Nalgonda Technique

News: The Government of India has commissioned a study to reassess fluoride removal technologies as existing standards based on the Nalgonda technique lag behind advancements.

About Nalgonda Technique

• The Nalgonda technique is a simple and cost-effective method used for removing excess fluoride from drinking water.
• Developed by: It was developed by the National Environmental Engineering Research Institute (NEERI), Nagpur, in 1974.
• Chemicals used:  The technique involves the sequential addition of three primary chemicals –
  • Alum (aluminium sulphate): Acts as a coagulant that reacts with fluoride ions to form “flocs“.
  • Lime (calcium oxide): Added to maintain the pH of the water and ensure proper flocculation.
  • Bleaching powder: Used for disinfection to remove pathogens.
• Process: The process follows four main sequential steps – 
  • Rapid mixing: Chemicals (alum, lime, and bleaching powder) are added to the raw water and mixed vigorously, usually for 1–2 minutes, to ensure they are properly dispersed.
  • Flocculation: The mixture is stirred gently for a longer duration, typically 10–20 minutes. This allows the formation of large, settleable “flocs” as the chemicals react, which trap the fluoride ions.
  • Sedimentation: The water is allowed to remain undisturbed for about 1–2 hours. During this phase, the flocs formed in the previous step settle to the bottom due to gravity.
  • Filtration: The clear, treated supernatant water is separated from the settled sludge by passing it through filters, such as a rapid gravity sand filter.
• Limitations: It produces high amounts of sludge, requires daily chemical addition and is less effective in water with high total dissolved solids or hardness.
• Significance : It provides an affordable and practical solution for safe drinking water in fluoride-affected regions.