The usage of calcium phosphate systems for onsite defluoridation treatment

Abstract

Over 200 million people in over 35 countries are affected by excessive fluoride in their waters. For people that do not have access to a centralized water treatment plant, there is a need for an on-site defluoridation system that requires no special operational expertise, does not use hazardous chemicals, and is sustainable by the local population. 8 different calcium phosphate precipitation systems were analyzed and tested for fluoride removal effectiveness. An effective system would have final fluoride concentrations less than 1.5 mg/L and final solutions with pH within drinkable limits. Phosphoric acid with the addition of a calcium carbonate source was found to have a 99.8% fluoride removal rate. Monosodium phosphate with addition of slaked lime was also found to be effective with a 99.98% fluoride removal rate. An optimal slaked lime to monosodium phosphate ratio that achieved effective fluoride removal and neutral pH was found. With 0.45 g of Ca(OH)₂ and 1 g of NaH₂PO₄, initial fluoride concentrations up to 100 mg/L or more could be reduced to near zero concentrations, and a volume of approximately 337 mL of water with a concentration of 5 mg/L F^- could to be reduced to less than 1.5 mg/L F^-.

Keywords:

• Water treatment
• calcium hydroxide
• monosodium phosphate
• fluorosis
• precipitation
• drinking water
• public health

Acknowledgements

We thank the University of California Los Angeles and Biola University for the support of this fluoride research. We thank Dr. Shailey Mahendra and Dr. Sim Lin Lau for technical assistance and training.