Wastewater Treatment MCQ with answer and solution

Concept

In anaerobic treatment, the first stage is liquefaction: anaerobic bacteria break complex solid organic matter into simple soluble compounds.

Step-by-step solution

1. Anaerobic bacteria act on sewage solids in septic tanks and sludge digesters. 2. Stage 1: complex solids (proteins, fats, carbohydrates) are broken into soluble simple compounds. This is liquefaction (hydrolysis / acid fermentation). 3. Later stages convert these compounds into gases such as CH4 and CO2 (gasification). 4. So the first stage is liquefaction. Answer is (B).

Explanation

Anaerobic bacteria first convert solid organic matter into liquid (soluble) form. This first stage is called liquefaction. After that, gases such as methane are formed.

Why the other options are wrong

A: Putrefaction is a general name for anaerobic decay with bad smell, not the name of the first stage. C: Clarification means settling of solids in a clarifier, which is a physical process. D: Oxidation is done by aerobic bacteria using oxygen, not by anaerobic bacteria.

Shortcut

Anaerobic stages: solids → liquid (liquefaction) → gas (gasification).

Common mistake

Choosing putrefaction because it also means anaerobic decay. The question asks for the name of the first stage.