IBX - Fermentation Reactors

Question 1

Yield coefficient represents

total biomass or product produced
conversion efficiency of a substrate into product
conversion rate of a substrate into biomass or product
production time of biomass or produc

Answer 1

conversion efficiency of a substrate into product

Question 2

The lowest biomass yield in a culture of Escherichia coli will be in

an aerated batch culture containing a initial high concentration of glucose
an aerated batch reactor containing an initial low concentration of glucose
an aerated fed-batch reactor having a low glucose concentration
an aerated continuous reactor having a low glucose concentration

Answer 2

an aerated batch culture containing a initial high concentration of glucose

Question 3

When two populations compete for a single growth limiting substrate in a continuous fermenter, which organism would not be washed out?

Organism maintaining the highest substrate concentration
Organism maintaining the lowest substrate concentration
Both (a) and (b)
Organism maintaining the moderate substrate concentratio

Answer 3

Organism maintaining the lowest substrate concentration

Question 4

The continuous cultures are not widely used in industry because

they are not suited for the production of secondary metabolites
contamination or mutation can have a disastrous effect on the operation
the government will not approve the licensing of pharmaceuticals produced in continuous cultures
all of the above

Answer 4

all of the above

Question 5

The lowest yield of ATP /is in

fermentation
aerobic respiration
anaerobic respiration
same in (a), (b) and (c)

Answer 5

fermentation

Question 6

Mixing in an anaerobic sludge blanket reactor is due to

rapid change in water temperatures throughout the reactor
release of gases by the microbial populations
swimming of microbes
none of the above

Answer 6

release of gases by the microbial populations

Question 7

In batch culture, protogon is produced from peptone during the stationary phase with a yield of 0.4 protogon mg per g of peptone. If it is to be produced in a chemostat at a dilution rate of 0.5 h-1 from a medium containing 10 g.l-1 of peptone, then the rate of protogon synthesis would be

0 g.l-1h-1
0.5 g.l-1h-1
1 g.l-1h-1
2 g.l-1h-1

Answer 7

0 g.l-1h-1

Question 8

Formation of end product by Lactococcus lactis will become non-growth associated as lactic acid accumulates because

cells will redirect ATP to anabolism
cells will redirect NAD+ to anabolism
cells will redirect ATP to facilitate the diffusion of lactic acid and H+ out of the cells
cells will redirect ATP to the active transport of lactic acid and H+ out of the cells

Answer 8

cells will redirect ATP to the active transport of lactic acid and H+ out of the cells

Question 9

Which of the following would not be subjected to the “glucose effect”?

Aspergillus fumigatus
Saccharomyces cerevisiae
Escherichia coli
Aspergillus niger

Answer 9

Escherichia coli

Question 10

Immobilized cell reactors for wastewater treatment have the advantage of having/being

higher cell concentration
more stable and prevent washout
higher dilution rate before the cells washout
all of the above

Answer 10

all of the above

Question 11

Which of the statement is true for continuous reactor at steady state?

The rates of biomass, substrate and product concentrations are zero
Biomass, substrate and product concentrations are zero
Biomass, substrate and product concentrations do not change with time
Biomass, substrate and product concentrations change with time

Answer 11

Biomass, substrate and product concentrations do not change with time

Question 12

A continuous bioreactor in which only the flow rate is used to control the rate of cell or product productivity is called

turbidostat
chemostat
level stat
pH

Answer 12

chemostat

Question 13

For organisms growing in a chemostat, the specific growth rate

cannot be determined
can be determined from the dilution rate
equals to the maximum specific growth rate of the culture
none of the above.

Answer 13

can be determined from the dilution rate

Question 14

Saccharomyces cerevisiae is being grown in a chemostat converts glucose to biomass, ethanol, glycerol and carbon dioxide. At steady state, the concentration of glucose, biomass, ethanol and glycerol will

decrease with time
increase with time
be constant
change randomly with time

Answer 14

be constant

Question 15

In aerobic yeast fermentation for production of citric acid from alkanes using a fed-batch culture, why alkanes are slowly fed to the yeast?

