Effects of Water Quality Changes on the Corrosion of Iron, Accumulation and Release of Inorganic Contaminants in Drinking Water Distribution Systems

Abstract

Corrosion and accumulation/release of trace inorganic contaminants in corrosion scales and sediments found in drinking water distribution systems (DWDSs) has gained considerable attention over the past several years. Many trace inorganic contaminants (e.g., lead, arsenic, nickel, vanadium and uranium) can accumulate on the surface of or be occluded within corrosion scales formed in DWDSs. However, little data are available on the actual concentrations of these contaminants beyond system entry-points. The accumulation of trace inorganic contaminants in DWDS solids can have consequences for the health of exposed populations if these contaminants are released from the scales thus resulting in their high levels at consumers' tap. This research ascertained the occurrence of inorganic contaminants in real drinking water systems. Corrosion scales and deposits from twenty drinking water utilities in the United States were characterized to determine the elemental, structural composition and the levels of inorganic contaminants in them. The modes of binding and mobility of these elements in the solids were also studied via sequential extractions. Effects of varying water quality conditions, including blending of desalinated water with surface water, NOM, and varying levels of anions (chloride and sulfate) on corrosion and accumulation/release of trace inorganic contaminants were thoroughly examined. Among the trace inorganic contaminants found in the scales, barium had the highest concentrations, followed by, in the decreasing order, lead, nickel, vanadium, arsenic, chromium, uranium, cadmium, antimony, selenium, and thallium. Speciation via sequential extractions demonstrated that arsenic, chromium and vanadium are the most stable elements, while nickel and manganese are much more mobile than all the other inorganic contaminants examined in this study. NOM had a more pronounced effect on corrosion, metal release and retention of inorganic contaminants than the blending ratio or anions.