Citation:

Wasserstrom, L., S. Miller, S. Triantafyllidou, M. DeSantis, AND M. Schock. Scale Formation under Blended Phosphate Treatment for a Utility with Lead Pipes. JOURNAL OF THE AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 109(11):E464-E478, (2017). https://doi.org/10.5942/jawwa.2017.109.0121

Impact/Purpose:

Intended to inform states, drinking water utilities and the scientific community on the effectiveness of blended phosphate treatment for lead corrosion control. This is the first publication examining excavated pipes from a blended phosphate system. Blended phosphate is commonly used for lead corrosion control by drinking water utilities across US states, but the mechanism of protection from drinking water lead contamination is not understood. This work fills critical knowledge gaps within the drinking water industry and answers urgent questions posed to EPA researchers by state representatives and drinking water utilities.

Description:

Conventional wisdom hypothesizes that the orthophosphate component of blended phosphate corrosion inhibitors causes the formation of low solubility lead-orthophosphate solids which inhibit lead release into drinking water. This study characterized the composition and morphology of scales formed on the interior surface of a lead (Pb) service line and a galvanized steel pipe from a distribution system using a proprietary blend of ortho- and poly-phosphate for over 20 years. Pipe scales were harvested by layers and analyzed by X-ray diffraction and X-ray fluorescence, while cross sections were analyzed in-situ by scanning electron microscopy and energy dispersive spectroscopy. Analysis of the Pb pipe scales revealed no crystalline Pb-orthophosphate solids. Instead, an amorphous layer rich in aluminum (Al), calcium (Ca), phosphorus (P) and Pb was observed at the pipe scale-water interface, which was porous and not well-adhered to the pipe wall. Thus, the mechanism inhibiting Pb release into the water by blended phosphate is not a thermodynamically predictable passivating low-solubility Pb-orthophosphate scale, but rather an amorphous diffusion barrier which could slough off due to hydraulic disturbance. Galvanized pipe scales showed relatively well-crystallized iron (Fe) and zinc (Zn) compounds, with additional surface deposition of Al, P, Ca and Pb.

URLs/Downloads:

Record Details: