Civil war Day 21-PWD-Sewage & house drainage

The lower surface of a sewer is known as

• Crown
• Haunch
• Invert
• Soffit

Answer explanation

The invert of a sewer refers to its lowest internal surface or bottom line, used for hydraulic gradient and level measurement.

The sewer which transports sewage to the point of treatment is called

• House sewer
• Main sewer
• Outfall sewer
• None of these

Answer explanation

The outfall sewer carries sewage from the main sewer or pumping station to the treatment plant or point of final disposal.

In the design of storm sewers, 'time of concentration' is relevant to determine the

• Rainfall intensity
• Velocity in the sewer
• Time of travel
• Area served by the sewer

Answer explanation

The time of concentration represents the time taken by runoff from the farthest point of the drainage area to reach the inlet; it is used to determine rainfall intensity for design discharge.

The main constituents of gas generated during the anaerobic digestion of sewage sludge are

• Carbon dioxide and methane
• Methane and ethane
• Carbon dioxide and carbon monoxide
• Carbon monoxide and nitrogen

Answer explanation

During anaerobic digestion, organic matter decomposes in the absence of oxygen, producing biogas mainly composed of methane (≈65%) and carbon dioxide (≈35%).

A complete thorough treatment should generally be given to sewage before its disposal in a stream or river if dilution factor available is

• Less than 150
• Less than 250
• Less than 300
• Less than 350

Answer explanation

When the dilution factor is less than 150, natural purification in the stream is inadequate, so complete sewage treatment must be done before disposal.

High COD to BOD ratio of an organic pollutant represents

• High biodegradability of the pollutant
• Low biodegradability of the pollutant
• Presence of free oxygen for aerobic decomposition
• Presence of toxic material in the pollutant

Answer explanation

A high COD/BOD ratio indicates that much of the organic matter is non-biodegradable, hence the pollutant has low biodegradability.

A ventilating pipe connected to or close to the outlet side of a trap seal

• Siphonage pipe
• Vent pipe
• Antisiphonage pipe
• Soil pipe

Answer explanation

An antisiphonage pipe is fitted near the outlet side of traps to maintain the water seal by preventing siphonage when fixtures discharge simultaneously.

The pipe which is used to discharge foul gases in drains or sewer into the atmosphere is known as

• Vent pipe
• Soil pipe
• Venturi pipe
• None of these

Answer explanation

A vent pipe allows the escape of foul gases from the drainage or sewer system into the atmosphere, preventing pressure build-up and trap seal loss.

The pipe that carries discharge from urinals, water closets etc. is termed as

• Waste pipe
• Sewer
• Soil pipe
• Vent pipe

Answer explanation

A soil pipe carries discharge containing human excreta from water closets, urinals, and similar fixtures directly to the sewer or septic tank.

The water supply to a house begins with the connection of the service pipe with the municipal water mains. The connection comprises I. Stopcock II. Goose neck III. Ferrule IV. Water meter. The correct sequence of these connections is

• I, II, III, IV
• III, II, I, IV
• III, I, II, IV
• I, II, IV, III

Answer explanation

The correct sequence is Ferrule → Goose neck → Stopcock → Water meter (III, II, I, IV). The ferrule connects to the main, the goose neck provides flexibility, the stopcock controls flow, and the water meter records usage.