Water Treatment Overview

At this time, the Water District continues to use a traditional four step water treatment process to purify Lake Michigan water for use by its customers as drinking water. This method has proven reliable over many decades for treatment of surface water, such as that in Lake Michigan, and is approved by the IEPA (Illinois Environmental Protection Agency).

Lake Michigan water is pumped from an intake pipe that extends out into the lake to the treatment plant where the following operations are performed:

1. Coagulation
2. Flocculation
3. Clarification
4. Filtration
5. Water Storage
6. Disinfection

Water Treatment Process

The operation of the plant is under the control of the Operations Manager and his staff providing 24/7 supervision of all process operations.

1. Coagulation
Alum is added to the raw water to coagulate solids (turbidity, sediments, and particles stirred up by wave action) that are present in the raw water. The alum solution and the raw water are mixed to assure thorough blending of both solutions. The alum causes the fine particles that cause water turbidity to stick together creating particles called “flocs” (flocculated particles).

2. Flocculation
These floc particles are further gathered together with the use of a positively charge polymer that is added with gentle mixing to form even larger flocculated particles that are heavier than water.

3. Clarification
The treated water containing the flocculated particles then flows into the settling zone of the solids contact units, where they settle out of solution and are either removed for disposal or recycled to seed (speed up) the flocculation process as mention previously.

4. Filtration
The clarified water now flows to the filters for final filtration. These units contain anthracite coal and sand to remove any remaining suspended particles – resulting in purified water. Before filtration IEPA regulations require the addition of a small amount of fluoride to help reduce dental tooth decay.

5. Water Storage
The water is now fully treated and meets regulatory requirements, other than final disinfection. After filtration the water is stored in a large storage tank. The size of this storage tank is large enough to level-out the flow of finished water to the customers so that during periods of low water use, the purification system can be slowed and during peak periods there is ample supply of water available.

6. Disinfection
Chlorine is added at three locations for disinfection. It is also used to help maintain chlorine disinfection residuals throughout the treatment process as well as through the distribution system for consumer consumption. The first application occurs at the intake pipe. Next it is added prior to entering the solids contact units. Then at the finished water pump discharge before distribution to the District’s customers. Chlorine residuals are monitored at the plant as well as the distribution system.

Laboratory Facilities

The District has laboratory facilities to run quality control analyses and for the control of chemical feeds to maintain water quality. All other federal and State regulatory analyses are performed by a certified contracted lab.

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