Fluoride Removal Filter

Fluoride  which is naturally in groundwater in concentrations ranging from 0.1 mg/L to 10 mg/L. The chemical originates in several minerals. As groundwater passes through the earth and comes into contact with these minerals, fluoride is dissolved and enters the water. The deeper the water flows through the earth, the more fluoride-containing minerals it will come in contact with, and the greater the fluoride concentration in the water will be Ordinarily groundwater having concentrations of 10 mg/L, or-more of fluoride are rare and surface waters seldom contain more than 1 mg/L of fluoride. Fluoride in excessive concentration is undesirable in waters used for drinking. According to WHO, and the Manual on Water Supply and Treatment published by the CPHEEO, Gal, the recommended higher limit for fluoride is 1.5 mg/L. High fluoride concentration in groundwater is a natural phenomenon in close to 23 countries such as China, Sri Lanka, West Indies, Spain, Holland, Italy and Mexico.
According to a Rajiv Gandhi National Drinking Water Mission (RGNDWM) report, the bedrock of the Indian peninsula consists of a number of fluoride-bearing minerals: fluorite, topaz, apatite; and rock phosphate, phosphatic nodules and phosphorite (all with high fluoride concentrations). When the bedrock weathers – a natural chemical process in which the rock slowly crumbles to form soils – the fluoride leaches into the water and the soil. High concentrations of fluoride have been found in parts of Andhra Pradesh, Bihar, Gujarat, Haryana, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Punjab, Rajasthan and Tamil Nadu in the country.
Fluoride mainly enters the human body through drinking water; 96-99% of it combines with bones, as fluoride has affinity for calcium phosphate in the bones. Excess intake of fluoride can lead to dental fluorosis, skeletal fluorosis, or non-skeletal fluorosis. According to WHO, the prevalence of Dental Fluorosis is correlated to drinking water fluoride in the following manner.
 Dental Fluorosis
Fluoride in water has been proven to prevent tooth decay among children and to prevent root tip rot. The chemical acts by strengthening the tooth enamel and by making the enamel more resistant to decay. Although fluoride is safe at the concentrations less than 1.5 mg/L, an excess amount of fluoride in water can result in mottled brown stains on teeth. These stains is called dental fluorosis, which results from fluoride concentrations of 1.5 mg/L in drinking water.Dental Fluorosis is characterized, by discolored, blackened, mottled or chalky-white teeth. Extreme concentrations of fluoride can cause skeletal Fluorosis. Skeletal Fluorosis leads to severe and permanent bone and joint deformations. Fluorosis is an irreversible disease and there is no cure. Fluorosis is a disease that neither allows a person to live nor to die. Non-skeletal Fluorosis leads to gastrointestinal problems and neurological disorders. Fluoride can damage a fetus, and adversely affect the IQ of children.
Fluorosis  can be detected in the neck, spine, knee, pelvis, shoulder and small joint of hands and feet. Gastro-intestinal symptoms include abdominal pain, diarrhea, and constipation. Some neurological manifestations are nervousness, excessive thirst and tendency to urinate frequently. In spite of all these symptoms, it is common Fluorosis to remain un-diagnosed for a long time. In India fluorosis has spread across states, and across a variety of ecological regions.

Fluoridation
Fluoridation is the process of adjusting the concentration of fluoride in public water supplies for the prevention of dental decay. Fluoride has been added to drinking water in the United States since 1945. With a few exceptions, fluoride can be added to water at any point between the raw water intake and the clear well. However, if fluoride is fed before filtration, about 10% of the fluoride sticks to the floc and is lost, so fluoride is usually added after filtration. In addition, if lime is fed, the fluoride should be added as far away from the lime injection point as possible. Three main chemicals used for fluoridation of drinking water are hydrofluosilicic acid, sodium silicofluoride, and sodium fluoride.

Methods of Defluoridation
Removal of fluoride from water is known as defluoridation. Once excess fluoride is detected in water, the obvious step is to defluoridate water. The technology to be adopted depends upon the fluoride levels in water and the volume of water to be defluoridated.
Fluoride removal plants installed in USA use beds of tricalcium phosphate as a base ~xchange material. These beds are regenerated by flushing with 1 to 1.5% sodium hydroxide solution followed by a dilute hydro-chloric acid wash, or by use of CO2 to neutralize the excessive alkalinity resulting from the intial wash. There are two processes available for the treatment fluoride contaminated water. They are

  • Activated Alumina Technology,
  • Reverse osmosis process, and
  • Nalgonda technique.

ActivatedAlumina Technology
In the Activated Alumina Technology, if local alumina is used it has to be regenerated using acid and alkali whereas imported alumina does not require any regeneration. However the operation of the plant which is depending upon the import of alumina is not possible for long run. The disposal of solid alumina waste may lead to leaching out of aluminium and fluoride which may cause health hazards and pollute the nearby ground water sources.
 Reverse osmosis process The Reverse osmosis process can be used for places where the quality of water is affected either by single parameter or multiple parameter such as fluoride, Total dissolved solids, Total hardness, etc. For operating the plant high technical skill is required which may not be available in the rural areas. Further, this process involves prohibitive cost of operation and maintenance.
In India various technologies have been tested. β€œIon exchange and chemical treatments are cost intensive, while physical methods suffer limitations, like frequent change in defluoridant beds and the inability to reduce fluoride to non-toxic levels. The clean-up schemes – both large and small have failed because of improper management.

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