Citric acid is toxic to the cells
Alkanes cause foaming
Fast addition of alkanes will inhibit the cells and reduce oxygen transfer rates
Fast addition of alkanes will cause the cells to grow too quickly

Answer 15

Fast addition of alkanes will inhibit the cells and reduce oxygen transfer rates

Question 16

A continuous reactor has a dilution rate of 0.5 h-1. Its residence time would be

ln(2)/0.5
ln(2) x 0.5
0.5 h
2 h

Answer 16

2 h

Question 17

Which of the following is used to calculate mass of substrate in the reactor?

Flow rate x substrate concentration in the reactor
Volume of reactor x substrate concentration in reactor
Flow rate x mass of reactor
Volume of reactor x Flow rate

Answer 17

volume of reactor x substrate concentration in reactor

Question 18

If biomass yields are constant, then the biomass productivity of a culture grown in continuous reactor will

always decrease with dilution rate
increase with dilution rate until washout
remain constant irrespective of the dilution rate
decrease with dilution rate until washout

Answer 18

increase with dilution rate until washout

Question 19

Low dissolved oxygen concentrations leads to

low biomass yields
high biomass yields
no effect on biomass yields
none of the above

Answer 19

low biomass yields

Question 20

In a continuous reactor, the medium contains 40 g.l-1 of maltose and the medium flow rate is 10 litres per hour and the effluent contains 20 g.l-l of lactate. What is the productivity of lactate production from this reactor?

50 g maltose.l-1
50 g lactate.l-1
200 g maltose.l-1
200 g lactate.l-1

Answer 20

200 g lactate.l-1

Question 21

A fed-batch reactor containing 1 g.l-1 of substrate in 2 litre of medium. It is fed with 1 g.l-l of substrate at the rate of 1 litre per hour. After 10 hours, the concentration of substrate in the reactor was 0.5 g.l-1 . The mass of substrate that was used by the culture in the reactor was

2g
6g
8g
12g

Answer 21

6g

Question 22

Toxins accumulated in a reactor can lead to low biomass yields probably due to which of the following?

NAD+ is diverted away from homeostasis to anabolism
ATP is diverted away from homeostasis to anabolism
NAD+ is diverted away from anabolism to homeostasis
ATP is diverted away from anabolism to homeostasis

Answer 22

ATP is diverted away from anabolism to homeostasis

Question 23

The cellular productivity in a continuous stirred tank fermenter (CSTF) increases with an increase in the dilution rate and reaches a maximum value. If the dilution rate is increased beyond the maximum point, the productivity will

decrease abruptly
increase
increase drastically
be zero

Answer 23

decrease abruptly

Question 24

Fluidized bed bioreactors provide higher mass transfer rates than packed bed bioreactors because

mixing is higher in fluidized bed bioreactors
particles move with the fluid in a fluidized bed bioreactor
immobilized particles are smaller in the fluidized bed bioreactors
all of the above

Answer 24

particles move with the fluid in a fluidized bed bioreactor

Question 25

In fed-batch fermentation, mass of substrate utilized is calculated using the relationship

initial mass of substrate in the reactor + final mass of substrate in the reactor + flow rate x [substrate in the feed]

initial mass of substrate in the reactor - final mass of substrate in the reactor + flow rate x [substrate in the feed]

initial mass of substrate in the reactor + final mass of substrate in the reactor - flow rate x [substrate in the feed]

initial mass of substrate in the reactor + final mass of substrate in the reactor - flow rate

Answer 25

initial mass of substrate in the reactor - final mass of substrate in the reactor + flow rate x [substrate in the feed]

Question 26

A chemostat has a liquid volume of 2 litres and is being fed at a rate of 4 litres per hour. Dilution rate for this reactor will be

2 litres
2 litres per hour
2 h-1
4 litres per hour

Answer 26

2 h-1

Question 27

Mixing per unit volume is observed to be poorest in

continuous packed bed reactor
continuous fluidized bed bioreactor
continuous airlift bioreactor
none of the above

Answer 27

continuous packed bed reactor

Question 28

The growth of an organism on glucose is described by the following Monod model parameters: μm = 0.5 h-1 and Ks =0.1 g.l-1, if the concentration of glucose in the feed is 10 g.l-1 and the dilution rate is set to 0.4 h-1, then the steady state concentration of glucose in the effluent will be

