Fluoride control technology in drinking water

 In India, technologies for controlling fluoride in drinking water include the Nalgonda technique (using alum, lime, and bleaching powder), activated alumina adsorption, and electrolytic defluoridation, aiming to reduce fluoride levels to the permissible limit of 1 ppm (mg/L). 

Here's a more detailed explanation of the technologies used for fluoride control in Indian drinking water:

1. Nalgonda Technique (Alum-Lime-Bleaching Powder Method):

Mechanism:

This method, developed by the National Environmental Engineering Research Institute (NEERI), involves adding alum, lime, and bleaching powder to the water, followed by coagulation, sedimentation, and filtration. 

Process:

Alum (aluminum sulfate) reacts with fluoride to form aluminum hydroxide, which precipitates out of the water. 

Lime (calcium hydroxide) is added to maintain the pH of the treated water and to help with sludge settling. 

Bleaching powder (calcium hypochlorite) is used as an optional disinfectant. 

Advantages:

Relatively simple and cost-effective, suitable for both household and community-level use. 

Disadvantages:

Requires trained operators for proper operation and sludge disposal. 

2. Activated Alumina Adsorption:

Mechanism:

Activated alumina, a porous material, is used to adsorb fluoride ions from the water.

Process:

Water is passed through a bed of activated alumina, where the fluoride ions are captured.

Advantages:

Highly effective at removing fluoride, can be used in both large-scale and small-scale applications.

Disadvantages:

Activated alumina needs to be replaced or regenerated periodically, and the process can be energy-intensive. 

3. Electrolytic Defluoridation (EDF):

Mechanism: This method uses electrolysis to remove fluoride from water.

Process: Aluminum plates are placed in the water, and an electric current is passed through the water, causing the fluoride ions to be removed.

Advantages: EDF is a promising technology for removing fluoride from water, and it is suitable for fluoride-affected areas with water containing excess fluoride.

Disadvantages: EDF requires electricity, and the process can be energy-intensive. 

4. Other Technologies:

Reverse Osmosis (RO): RO membranes can remove a high percentage of fluoride ions from water. 

Nanofiltration: Similar to RO, nanofiltration membranes can also be used to remove fluoride. 

Rainwater Harvesting and Artificial Recharge: Collecting rainwater and using it to recharge groundwater can help dilute fluoride-contaminated groundwater. 

5. Indian Standard for Drinking Water:

The Indian Standard (IS 10500) specifies a maximum permissible fluoride concentration of 1 ppm (mg/L) in drinking water.

However, in the absence of a suitable alternative source, the permissible limit can be extended to 1.5 ppm.