Household Water Treatment and Safe Storage Factsheet: Source ...

Household Water Treatment for Fluoride Removal
Factsheet: Nalgonda Technique
Potential Treatment Capacity
Very Effective For: Somewhat Effective For: Not Effective For:
Turbidity
Fluoride
Bacteria
Viruses
Protozoa
Helminths
Hardness
Taste, odour, colour
Other chemicals
What Is the Nalgonda Technique?
The Nalgonda technique was first developed
by the National Environmental Engineering
Research Institute (NEERI) in Nalgonda, India.
It involves adding alum (aluminum sulphate,
(Al 2 (SO 4 ) 3 . 16H 2 O)) and lime (calcium
carbonate) to the raw water to precipitate the
fluoride.
Compared with normal drinking-water
flocculation processes, a much larger dose of
alum is required in the defluoridation process.
Because the alum solution is acidic, addition of
lime is needed at the same time to maintain a
neutral pH in the treated water and to complete
precipitation of aluminum.
Calcium hydroxide may be added instead of
lime. Chlorine or bleaching powder can also be
added to the raw water to disinfect it against
microbiological contamination.
After treatment with the chemicals, the treated
water can be decanted or poured into another
container. The water may be passed through a
filter or cloth while decanting to ensure that no
sludge particles escape with the treated water.
How Does It Remove Contamination?
Aluminum salt is responsible for removal of the
fluoride from the water. During the flocculation
process (creation of large particles in the water
which stick together) many kinds of microparticles
and negatively charged ions
(including fluoride) are partially removed by
electrostatic attachment to the flocs.
In this technique, up to a third of the fluoride is
precipitated, while up to 82% reacts with the
alum to make a soluble and toxic aluminum
fluoride complex (Miller, 2007) which will settle
to the bottom as sludge. This should be
disposed of away from water sources.
The process can produce treated water with
fluoride concentrations of 1 to 1.5 mg/L.
Household Defluoridation Using Nalgonda Technology (Credit: Lyengar, 2002)