Question

In Waste Water Treatment Plants, the process of treating wastewater with alum to coagulate or flocculate is termed as

• A. Primary treatment
• B. Secondary treatment
• C. Tertiary treatment
• D. Settling treatment

Hint:

Primary treatment = Physical settling and chemical coagulation/flocculation; Secondary treatment = Biological oxidation of BOD.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Wastewater treatment trains are systematically organized into primary (physical/chemical), secondary (biological), and tertiary (advanced polishing) stages.

Step 2: Detailed Explanation:
Primary wastewater treatment focuses on removing settleable solids and suspended colloidal matter.
The addition of chemical coagulants like alum (aluminum sulfate, $\text{Al}_2(\text{SO}_4)_3$) neutralizes surface charges of suspended colloids, promoting flocculation and rapid sedimentation in primary settling tanks (chemically enhanced primary treatment).
Secondary treatment uses biological microbial digestion (activated sludge/trickling filters), and tertiary treatment involves advanced disinfection/filtration.

Step 3: Final Answer:
Therefore, coagulation/flocculation with alum is termed primary treatment.