Questions for PhD qualifiers : Bioprocess Engineering

PROBLEMS FROM BIOPROCESS ENGINEERING SHULER AND KARGI

CHAPTERS – 3, 7, 9 and 10

Q1. The hydrolysis of urea by urease can be described by Michealis-Menten kinetics with the maximum reaction rate Vmax = 5 moles/l-min and Km = 0.05 M. Determine the time required to consume 90% of the initial urea concentration (S0), when (i) S0 = 10 moles and (ii) S0 = 0.1 mole?

Q2. Evaluate the pH value at which the maximum enzymatic rate occurs for the below pH dependent mechanism for a given substrate concentration of S0 assuming Haldane’s approach?

Q 3. Enzyme inhibition kinetics: The following data was obtained for an enzyme ‘E’ for a fixed substrate concentration S0

Substrate concentration
S0 / Inhibitor concentration
(mM) / v/vmax
50
50
25 / 0
10
10 / 0.9
0.75
0.6

Determine the enzymatic rate as a fraction of vmax for a substrate concentration of 10mM and an inhibitor concentration of 25 mM.

Q1. Lactobacillus bulgaricus is used to ferment milk to yogurt. The growth rate of L. bulgaricus on lactose (S) in milk is given as follows:

where P is the lactic acid concentration. It is known that L. bulgaricus produces lactic acid only while it is growing. A chemostat (CSTR) is operated for the preproduction stage, where the input to the reactor is sterilized milk with 5 g/L of lactose. The outlet stream contains 3 g/L of Lactose. It is known that YX/S = 0.5 and YP/X = 2 for L. bulgaricus. Another organism has contaminated the fermentation, whose growth rate is given by

Will the organism spoil the chemostat operation through contamination?

Q2. Fed-Batch Operation: A fermentor is operated as a fed-batch process. The substrate concentration is kept constant in the reactor at S. The feed stream has a substrate concentration of Sf. The growth rate of the organism is represented by Monod’s kinetics. Determine the feed flow rate for the process and determine the final biomass concentration? Assume Yx/s as the yield coefficient?

Q3. In a fed batch culture operating with intermittent addition of glucose solution, values of the following parameters are given at time t=2 h, when the system is at quasi-steady state. V =1000 ml, F=200ml/h, S0 = 100g/l, mumax=0.3 1/hr, Ks=0.1g/l, Yx/s=0.5g/g, X0=50 g/l

Find V0 (initial volumn). Determine the concentration of biomass at t=2h assuming quasi steady state. If alpha=0.2g/g Determine the concentration of product at t=2h assuming P0=0.

Q4. In a chemostat with cell recycle, the feed flow rate and culture volumes are F=100ml/h and V=1000ml, respectively. The system is operated under glucose limitation and the yield coefficient, Yx/s =0.5g/g. Glucose concentration in the feed is S0=10g. The kinetic constants of the organisms are mumax=0.21/h, Ks=1g/l. The value of C is 1.5 and the recycle ratio is 0.7. The system is at steady state. Find the substrate concentration in the recycle stream Find the specific growth rate of the organisms. Find the cell concentration in the recycle stream. Find the cell concentration in the centrifuge effluent.

Q2. A methanol utilizing strain has a specific growth rate given by:

Methanol concentration in the feed solution is 100 g/L with an initial cellmass of 20 g/L and an initial volume of reactor of 500L. Determine the final volume and cellmass concentration for operating a fed batch reactor at maximum growth rate in the reactor. The yield coefficient YX/S = 0.4 g dw cells/g glucose. [Marks: 3.5]

Q3. Determine the dilution rate, amount of substrate consumed, product and biomass formed to maximize (a) product productivity and (b) Biomass Productivity for an organism with the following growth parameters:

; growth related product formation constant, alpha = 2; non growth associated constant, beta=1 and YX/S = 2 g/g [Marks 3.5]

Q2 Chemostat Operation:Lactobacillus bulgaricus is used to ferment milk to yogurt. The growth rate of L. bulgaricus on lactose (S) in milk is given as follows:

where P is the lactic acid concentration. It is known that L. bulgaricus produces lactic acid only while it is growing. A chemostat (CSTR) is operated for the preproduction stage, where the input to the reactor is sterilized milk with 5 g/L of lactose. The outlet stream contains 3 g/L of Lactose. It is known that YX/S = 0.5 and YP/X = 2 for L. bulgaricus. Another organism has contaminated the fermentation, whose growth rate is given by

Will the organism spoil the chemostat operation through contamination? Justify your solution with an explanation.

Q1.Consider the following reaction sequence:

S + E  (ES)1(ES)2 P + E

Develop a suitable rate expression for the product formation (dP/dt = k4(ES)2) assuming quasi-steady state approximation?