Hi Chandrasekaran. I'm Erik ...

Hi Chandrasekaran.

I'm Erik from Denmark. I worked with low-tech fluoride removal early 90'es while a student and after graduation.

I don't see below the Nalgonda Technique (precipitation with Aluminum Sulphate + Lime). The optimum pH removal of Fluoride is at 6.5 during coagulation. Take care of the pH adjustment capacity of the Lime being reduced during storage, resulting in too low pH at coagulation and lower fluoride removal.

If using pressurized water no paddle needed in batch mixing vessel, as the movement of water coming into the vessel from bottom (e.g. 1500 L) will stir the water for first mixing line (added when 50% full), then assist coagulation and flocculation after adding ALUM (added when 75% full). The flocculation will continue until 100% full and afterwards for some time, while settlement start. After 8-10 hours (overnight) there is a clear and fluoride reduced layer above the settled sludge (10-15% of total volume going to waste). Actually the water inlet at the bottom must be build with a siphon to prevent backflow into the feeding pipe. The siphon will during the filling suck air into the pipe resulting in bobbles in the vessel, creating violent mixing.

For Bone Char the apatite crystal structure is destroyed with too high temperature, thus loosing the ability to absorb (ion exchange) the fluoride. The best Bone Char is produce at about 400 degrees Celsius and long time burning to remove organics without destroying the apatite crystal structure. The product after burning will be light grey in color. To be crushed to mm size granules. The longer the filter the more efficient before break through. Ideally 2 filters in series will assist to exhaust the capacity in the first filter while still removing fluoride in the second filter. Then move up the 2nd filter to be the first and insert a newly filled filter at no. 2.

Prem Baboo worte:

Bone Char

The uptake of fluoride onto the surface of bone was one of the early methods suggested for defluoridation of water supplies. The process was reportedly one of the ion exchange in which carbonate radical of the apatite comprising bone, Ca(PO4)6.CaCO3, was replaced by fluoride to form an insoluble fluorapatite. Bone char produced by carbonizing bone at temperature of 1100-1600ºC had superior qualities than those of unprocessed bone and hence replaced bone as defluoridating agent averted in this method.