Course: BFM 203 Water Treatment and Control

Lecture

What is Coagulation?

What is Coagulation

Coagulation is the clumping together of very fine particles (floc) caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of fine particles, allowing them to come closer and form larger clumps. Clumping makes it easier to separate the solids from water by settling, draining, or filtering.

Coagulation in the water industry includes the mixing of a coagulant chemical and raw water in a process called flash mixing. Flash mixing may be achieved mechanically or hydraulically and takes only a few seconds. Coagulant chemicals are either primary coagulants, which neutralize the electrical charges of particles, causing them to begin to clump together, or coagulant aids, which add density to slow-settling floc and add toughness so the floc will not break up during subsequent processes. These aids may also be referred to as flocculation or sedimentation aids.

A number of chemical are used as coagulants, as noted in the following list:

- Aluminum sulfate
- Ferric sulfate
- Ferrous sulfate
- Ferric chloride
- Calcium hydroxide
- Calcium oxide
- Sodium aluminate
- Bentonite
- Calcium carbonate
- Sodium silicate

In addition to these coagulants, there are also three synthetic organic polymers:

- Cationic: contains positively charged ions
- Anionic: contains negatively charged ions
- Nonionic: contains no net electrical charge

Aluminum sulfate and ferric chloride are commonly used with a cationic or anionic polymer depending on the characteristics of the water being treated.The following photo album contains images of powdered coagulant aids, coagulant storage facilities, and a mixing room.