What is the primary purpose of coagulation in water treatment?

• A. Destabilize particles by neutralizing charges so they can be removed.
• B. Kill pathogens directly.
• C. Remove dissolved inorganic nutrients.
• D. Increase water temperature.

Answer: (A)

Coagulation works to destabilize suspended particles so they can be removed. Tiny colloids like clay and natural organic matter often carry negative surface charges that repel each other, keeping them dispersed in water. When coagulants such as aluminum or iron salts are added, they introduce positively charged ions that neutralize these surface charges. With the charges neutralized, the particles no longer repel one another and can collide and stick together to form larger clumps, or flocs. These bigger particles are then easy to settle out in sedimentation tanks or be filtered out. This process is not about killing microbes, removing nutrients, or changing the water’s temperature, but about making dispersed particles gather into removable lumps.