Environmental Engineering Sheet 8

1) Question.

The typical density in kg/cum(in situ) of well-compacted municipal solid waste in landfill is in the range of
Answer.
- 1
  
  100 to 300
- 2
  
  310 to 500
- 3
  
  550 to 850
- 4
  
  900 to 1100
Answer: 2

Explanation:
2) Question.

In the design of storm sewers, "time of concentration" is relevant to determine the
Answer.
- 1
  
  rainfall intensity
- 2
  
  velocity in the sewer
- 3
  
  time of travel
- 4
  
  area served by the sewer
Answer: 1

Explanation:
3) Question.

Sewage sicknes occurs when
Answer.
- 1
  
  sewage contains pathogenic organisms
- 2
  
  sewage enters the water supply system
- 3
  
  sewers get clogged due to accumulation of solids
- 4
  
  voids of soil get clogged due to contanuous application of sewage on a piece of land
Answer: 4

Explanation:
4) Question.

The following date pertain to a sewage sample:

Initial D.O. = 10 mg/I

Final D.O. = 2 mg/I

Dilution to 1%

The BOD of the given sewage sample is
Answer.
- 1
  
  8 mg/I
- 2
  
  10 mg/I
- 3
  
  100 mg/I
- 4
  
  800 mg/I
Answer: 4

Explanation:
5) Question.

Which of the following are claimed as advantageous in respect of aerobic sludge digestion as compared to anaerobic sludge digestion?

1. lower BOD concentration in supernatant liquor

2. production of a sludge with excellent denaturing propensity

3. greater production of methane

4. lesser operatio cost

5. lesser capital cost

Select the correct answer using the codes given below.

Codes:
Answer.
- 1
  
  1, 2 and 4
- 2
  
  2, 3, 4 and 5
- 3
  
  3, 4 and 5
- 4
  
  1, 2 and 5
Answer: 4

Explanation:
6) Question.

A grit chamber of dimensions 12.0 m x 1.50 m x 0.80 m liquid depth has a flow of 720 $m^{3} / h r$ . Its surface loading rate and detention time are, respectively,
Answer.
- 1
  
  40000 $m^{3} / h r / m^{2}$ and 1.2 minutes
- 2
  
  40000 $l p h / m^{2}$ and 40 minutes
- 3
  
  40 $m^{3} / h r / m^{2}$ and 12 minutes
- 4
  
  40000 $l p h / m^{2}$ and 1.2 minutes
Answer: 4

Explanation:
7) Question.

Self-cleansing velocity is
Answer.
- 1
  
  the minimum velocity of flow required t maintain a certain amount of solids in the flow
- 2
  
  the maximum velocity of flow required to maintain a certain amount of solids in the flow
- 3
  
  such flow velocity as would be sufficient to flush out any deposited solids in the sewer
- 4
  
  such flow velocity as would be sufficient to ensure that sewage does not remain in thesewer
Answer: 3

Explanation:
8) Question.

Zero hardness of water is achieved by
Answer.
- 1
  
  using lime soda process
- 2
  
  excess lime treatment
- 3
  
  ion exchange method
- 4
  
  using excess alum dosage
Answer: 3

Explanation:
9) Question.

Uniformity coefficient of filter sand is given by
Answer.
- 1
  
  $D_{50} / D_{5}$
- 2
  
  $D_{50} / D_{10}$
- 3
  
  $D_{60} / D_{5}$
- 4
  
  $D_{60} / D_{10}$
Answer: 4

Explanation:
10) Question.

A river is the source of water for water supply to a town. Its water is very turbid and polluted. The correct sequence of steps for treating the river water would be
Answer.
- 1
  
  presedimentation $\to$ prechlorination $\to$ coagulation $\to$ sedimentation $\to$ filtration $\to$ post-chlorination
- 2
  
  coagulation $\to$ sedimentation $\to$ post-chlorination
- 3
  
  coagulation $\to$ filtration $\to$ sedimentation $\to$ post-chlorination
- 4
  
  sedimentation $\to$ post-chlorination
Answer: 1

Explanation:
11) Question.

The maximum permissible fluorine content in water for domestic supplies should be -
Answer.
- 1
  
  0.15 ppm
- 2
  
  1.5 ppm
- 3
  
  15 ppm
- 4
  
  150 ppm
Answer: 2

Explanation:
12) Question.

The maximum permissible quantity of lead in water for domestic supplies is -
Answer.
- 1
  
  0.01 ppm
- 2
  
  0.05 ppm
- 3
  
  0.50 ppm
- 4
  
  1 ppm
Answer: 1

Explanation:
13) Question.

The pH value of water for public supplies is limited from -
Answer.
- 1
  
  2.5 to 6.5
- 2
  
  6.5 to 8
- 3
  
  8 to 10.5
- 4
  
  10.5 to 15
Answer: 2

Explanation:
14) Question.

The maximum permissible quantity of iron and manganese in water for domestic purposes should be -
Answer.
- 1
  
  0.1 ppm
- 2
  
  0.3 ppm
- 3
  
  0.6 ppm
- 4
  
  0.8 ppm
Answer: 2

Explanation:
15) Question.

The maximum permissible chlorine content for public supplies should be between -
Answer.
- 1
  
  0.1 to 0.2 ppm
- 2
  
  0.3 to 0.4 ppm
- 3
  
  1.2 to 4 ppm
- 4
  
  6.5 to 8 ppm
Answer: 1

Explanation:
16) Question.

The alkalinity in water is caused by -
Answer.
- 1
  
  sodium carbonate
- 2
  
  potassium carbonate
- 3
  
  calcium hydroxide
- 4
  
  all of these
Answer: 4

Explanation:
17) Question.

When the pH value of water is more than 7, it represents......water.
Answer.
- 1
  
  neutral
- 2
  
  acidic
- 3
  
  alkaline
Answer: 3

Explanation:
18) Question.

When the pH value of water is......the water is said to be acidic.
Answer.
- 1
  
  equal to 7
- 2
  
  less than 7
- 3
  
  more than 7
Answer: 2

Explanation:
19) Question.

The most common cause of acidity in water is -
Answer.
- 1
  
  hydrogen
- 2
  
  oxygen
- 3
  
  carbon dioxide
- 4
  
  all of these
Answer: 3

Explanation:
The most common cause of acidity in natural water is dissolved carbon dioxide (CO₂).

CO₂ dissolves in water and forms carbonic acid (H₂CO₃):

CO2 + H2O ------> H2CO3

Carbonic acid lowers the pH of water, making it acidic.

Quick Memory Trick:

CO₂ → Carbonic acid → Acidity

O₂ → Dissolved oxygen

H₂ → Not responsible for water acidity

N₂ → Inert gas
20) Question.

The maximum acidity in water will occur at a pH value of -
Answer.
- 1
  
  0
- 2
  
  2
- 3
  
  7
- 4
  
  14
Answer: 1

Explanation:

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