Water Treatment MCQ with answer and solution

Concept

Coagulation involves the addition of chemical agents (coagulants) to destabilize colloidal suspensions and finely divided suspended matter in water, allowing them to clump together into flocs that can be easily removed by sedimentation and filtration.

Step-by-step solution

1. Identify the purpose of water treatment units: removal of turbidity, colour, and pathogens. 2. Recall common coagulants used in water treatment practice: Alum, Copperas, Chlorinated Copperas, Sodium Aluminate, and Magnesium Carbonate. 3. Identify Alum (Hydrated Aluminum Sulphate, Al2(SO4)3·18H2O) as the most universally and commonly used coagulant due to its economic and operational advantages.

Explanation

Alum (Aluminum Sulphate) is the most widely and commonly used coagulant in water treatment plants worldwide due to its cost-effectiveness, ease of handling, and high efficiency in removing turbidity and suspended impurities over a wide pH range.

Why the other options are wrong

A: Lime is primarily used for softening and pH adjustment, not as the primary coagulant. B: Chlorine is a disinfectant used for killing pathogens, not a coagulant. D: Ozone is a powerful disinfectant and oxidizing agent, not a coagulant.

Shortcut

Whenever asked for the 'most common' coagulant in standard Indian civil engineering exams, the default answer is almost always Alum.

Common mistake

Confusing coagulants with disinfectants like chlorine or pH-adjusting chemicals like lime.