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Long-Term Effects of Orthophosphate Treatment on Copper Concentration
Citation:
SCHOCK, M. R. AND A. M. Sandvig. Long-Term Effects of Orthophosphate Treatment on Copper Concentration. JOURNAL OF THE AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 101(7):71-82, (2009).
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Description:
Laboratory, pilot, and field data collected support the theoretical “cupric hydroxide” copper solubility model. For the short time frames inherent in laboratory and pilot studies of copper solubility, and in initial field monitoring for the LCR from Tier 1 soldered copper sites, cupric hydroxide or a very microcrystalline tenorite appears to be the dominant solid phase, whereas over time, the pipe will “age” and tenorite or malachite will form and predominate as the surface phase. Orthophosphate treatment will initially lower copper levels, when applied in the proper pH range. Unlike systems optimizing pH and DIC adjustment for corrosion control, the orthophosphate-treated systems tend to yield temporally stable copper levels, rather than displaying this “aging” phenomenon. Given enough time (years to decades), in similar systems without orthophosphate, the copper levels will probably eventually drop below what would be achieved with orthophosphate. Systems employing orthophosphate may see rapid copper level reductions initially, but the stabilization long-term could be difficult to overcome if there are later issues with limits on phosphate or copper levels in wastewater that require more stringent control of copper release. Compliance monitoring required for the LCR is biased towards sites that may exhibit elevated lead levels rather than elevated copper levels. Current LCR targeting will likely show that Cu levels will continue to decline at the older houses or developments with lead service lines or lead solder, so the discrepancy between copper levels measured for LCR monitoring and copper levels in locations with the potential for highest exposure to copper (newer housing and developments) will increase over time.
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