Wastewater Treatment MCQ with answer and solution

Concept

Sewage is treated in stages: primary (remove settleable solids), secondary (biological removal of organic matter) and disinfection (kill pathogens).

Step-by-step solution

1. Primary treatment removes floating and settleable solids by screening and sedimentation. 2. Secondary treatment removes dissolved and colloidal organic matter using microbes (activated sludge, trickling filter). 3. Disinfection (for example, chlorination or UV) kills pathogens before discharge. 4. Only option D lists all three stages, so the answer is D.

Explanation

Sewage treatment is done step by step. First, solids are removed (primary). Then organic matter is removed by bacteria (secondary). Finally, germs are killed by disinfection.

Why the other options are wrong

A: Misses secondary (biological) treatment. B: Misses disinfection. C: Misses primary treatment.

Shortcut

Choose the option that lists the most complete sequence: primary, secondary, disinfection.

Common mistake

Choosing B because primary and secondary are the most commonly mentioned stages, and forgetting disinfection.