Comparison of film formation using phosphate inhibitors in systems with comparable water qualities

Scott M. Vesecky, Jingyue Liu, Robert Mark Friedman, Frank Pacholec, John B. Lechner

Research output: Contribution to journalReview article

2 Scopus citations

Abstract

Significant research efforts have been directed towards studying inhibitors for Pb and Cu corrosion in potable water supplies. The EPA's "Lead and Copper Rule," which sets a regulatory action level for Pb and Cu at concentrations of 15 ppb and 1.3 ppm, respectively, has prompted much of this effort. Many different approaches are being used effectively to control corrosion in drinking water systems, e.g., the addition of certain natural high molecular weight substances, or pH adjustment by the addition of lime. However, only phosphate and silicate based chemical inhibitors are currently acceptable for low dosage metering as chemical additives to retard electro-chemical corrosion and metal corrosion by-product release in potable water supply lines. The focus of this study is to compare the efficacy of various phosphate inhibitors on forming films on Pb and Cu test coupons. Low voltage field emission scanning electron microscopy (FESEM) was used to image topographical features on films formed on Pb and Cu coupons after two months of exposure to various treated water supplies. Test coupons from three New England water supplies (A, B and C) with similar hardness, pH and alkalinity values were compared. The three New England utilities treated their water as follows: New England A - phosphoric acid, New England B-zinc orthophosphate, and New England C - 65/35 blend of polyphosphate/orthophosphate. In addition, data are also presented for Pb and Cu coupons exposed for two months at a Florida water utility. Although the water at the Florida site has much higher hardness and alkalinity values than the New England water supplies, the treatment, 60/40 polyphosphate/orthophosphate, was very similar to that used for New England C. In addition to topographical imaging with FESEM, detailed studies were performed using electron spectroscopy for chemical analysis (ESCA) to determine the elemental composition of the surface films. ESCA was also combined with sputter etching to determine the relative film thicknesses as well to provide a profile of the atomic concentrations at various depths into the films.

Original languageEnglish (US)
Pages (from-to)258-267
Number of pages10
JournalJournal of the New England Water Works Association
Volume111
Issue number3
StatePublished - Sep 1 1997
Externally publishedYes

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology

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