Norfolk's Water Treatment Process

Flash Mixing/Coagulation

Once the water comes into the treatment plant, chemicals are added and the water is mixed rapidly in a container called a flash mixer.

These chemicals include: chlorine  and ammonia for disinfection, powdered activated carbon (PAC) for taste and odor control, hydrated lime for pH (acidity) adjustment and aluminum sulfate (alum) and a polymer for coagulation.

The alum reacts with the dirt in the water to form a "floc" (coagulated sediment). These floc particles trap the dirt present in the raw water.

Flocculation

After the water passes through the flash mixer, it then flows into the flocculation chamber.  In here,  the water is mixed at a very slow speed by large paddles. 

This allows  the delicate floc particles to grow in size like a snowflake on its way to earth.  As the floc grows, it traps additional dirt and suspended material.

Sedimentation

Once the floc is completely formed (looks like a large brown snowflake), the water flows into the sedimentation basin.   Because the floc is heavier than water, it settles by gravity to the bottom of the sedimentation basin and forms a layer of sludge on the bottom.  

At the Moores Bridges Plant, Llamella plate settlers are used to enhance floc sedimentation. This sludge is collected and pumped to our Solids Dewatering Facility where the water is removed under great pressure, leaving the solids behind. The dry solids are then disposed of in a sanitary landfill owned by the Southeastern Public Service Authority.   The clear water flows on to its next stop, the filters.

Filtration

From the sedimentation basin, the water enters dual media filters for final cleaning. These filters consist of two layers of material, anthracite coal (on the top) and sand (underneath).  As the water passes through the filters, any remaining suspended material is removed.  It is here that the smallest particles of dirt and algae are removed.

In order for the water to pass through the filter, the bottoms are made of porous plastic cubes that allow the filtered water to pass through to the next stage of the treatment process.

Chlorine is also added at this stage for two reasons; it oxidizes dissolved iron and manganese allowing them to be trapped on the filter media and it also disinfects the water making it safe to drink.

After Filtration

After filtration, the pH (acidity) of the water is adjusted to neutral with hydrated lime. Fluoride is added to prevent tooth decay in children. The water is then pumped into elevated storage tanks where it remains for several hours. 

From the storage tanks, the water is delivered on demand, into the water pipes through powerful centrifugal pumps that maintain the water pressure at a constant 65 to 70 pounds per square inch. The water distribution system consists of many miles of pipes of various sizes that bring the water to your house or business.

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EMERGENCY NUMBERS:

Water or Sewer Main Breaks (757) 823-1000

Water Turn On/Turn Off (757) 664-6700

Miss Utility (Call Before You Dig)

1-800-552-7001