Wiki Page, Community Fluoridation: Module 3 - Overview of Water Treatment Part 1

Wiki Page
2017-06-20T22:32:14-06:00

Conventional treatment of surface water sources involves a sequence of processes that have the purpose of removing suspended sediments from the water, then disinfecting the water. The unit processes of conventional surface water treatment are:

Coarse screening or pre-sedimentation

Coagulation, flocculation

Sedimentation

Filtration

Fluoridation

Disinfection

Treatment Process Illustration

In this part of the Module, the following components of the water treatment process that are going to be covered are shown below. The components that are not covered in this part are shaded.

Coagulation

Coagulation is the destabilization of colloidal particles.

Colloidal particles are usually less than 1 micrometer in diameter and have an associated electrical charge.

The presence of similar colloids in suspension results in the mutual repulsion of these particles, and therefore they do not readily settle.

Colloidal particles in water is a problem as they can harbor bacteria and interfere with disinfection.

Treatment Process Illustration.

Chemical Feed/Mixing

In order to mask the charge on the colloidal particle, coagulant chemicals are added.

These chemicals, called coagulants, are usually salts of aluminum or iron.

They are added in the rapid or flash mix zone.

When the coagulants are added to water, they form ions. The metal ions react with alkalinity in the water to form hydroxide salts, aluminum hydroxide, ferric hydroxide or ferrous hydroxide. The hydroxide salts are not very soluble in water, so they precipitate out as solid particles.

This precipitate helps to group the colloidal particles into big clumps called floc.

Treatment Process Illustration.

Flocculation

Flocculation is the process of having floc particles collide and stick together to form larger particles.

The mixture is slowly blended in a square or rectangular basin with a large paddlewheel.

The flocculation speed should keep particles mixed so they do not settle out immediately, but the speed should not be so fast that it causes the particles to shear one another when they collide.

Treatment Process Illustration.

Sedimentation

By slowing water velocity, gravity assists in settling the flocculation particles into a sludge at the bottom of the tank.

The sludge is periodically removed and transported elsewhere for further dewatering and disposal.

Effluent should only contain the smaller flocculation particles that were formed by coagulation.

The filter is the last opportunity to remove suspended particles before the finished water goes to the distribution system.

Treatment Process Illustration.

VIDEO 1 SOURCE PUMP FLOCCULATION SEDIMENTATION-Final from Enos C Inniss on Vimeo.

Now, it's time for a quiz! Click next at the bottom for Module 3 - Quiz 1.