This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Septic Tanks”.
1. Which of the following materials is not used in the construction of a septic tank?
a) Concrete
b) Rubber
c) Fibreglass
d) Plastic
View Answer
Explanation: A septic tank is a watertight chamber made of brick-work, concrete, fiberglass, PVC or plastic, through which black water from the cistern or pour-flush toilets and grey water through a pipe from inside a building or an outside toilet flows for primary treatment.
2. Septic tank is a small scale treatment unit.
a) True
b) False
View Answer
Explanation: The septic tank is the most common small-scale decentralized unit for grey water and black water from cistern or pour-flush toilets. It is basically a sedimentation tank.
3. The shape of the tank is circular.
a) True
b) False
View Answer
Explanation: The shape of the septic tank can be rectangular or cylindrical. Septic tanks are used for wastewater with a high content of settleable solids, typically for effluent from domestic sources.
4. The heavy particles in the tank _____
a) Float
b) Sink into the bottom
c) Separated using magnetic methods
d) Flow along liquid
View Answer
Explanation: Liquid flows through the top and heavy particles sink to the bottom, while scum floats to the top. Over time, the solids that settle to the bottom are degraded anaerobically.
5. The scum formed in the tank _____
a) Flows
b) Gets dissolved
c) Sink into the bottom
d) Floats on top
View Answer
Explanation: The scum formed in the tanks floats over the top. Over time, the solids that settle to the bottom are degraded anaerobically.
6. Which of the following methods are not used for the dispersion of the effluent out of a septic tank?
a) Wetlands
b) Soak pit
c) Evapo-transpiration mound
d) Leach field
View Answer
Explanation: By using a soak pit, Evapo-transpiration mound or leach field, the effluent of the septic tank must be dispersed or transported to another treatment technology via a solids-free sewer, simplified sewer or solids-free sewer.
7. During the disposal of the sludge, it must be ______
a) Liquefied
b) Dried
c) Burned
d) Fluidized
View Answer
Explanation: The sludge can be dried in planted or unplanted drying beds, settling or thickening ponds. If the sludge is dried or composted, it can be applied in agriculture as a valuable nutrient.
8. What is the amount of water used per person per day for flushing?
a) 2-3 L
b) 3-10 L
c) 4-30 L
d) 5-40 L
View Answer
Explanation: The amount of water used by a person per day for flushing is 5-40 L. When septic tanks are used for a primary treatment in DEWATS systems, they are generally followed by anaerobic filters.
9. The first chamber in a septic tank should be at least ______ of the total length.
a) 10 %
b) 20 %
c) 35 %
d) 50 %
View Answer
Explanation: The first chamber should be at least 50% of the total length and when there are only two chambers, it should be two thirds of the total length. Most of the solids settle out in the first chamber.
10. Which of the following reasons is correct with respect to the need of providing baffle walls?
a) Mixing of scum and wastewater
b) Settling of heavy particles
c) Increase velocity of the liquid
d) Prevent scum and solids from escaping
View Answer
Explanation: The baffle or the separation between the chambers is to prevent scum and solids from escaping with the effluent. A T-shaped outlet pipe, the lower arm of which divides 30 cm below water level, further reduces the scum and solids that are discharged.
11. What are the product gases of anaerobic digestion?
a) Carbon-dioxide and methane
b) Methane and oxygen
c) Oxygen and carbon-dioxide
d) Nitrogen and methane
View Answer
Explanation: Over time, anaerobic bacteria and micro-organisms start to digest the settled sludge anaerobically, transforming it into CO2 and CH4 and some heat. Optimal physical treatment by sedimentation takes place when the flow is smooth and undisturbed.
12. What is the mixture of methane and carbon-dioxide of anaerobic digestion called?
a) Waste gases
b) Poisonous gas
c) Biogas
d) Carbo-methane
View Answer
Explanation: The mixture of methane and carbon-dioxide of an anaerobic digestion is called biogas. Over time, anaerobic bacteria and micro-organisms start to digest the settled sludge anaerobically, transforming it into CO2 and CH4 and some heat.
Sanfoundry Global Education & Learning Series – Waste Water Engineering.
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