University of Saskatchewan Department of Chemical Engineering Introduction to Biochemical Engineering- ChE 461.3 FINAL EXAMINATION DATE: INSTRUCTOR: TIME: Thursday 11 December 2003 Professor M. Nemati 3 Hours
PART A – CLOSED BOOK Instructions: This part of the examination is closed book. There are five questions in this part of examination. Answer all questions. TIME: 40 minutes
Question #1 (10 Marks) Describe the following terms or processes: • • • • • Concentration polarization Osmotic pressure Affinity chromatography Fed-batch culture Silent mutation
TOTAL MARKS: 30
Question #2 (6 Marks) What are the three main mechanisms for gene transfer from one organism to another organism? Provide a brief description for each mechanism. Question #3 (4 Marks) Indicate the driving force in each of the following separation processes. What do all these separation processes have in common? • • • • Dialysis Ultrafiltration Reverse osmosis Electrodialysis 1 of 5
Question #4 (4 Marks) Describe four processing advantages that immobilized cell cultures have over freely suspended cell cultures. Question #5 (6 Marks) a) Empirical Freundlich adsorption isotherm, given below, is frequently used to describe the adsorption of antibiotics, steroids and hormones. The equilibrium data for adsorption of an antibiotic on resin particles is available. How would you use the data to determine the coefficients of the Freundlich isotherm? 1 Freundlich isotherm C = K (C * ) n S L b) The following figure shows two different types of adsorption equilibrium isotherms. Which one of these isotherm is favorable and why?
Concentration of adsorbed solute (CS) Concentration of solute in the liquid (CL*)
END OF PART A
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PART B – OPEN BOOK Instructions: This part of the examination is open book (only textbook is allowed, no notes or solved problems). Programmable, handheld calculators are permitted. Computers and laptops are not permitted. There are four questions in this part of examination. Answer all questions. Clearly state all assumptions you make. TIME: 2 hours and 20 minutes TOTAL MARKS: 70
Question #1 (20 Marks) A 1500-L continuous bioreactor is used for production of biomass with glucose as the limiting substrate. The concentration of glucose in the feed is 10 g/L. The microbial growth follows the Monod equation with: µm = 0.5 h-1 KS = 1.2 g glucose/L YX/S = 0.6 g biomass/g glucose a) What should be the flow rate of the feed to produce an effluent containing 5 g/L of biomass at steady-state? Determine the concentration of glucose in the effluent at steady-state. b) To increase the conversion of glucose, cells in the bioreactor effluent are separated in a sedimentation tank and recycled back to the bioreactor. The flow rate of the recycle stream is 45 L/h and biomass concentration in the recycle stream is 4 times as large as that in the reactor effluent. Determine the concentrations of the glucose and biomass in the bioreactor effluent, if feed is introduced into the bioreactor at a rate of 450 L/h. What would be the concentration of biomass in the effluent from the sedimentation tank?
Question #2 (15 Marks) A medium containing 50 mg/L of a heat-sensitive amino acid is to be sterilized at 121°C. The initial concentration of spores in the medium is 1×105 spores/L. The thermal death constant for the spores shows an Arrhenius dependency on temperature with the following constants:
K =α e −E 0d / RT
d
α = 1×1036 (min-1) and
E0d = 65 kcal/gmol 3 of 5
a) Calculate the required time for sterilization of 10,000 L of medium, if the acceptable probability for unsuccessful sterilization is 0.001. b) Assuming that the thermal inactivation of amino acid is first order with a rate constant of Kda= 0.0285 min-1, determine the concentration of active amino acid in the sterilized medium. (R = 1.987 cal/gmol-°K)
Question #3 (15 Marks) During a dynamic test for determination of KLa, air supply to a laboratory fermenter cultivating a bacterial population was turned off for two minutes and then restarted. The following data were collected for the concentration of dissolved oxygen.
Air off
Air on
Time (seconds) -20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
DO (mg/L) 6.0 6.0 5.0 3.9 2.2 1.2 0.5 0.3 1.5 2.3 3.0 3.9 4.8 5.3 5.9 6.0 6.0
During the test biomass concentration remained constant at 5 g dry weight/L and the saturated concentration of oxygen under the experimental conditions was determined to be 7.5 mg/L. Determine the specific oxygen uptake rate and KLa for this system (In your calculations use as many data points as possible).
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Question #4 (20 Marks) Biomass present in a fermentation broth is to be separated by vacuum filtration. A laboratory test was conducted and the following data were collected for filtration of broth at a constant pressure.
Filtration time (min) 1 2 3 4 5
Volume of filtrate (m3) 5.2×10-6 9.2×10-6 12.4×10-6 16×10-6 18×10-6
The characteristics of the laboratory filter and broth are given below: A = 5×10-3 m2 µ = 0.002 kg/m-s C = 65 kg/m3 gc = 1 kg-m/s -N a) Using the provided information, determine the average specific resistance of the cake (α) and filter medium resistance (rm). b) Calculate the surface area of a continuous rotary vacuum filter required to process 2 m3/h of the fermentation broth under the same pressure drop. The rotational speed of the drum will be 1 rpm (revolution per minute) and 30% of the drum surface will be submerged in the suspension (ϕ = 0.3). Assume a value of 1×1013 m/kg for α and neglect the resistance of the filter medium.
2
(filter surface area) (viscosity of broth) (weight of the cake deposited per unit volume of filtrate)
P = 7×104 N/m2 (pressure drop)
END OF PART B 5 of 5