AWWA WQTC69288

Lead can be released to drinking water from corrosion and dissolution of lead-containingpipes, fittings and solders in existing old drinking water service lines.Resulting high lead concentrations can cause adverse health effects. Pb(II) solids andPb(IV) oxides, discovered as the corrosion products covering the walls of lead pipes, arethe major contributors to lead release. Among them, Pb(II) solids are presumed to havehigher solubility relative to Pb(IV) oxides. Thus, switching the residual disinfectionmethod from chlorine to chloramines can lower the oxidation-reduction potential (ORP),thereby enabling the breakdown of Pb(IV) oxides and consequently higher leadconcentration. However, there is limited data on the equilibrium solubility or dissolutionand transformation rates of Pb(IV) oxides. Also, substantial research on the waterchemistry conditions in which Pb(IV) oxides form and stabilize over time is needed for ascientific strategy of controlling lead concentration in drinking water distribution systems.In this research, the equilibrium solubility, dissolution and transformation rates of purePb(IV) oxides are investigated as a function of pH, dissolved inorganic carbon (DIC),orthophosphate, and the presence of chloramines. New lead pipes are conditioned usingchlorine to form Pb(IV) oxides, and release rates of lead from them are investigatedunder varied water chemistry, stagnation time and flow velocity. The lead corrosionproducts and possible transformation of them are characterized with respect tomineralogy, size, morphology, surface area, and molecular structure. Water chemistryconditions, including pH, ORP in terms of chlorine concentration, lead concentration andDIC, in which a-PbO2 and ß-PbO₂ form and stabilize over time are also studied. Includes 11 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

11

File Size:

1 file , 880 KB