In water treatment, which polymer charge is typically used as a coagulant aid to destabilize colloids?

• A. Nonionic
• B. Amphoteric
• C. Anionic
• D. Cationic

Answer: (C)

When colloids in water are destabilized, you need something that can neutralize their surface charge and help particles stick together. A positively charged polymer does this effectively because it is attracted to the negatively charged surfaces of most colloids. The long chains of a high-molecular-weight cationic polymer can adsorb onto multiple particles, providing charge neutralization and then bridging to form larger flocs that settle or filter more easily.

Anionic polymers, while useful later as flocculants to bridge already destabilized particles, would not promote destabilization since they repel negatively charged colloids and can hinder initial charge neutralization. Nonionic polymers don’t contribute charge to counteract the surface charges, so they’re less effective for triggering destabilization. Amphoteric polymers’ charge varies with pH, making their performance less predictable for this function.

So the polymer charge typically used as a coagulant aid to destabilize colloids is cationic.