Bioprocess Engineering Questions and Answers – Solving Unsteady – State Mass Balances

This set of Bioprocess Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Solving Unsteady – State Mass Balances”.

1. A compound dissolves in water at a rate proportional to the product of the amount of undissolved solid and the difference between the concentration in a saturated solution and the actual solution; i.e., C_sat – C(t). A saturated solution of this compound contains 40 g per 100 g of water. In a test run starting with 20 kg of undissolved compound in 100 kg of water, it was found that 5 kg dissolved in 3 hr. if the test continues, how many kg of compound will remain undissolved after 7 hr? Assume that the system is isothermal.
a) 11.56 kg
b) 10.72 kg
c) 11.76 kg
d) 10.52 kg
View Answer

Answer: b
Explanation: Definitions of variables used:
C = kg dissolved compound/ kg water C_s = saturated
m = mass of undissolved solid m_o = initial mass of solid
W = kg of water



C₇= 0.093 and m: m_o – C₇.100 kg
m = 10.72 kg.

2. What is the first – order decay?
a) The rate of loss of the pollutant is constant
b) The rate of loss of the reactant is constant
c) The rate of loss of the pollutant is directly proportional to its concentration
d) The rate of loss of the reactant is directly proportional to its concentration
View Answer

3. The water level in a municipal reservoir has been decreasing steadily during a dry spell, and there is a concern that the drought could continue for another 60 days. The local water company estimates that the consumption rate in the city is approximately 10⁷ L/day. The state conservation service estimates that rainfall and stream drainage into the reservoir coupled with evaporation from the reservoir should yield a net water input rate of 10⁶ exp (-t/100) L/day, where t is the time in days from the beginning of the drought, at which time the reservoir contained an estimated 10⁹ liters of water.
Integrate the balance to calculate the reservoir volume at the end of the 60 days of continued drought.

a) 4.50 × 10⁹ L
b) 4.50 × 10⁸ L
c) 4.45 × 10⁸ L
d) 4.45 × 10⁹ L
View Answer

Answer: c
Explanation: We now separate variables and integrate the differential balance equation from t=0 to t= 60 days.

4. Which one process is not a transient process?
a) Fed- batch
b) Batch
c) Continuous
d) Semi- batch
View Answer

5. Which of the following is the steady state condition based on the water tank concept?
a) Q_in ≠ Q_out
b) Q_in = Q_out
c) Q_in > Q_out
d) Q_in < Q_out
View Answer

6. Determine the volume required for a PFR to obtain the degree of pollutant reduction, Assume that the flow rate and first-order decay rate constant are unchanged (Q = 50 m³/day, k = 0.216 day^-1), C_out / C_in = 32/100 = 0.32.
a) 204 m³
b) 234 m³
c) 254 m³
d) 264 m³
View Answer

Answer: d

7. In a batch process, the reaction takes place in the presence of an acid medium. The acid is drained from the reaction vessel at the rate of 15ml/s as a result of the density difference of the acid from the reacting component. To avoid wastage of acid, it is recycled to an acid tank which has 1000 L capacity. The acid drained from the reaction vessel, picks up 50 g/L solids from the reactor. Acid is fed once again to the process from acid tank. When the process is started, the acid is almost pure in the tank as a result of filtration. As the reaction proceeds, acid in the tank gets more and more contaminated with the solids. The concentration of the solids should not exceed 100 g/L from the process point of view. The batch time is 16h. Estimate whether the concentration of the solids will exceed 100g/L during the batch reaction.
a) 37.04 h
b) 30.05 h
c) 36.04 h
d) 32.05 h
View Answer

8. Which of the following is not an example of batch process?
a) Cooking
b) Specialty chemicals
c) Refining
d) Brewing
View Answer

9. Due to algal growth in a water supply reservoir in a neighborhood, the water has acquired an unpleasant taste. The compound is non-degradable, and the water utility has decided that the best way to deal with the situation is simply to flush the contaminant out of the system. The reservoir contains 11,000 m³ of water, and the proposal is to pump 300 m³/h of clean water through the system and discharge the effluent to the sewer system until 95% of the offending compound has been removed. If the reservoir is intensely mixed, how much flushing water will be required?
a) 30, 000 m³
b) 33, 000 m³
c) 35, 000 m³
d) 39, 000 m³
View Answer

Answer: b
Explanation: The compound is non-reactive and therefore behaves as a tracer. The contaminant concentration in the flushing water is zero. When 95% of the contaminant has been flushed out, the concentration will be 5% of the initial concentration, so:

10.” A balloon is filled with air at a steady rate.” Which process can be correct for this condition?
a) Semi – batch
b) Batch
c) Fed – batch
d) Continuous
View Answer

Sanfoundry Global Education & Learning Series – Bioprocess Engineering.

To practice all areas of Bioprocess Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]