Fluoride: A Water Filter Problem That’s Not Going Away!
At AlkaWay we’ve responded to the problem of fluoride filtering of your water in a number of ways, depending upon the AlkaWay system you choose.
Fluoride is a very difficult mineral to remove from water – far harder than chlorine or chloramines or even heavy metals! There are only two recognised ways to remove fluoride; specialised filter media and Reverse Osmosis.
Some filters employ ion exchange, a system of exchanging one ion for another, but often suffer from unexpected ‘dumping’ of accumulated fluoride.
One big reason AlkaWay UltraStream, Jugs and Bottles are so popular is that they all address the problem and greatly reduce the volume of this nasty chemical in your drinking water.
One-sheet summary of Fluoride compiled by the Water Quality Association Download the PDF.
View fluoride documentary (9 parts).
Before getting into choosing a product, let’s quickly familiarise you with each form of fluoride reduction media.
1. Bone Char
Made from cow’s bones turned into charcoal. Bone charcoal contains a carbon structure while supporting a porous hydroxyapatite matrix (a calcium phosphate hydroxide in crystalline form which is rich in surface ions which can be readily replaced by fluoride ion). Adsorption and ion exchange are thought to be the mechanism for fluoride reduction by bone char. Reduction of fluoride using bone charcoal is somewhat pH-dependent, the challenge water should be below 6.5 pH to suppress any ion competition. (Unfortunately, your drinking water in Australia is regulated to be over pH 7.)
Stilbite zeolite (STI), a natural zeolite with high crystallinity and an open pore system, was modified with FeCl3 solution for the removal of fluoride from drinking water. Under ideal conditions, it can reduce fluoride to below 1ppm.
Note that this isn’t all that good given our municipal water fluoride levels are controlled at 1.5ppm.
3. Ion Exchange
There are many, many forms of ion exchange media. Most are created specifically for use in industrial uses. Although fluoride-specific ion exchange resin is very efficient, the problem with its use in a domestic scenario is that once it is ‘full’ of retained fluoride, it can dump all of it into the output water. There is no way to tell when this may happen, meaning your filter may be working perfectly one day, and dump all the accumulated fluoride into your next glass of drinking water.
4. Reverse Osmosis
Point of use reverse osmosis is a good choice if all you want is fluoride reduction. Using a cellulose acetate/cellulose triacetate (CA/CTA) membrane, rejection rates of 80-90 percent are achievable when the pH is in the 4-8.5 range. Note again, that it is pH-dependent, and the optimum range is over 100 times more acidic than your drinking water.
5. Activated Alumina
For large municipal treatment systems, the use of activated alumina is probably the most commonly used fluoride removal technology. Activated alumina requires a two-step, caustic (NaOH) regeneration followed by acid (H2SO4) neutralization, regeneration process. This technology is now being used in exchange tanks for POE (point-of-entry) and disposable filters for POU (point-of-use) applications. For activated alumina to operate most effectively the pH range should be held to 5.5 to 6.5. Activated alumina is generally specific for fluoride and is not affected significantly by the common other competing sulphates, nitrate, or chloride anions in the influent water.