Mid Semester Test Bio 301

Student number:……………Student name:…………………………………

Answer all questions. All questions have equal value.

  1. A bioreactor with a kLa of 20 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?
  1. The airflow to a chemostat running at steady state DO of 5 mg/L (cS was 8 mg/L) was temporarily interrupted. The oxygen concentration decreased steadily by 0.05 mg/L every second. What is the kLa of the chemostat in h-1 ?
  1. What is the maximum possible rate (in mM/h) of lactate (CH3-CHOH-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?
  1. 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-CH2-CH2OH, HOOC-COOH, CH3-CO-CH3

  1. List the four growth constants with their units. State in one short sentence what this growth constant means by referring to its units.
  1. How much NADH can be produced from the complete oxidation to CO2 of the following compounds:

CH3-CHOH-CH2-CH2OH, CHOOH ,

benzoate (aromatic ring with a COOH group attached to one of the carbons

  1. 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).
  1. A chemostat is used to produce microbial biomass for the purpose of recombinant protein production. Lactate (CH3-CHOH-COOH) from dairy wastewater is used as the substrate. The yield coefficient of the recombinant strain is 0.3 g of cells per g of lactate degraded.When interrupting the air flow the oxygen concentration decreased as follows (time is time in sec after interruption): 0 sec: 3 mg/L, 2 sec: 2.5 mg/L, 4 sec: 2 mg/L, 8 sec: 1 mg/L, 12 sec 0.2 mg/L. What is the a) lactate oxidation rate, b) the biomass productivity (mg biomass formed/L/h)?
  1. A 20L chemostat is operated with a flowrate of 0.6 L/h. An equilibrium is established with a constant oxygen, concentration, pH, biomass (2g/L) and substrate concentration. What is the specific growth rate of the microbes in the chemostat and what is the biomass productivity R (g/L/h) of the chemostat?
  1. In the absence of oxygen, many bacteria can use nitrate (NO3-) as electron acceptor and produce N2 as the endproduct (nitrate respiration or denitrification). What rate of nitrate reduction to N2 would you expect of a reactor that was switched from aerobic (aerated) conditions to nitrate reducing conditions, if the aerobic reactor had an oxygen uptake rate of 80 mg/L/h?
  1. Contrast batch culture against chemostat culture by pointing out advantages and limitations.
  1. How can you calculate the productivity of a chemostat? Give 3 examples of how the productivity of a chemostat can be approximately doubled by the operator and one statement for each example how this works.

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