Nalgonda Technique

This technique was developed in India in the 1970’s. Alum (Al₂(SO₄)₃) and lime (Ca(OH)₂) are added to the contaminated drinking water.

Al₂(SO₄)₃ + 3Ca(OH)₂ → 2Al(OH)₃ + 3Ca²⁺ + 3SO₄^2-

Fast stirring for good mixing is followed by the coagulation/precipitation process and sedimentation of the Al(OH)₃ precipitate, together with the sorbed fluoride. The technique has been implemented both on community and household scales in several countries.

Community unit applying the Nalgonda technique for fluoride removal in the Ethiopian Rift Valley		Nalgonda technique for household use, Ethiopia

Advantages:

• Materials are cheap and generally locally available
• Treatment is well accepted by locals
• Removal processes are well understood
  
  

Disadvantages:

• Fluoride elimination rate is low (70 - 80%)
• The right amounts of chemicals need to be added
• Residual aluminium in the water is a constant danger
• High sulphate concentrations in the water make it taste salty.
• Daily maintenance effort is very high
• Sludge disposal

 

Bone Char / Hydroxyapatite

Activated Alumina

Contact Precipitation

Reverse Osmosis