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Investigation of Lead Solubility and Orthophosphate Addition in High pH Low DIC Water

Miller, Stephanie A.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821208

Abstract Details

2014, MS, University of Cincinnati, Engineering and Applied Science: Environmental Science.
Lead (Pb) is a highly toxic metal that has long be recognized as a threat to human health. Drinking water is a major contributor of Pb exposure due to Pb plumbing present in drinking water distribution systems, specifically Pb service lines, solders, and brass fixtures. Drinking water utilities are required to employ corrosion control treatment if routine sampling reveals 90th percentile results greater than 15 µg/L of Pb. Addition of the chemical orthophosphate (o-PO4) is a common treatment technique, which is intended to form insoluble Pb-phosphate solids on the pipe wall. Optimum effectiveness of o-PO4 occurs around pH 7.4 – 7.8, but it is unclear if dosing could provide some benefit to utilities operating at higher pH. This study used a recirculating tank and pipe loop experimental design to examine lead solubility behavior under a variety of conditions. The first objective was to examine Pb-carbonate solubility from pH 9.0 – 10.5 to determine the controlling mineral phase in this pH range. The second objective was to determine whether o-PO4 dosing resulted in a reduction of Pb levels in the water at pH 9.0, and to identify the optimum dose for Pb solubility reduction. Thermodynamic modeling was used to interpret the data using solubility curves and saturation indices with respect to the controlling solids for each system. The corrosion products present on the interior of the pipe walls were examined with X-ray diffraction at the end of the run to determine which mineral phases were present. Hydrocerussite was revealed to be the dominant solid for the carbonate passivated pipes from pH 9.0 – 10.5. Pb levels in these tanks correlated well with solubility curves generated for hydrocerussite, and saturation index calculations were close to zero, confirming that the system was approaching equilibrium with this solid. Analysis of the corrosion scales using XRD confirmed the presence of this solid. Results of the investigation of o-PO4 addition at pH 9.0 indicated that there was a measurable benefit to o-PO4 dosing, and that the optimum reduction occurred at 1.0 mg PO4/L. Soluble Pb increased as PO4 dose was increased beyond 1.0 mg PO4/L, contradicting the linearly inverse relationship between PO4 dose and Pb solubility that is observed at lower pH. Further investigation of this phenomenon is needed to confirm the observed trend and identify at what dose and pH the traditionally observed relationship begins to break down.
Dionysios Dionysiou, Ph.D. (Committee Chair)
Michael R. Schock, M.S. (Committee Member)
George Sorial, Ph.D. (Committee Member)
74 p.
Environmental Science
drinking water; corrosion control; orthophosphate; lead; high pH; low alkalinity

Recommended Citations

Citations

  • Miller, S. A. (2014). Investigation of Lead Solubility and Orthophosphate Addition in High pH Low DIC Water [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821208

    APA Style (7th edition)

  • Miller, Stephanie. Investigation of Lead Solubility and Orthophosphate Addition in High pH Low DIC Water. 2014. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821208.

    MLA Style (8th edition)

  • Miller, Stephanie. "Investigation of Lead Solubility and Orthophosphate Addition in High pH Low DIC Water." Master's thesis, University of Cincinnati, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406821208

    Chicago Manual of Style (17th edition)

ucin1406821208
1,035
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This open access ETD is published by University of Cincinnati and OhioLINK.