Environmental Engineering Multiple Choice Questions on “Construction of Septic Tank”.
1. The disposal of sewage from the septic tank is done by which of the following?
a) Clarifier
b) Soak pit
c) Aerated lagoon
d) Lamp holes
Answer: b
Clarification: Soak pit is a circular pit through which sewage is disposed in the soil.
2. The detention period of a septic tank is ___________
a) 2 hours
b) 12-36 hours
c) 4 hours
d) 1 week
Answer: b
Clarification: The septic tank has a long detention period in comparison to sedimentation than with a detention period of 12 to 36 hours.
3. The concentration of biodegradable organic matter after the septic tank is ___________
a) 50ppm
b) 100ppm
c) 200ppm
d) 75ppm
Answer: c
Clarification: The effluent contains 200-250 ppm of biodegradable organic matter after the treatment from the septic tank.
4. What is the maximum design flow of sewage in a septic tank?
a) 70 liters per person per day
b) 100 liters per person per day
c) 30 liters per person per day
d) 40 liters per person per day
Answer: a
Clarification: The design flow of sewage in a septic tank lies between 40 to 70 liters per person per day.
5. Which of the following is not the method of disposal of sewage from septic tank?
a) Upflow anaerobic filter
b) Soil absorption system
c) Vacuum filter
d) Biological filters
Answer: c
Clarification: Vacuum filter is used in the sludge dewatering process and upflow anaerobic filter, soil absorption system and biological filter are the method of disposal of sewage from the septic tank.
6. The minimum depth of septic tank as per design consideration is ___________
a) 1.8m
b) 1m
c) 1.2m
d) 1.5m
Answer: c
Clarification: The design depth of septic tank lies between 1.2m and 1.8m, so its minimum depth is 1.2m.
7. What is the type of filter used in the septic tank when the rate of percolation is 90 minutes?
a) Slow sand filter
b) Rapid sand filter
c) Biological filter
d) Trickling filter
Answer: c
Clarification: Biological filters are used in a septic tank for the treatment of sewage when the percolation rate is >60minutes. The percolation rate is the rate at which water flows through the soil.