The World needs Fluoride and that’s why it is here as one of the most prevalent 15 minerals. In nature it exists primarily as hard, slowly dissolving calcium fluoride (CaF2). As low pH rain water passes through the ground causing it to dissolve the water hardness and fluoride concentration both increase in ground water (well water). Likewise, rain runoff across exposed calcium fluoride adds hardness and fluoride to surface water (rivers, lakes, streams). In most of the world the net amount in water of naturally occurring fluoride is in the 0.3 mg/l range. The notable exceptions are parts of Russia and India where because of the high concentrations of calcium fluoride, water contains beyond 10 mg/l.
In the lower concentrations, fluoride in soil and water is classified as a micro-nutrient that contributes to plant growth and, in humans, healthier, cavity-free teeth and stronger bones. As WWII ramped up, it is rumored that dentists could accurately predict draftees from certain cities because of excellent teeth— one being Green Bay, WI. Fluoride from plants and water gravitates toward calcium in humans thus its ultimate effect on teeth and bones.
If fluoride concentrations are too high, plants and humans accumulate it. Humans absorb 80% of fluoride ingested and 50% of that migrates to teeth and bones with the balance eliminated through urine. Plants simply store it and tea leaves probably store more than any other edible plants.
Most fluoride is used in industrial processes and waste from the processes is converted to Hexaflurosilicic acid (F6H2Si) that dissociates in water to 6F– + SiO2 + 4H+. This acid is the primary additive used by municipalities along with sodium fluorosilicate or sodium fluoride to increase drinking water natural fluoride to approximately 1 mg/l based on the dental profession’s recommendations for healthy teeth. This added fluoride is welcomed by many and passionately opposed by others. The opposing group spends huge amounts to have the fluoride removed from their water. The current options for reduction are:
BONE CHAR.
This method is currently the most popular. Forget “removal” that is not going to happen “reduction” to some extent will. In addition to the issue of the level of reduction are capacity (how many gallons will it treat) and effective flow rate. As its name implies, bone char is nothing more than ground cattle bones heated to 900o F in a low/no oxygen atmosphere within a rotating kiln. The resulting product is a fine, black particle consisting of approximately 70% hydroxyapatite [Ca10(PO4)6(OH)2] and the balance somewhat activated carbon (C). The reduction of fluoride is a combination of adsorption of fluoride by the hydroxyapatite, adsorption by the activated carbon and partial ion exchange with available OH ions.
Each cubic foot weighs 40 pounds and has the following characteristics –
- Literature is scant on this. We began using material from an east coast suppler in 2006. Their stated capacity was 0.005 pounds of fluoride removal per pound of bone char. This converts to 23,950 gallons per cubic foot based on 1 mg/l challenge. 100 days for a family of 4. We participated in a WQA test of the same material in 2009 and results were 11,900 gallons. 50 days for a family of 4. A recent in-house test on a sample from a national sample had a yield of 1517 gallons or about 2 weeks for a family of 4.
- Percent Removal. On average, fluoride removal was 67% thus leaving 33% or 1/3 of the fluoride in the water.
- Flow rate. The reactions taking place between the media and the fluoride take a long take a long time. To obtain even the modest results requires a flow rate of approximately 1.5 GPM per cubic foot of media. Higher flow rates cause the percentage of fluoride left in the treated water to increase significantly.
- Water Chemistry. Chlorine in the water to a bone char system will occupy some of the available sites which reduces capacity as will chloride. Effectiveness favors a pH in the 6-7 range and unfortunately cities are elevating their water pH to the 8+ level to prevent corrosion in their distribution system.
Recommendation for Bone Char Systems: AVOID.
ACTIVATED ALUMINA
The use of this material predates bone char for fluoride. It is a factory processed form of Aluminum Oxide (Al2O3) and normally appears as small white/light tan spheres 16-30 US mesh in size. For unexplained reasons, the USEPA classifies Activated Alumina as Best Available Technology (BAT) for fluoride and arsenic from water.
The material as originally processed contains sodium oxide (Na2O) which converts to sodium hydroxide (NaOH) when first wetted. The resulting high pH reduces the capacity for Fluoride to nearly zero. Treatment of the material with hydrochloric (HCl) or sulfuric (H2SO4) acid before use is imperative. Some, but not all, providers of activated alumina offer material that has been acid washed for immediate use—beware.
Effective system flow is 2 GPM/cu. ft. of media in tanks(s) and removal of fluoride is approximately 65% at this flow rate. Capacity for fluoride is estimated at 1.5% or 6 lbs. fluoride per 40 pounds (1 cu.ft. ) of activated alumina. This is roughly 25x the capacity of bone char. However, properly prepared activated alumina can cost 20x that of bone char.
Water chemistry. Here is where the efficacy of activated alumina falls apart. The capacity for fluoride drops precipitously by 50% or more when feed water pH is 8.2 and bicarbonate alkalinity (essentially hardness) exceeds 50 PPM (3 grains). This eliminates effectiveness on 85% of municipal water supplies.
Recommendation for Activated Alumina Systems: AVOID.
ION EXCHANGE
As a weakly charged anion (negatively charged ion), fluoride can be reduced by approximately 50% by employing a system similar to a water softener where the softening resin has been replaced with typically a Type 2 strong base anion resin. Such systems are regenerated with sodium chloride (NaCl) and usually have a capacity of 12,000 grains for ALL anions in the water exclusive of silica and carbon dioxide when 5 pounds of salt per cubic ft. of resin. The removal of all anions is concerning. First, this could lead to a corrosive water as carbonate, bicarbonate and hydroxyl ions are removed. Second, there is always a chance of taste and odor issues when anion resins are used and in addition a very briny water could be created. Third and of primary importance, these resins are not fluoride selective and thus if not regenerated accurately and timely, they can dump extremely high, toxic levels of fluoride into the facility water stream.
A search for a fluoride selective resin yielded one manufacturer located in India. Overall capacity information contained numerous chemistry and flow rate caveats. The main problem is Aluminum Chloride is required for regeneration and its cost and availability is unknown.
Recommendation for Ion Exchange Systems: USE EXTREME CAUTION
REVERSE OSMOSIS
A properly designed under counter system will produce approximately 1 gallon of treated water every half hour at a water use efficiency of 50% when operated at 65 PSI. Reduction of fluoride is 90-97% which means the remaining fluoride will be below detection levels or essentially zero on water tests. A basic battery operated total dissolved solids (TDS) meter should be included to monitor the effectiveness of the membrane. The system should also have a PERMEATE PUMP to eliminate TDS Creep which is an operational phenomenon of small RO systems that lowers water quality (increases fluoride in treated water).
Recommendation for Under Counter RO systems: Least expensive/most effective
Although there is no reliable (Government agency, university study, etc.) study indicating fluoride uptake by humans other than by oral ingestion, there are those who wish to have it removed from their entire home. A reverse osmosis system designed and constructed to treat all water within a home will reduce fluoride as well as or better than an under counter system.
Recommendation for Whole House R.O. systems: Expensive but highly effective
