for the fluoride extraction from groundwater, coagulation process which is in consistent with calcium carbonate or electrolytic process can be experimented. Treatment with activated alumina is also useful. Application depend on concentration of Fluoride  and presence of other trace elements in groundwater.

As specifically suggested by Dr. Serena it is common technique employed for precipitation of fluoride from rural groundwater supplies in India. This method is known as Nalgonda technique of Defluoridation.

 As suggested by Dr.Saxena, this method is widely used for Defluoridation of rural groundwater supplies due to its economical feasibility and simple operation. The method is known as Nalgonda Technique, where Hydrated Potassium Aluminium Sulfate or Alum is dosed in a simple batch reactor.

There are Several demerits of Nalgonda techniques as due to adding up of aluminum sulfate as coagulant, the sulfate ion concentration increases greatly and at some times goes beyond maximum permissible limit of 400 mg/l, which causes cathartic effect on human beings.  Further, discarding the sludge from the Nalgonda process is a serious environmental matter of concern. The evolved sludge will be a toxic one and it contains the removed fluoride in a concentrated form  and Sludge disposal is a major problem with the Nalgonda technique...

The fluoride comes into ground water by various ways, for example, weathering of rocks, industrial effluents and geo-chemical reactions. Traces of fluoride in minute amounts is an essential component for bones and for the formation of dental enamel in animals and human but its high concentration more than 1.5 mg/l causes irreversible de-mineralization of bones and tooth tissues i.e. skeletal and dental fluorosis, damage to the brain, harmful effects on kidney and liver, headache, skin rashes, bone cancer and even death in extreme cases. Various treatment technologies for removing fluoride from groundwater has been promoted. However, Adsorption process for de-fluoridation has been favored as it is techno-economical viable method, environmental friendly and straight forwardness in its operation.

Any technology to be promoted should be a user friendly one with locally available materials. Therefore it is required to observe de-fluoridation by cheap and easily available material and methodologies.

A few natural absorbent like coconut husk, Moringa olifera seeds, Neem stem charcoal, Rice Husk etc which are cheap and effective and gives perfect removal of fluoride in drinking water at a very local community/ individual level. Optimal dose of adsorbent can be determined on field based on the amount of fluoride content and testing through various trials. Also, there is no issue of sludge generation in adsorption processes. There are several documents and time tested reports are available in India towards the above eco-friendly practices in de-fluoridation.

Thanks,

Murali.K.

Dear Dr. Amadi Akobundu Nwanosike,   

Brief review on the defluoridation of groundwater:

Various techniques and materials were explored throughout the world for defluoridation of groundwater.

The techniques can broadly be classified into four categories:

Adsorption, Ion-exchange, Precipitation and Other techniques, which include electrochemical defluoridation and reverse osmosis.

Materials used as defluoridation agents in these four techniques are:

Adsorption: Carbon materials, Activated Alumina, Magnesia, Tricalcium phosphate, Calcite, Hydroxy apatite, Wood, Lignite, Activated char coal, Fish bone char, Processed bone, Nut shells, Avaram bark, Paddy husk, Coffee husk, Tea waste, Jute waste, Coir pitch, Fly ash, Bauxite, Serpentine etc.

Ion-exchange : a) Anion exchange resins-  NCL poly anion resin, Tulsion A27, Lewatit-MIH-59, Amberlite IRA-400, Deacedodite FF-IP, Waso resin-14, Polystyrene. b) Cation exchange resins: Defluoron-1, Defluoron-2, Carbion.

Precipitation: Lime, Alum, Lime & Alum (Nalgonda technique), Alum flock blanket method, Poly Aluminium Chloride (PAC), Poly Aluminium Hydroxy Sulphate (PAHS), and Brushite.

Others:  Electrochemical method (Aluminium electrode), Electro dialysis, Electrolysis, Reverse Osmosis.

The basic characteristics of an ideal defluoridation process are the following:

Defluoridation can be introduced at two organizational levels; as household defluoridation for consumption of single household members, and as community defluoridation  for the public use in a village.

The domestic defluoridation processes available today are not totally successful. Nalgonda and  Krass processes for defluoridation have some merits.

I like to inform  that recently we have developed a new process for defluoridation of water based on adsorption technique. The process  entitled "A spinel alkaline earth metal ferrite impregnated activated alumina adsorbent and a process thereof" has been filed for grant of patent.  

The development of the process is not yet published. However, you can get a brief idea from the given link.

Based on the invented process, we have developed a domestic filter unit (for defluoridation of water).The unit is comprised of novel adsorbent which shows improved defluoridation capacity than the traditional activated alumina. In addition to fluoride, the filter removes particulate materials as well as arrests the microbial growth. The filter is developed for the use of people of fluoride affected rural areas, where groundwater is the primary source for drinking. The cost of the unit is suitable for rural people. The product has already been deployed for field trial. We hope that this unit will solve the potable water crisis in fluoride affected regions. The product leaflet along with working principle is attached for your information.

To make a defluoridation process environment friendly, you have to go for proper disposal of fluoride rich sludge. We are also working in this area.

Please give your feedback. Regards

Patent 'Spinel magnesium ferrite impregnated activated alumina adso...

Dear Dr. Nwanosike

Bone char is a good option, there are several studies of groundwater fluorine removal using this material:

Article Adsorption of Fluoride from Water Solution on Bone Char

Article Bone char as a green sorbent for removing health threatening...

Article Bone char with antibacterial properties for fluoride removal...

Best Regards.

Thank you very much for your detailed explanation. I sincerely appreciate, it has been wonderful. My warm regards to all.

Karthikeyan B and Elango L (2011) identified environmentally friendly way of extracting fluoride from groundwater contaminated with fluoride as follows:

(1) Dilution of groundwater contaminated with fluoride employing artificial recharging structures which can be build in suitable places that will decrease its concentration.

(2) Rain water harvestimg through through existing Wells also will prove effective to reduce the groundwater fluoride concentration.

(3) Exsitu method which are conventional treatment method like adsorption, ion exchange, reverse osmosis, electrodialysis, coagulation and precipitation etc can be practiced at community level or at household s to reduce fluoride concentration before Ingestion.

Thank you and Kind Regards

Dr Gabriel Ike Obiefuna