Bio 301 Mid-Semester Test 2013

Bio 301 Mid-Semester Test 2013

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

Answer all questions. All questions have equal value.

1. A bioreactor with a kLa of 25 h-1 with active microbes is aerated resulting in a steady oxygen concentration of 1 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 Vinegar producing chemostat running at steady state was interrupted (at 90 sec. below) and oxygen data recorded.

a. What is the kLa of the chemostat in h-1 ?

b. What was the ethanol (CH3-CH2OH) to acetic acid (CH3-COOH) conversion rate of the process when it was at steady state?

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-CH2-CH2OH , HOOC-COOH , CH3-CO-CH3

5. List (in the box next to the molecule) the number of moles of NAHD that can be generated from the complete oxidation to CO2 of the following compounds:

Pentose (CH2O)5 , CH3-COOH , H2CO3

6. List (in the box next to the molecule) the number of moles needed for an anaerobic microbe using these substances instead of oxygen as the electron acceptor for the complete oxidation to CO2 of ethanol (CH3-CH2OH):

NO3- à N2 , SO42- à H2S , Fe3+ à Fe2+

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 end product that would be formed (in the case you think it is feasible).

8. A 10L chemostat is operated with a flowrate of 0.6 L/h. An equilibrium is established with a constant oxygen, concentration, pH, biomass (3 g/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?

9. How would you determine the microbial Yield coefficient from a batch culture and a chemostat culture respectively?

10. Explain the effect of biomass feedback (recycle, retention) on the biomass concentration and productivity R of a chemostat. Use a plot of biomass (X) and productivity (R) versus the dilution rate to illustrate the point.

11. Sketch below an example graph of the specific growth rate of a microbe (Y-axis) dependent on the limiting substrate concentration (X-axis). Put a scale (numbers and units) on both axes. Point out in your graph (with an arrow) where 3 of the 4 growth constants can be read from and give their values and units as read from your example graph.

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