Lead Release from Corrosion Scales on Lead Service Lines: Impact of Phosphate and Scale Composition
Date of Award
Doctor of Philosophy (PhD)
Lead release from corrosion scales formed on lead service lines (LSLs) poses a significant danger to human health. One of my main goals was to understand the ability of phosphate to limit lead release from scales on lead pipe surfaces. First, I investigated how phosphate addition can prevent lead release from scales rich in PbO2(s) when the disinfectant is switched from free chlorine to monochloramine. I discovered that adding phosphate to the lead pipe system in advance of and during the switch can limit release of both aqueous-phase lead species and lead-containing particles to the water. For a different scenario of phosphate addition, I studied the impact of phosphate for mitigating lead release from LSLs in high-pH tap water by interacting pipes from Providence, RI, with an artificial water similar to that in Providence. Here, long-term continuous phosphate addition mitigated both particulate and dissolved lead. In both pipe systems, calcium-lead-phosphorus (Ca-Pb-P) scales were formed on the surfaces of the lead pipes. The Ca-Pb-P scales that formed on the pipe surface probably promoted low lead levels by controlling the lead solubility, and for the Providence pipes, they may also have acted as a physical barrier to lead release. My dissertation also presents two investigations that addressed questions that came up in the course of the longer-term pipe reactor experiments. One of these investigations was regarding how the rates of lead release were affected by the types of lead corrosion scales under different hydraulic regimes (stagnation time and flow rates). Depending on the scale types and hydraulic conditions, the lead release rate was affected by either mass transfer or by the chemical kinetics of the dissolution of the lead-containing solids in the scale. The other investigation was of a thick coating of iron oxide scale that was found on a surface of a harvested lead pipe from Providence, RI. I evaluated how the chemical and microstructural character of this iron oxide scale affected lead release from the pipe surface to the water.
Daniel E. Giammar
Jeffrey G. Catalano, John Fortner, Young-Shin Jun, Jill D. Pasteris,
Available for download on Friday, August 29, 2121
Permanent URL: https://doi.org/10.7936/4eaq-fm34