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The effect of zinc orthophosphate and pH/alkalinity adjustment on copper and lead levels in drinking water

University of British Columbia

A twelve month pilot plant study was conducted to evaluate the relative ability of various corrosion control treatments to reduce metal leaching from typical household plumbing materials. A pipe loop system with seven loops, each consisting of lead/tin soldered copper piping, coils of lead/tin solder material and brass faucets, was used to test six treatment options and a control. pH and alkalinity were adjusted by the addition of lime (Ca(OH)2) and sodium bicarbonate (NaHC03) respectively, and two different doses of zinc orthophosphate were tested. Treated water samples, that had been left standing in the pipe loop system for a predetermined time period of eight or sixteen hours, were drawn at regular intervals and measured for lead, copper, and zinc. The results led to the following conclusions. There were some small reductions of lead and copper in the pH/alkalinity loops; however, overall, when compared to the control loop, pH/alkalinity treatment appeared to exacerbate metal leaching in standing samples. Metal levels in the treated loops were very unstable, with some spikes of very high concentrations. It is thought that these high spikes were a result of, not just leached metals, but sloughing off the scale that forms during flowing conditions. The instability of the scale may be related to the high variability of the pH that occurred in the treated loops. The control loop which had relatively stable metal concentrations and no episodes of extremely high metal spiking, maintained a relatively stable pH. The zinc orthophosphate showed good results and was consistently effective at reducing lead and copper levels to below that of the control. The two different standing times showed little difference in the levels of metals that were leached into the water from the pH/alkalinity loops and the lower dose zinc orthophosphate loop. The exception to this, however, was the higher dose zinc orthophosphate loop, which had higher copper and zinc levels at the longer standing time.

Thesis/Dissertation

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2009-03-21

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http://hdl.handle.net/2429/6340

Civil Engineering

University of British Columbia

UBCV

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