It sounds like you have a ...

It sounds like you have a challenge as you would be looking to have a maximum amount of 1mg/L which is the Health Department recommendation. From a treatment perspective, the most appropriate and effective treatment is using reverse osmosis however in remote areas it is not always practical.

Following is an extract from the Degremont Water Handbook which is available on line free of charge and offers various methods of eliminating fluoride (fluorine). I hope it is useful.

Eliminating fluorine: 

Some natural waters contain more than 10 mg · L–1 of fluorine. This concentration has to be reduced to approximately 1 mg · L–1 (the acceptable residue falling as the average annual temperature rises); the European standard has set 1.5 mg · L–1. The following processes are used :

filtration through activated alumina

This is the most widely used process. Fluoride ion fixing is reversible and regeneration is carried out with aluminium sulphate or, preferably, with sodium hydroxide and sulphuric acid. Screening-out capacity can vary considerably: depending on the water’s initial fluorine content,  pH  and overall salinity, the material’s particle size and operating conditions, 0.3 to 4.5 g of F–ion can be fixed per litre of product. We recommend carrying out preliminary tests in the laboratory in order to identify optimum conditions and the consequences for the composition of the treated water.

coagulation-flocculation

The aluminium sulphate treatment constitutes another way of using fluorine’s affinity for alumina but the coagulant demand will be very high (50 to 150 g per g of F– to be eliminated); therefore, it can only be used on raw water that requires sedimentation and that has a low fluoride content.

lime used to soften water

This method can be used but with a  pH  >10 and providing that the water has a sufficiently high magnesium level because it is the magnesium oxide that will adsorb the fluorine. It is felt that approximately 50 mg · L–1 of magnesium will be required to remove 1 mg · L–1 of fluorine.

using tricalcium phosphate

The affinity of fluorine for this compound has long since been noted because significant levels of fluorine have always been found in natural phosphates such as apatites, phosphorites (2 to 5%) and even in bones. Consideration has been given to using the following :

• either natural products: bone ash (animal charcoal) or powdered bone;
• or synthetic apatite that can be produced within the water through the controlled combination of lime and phosphoric acid.

other processes

When the fluoride ion has to be eliminated at the same time as excessive water mineralization, then reverse osmosis may provide the answer.

Electro dialysis can also be considered.

Regards

Kim