PART 1 - Design and Analysis of Bioreactors Flashcards
Ideal Reactors
The __________________ differs from the traditional batch process in that nutrients are added in stages to maximize cell growth.
fed-batch process
Features of a Fed-Batch Cultivation
- A fed-batch culture is a semi-batch operation
- Nutrients are fed either intermittently or continuously during the course of otherwise batch operation
- The culture broth is harvested only at the end of the operational period (full
volume), either fully or partially - Repeated fed-batch till the cells remain fully viable and productive
- One or more feed streams but no effluent
- Manipulating the feed rates during the run
- The culture volume increases continuously
- A dynamic operation
- Concentrations of limiting nutrients in the culture can be manipulated
- Nutrient concentration profile: can remain at a constant level to follow a
predetermined profile - A batch mode is used to end the fermentation (maximum product titer and
yield) - Manipulation of one or more feed rates, a means of regulating the nutrient
concentration controlling the key reaction rates. What compounds should be
fed and how they should be added
Simple Case of Fed-Batch
- Maximize the cell formation rate for constant cell mass yield
- The substrate concentration maintained at a value that maximizes the specific the growth rate
- Maximum cell concentration achieved at the end of the run
- Feed rate regulated to hold the substrate concentration constant at the desired value until the reactor is full
- Once the fermenter is full, it is run in a batch mode.
Advantages of Fed-Batch Reactor
- Intermittent feeding of substrate and maintaining low substrate concentration
to prevent substrate inhibition - High Cell density
- Catabolite repression (penicillin fermentation)
- Crabtree effect (baker’s yeast fermentation)
- Auxotrophic mutants, expression control of genes (inducers and repressors)
- Extension of operation time, supplement of water lost by evaporation and
decreasing viscosity of culture broth.
The analysis of fed-batch with substrate continuously fed and no output: At
t=0,
F is constant
The ________________, observed in certain microorganisms like baker’s yeast (Saccharomyces cerevisiae), refers to the phenomenon where these organisms preferentially ferment sugars to ethanol even in the presence of oxygen.
Crabtree effect
Catabolite repression is advantageous in fed-batch reactors when the emphasis is on _____________________________________ to achieve specific bioprocess goals, such as high biomass production or the synthesis of a particular product.
controlled and efficient utilization of preferred carbon sources
____________________ is a regulatory mechanism in microorganisms (such as bacteria and yeast) that involves the inhibition or repression of the expression of certain genes involved in the metabolism of alternative carbon sources when a preferred carbon source is available.
Catabolite repression
__________________ is only possible if the enzymes can be easily retrieved from the product stream exiting the reactor.
Enzyme recycling
Regardless of which technique is used, the common goal is to keep the appropriate __________________ within the CSTR.
enzyme concentration
(CSTF)
continuous stirred-tank fermenter
The cell concentration in a single chemostat can be increased by ________________ in the product stream back to the reactor.
recycling the biomass
______________________ is characterized by containing a homogeneous liquid phase into which nutrients are continuously fed and from which the suspension of microorganisms and depleted feed are continuously removed.
The continuous stirred-tank fermenter (CSTF)
Because the fermenter is well mixed, samples taken from any location in the fermenter will be ________ and the composition of the exit stream will be identical to that of the liquid in the fermenter.
identical
In a chemostat, the flow rate is set at a ___________ and the rate of growth of the culture adjusts to this flow rate.
fixed value
Continuous Stirred-Tank Fermenter (CSTF) have many applications, a few of which are listed below.
Pharmaceuticals: Used to study a number of different bacteria, a specific
example being analyzing how bacteria respond to different antibiotics.
Bacteria are also used in the production of therapeutic proteins such as insulin
for diabetics.
2. Manufacturing: Used to produce ethanol, the fermentation of sugar by bacteria
takes place in a series of chemostats. Also, many different antibiotics are
produced in chemostats.
3. Food Industry: Used in the production of fermented foods such as cheese.
4. Research: Used to collect data to be used in the creation of a mathematical
model of growth for specific cells or organisms.
As the concentrations in the chemostat adjust to the feed rate, the _____________ remains constant, and a steady-state is established.
dilution rate
In a turbidostat, the ______________ is kept constant by setting the outlet flow rate equal to the inlet flow rate; however, the inlet flow rate is modified to maintain a constant biomass concentration.
liquid volume
As a result, the dilution rate in a turbidostat adjusts to the ________________ needed to produce the required biomass concentration.
steady-state value
It is easier to operate chemostat than turbidostat, because the former can be
done by ____________________, whereas the latter requires an _________________________.
setting the pump at a constant flow rate
optical sensing device and a controller
However, the _____________ is recommended when continuous fermentation needs to be carried out at high dilution rates near the washout point, since it can prevent washout by regulating the flow rate in case the cell loss through the output stream exceeds the cell growth in the fermenter.
turbidostat
The chemostat setup consists of a
sterile fresh nutrient reservoir connected to a growth chamber or reactor.
