Septic Tank MCQ Questions and Answers

Septic tank MCQ 1

A septic tank is-

1. an aerobic method of on site sewage treatment
2. an anaerobic method of on site treatment
3. a physical method of water treatment
4. a physicochemical method of water treatment

Answer: A. an anaerobic method of on site treatment

Solution

This is a highly anaerobic tank, where both sedimentation and digestion takes place in one chamber, where raw treatment of sewage can directly be done. Hence, it is also called the primary unit. It is an anaerobic method of on site treatment. In this tank, dispersion problem occurs.

Septic tank MCQ 2

The effluent of a septic tank is-

1. Fit for discharge into any open drain
2. foul and contains dissolved and suspended solids
3. as good as that from a complete treatment
4. none of these

Answer: A. Fit for discharge into any open drain

Solution

This is a highly anaerobic tank, where both sedimentation and digestion takes place in one chamber, where raw treatment of sewage can directly be done. Hence, it is also called the primary unit.

• Reduction of solids and organics  is occurred by settling and anaerobic processes, but the treatment is moderate.
• Effluent creeps into the ground and is transmitted through a sewer to the centralized treatment plant.

Septic tank MCQ 3

Pick the correct options from the following.

1. Septic tank is a highly aerobic tank.
2. In a septic tank, sedimentation and digestion takes place in the same chamber.
3. In a septic tank, sedimentation and digestion takes place in different chambers.
4. None of these

Answer: B. In a septic tank, sedimentation and digestion takes place in the same chamber.

Solution

Septic tank is a highly anaerobic tank. In a septic tank, both sedimentation and digestion takes place in one chamber, where raw treatment of sewage can directly be done. It is also called the primary unit.

Hence, Option B is correct.

Septic tank MCQ 4

Detention time for septic tank is

1. 4-6 hour
2. 20-30 days
3. 2-6 weeks
4. 12-36 hour

Answer: D. 12-36 hour

Solution

Detention time for different treatment unit type is given below.

• For Primary sedimentation tank, Detention time is 2-2.5 hour
• For Grit Chamber, Detention time is 30-60 seconds
• For Sludge digestion, Detention time is 20-30 days
• For Activated sludge process, Detention time is 4-6 hour
• For Primary sedimentation tank, Detention time is 2-2.5 hour
• For Septic tank, Detention time is 12-36 hour
• For Oxidation pond, Detention time is 2-6 weeks

Septic tank MCQ 5

Sludge Accumulation rate in a septic tank is,

1. 20 l / capita - year 
2. 30 l / capita - year 
3. 50 l / capita - year 
4. 60 l / capita - year 

Answer: B. 30 l / capita - year 

Solution

Design parameter for Septic tank:

• Minimum width should not less than 0.9 m
• Minimum depth should not less than 0.75 m
• L/B ratio : 2 to 3
• Detention period : 12 to 36 hours
• Sludge Accumulation Rate : 30 l / capita - year

Hence, correct option is B.

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