Sewerage Systems MCQ with answer and solution

Concept

An outfall sewer carries sewage from the end of the collection system or treatment plant to the final disposal point.

Step-by-step solution

1. List the sewers in flow order: house sewer → lateral sewer → branch (sub-main) sewer → main (trunk) sewer → outfall sewer. 2. The outfall sewer is the last sewer in this chain. 3. It carries sewage from the treatment plant (or end of the main sewer) to the disposal point, such as a river, sea or land. 4. So the answer is (C).

Explanation

The outfall sewer is the final part of the sewerage system. It takes sewage, usually after treatment, to the final disposal point like a river, sea or land. All other sewers come before it in the collection system.

Why the other options are wrong

A: This is a house sewer (building connection). B: Laterals discharge into branch sewers, but these are collection sewers, not the outfall. D: This describes a branch sewer joining the main (trunk) sewer, not the outfall.

Shortcut

'Out-fall' means the sewer that lets sewage fall out of the system to the disposal point.

Common mistake

Confusing the outfall sewer with the main or trunk sewer.