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Water Treatment | Coagulation Chemistry Basics

Learn the basics of Coagulation Chemistry. This video is an excerpt from the American Water College Water Treatment Exam Review course.

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After a quick overview we look at the different types of coagulants.

There are three kinds of coagulants. Namely: Trivalent, Bivalent and Monovalent.

Trivalent Coagulants include:

  • Aluminum
  • Iron

Bivalent Coagulants include:

  • Calcium

Monovalent Coagulants include:

  • Sodium


We also take a look at different uses for different compounds.


Aluminum Sulfate – The most common and is often used with cationic polymer.

Aluminum Chlorohydrate – Produces less sludge and is less corrosive than aluminum sulfate.

Ferric chloride – Effective over a wider pH range than alum.

Ferric sulfate – Often used as part of he lime softening process.

Ferrous Sulfate – Less pH dependent than alum.

Aluminum Polymer – Polyaluminum Chloride (PAC) and Poly Aluminum Sulfate are examples.

Cationic Polymers – Large molecules, synthetic polyelectrolytes.

Sodium Aluminate – Often used with alum because it improves the alum process.

Sodium Silicate – Used to make the coagulant aid activated silica. Activated silica is added in addition to a primary coagulant to enhance the coagulation process.


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