Which of the following are coagulants used in the treatment process?

• A. Alum, ferric chloride, polymers
• B. Sand, gravel
• C. Chloramines
• D. Activated carbon

Answer: (A)

Coagulation in water treatment relies on chemical coagulants that neutralize the negative charges on tiny particles, allowing them to come together and form larger clumps (flocs) that can be removed later.

Alum (aluminum sulfate) and ferric chloride are classic inorganic coagulants. They release positively charged ions that neutralize particle charges, reducing repulsion and promoting aggregation. Polymers act as coagulant aids or flocculants, helping bridge particles to form larger flocs and improving settling and filtration.

Sand and gravel are filtration media, used after coagulation to physically remove flocs. Chloramines are disinfectants, used to kill microbes, not to destabilize particles. Activated carbon adsorbs organic contaminants and tastes/odors, not to cause coagulation.