Wastewater Treatment MCQ with answer and solution

Concept

Functional classification and working of septic tanks

Formula

NONE

Step-by-step solution

1. A septic tank is an primary on-site sewage treatment unit that receives raw wastewater. 2. Heavy organic solids settle to the bottom, functioning as a primary settling tank. 3. Anaerobic microorganisms digest the settled sludge in the tank, making it simultaneously a digestion tank. Answer: C

Explanation

A septic tank functions as a primary treatment unit that combines physical sedimentation and anaerobic biological digestion. Suspended solids settle to the bottom of the tank to form sludge, while anaerobic bacteria break down the organic content in that sludge. Therefore, it acts simultaneously as a settling tank and an anaerobic digestion tank.

Why the other options are wrong

A) A septic tank functions as a settling tank, but this option ignores its anaerobic digestion process. B) A septic tank functions as an anaerobic digestion tank, but this option ignores its sedimentation process. D) Option C is correct because a septic tank performs both primary sedimentation and sludge digestion simultaneously.

Shortcut

A septic tank combines both sedimentation (settling) and anaerobic digestion in one unit.

Common mistake

Selecting only settling tank or digestion tank rather than recognizing that a septic tank performs both operations.