Download Example exam questions2006

• Section one Answer 5 of the following 6 problems (3
marks each)
• 1.1) Explain the major reactions of the Sulfur cycle by
pointing out:
• a) the environmental conditions needed (e.g. electron
donors or acceptors, the type of microbes involved)
• c) the significance of the process to industry and
environment
• d) speculate on the likely mechanisms of ATP generation
• e) Show the stoichiometrically correct equation of two
important reactions involved
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Exam format:
Detailed questions (e.g. 6 out of 8) 50%
Short answer questions (e.g. 10 out of 12) 25%
Calculations (e.g. growth contants, stoichiometry, chemostat)
25%
• Calculatios can be integrated within short answer questions
• 1.1) Explain the major reactions of the Sulfur cycle by pointing out:
• a) the environmental conditions needed (e.g. electron donors or
acceptors, the type of microbes involved)
• c) the significance of the process to industry and environment
• d) speculate on the likely mechanisms of ATP generation
• e) Show the stoichiometrically correct equation of two important
reactions involved
1.2) Explain what the 4 growth constants
are that describe microbial growth.
Explain how you can determine the
growth constants from experimental
data.
1.3) Explain the fermentation pathway of either butyric,
propionic or the acetone butanol fermentation under
the following headings:
a) Overall “strategy” of fermentation.
b) Points and mechanism of ATP generation
c) Internal electron acceptors used to regenerate
NADH
d) Describe in words to individual reactions of the
pathway
e) Show by using an electron and carbon flow diagram
that the electron and carbon balance is correct
Nitrogen cycle, nutrient removal
1.4) Nitrification and Denitrification are important in nitrogen removal
from wastewater. Elaborate on the principle of biological nitrogen
removal in waste water treatment plants. In your answer explain:
a) The need for nitrogen removal from wastewater
b) The respective role of nitrification and denitrification in nitrogen
removal
c) Chemical equations for both reactions
d) process conditions needed for nitrification and denitrification for
waste water treatment
e) The traditional way of making use of sequential nitrification and
denitrification in waste water treatment
f) The principle of simultaneous nitrification and denitrification (SND)
g) How SND can be accomplished
1.5) Explain the phenomenon of interspecies
hydrogen transfer (e.g. Methanobacillus
omelianskii) as part of the anaerobic digestion
bioprocess. Explain in detail how ΔG calculations
(Gibbs Free Energy Change) can be used to
determine under at which hydrogen concentrations
the hydrogen producing or hydrogen consuming
bacterium can operate under energetically
favourable conditions (spontaneous reaction). If
possible, use a sketch that relates the Gibbs Free
Energy Change to the hydrogen concentration
1.6) Glutamate is the most widely
produced amino acid. Explain the
biochemistry of the process and point
out the requirements to the organisms to
allow overproduction and excretion of
this amino acid.
•Section 2 short answer questions: Answer 10
out of the following 12 questions (1.5 marks
each)
•2.1) Explain how citric acid is produced during
•a) growth (idiophase)
•b) product formation (trophophase)
•Explain why the citric acid cycle (TCA cycle) is
not interrupted when citric acid is excreted.
2.2) During the microbial reduction of
nitrate (NO3-) to nitrite (NO2-) bacteria
use nitrate as electron acceptor. Explain
why it is not quite correct to say that
nitrate reducing bacteria make use of the
oxygen atoms in the nitrate molecule as
an electron acceptor.
2.3) How would you predict the expected
growth yield (Y) of an organism (g of
biomass formed per g of substrate
degraded) that aerobically oxidises
ethanol to acetic acid (vinegar
production)? Show your calculation and
explain all your assumptions.
2.4) An unknown organic substrate is
degraded in a biogas digester to 4.9 L of
methane gas. If this substance was
degraded by aerobic bacteria, how much
oxygen would be used?
2.5) How much methane will be produced
from the anaerobic digestion of hydroxybutyrate (CH3-CHOH-CH2-COOH)? What
is the expected ratio of CH4/CO2 from
this conversion?
2.6) A reactor with a kLa of 25h-1
aerobically converts propanol (CH3-CH2CH2OH) to CO2. What is the maximum
propanol oxidation rate that can be
obtained by the limited oxygen supply?
2.7) What is the advantage of biomass
feedback in bioprocesses. Give an
example and show the effect on
productivity (R).
2.8) Sketch the effect on oxygen
concentration and oxygen uptake rate
that will be the result of a substrate spike
added to a starved, aerobic bacterial
culture. Show by using units how you
can quantify the amount of organic
substrate that was degraded. Use acetate
(CH3-COOH) as an example.
2.6) A reactor with a kLa of 25h-1
aerobically converts propanol (CH3-CH2CH2OH) to CO2. What is the maximum
propanol oxidation rate that can be
obtained by the limited oxygen supply?
2.9) Explain the advantages and
limitations of using chemostats for
industrial processes compared to batch
cultures.
Productivity, contamination, revertants
(back-mutation to wild strain =
“contamination from inside)
2.10) Establish the stoichiometrically
correct equation for the conversion of
ethanol (CH3-CH2OH) to CO2 (to be more
precise to bicarbonate) for sulfatereducing bacteria using sulfate (SO42-)
as electron acceptor to produce HS-.
2.11) In continuous culture (e.g.
chemostat) the productivity is related to
the flowrate into the reactor and the
biomass concentration. What would be
the productivity (assuming the biomass,
X is the product) of a 10 L chemostat with
a flow rate of 2.5 L/h and a biomass
concentration of 15 g/L ?
2.12) Explain the effect of oxygen use by
heterolactic bacteria. What is their
advantage in using oxygen when they
have not electron transport chain?
2.10) Establish the stoichiometrically
correct equation for the conversion of
ethanol (CH3-CH2OH) to CO2 (to be more
precise to bicarbonate) for sulfatereducing bacteria using sulfate (SO42-)
as electron acceptor to produce HS-.
Process control of high cell density cultures.
Recombinant strains of E.coli have been shown to excrete
acetate as an undesired and disruptive endproduct if
glucose as the principal stubstrate is present in excess.
This fermentation behaviour in spite of the excesss of
oxygen is called Crabtree effect.
Explain how a process control program could be designed
that provides the glucose to a growing E.coli cultures such
that it does not become saturating (and hence avoids the
production of acetate). Give possible reasons why acetate
is excreted in spite of the presence of oxygen.
Batch (productivity (max total)
Chemostat
Fed batch (HCDC)
SBR
Anaerobic respirations are different to anaerobic
fermentation in that external electron acceptors other
than oxygen are used to build up a proton gradient that
allows ATP generation via the ATP synthase. In
contrast to oxygen respiration, anaerobic respirations
form reduced endproducts, which can in turn serve as
the electron donor for aerobic bacteria. Explain with an
example the endproduct that is formed and the reoxidation of the reduced endproduct (we had examples
of the deep ocean environment). Show exactly how
many electrons are being added / removed for both the
anaerobic respiration and the re-oxidation.
Explain the purpose of SND via NO2-
Explain the reasoning that allows
nitrification and denitrification to occur at
the same time. Point out the significance
of N removal to protect the environment
Explain PID control
Competition of organisms for the same
substrate. Explain how the growth
constants and the Gibbs Free energy
change of the reaction can determine the
outcome of competition for a common
substrate (such as hydrogen).
2.10) Establish the stoichiometrically
correct equation for the conversion of
ethanol (CH3-CH2OH) to CO2 (to be more
precise to bicarbonate) for sulfatereducing bacteria using sulfate (SO42-)
as electron acceptor to produce HS-.