0 g.l-1
0.5 g.l-1
1.0 g.l-1
10 g.l-1

Answer 28

0.5 g.l-1

Question 29

A continuous reactor at steady state contains 0.04 g.l-1 of biomass and 0.02 g.l-1 of phenol. The feed contained 0.1 g.l-1 of phenol. The biomass yield would be

0.4 g.g-1
0.5 g.g-1
1.0 g.g-1
5.0 g.g-1

Answer 29

0.5 g.g-1

Question 30

A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.

continuous
batch
fed-batch
semi continuous

Answer 30

continuous

Question 31

The main reason for production of antibiotics in fed batch reactors is

the presence of precursors is often toxic to the cells
higher yields when cells enter the stationary phase
higher yields when cell growth slows
all of the above

Answer 31

all of the above

Question 32

Fed batch reactors is used to produce vinegar because

it can maintain low ethanol concentrations
it can maintain low acetic acid concentrations
acetic acid bacteria tend to ferment at high ethanol concentrations
all of the above

Answer 32

it can maintain low ethanol concentrations

Question 33

When a culture of fermenting yeast becomes metabolically uncoupled, ethanol

becomes a secondary metabolite
production becomes growth associated
production becomes non-growth associated
becomes a growth nutrient

Answer 33

production becomes non-growth associated

Question 34

Mixing profiles closest to plug flow are observed in

continuous packed bed reactor
stirred tank reactor with biomass recycles
continuous fluidized bed bioreactor
all of these

Answer 34

continuous packed bed reactor

Question 35

On a glucose medium, the growth of an organism is characterized by the following Monod model and stoichiometric parameters μm = 0.3 h-1, Ks =0.05 g.l-1 and Yxs = 0.3 g.g-1 When this organism is grown in a 2 litre continuous on a medium containing 10 g.l-1 of glucose added at 1 l.h-1, the steady state concentration of biomass in the reactor will be

0 g.l-1
0.4 g.l-1
0.5 g.l-1
10 g.l-1

Answer 35

0 g.l-1

Question 36

Unsteady state mass balance for dynamic model of continuous stirred tank reactor (CSTR) is

time rate of total amount in rector = rate of addition to reactor -rate of removal + rate of formation

total amount in rector = rate of addition to reactor - rate of removal + rate of formation

rate of total amount in rector = rate of addition to reactor - rate of removal + rate of formation

none of the above

Answer 36

time rate of total amount in rector = rate of addition to reactor -rate of removal + rate of formation

Question 37

A fed-batch reactor initially contains 2 litre of medium. If it was fed at 1 litre per hour, then after 10 hours, the volume of the reactor will be

1 litre
2 litre
3 litre
13 litre

Answer 37

2 litre

Question 38

A Bacillus sp. produces an antibiotic only during the stationary phase when grown in a batch culture. If grown in a 5 litre continuous culture, the steady state productivity of the antibiotic

will increase until the culture washes out
will decrease after washout
will be zero
will be infinite

Answer 38

will be zero

Question 39

In a fluidized bed reactor, the function of the disengagement zone is to

reduce loss of particles from the reactor
reduce the velocity of the particles near the surface of the reactor
reduce foaming problems
all of the above

Answer 39

all of the above

Question 40

Saccharomyces cerevisiae produces high biomass yields at low glucose concentrations and high dissolved oxygen concentrations. Which of the following should be followed for maximizing its biomass productivity?

Batch fermenter with a high initial glucose concentration
Continuous fermenter with a low initial glucose concentration
Fed batch fermenter
All of the above

Answer 40

Fed batch fermenter

Question 41

In a glucose-yeast extract medium, Lactococcus lactis has a maximum specific growth rate (um) of 1.23 h-1. What would be the specific growth rate of this organism at steady state in a 4 litre reactor being fed at 2 litres per hour?

0.5 h-1
1.2 h-1
2.4 h-1
4 h-1

Answer 41

0.5 h-1

Question 42

Which of the following is not correct with regards to continuous cultures?

