Degasification and Stabilization
The product water from the RO membranes at this point is very unstable and aggressive. There is very
little calcium, magnesium, or alkalinity in the water. In order to provide a stabile, cost effective product to
the consumer, filtered raw water is "Blended" with the R/O product water. This provides some natural
stability to the water while reducing the cost of production. The blend water is filtered through the
greensand pressure filters and 20 micron cartridge filters to ensure quality. The degasification process removes any residual hydrogen sulfide in addition to stripping carbon dioxide.Carbon dioxide is indicative of corrosive water and results when pH of the feedwater is lowered and carbonate changes to bicarbonate and ultimately to carbon dioxide and water:
CO3 « HCO3 « H2CO3 « CO
2 + H20
Degasification is performed by mixing air with the water to remove the hydrogen sulfide and carbon
dioxide as gasses. The water enters two cylindrical towers from the top of the units and cascades
downwards across a packing material. To more effectively remove the gasses, air is induced in the bottom
of the units. The gasses emitted from these units is vented to the atmosphere. After the water exits the
degasifier towers, it enters the clearwell located underneath.
Chlorination, pH Adjustment, Fluoridation, Ammonia Injection
As the water enters the clearwell, chlorine is added for disinfection. The clearwell was designed to allow
for maximum contact between the chlorine and the water for complete disinfection.
A small amount of sodium hydroxide is added to the water to increase the pH of the water. This provides
for a more stable water that is non-corrosive nor scale forming in the distribution system.
A grant from the Department of Health and Rehabilitative Services was obtained by the City to pay for a
fluoride chemical feed system. Hydrofluosilicic acid is added to the water as a means to reduce dental
caries. The dosage rate is 0.8 parts per million as fluoride.
With the possibility of more stringent regulations on total trihalomethanes being imposed by EPA,
ammonia facilities were incorporated into the design of the plant. This provision for disinfection with
chloramines is an alternative to major treatment changes should the TTHM regulations become more
Ground Storage, High Service Pumps
The water is pumped from the clearwell to the 2-two million gallon ground storage tanks located on plant
site. At this point the water is available for pumping to the consumer.
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