How the Water is Treated

Raw water is pumped from the Tennessee River to the water treatment plant.  Coagulant polymer, chlorine, sodium permanganate, and sometimes sodium hydroxide (caustic soda) are added.  After the pre-chemicals are added, the water is rapidly mixed in a flash mix.  The next step is the flocculation/coagulation process in which the water and chemicals are gently stirred. Next, is the settling, or sedimentation phase in which the heavier particles, called floc, settle out by gravity.

The water then passes through membrane filters.  Finally, we add the post-chemicals such as more chlorine, HFS (fluoride) and a sodium phosphate blend to the effluent before it is pumped to the tanks in the distribution system.

Chemicals:

Coagulant polymer - is a positive charged coagulant used to attract the negative charged suspended particles found in water.

Chlorine = Cl2 - Chlorine is used to disinfect the water.

Sodium Permanganate = NaMnO4 - Marketed as CARUSOL20. Used to aid coagulation/flocculation and settling and to reduce tastes and odors.

Sodium Hydroxide = NaOH - Used to add alkalinity in water and to increase pH of water.

Hydrofluosilisic acid = HFS - Provides fluoride to finished water.

Sodium Phosphate - Marketed as AQUAMAG. Used as a corrosion inhibitor.

Definitions:

Flash mix: The process where the chemicals are rapidly mixed.

Coagulation: Gentle mixing action that causes the impurities in water and the added chemicals to form larger floc particles.

Flocculation: See coagulation.

Floc: A larger, heavier particle formed by the reaction of chemicals and impurities in the water that will eventually settle out in the sedimentation basins.