The major industrial scale application of continuous cultures is in waste water treatment
Mutation and contamination present a major risk to the operation of continuous cultures for the production of metabolites
The continuous cultures is very useful for the production of pharmaceuticals
Continuous cultures have an advantage that they do not need to shut down as regularly as batch culture reactor

Answer 42

The continuous cultures is very useful for the production of pharmaceuticals

Question 43

In a plug flow reactor, the highest concentration of substrates is exposed to the cells that

are near the effluent or exit of the reactor
are in the mid way along the reactor
are located near entrance of feed
are near the wall of the reactor

Answer 43

are located near entrance of feed

Question 44

In an activated sludge process, the biomass is recycled to

increase the efficiency of the process
reduce sludge volumes
increase the concentration of cells
all of the above

Answer 44

all of the above

Question 45

A strain of Escherichia coli has a maximum specific growth rate of 0.8 h-1 on a glucose based medium. If this organism is being grown in a chemostat with a dilution rate of 1.2 h-1, then at steady state the concentration of E. coli in the same medium will

increase
be zero
change randomly
decrease

Answer 45

be zero

Question 46

A fed-batch reactor containing 2 litre of medium and 0.1 g.l-l of biomass is fed with a medium containing 1 g.l-1 of substrate at 1 litre per hour. If after 10 hours, the concentration of biomass in the reactor was 0.2 g.l-1, then the biomass produced during the 10 hour period is

1.5 g
2.2 g
3.0 g
6.0 g

Answer 46

2.2 g

Question 47

Which of the following organisms will continue their metabolism at high substrate concentrations?

Pseudomonas aeruginosa
Saccharomyces cerevisiae
Bacillus subtilis
Escherichia coli

Answer 47

Pseudomonas aeruginosa

Question 48

Yeast is typically produced in fed batch reactors because

yeast cells produce ethanol at low glucose concentrations
yeast cells ferment at low glucose concentrations
yeast cells respire at low glucose concentrations
all of the above

Answer 48

yeast cells respire at low glucose concentrations

Question 49

Two continuous bioreactors containing the same organisms, fed with the same feed at the same dilution rate were compared. Reactor 1 started with an initial concentration of glucose of 10 g.l-1, while reactor 2 contained 0.1 g.l-1 of glucose at the start of the process then at steady state

the concentration of glucose in reactor 1 would be greater than that in reactor 2
the concentration of glucose in reactor 1 would be equal to reactor 2
the concentration of glucose in reactor 1 would always be zero.
the concentration of glucose in reactor 1 would be less than that in reactor 2

Answer 49

the concentration of glucose in reactor 1 would be equal to reactor 2

Question 50

In a fluidized bed reactor mixing is achieved by

gravity flow of fluid
upward movement of the incoming feed
diffusion
both (a) and (b)

Answer 50

both (a) and (b)

Question 51

The production of an amylase from starch by Aspergillus niger is often performed in a fed batch fermenter. This is due to the reason that

fed-batch reactor can be used to minimize starch concentrations and prevent a. niger from fermenting
fed-batch reactor can be used to minimize starch concentrations and thus reduce the viscosity of the medium
continuous reactor can be used to minimize starch concentrations and their inhibitory effects
all of the above

Answer 51

fed-batch reactor can be used to minimize starch concentrations and thus reduce the viscosity of the medium

Question 52

The fastest route of NADH reoxidation is

aerobic respiration
anaerobic respiration
fermentation
decomposition

Answer 52

fermentation

Question 53

In fed batch bioreactor modelling, the rate of change in the bioreactor volume is assumed to be equal to

flow rate
initial volume
volume of solids in the reactor
none of these

Answer 53

flow rate

Question 54

Monoclonal antibodies are typically produced in fed batch reactors because

hybridoma cells ferment at high maltose concentrations
hybridoma cells yield higher lactate at high glucose concentrations
hybridoma cells respire at high glucose concentrations
none of the above

Answer 54

hybridoma cells yield higher lactate at high glucose concentrations

Question 55

In plug flow tubular reactor the axial velocity profile on cross-section will be

constant
varying with time
non-linear
power function of time

Answer 55

constant

Question 56

Production of organic acids in batch culture is generally growth associated phase followed by non-growth associated production. The probable reason for this is that

organic acids uncouple catabolism from anabolism
biomass yields increase as the fermentation proceeds
organic acids are secondary metabolites
high concentrations of organic acid promote the growth of the microbial population

Answer 56

organic acids uncouple catabolism from anabolism

Question 57

The concentration of biomass in a continuous stirred tank reactor is 20 g dry weight per litre. What would be the concentration of biomass in the effluent?

