A calcium phosphate solid formed as an unintended consequence of a novel high-pH orthophosphate lead corrosion control strategy in Providence, RI, causing some consumer complaints and clogged plumbing. The calcium phosphate initially precipitated at orthophosphate doses above about 2 mg/L as PO4 during field testing, and the extent of precipitation increased with water age and higher temperature. Lab scale tests confirmed that doses above about 2 mg/L were required to form the precipitate in the absence of pre-existing calcium phosphate solids, and that the solid formed quickly at 60 °C (upper range for hot water heaters) and tended to dissolve at lower pH. Solubility modeling and other techniques suggest the solids are a mixture of compounds. For water systems currently practicing a high pH/low alkalinity corrosion control strategy, orthophosphate dosing can enhance plumbosolvency control without risky pH reduction, but calcium hardness puts a constraint on the maximum orthophosphate level that can be applied and tolerated.

This dataset is associated with the following publication: Devine, C., K. Mello, M. Desantis, M. Schock, J. Tully, and M. Edwards. Calcium Phosphate Precipitation as an Unintended Consequence of Phosphate Dosing to High-pH Water. ENVIRONMENTAL ENGINEERING SCIENCE. Mary Ann Liebert, Inc., Larchmont, NY, USA, 41(5): 171-215, (2024).