biomass production of phototrophic liquid cell suspension cultures.
All photobioreactor systems, regardless of configuration, must provide illumination, gas exchange, and
mixing. Phototrophic cultures need light as the energy
source to drive photosynthesis, and so the photobioreactor must deliver sufficient light to the culture vessel.
Phototrophic cultures also use dissolved CO 2 as the
inorganic carbon source for photosynthetic biomass
production and evolve O 2 .
Gas exchange is the process of adding CO 2 to the
culture and removing evolved O 2 from the culture.
Usually, gas exchange is accomplished by sparging an
aeration gas into the liquid suspension culture. The aeration gas contains CO 2 that dissolves into the liquid. For
example, ambient air contains about 350 parts per million (ppm) CO 2 . The aeration gas also removes evolved
O 2 by stripping the dissolved O 2 from the culture liquid
to the aeration gas stream. The aeration gas stream exits
the culture and carries out the evolved O 2 along with it.
Mixing of the liquid culture is required to suspend the biomass and to promote contact between the
liquid nutrient medium and the cells. Mixing also promotes the process of gas exchange. A uniform biomass
suspension allows light to uniformly penetrate the
culture.
9.3.2 Biomass Production in Well-Mixed
Batch or Continuous Operation
Photobioreactors can be operated in either batch or continuous modes, as illustrated in Fig. 9.5. The concepts
underlying biomass production in batch and continuous
bioreactors are described below.
Part B | 9.3
Table 9.4 Common light-saturation growth models for phototrophic marine organisms
Light-saturation growth
model
Equation
Adjustable parameters Limiting cases
Monod model (Model 1)
0 D
max I
IkCI
max , I k
I I k , 0 D max
I
Ik ; I D I k ; ; 0 D
0:5 max ; I ! 1, 0 ! max
Exponential model (Model 2)
0 D max
1 e
I
I k
Á
max , I k
I I k , 0 D max
I
Ik ; I D I k ; 0 D
0:632 max ; I ! 1, 0 ! max
Monod model with photoinhibition (Model 3)
0 D
max I
IkCICKiI 2
max , I k , K i
I I k , 0 D max
I
Ik ; I ! 1, 0 ! 0
Bannister–Monod model
(Model 4)
0 D
max I
.I
m
k CI m /
1=m
max , I k , m
m D 1, Monod model; I ! 1, 0 ! max
are usually dependent on the conditions under which
the organism is maintained. Specific factors include the
cell line of the organism, maintenance conditions for
pH, temperature, salinity, and light intensity, and finally the particular constituents of the liquid medium
formulation.
Phototrophic marine organisms are often subjected
to an illumination cycle, commonly known as a photoperiod. Usually, the photoperiod is referenced with
respect to a 24 h day and abbreviated as, for example,
16 W 8 LD, which refers to 16 h of light to 8 h of dark
for one cycle on a 24 h photoperiod. During the dark
phase of the photoperiod, it is assumed that no photosynthetic biomass production occurs. Therefore, the net
specific growth rate over the entire photoperiod can be
estimated by
photoperiod D continuous light f ;
(9.14)
where f is the fractional photoperiod, defined as the
time of culture illumination divided by the total time
of the photoperiod, e.g., for a 16 W 8 LD photoperiod, f
is equal to 0:67.
9.3 Basic Elements of Photobioreactor Design and Operation
Photobioreactors can assume many configurations. The
common requirements and process material balances
for well-mixed and tubular photobioreactors in batch
and continuous operation are described below.
9.3.1 Common Requirements
A photobioreactor is an enclosed, illuminated culture
vessel designed for the controlled biomass production of phototrophic liquid cell suspension cultures.
All photobioreactor systems, regardless of configuration, must provide illumination, gas exchange, and
mixing. Phototrophic cultures need light as the energy
source to drive photosynthesis, and so the photobioreactor must deliver sufficient light to the culture vessel.
Phototrophic cultures also use dissolved CO 2 as the
inorganic carbon source for photosynthetic biomass
production and evolve O 2 .
Gas exchange is the process of adding CO 2 to the
culture and removing evolved O 2 from the culture.
Usually, gas exchange is accomplished by sparging an
aeration gas into the liquid suspension culture. The aeration gas contains CO 2 that dissolves into the liquid. For
example, ambient air contains about 350 parts per million (ppm) CO 2 . The aeration gas also removes evolved
O 2 by stripping the dissolved O 2 from the culture liquid
to the aeration gas stream. The aeration gas stream exits
the culture and carries out the evolved O 2 along with it.
Mixing of the liquid culture is required to suspend the biomass and to promote contact between the
liquid nutrient medium and the cells. Mixing also promotes the process of gas exchange. A uniform biomass
suspension allows light to uniformly penetrate the
culture.
9.3.2 Biomass Production in Well-Mixed
Batch or Continuous Operation
Photobioreactors can be operated in either batch or continuous modes, as illustrated in Fig. 9.5. The concepts
underlying biomass production in batch and continuous
bioreactors are described below.