Question

Which is the most important coagulant used in waste water treatment?

• A. Alum
• B. Ferric sulphate
• C. Limestone
• D. Coal

Hint:

Alum performs optimally within a specific pH range of \(5.5\text{ to }6.5\).
Maintaining the appropriate pH is essential to ensure maximum solubility of the aluminum ions and successful sweep flocculation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Primary treatment of food processing wastewater involves removing suspended colloidal particles.
Coagulants are added to neutralize the electrical charges on colloidal particles, allowing them to aggregate into larger clumps (flocs) that easily settle out.

Step 2: Detailed Explanation:
Alum (Aluminum sulfate, \(\text{Al}_2(\text{SO}_4)_3 \cdot 14\text{H}_2\text{O}\)) is the most widely used inorganic chemical coagulant in water and wastewater treatment systems.
When dissolved in water, it releases highly charged trivalent aluminum ions (\(\text{Al}^{3+}\)).
These ions neutralize the negative charges of suspended colloidal particles, promoting micro-floc formation through charge neutralization and sweep flocculation.
While ferric sulfate is also a coagulant, alum remains the most common and important choice due to its efficiency, cost-effectiveness, and ease of handling.

Step 3: Final Answer:
The most important coagulant used is Alum, which corresponds to option (A).