# Waste Water Engineering Questions and Answers – Dilution & Oxygen Sag Analysis

This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Dilution & Oxygen Sag Analysis”.

1. C= xv
What does x stand for in the above formula?
a) Particles
b) Quantity
c) Volume
d) Area

Explanation: The formula is for the concentration of the liquid sample. C stands for concentration, P stands for particles and V stands for volume. So the actual formula is C=P/V.

2. Dilution=volume added/total volume. What does total volume indicate?
a) Volume of the sample
b) Volume of the sample including blank
c) Volume of the sample excluding blank
d) Volume of the blank

Explanation: Dilution = volume added / total volume

3. Dilution factor is the reciprocal of dilution.
a) True
b) False

Explanation: The total dilution is the product of all dilutions.
Dtotal = D1 * D2 * D3…..
The Dilution Factor (DF) is the reciprocal of the dilution or 1/dilution.

4. _________ is a step-wise and geometric series of dilutions which starts with a small amount of starting material.
a) Simple dilution
b) Serial dilution
c) Continuous dilution
d) Chemical dilution

Explanation: A serial dilution is a step-wise and geometric series of dilutions which starts with a small amount of starting material and amplifies the dilution factor serially by using a diluted material as a source for subsequent dilutions.

5. Which of the following is commonly used?
a) Three – fold dilutions
b) Ten – fold dilutions
c) Five – fold dilutions
d) Six – fold dilutions

Explanation: Two-fold and ten-fold serial dilutions are commonly used to titer antibodies or prepare diluted analytes. Serial dilutions are often performed when titering antibodies or when generating amplified dilutions.
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6. A dilution is a process that increases the concentration of a substance in a solution.
a) True
b) False

Explanation: A dilution in chemistry is a process that reduces the concentration of a substance in a solution. The repeated dilution of a solution to amplify the dilution factor quickly is called serial dilution.

7. Bacteria is diluted in __________
a) Distilled water
b) Water
c) Culture media
d) Solution

Explanation: Many solutions will be diluted in distilled water, but this is not always the case. If we are diluting bacteria or other cells, it is likely to be diluted it in culture media.

8. What is the minimum amount of sample required to perform serial dilution?
a) 1 ml
b) 5 ml
c) 2 ml
d) 2.5 ml

Explanation: The minimum amount needed to perform the serial dilution is 1 mL of undiluted solution. If there is only 1 mL there will not be any remaining undiluted solution. Solution should be thoroughly mixed before proceeding to the next step.

9. ___________ means that a substance can be converted into simpler compounds by biologically mediated reactions.
c) Dilution
d) Assimilation

Explanation: Biodegradable means that a substance can be converted into simpler compounds by biologically mediated reactions. The second law of thermodynamics predicts that oxidation of high energy level organics (relative to low energy level CO2) is favoured.

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

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.

11. 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

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.

12. 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

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.”

13. 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

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.

14. 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

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.

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