Mid Semester Test Bio 301
Student number:……………Student name:…………………………………
1. A bioreactor with a kLa of 60 h-1 with active microbes is aerated resulting in a steady
oxygen concentration of 2 mg/L. What is the microbial oxygen uptake rate (in
mg/L/h) assuming the oxygen saturation concentration is 8 mg/L?
2. The airflow to a chemostat running at steady state DO of 1 mg/L (cs was 8 mg/L) was
temporarily interrupted. The oxygen concentration decreased steadily by 0.25 mg/L
every second. What is the kLa of the chemostat in h-1 ?
3. What is the maximum possible rate (in mM/h) of acetate (CH3-COOH) oxidation to
CO2 by an aerobic reactor that is limited by an oxygen supply due to a kLa of 50 h-1
assuming an oxygen saturation concentration of 8 mg/L?
4. List (in the box next to the molecule) the number of moles of oxygen needed for the
complete oxidation to CO2 of the following compounds:
CH3-CO-COOH
, glucose (CH2O)6
, CH3-CH2-CHOH-COOH
5. What is the formula that describes the specific growth rate u of a microbe by
considering its four growth constants?
6. How much NADH can be produced from the complete oxidation of glycerol
(CH2OH-CHOH- CH2OH) to CO2 ?
7. Can microbes use the oxygen atom in the H2O molecule as an electron acceptor? Give
reasons for your explanation and an example of the endproduct that would be formed
(in the case you think it is feasible).
8. Answer either a or b:
a) Under what conditions is NADH an advantage/disadvantage for the growth of
microbes?
b) Under what conditions can protons be used as an electron acceptor by fermenting
bacteria and what is the endproduct?
9. Explain the effect of 3 of the four growth constants (umax, mS, kS, Ymax) on the
maximum biomass productivity (Rmax) that is possible in a chemostat. State wether a
doubling of each value would increase or decrease the (Rmax), estimate by how much
and explain why. You may use sketch to illustrate your explanation on the back of this
page.
10. Give two examples of organic electron acceptors used in anaerobic fermentations.
 Name the compound
 In which fermentation are they used
 Show either the structural formula or give the number of reducing equivalents
(electrons) and number of carbons of the compound
 Give name or formula of the resultant end-product