What is the primary purpose of adding coagulants in water treatment?

• A. To increase the taste and odor of water.
• B. To sterilize water.
• C. To destabilize particles and form flocs.
• D. To remove minerals through ion exchange.

Answer: (C)

Coagulation aims to make suspended particles in water come together so they can be removed. Many natural particles are tiny and carry negative charges, which makes them repel one another and stay dispersed. When a coagulant (usually a positively charged metal salt like aluminum or ferric salts) is added, it neutralizes those negative surface charges and helps particles stick together. This charge neutralization, sometimes aided by the formation of small hydroxide precipitates, allows the particles to collide and form larger aggregates called flocs. Those flocs are much easier to remove in sedimentation and filtration steps.

Disinfection handles killing or inactivating pathogens, not particle aggregation. Taste and odor control involves other treatments like aeration or activated carbon. Ion exchange removes minerals, which is a different treatment purpose altogether.