Fluoride is a naturally occurring mineral that is beneficial for strengthening the bones and teeth. However, inadequate or excess intake of fluoride can lead to several health problems. Some of the potential risks of ingesting an excess of fluoride include dental and skeletal fluorosis. Therefore, defluoridation is adapted to adjust the levels of fluoride in the water.
Defluoridation is a process of downward adjustment of the fluoride in the drinking water. Moreover, it helps to minimize industrial fluoride pollution. There are several defluoridation techniques used worldwide. Some of them include – ion exchange method, adsorption, and precipitation technique. Nalgonda technique is also one of the most commonly used defluoridation processes which are adapted to provide optimal fluoride level in the drinking water.
Today’s article will highlight the process of defluoridation. Moreover, we will discuss the different defluoridation techniques in current use.
Fluoride is an essential mineral that is found naturally in the air, sand, and water bodies such as lakes and rivers. Typically, fluoride is found in abundance in the groundwater because of the leaching of the minerals. Until recently, fluoride was never identified as a problem. Fluoride is often described as a double-edged sword.
In rural areas, groundwater is consumed regularly. It accounts for 98% of the earth’s potable water. The presence of excess fluoride may pose a threat to the health and well-being of the people. In some cases, excess of fluoride can lead to dental and skeletal fluorosis. (1)
Inadequate ingestion of fluoride also has some consequences such as – high risk of caries development and weak bones. The World Health Organization recommended a guideline value of 1.5 mg/L as the optimal concentration of fluoride in drinking water.
What is defluoridation?
Defluoridation is a process used on a large scale to maintain the levels of fluoride in drinking water. It is described as the downward adjustment of the level of fluoride in drinking water. Defluoridation was first attempted in the 20th century using an aluminum and sand filter. This process was used to remove fluoride from the water. Later on, activated alumina came into use for defluoridation of the community water in the United States. (2)
- Suggested read: An Insight on the Alternatives to Water Fluoridation
What are the standard defluoridation techniques?
While there are various defluoridation techniques been explored all around the world, each method has its limitations. Some of the standard defluoridation techniques that are being used currently are listed below –
As the name suggests, this technique functions on the adsorption of fluoride ions onto the surface of the active agent. In this technique, the active agent has activated alumina, bone char, or activated carbon. All of these agents have some limitations –
- Activated alumina – requires a specific pH range to allow adsorption of fluoride. Moreover, frequent activation of alumina makes this technique expensive.
- Bone char – it requires optimal pH and temperature of raw water. Moreover, bone char takes a long time to filter the water. (3)
Many natural adsorbents such as the seeds of drumstick tree, roots of Vetiver grass and Tamarind seeds were also used as an alternative to the agents mentioned above.
The ion-exchange technique uses synthetic chemicals, namely the cations and anion exchange resins to remove fluoride from drinking water. Typically, fluoride is removed by the ion-exchange method or surface chemical reaction with the active agent. The water is then passed through filters to remove the impurities.
Some of the chemicals used in this process include –
- Carbanion – it is a cation exchange resin with excellent durability. (4)
- Defluoron 1 – it is sulfonated sawdust impregnated with 2% alum.
- Defluoron 2 – it is sulfonated coal, which uses aluminum solution as a reagent.
A limitation of this technique is that these chemicals are commercially produced resins, which makes this process expensive.
Precipitation technique was used to overcome the problems of adsorption and ion-exchange methods. Precipitation technique is performed by adding coagulants into the water that react with fluoride and forms insoluble fluoride salts. (5)
Some of the typical precipitation coagulants include –
- Aluminum salts
Nalgonda technique is one of the most economical and straightforward methods for the removal of fluoride. Moreover, it is beneficial for both domestic and community water supply.
In this technique sodium aluminate, lime and bleaching powder are used in sequential order and passed through three different processes –
- Flocculation – formation of insoluble fluoride salts in the water caused by coagulation from the active agents.
- Sedimentation – settlement of the insoluble salts on the water bed. (6)
- Filtration – safe drinking water on the surface level is collected.
Take away message
Fluoride is an essential mineral beneficial for proper development and strengthening if the bones and teeth. However, it acts as a double-edged sword. Excess of fluoride causes dental and skeletal fluorosis, which is a significant public health problem. The optimal levels of fluoride in drinking water should be 1.5 mg/L. To maintain this optimal level, defluoridation techniques were adapted in the 20th century.
Defluoridation is referred to as a downward adjustment of fluoride levels in drinking water. Some of the standard defluoridation techniques include adsorption, ion-exchange, and precipitation methods. However, all these techniques had certain limitations. Nalgonda technique is one of the most economical and commonly used defluoridation techniques.
Communities must adopt one of these techniques to maintain optimal levels of fluoride and provide safe drinking water to the people of the city.