Test: Fluoridation and Defluoridation - Civil Engineering (CE) MCQ

When the fluoride content is low, it will cause dental caries. So the fluoride content of water is raised and the process is called fluoridation.

Dental caries occurs in children. It can be prevented when the concentration of fluoride in water is between 0.7 to 1.2mg/l.

Sodium fluoride is the most purest compound having 95-98% purity due to which, they are commonly used for fluoridation.

Sodium fluoride, sodium silico fluoride, hydrofluosilicic acid and sodium fluro carbonate are the fluoride compounds used for fluoridation.

Dental fluorosis is caused when fluoride concentration is above 3 ppm, whereas Crippling fluorosis is caused when the concentration of fluoride in water is between 8 and 20ppm.

For safer handling, hydrofluosilicic acid is preferred as even if it is spilled on the skin, it can be removed easily by washing in cold water.

Copper sulfate is used to remove taste, odor, color and control of algae growth and it is not used for fluoridation.

When the fluoride content in water is high, it is essential to reduce the fluoride content to avoid health related problems and the process of reducing the fluoride content is called defluoridation.

• Defluoridation means the removal of fluoride from the water.
• The following technologies are generally used for removing fluorides from water.
  • Absorbing by activated alumina (commonly known as Prashanti Technology)
  • Nalgonda Technique
  • Ion exchange absorption method
  • Reverse osmosis process

Nalgonda Technique:

• Mainly used in rural areas, groundwater containing excess fluoride.
• Nalgonda technique uses aluminum salt (alum) for removing fluoride.

Activated sludge treatment:

• It is an aerobic suspended growth type biological process that uses the active microorganisms kept in suspension in the reactor to decompose and stabilize the soluble and particulate (colloidal and suspended) organic matter present in wastewater.

Lime soda process:

• Lime soda process is the method of removal of hardness (permanent hardness) from the water.
• The Lime soda process is used for the removal of all forms of calcium hardness.
• Complete removal of hardness cannot be accomplished by chemical precipitation, under normal condition in the treatment plant, 40 mg/l of CaCO3 and 10 mg/l of Mg(OH)2 usually remains in softened water.

Co-precipitation:

• The co-precipitation method refers to obtain a uniform composition in two or more cations of homogeneous solution through precipitation reaction, which is one of the important methods for the synthesis of composites containing two or more kinds of metal elements.

During defluoridation by calcium phosphate, the bone is calcinated at 400-600ºC for 10 minutes followed by mineral acid treatment.