Hi Hannah Simcoe-Read,  I ...

Hi Hannah Simcoe-Read, 

I did my MSc Thesis (1990) on " low cost ​safe solution ​to  remove ​Fluoride from ​pumped ​groundwater ​ for rural ​communities" in Tanzania. 

There are two low-cost appropriate technologies, with

1) household treatment using "bone char"  and

2) Nalgonda village level treatment  (lime and aluminium sulphate precipitation of fluoride).

Both methods only treat water for consumption (drinking, cooking).

Bone char household filter is made with animal bones charred above 400 C to remove organics but retain the apatite crystal structure, where when applied in a filter unit the fluoride ion will substitute H+, and fluoride free water comes out of filter). The amount of bone char in the filter can be adjusted to a lifespan of 1 year, 20 L per day. The amount needed depends on initial fluoride concentration in raw water. At some stage the the fluoride front will break through the column (long pipe used for filter) and fluoride concentration in output water start to increase until the filter material is exhausted.  The charring of the bones is best done in a closed container with limited air, over long time. Then the bones are crushed to granules of 1-4 mm before put in filter. The colour of the crushed bone granules must be light grey, as darker colour indicates residual organic material (giving colour and taste to the treated water), but not white as this colour indicates a too high temperature destroying the apatite crystal structure thus eliminating the fluoride removal capacity. 

The challenge for promoting bone char household filters in rural areas is not really technical, but socio-health related. The expecting mother needs to drink treated water to prevent the permanent teeth in the fetus to be damaged. The children need to drink treated water to reduce/eliminate development of skeletal fluorosis. Due to the long time from exposure to visible effects it is difficult to convince families to invest in the filter, annual replacement of bone char and daily operation. 

The Nalgonda technique is developed in India, with lime and aluminum sulphate (Alum) using batch treatment in large tank, using paddles for stirring the water. An improved design (my design) will use the pressured water to stir the water volume, for mixing chemicals, flocculation / coagulation. Hence no need for electricity or manpower for stirring. The intensity for stirring will reduce while the tank fills up. The stirring is partly done by the water jet (horizontal rotation), partly done by air sucked into the water jet (vertical rotation). A lime water solution (CaCo2) with PH 11 is added for PH adjustment initially of raw water, while the Alum water solution with PH 4 is removing fluoride (and other stuff), while adjusting the out put water to PH 6.5 or 7. The optimal PH for coagulation is 6.5. Due to the extreme high and low PH in the dissolved concentrated chemicals this process should not be done at household level, but can be done by e.g. a women group trained in daily operation and handling of chemicals. The filter constructed outside Arusha would deliver about 1500 L treated water and 100 L sludge per day. The filter is operated in the afternoon, when empty, first cleaned for sludge then filled with raw water and chemicals and left overnight to settle. Next morning treated water can be tapped from the tank via a tap situated just above the sludge level. On a weekly basis the women group weights out portions of chemicals using a basic scale, for the proper amounts of chemicals to be applied every day by the daily operator (women taking turns during the week). - It is important to monitor the PH in the treated water on a monthly basis, as the Lime lose PH adjusting capacity during storage, and Lime dosage needs to be increased over time.  Provided there is access to the chemicals this process is very VLOM and low-cost. The raw water was about 9-10 mg/L treated down to about 2 mg/L. There is a maximum dosage of Alum, actually the sulphate, that should noticed, as excess will act as a laxative.  

The treated water has a production cost, so it is essential that there is established some kind of sustainable user-payment to secure funds for buying chemicals in bulk, transport of chemicals, maintenance of tank, balance, small containers for daily chemical dosage. 

For low-cost fluoride removal using bone char in Tanzania google: 

Ngurdoto Defluorination Research Station,  Godfrey Mkongo

Regards,

Erik Thorbjoern Noerremark