Fluoride
compounds contained in municipal water systems
begin as salts forming when the element fluoride
combines with minerals in soil or rocks. Some
fluoride compounds such as sodium fluoride and
fluorosilicates dissolve easily into ground
water as it moves through gaps and pore spaces
between rocks. This is a significant problem in
some regions of the United States, including New
Mexico, West Texas, Colorado, Indiana and
Illinois. Fluorides are also a waste product
found in industrial waste waters from coal,
minerals and clays heated to high temperatures
and then released during glass manufacturing,
electroplating, and the production of steel and
aluminum, pesticides, fertilizer and
semiconductor manufacturing. High levels of
fluoride are generally reduced by the
precipitation of calcium fluoride with lime.
However the solubility of calcium fluoride is
such that 8 ppm fluoride remains in distilled
water, and in industrial water residual fluoride
levels may be even higher.
Orally ingested
fluoride is readily adsorbed from the GI tract.
Nearly all of the fluoride in the body is found
in calcified tissues and elimination is through
glomerular filtration in the kidneys. Excessive
fluoride intake can lead to fluorosis of both
teeth and bones. Children between the ages of
2-3 are at most risk of suffering from cosmetic
fluorosis. Tooth discoloration and/or pitting
may be caused by excess fluoride exposure during
the formative period prior to tooth eruption.
Additionally in many urban communities up to 10%
of children manifest enamel fluorosis in primary
teeth as the result of ingesting formula as
infants which is reconstituted with fluoridated
municipal water.
Fluoride as a
strong oxidant had historically over the past 50
years been added in concentrations of 1 ppm to
many drinking waters in order to prevent dental
caries. However, fluoridation of water is not
regulated nationwide. Additionally, the addition
of fluoride to the water supply is now banned by
virtually every European nation because of the
potential and real long term complications of
fluorosis. Fluoride is believed to be a
carcinogen with high affinity for bone and is
linked to hip fractures and brittling of bones.
The International Agency for Research on Cancer
(IARC) has determined that the carcinogenicity
of fluoride to humans is not classifiable.
Skeletal
fluorosis results from ingesting excessive
levels of fluoride for prolonged periods of
time. The first obvious symptoms include pain
and stiffness in joints and osteosclerosis and
this may then become crippling due to
calcification of ligaments, osteoporosis of long
bones and neurological defects due to
hypercalcification.
All salts of
fluoride are toxic. The adequate adult intake
(AI) for fluoride is 0.05 ug/kg/day while the
tolerable upper intake level is 0.1 ug/kg/day.
Although water ingestion is the primary source
of fluoride in the diet other sources such as
formula may contribute to intake in children.
Any food that absorbs water while cooking such
as rice, paste and vegetables may be affected by
the fluoride content of water. Additionally,
significant amounts of fluoride are ingested by
swallowing toothpaste, fluoride rinses and
mouthwash products. The maximum contaminant
level for fluoride established by the
Environmental Protection Agency is currently
established at 4 mg per liter (mg/L) or 4 parts
per million. The EPA has set a secondary
standard for fluoride at 2 mg/L. EPA recommends
secondary standards to water systems but does
not require systems to comply. However,
individual states may choose to adopt them as
enforceable standards.
Removal of
fluoride from industrial waste water may be
obtained using precipitation, as well as
membrane and adsorption processes. The membrane
processes include reverse osmosis,
nanofiltration, electrodialysis and donnan
dialysis. The best way, bar none, to reduce the
concentration of fluoride to 1 ppm or below is
through adsorption onto specially designed wide
pore size activated alumina.
DAI Dyna-AquaTM
Fluoride
DAI provides
pretreated activated alumina designed to address
commercial and industrial needs reducing the
concentration of fluoride in wastewater effluent
and municipal water systems to less than 1 ppm.
This specially designed wide pore activated
alumina is cost competitive with any other form
of purification and provides simplicity of
design and ease of utility. This novel product
is an exciting addition to the expanding line of
custom designed activated alumina compounds
offered to purify municipal and industrial
wastewaters.
A key advantage
in using activated alumina for fluoride removal
is that fluoride extraction is in part dependent
upon the pH of waste water contents. Because of
its unique amphoteric properties activated
alumina works optimally in a pH range of 5.5 to
8.5. If the effluent stream is extremely
alkylotic the source waste water may need to be
pretreated in order to reach a pH range of 5.5
to 6.5 to achieve peak fluoride removal
efficiency. Furthermore there is no simpler
means to remove fluoride than through the use of
a column of adsorbent material containing
specialized activated alumina. Flow rate
efficiency is affected by particle size. The
smaller the particle size, the higher the flow
rate that can be used. This must be balanced
against the higher pressure drop which results
from smaller size material. Competitive
adsorption may occur in the setting of high
concentrations of bicarbonate ions. For this
reason Dyna-AquaTM Fluoride is of such high
efficiency that even with competitive binding
with bicarbonate ions the total effluent
concentration of fluoride will remain less than
1%.
Dyna-AquaTM
Fluoride
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