Which chemical is used as a flocculant to remove fine solids and colloids?

Prepare for the American Water Works Water Treatment Plant Operator Test. Study with multiple choice questions, each with hints and explanations. Get ready to excel!

In water treatment, a coagulant like ferric chloride is added to destabilize fine solids and colloids. It hydrolyzes to form ferric hydroxide, which carries a positive charge that neutralizes the negative charges on tiny particles. As this destabilization occurs, particles start to clump together into larger flocs that can be easily removed by sedimentation or filtration. This makes ferric chloride an effective flocculant/coagulant for removing haze and turbidity.

The other options have different roles: sodium chloride is simply a salt that affects taste or ionic strength but doesn’t promote floc formation; calcium carbonate mainly adjusts alkalinity and pH rather than removing solids; chlorine gas is a disinfectant used to kill microorganisms after the solids have been removed, not for forming flocs.