Greater than 20 g dry weight per litre
Approximately 20 g dry weight per litre
Lesser than 20 g dry weight per litre
More than 30 g dry weight per litre

Answer 57

Approximately 20 g dry weight per litre

Question 58

The ideal tubular-flow fermenter without radial variations is called a

plug flow fermenter
continuous stirred tank fermenter (CSTF)
column fermenter
any intensity of dilution rate near the wash out points

Answer 58

plug flow fermenter

Question 59

Pseudo-steady state in a continuous reactor refers to a reactor in which

Pseudomonads are being cultured
concentration oscillate around a mean value
concentration increase with time
concentration decrease with time

Answer 59

concentration oscillate around a mean value

Question 60

The toxicity of organic acids to cells

enhances as the pH falls
reduces as the pH falls
is not affected by pH
is highest at pH 7.0

Answer 60

enhances as the pH falls

Question 61

Which of the following is best described as secondary metabolite?

Acetic acid produced from the oxidation of ethanol
Ethanol from the fermentation of glucose
Penicillin
Citric acid from the partial oxidation of glucose

Answer 61

Penicillin

Question 62

A microorganism which is subjected to the Crabtree effect is most likely to

ferment in the presence of low concentrations of sugar and dissolved oxygen
respire in the presence of low sugar and high dissolved oxygen concentrations
ferment in the presence of high concentrations of sugar and dissolved oxygen
respire in the presence of high sugar and low dissolved oxygen concentrations

Answer 62

ferment in the presence of high concentrations of sugar and dissolved oxygen

Question 63

When the product formation is approximately equal to the rate of cell growth, the pattern of product formation is termed as

uncoupled
growth associated
non-growth associated
metabolically uncoupled

Answer 63

growth associated

Question 64

Which of the following would be correct concerning the concentration of biomass (X). growth limiting substrate (S) and product (P) in a chemostat when the cells have been washed out?

X,S and P will be zero
X,S and P can not be predicted for the above condition
X and P will be zero while S is equal to the substrate concentration in feed
None of the above

Answer 64

X and P will be zero while S is equal to the substrate concentration in feed

Question 65

Pseudomonas aeruginosa has a maximum specific growth rate of 0.8 h-1 in a medium with glucose as a growth limiting substrate. To prevent wash out, the dilution rate must be set to

greater than 0.8 h-1
less than 0.8 h-1
equal to 0.8 h-1
1.6 h-1

Answer 65

less than 0.8 h-1

Question 66

Saccharomyces cerevisiae when grown in high glucose concentration medium, the cells activity depends on which of the following?

High concentration of dissolved oxygen
Low concentration of dissolved oxygen
No effect of dissolved oxygen
High concentration of dissolved oxygen and sodium salts

Answer 66

No effect of dissolved oxygen

Question 67

Continuous culture has an advantage over to a batch cultures as

continuous reactors do not need to be shut down and cleaned as regularly as a batch reactor
most downstream and upstream processes are continuous in nature and thus the operation of continuous bioreactor can be better integrated into the overall manufacturing process
cells can be maintained at a constant physiological state simply by setting the dilution rate
all of the above

Answer 67

all of the above

Question 68

In the batch-fed mode, substrate will be added

only at the beginning of the fermentation process
periodically throughout the fermentation process
only at the end of the fermentation process
substrate is never added

Answer 68

only at the end of the fermentation process

Question 69

When Escherichia coli grow in a well aerated medium, which of the following will occur?

Fructose di-phosphate accumulation inside the cells leading to cell respiration
Fructose di-phosphate accumulation inside the cells leading to fermentation
Fructose di-phosphate will accumulate regardless of the medium composition
Fructose di-phosphate will accumulate inside the cells leading to anaerobic respiration

Answer 69

Fructose di-phosphate accumulation inside the cells leading to fermentation