Waste Water Engineering Questions and Answers - Dilution & Oxygen Sag Analysis Part-2

1. Oxygen in water is consumed during aerobic biodegradation of organic compounds.
a) True
b) False

Answer: a
Explanation: Oxygen in water is consumed during aerobic biodegradation of organic compounds and is replenished from the atmosphere. The two processes have different kinetics, but are coupled.

2. The rate at which oxygen is dissolved into the water from the atmosphere is proportional to the deficit of oxygen in the water.
a) True
b) False

Answer: a
Explanation: The rate at which oxygen is dissolved into the water from the atmosphere is proportional to the deficit of oxygen in the water. The oxygen deficit is simply the difference between the equilibrium oxygen concentration and the actual oxygen concentration.

3. What is endogenous respiration?
a) Discrete use of oxygen
b) Less use of oxygen
c) Higher amount of oxygen production
d) Continual use of oxygen

Answer: d
Explanation: Bacteria utilize oxygen for respiration and for cell synthesis. When no substrate is present the bacteria cease synthesis, but must continue respiration. This continual use of oxygen is termed “endogenous respiration.”

4. When the deoxygenation rate exceeds the reoxygenation rate, the oxygen sag curve shows ________ in a deficit of oxygen.
a) Increase
b) Decrease
c) Constant
d) Same

Answer: a
Explanation: When both the rates become equal, the critical point is reached and then finally when the rate of deoxygenation fall below of reoxygenation, the oxygen deficit goes on decreasing till it becomes zero.

5.During which of the following conditions, the deoxygenation is equal to reoxygenation?
a) Stream exposed to atmosphere
b) Increased volume
c) Greener vegetation
d) High temperature

Answer: a
Explanation: In a running polluted stream exposed to the atmosphere, the deoxygenation as well as reoxygenation goes hand in hand. If the deoxygenation is more rapid than the reoxygenation, oxygen depletes

6. Which one of the following is the basic indicator of river health?
a) BOD
b) COD
c) DO
d) ThOD

Answer: c
Explanation: The amount of dissolved Oxygen (DO) in water is one of the most commonly used indicators of a river health. Below 4 or 5 mg/l, the life forms that survive are reduced.

7. What is the minimum amount of DO required for the life survival of aquatic animals?
a) 10 mg/l
b) 5 mg/l
c) 2 mg/l
d) 1 mg/l

Answer: c
Explanation: As DO drops below 4 or 5 mg/L the forms of life that can survive begin to be reduced. A minimum of about 2.0 mg/L of dissolved oxygen is required to maintain higher life forms.

8. Oxygen demanding wastes improves DO.
a) True
b) False

Answer: b
Explanation: Oxygen demanding wastes remove DO. Plants add DO during the day but remove it at night. Respiration of organisms removes oxygen. Temperature is reduced in summer which inturn reduces flow.

9.In the concept of self purification of natural streams, complete the following phrase. Solution to pollution is _________
a) Control
b) Dilution
c) Reuse
d) Recycle

Answer: b
Explanation: Waste water disposal practices are based on the premise that “the solution to pollution is dilution”. In this method relatively small quantities of waste are discharged into large bodies of water

10. _________ is accomplished by the replenishment of oxygen lost to bacterial degradation of organic waste.
a) Gas transfer
b) Dilution
c) Filtration
d) Re-suspension

Answer: a
Explanation: The transfer of gases into and out of water is an important part of the natural purification process. Gas transfer is accomplished by the replenishment of oxygen lost to bacterial degradation of organic waste.