In Chemo Defluoridation, the chemical salts are used to reduced Raw Water Fluoride concentration from 5 - 10 mg/lit. to < 1.0 mg/lit/ the process is free from interference of anions in water & does not affect the palatability of water. Treatment cost of process is Rs. 0.10 per liter to get < 1 mg/lt. from 5 mg/lit. raw fluoride concentration.
CSIR-NEERI has developed the Household Chemo-defluoridation Unit. In Chemo-defluoridation, the salts of calcium and phosphorous have been used to reduce the raw water fluoride concentration in the range 2- 10.0 mg/L to < 1.0 mg/L. Required dose of chemicals are added in the fluoride contaminated raw water and mixed with the stick. The chemicals react with each other to form the chemical complex which absorbs fluoride and precipitated out. After 15 to 20 minutes of mixing of the chemicals, water is allowed to flow by gravity into the sand filter at the rate of 300 – 400 ml/min. Filtered water with fluoride concentration less than 1 mg/L is collect in the container and can be used for drinking and cooking purposes. The layer of chemical complex precipitate formed on the sand filter also removes some fluoride from the water during filtration. After about 1 to 2 months of operation, filter is choked by the formation of thick layer of sludge. The Nylobolt cloth kept below the 2-5 cm of sand layer is lifted along with the sand and the sand is washed separately in a tub or bucket. The Nylobolt cloth is cleaned and replaced on the sand bed. Washed sand is again placed over the Nylobolt cloth. The filter is ready to use.
• Simple to fabricate and easy to operate
• Minimum maintenance
• Gravity operated
• No power requirement
• Taste of the treated water is palatable
• Typical Capacity - 30 L
• Process involves formation of insoluble fluoride complex with salts of calcium and phosphorous and filtration through sand filter
• Reduces the fluoride concentration in water to <1 mg/L
• A typical unit, of 30 L capacity can serve a family of 5-6 persons, on the basis of 5-6 litres per capita/day for drinking and cooking purposes
• Suitable for treating the water upto fluoride concentration of 10 mg/L
• No leaching of fluoride from sludge back into the water at normal pH range (6.5-8.5)
• Most reliable for small fluoride affected villages where community water treatment plant is not economically feasible
• Unit cost Rs. 3000-4000 and operating cost Rs. 0.20-0.30 per litre
Under the research project sponsored by Rajiv Gandhi Science and Technology Commission, Govt. of Maharashtra, 70 defluoridation plants are installed in Sakhara village in Yavatmal District and 30 plants have been installed in Chichkavatha village in Nagpur District in Maharashtra to test the performance of the units.