Like Activated Alumina cartridges Bone Char has also been widely promoted by smaller water filter resellers as being effective for fluoride removal.
What is Bone Char?
Like the name implies, Bone Char is actually the remains of animal bones that have been crushed, exposed to high furnace temperatures and carbonised.
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 that can be readily replaced by fluoride ions). Adsorption and ion exchange are the mechanism for fluoride reduction.
Is it effective?
The effectiveness of Bone Char is similar that of Activated Alumina. It requires a low pH (again, below 6.5 is recommended), low flow rates and frequent replacement of cartridges.
While new Bone Char cartridges are claimed to reduce fluoride by up to 90%, in controlled laboratory tests we found that after only 50 litres (10 gallons) fluoride removal dropped from 80% to 50%. And, after just 100 litres fluoride removal was only 25%.
This means in order to remove fluoride at anywhere near an effective rate a Bone Char cartridge would need to be replaced at least every week. This is neither practical or cost effective.
In published advice from the independent Water Quality Association examining Bone Char and Activated Alumina they made the following comment:
"Because of the diverse influent water chemistries and product designs, water analysis tests to confirm effective treatment by any of the POE (Point of Entry/Whole Home) units for fluoride removal is recommended. Only POU (Point of Use) units tested and certified for fluoride reduction are recommended to be used for such purposes."
WQA - Technical Advice Bulletin
In other words, as early as 2004 WQA recognised that fluoride removal claims made for Bone Char require confirmation by scientific testing and certification. We also note that as of 2012 there were no Bone Char filter cartridges registered or certified with either WQA or NSF.
Whole Home Fluoride Removal
In order to be effective at removing fluoride from the entire home water supply Bone Char media requires a pH below 6.5 (the lower the better) and a contact time of around 20 minutes. This would require the installation of a filtraton system, allowing for a flow rate of at least 20 litres per minute (most whole of home systems offer 60 litres per miniute), of approximately 200 liters worth of Bone Char media. With associated equipment the installation footprint would be the size of a small car.
Again, like the claims made for Activated Alumina, whole of home fluoride removal claims using Bone Char are equally misleading.
Bone Char is ideal for fluoride removal in third world situations where fluoride presents a serious health risk at greater than 5ppm. In these situations contact time can be well in excess of 60 minutes and the volume of media used is not limited by cartridge size.
In domestic Point of Use filter systems for drinking water Bone Char achieves less than 50% removal rates, often far less, and requires cartridge replacement every 100 litres. Bone Char is simply not a suitable technology for fluoride removal for use on municipal water sources.