Investigation of Copper Contamination and Corrosion Scale Mineralogy in Aging Drink Water Distributions Systems

摘要

Research has shown higher levels of copper appear in drinking water conveyed through relatively new copper piping systems; older piping systems typically deliver lower copper levels in their drinking water. This research contributes field data from a real drinking water distribution system, providing a better understanding of this phenomenon, as it relates to treatment considerations and compliance with the Lead and Copper Rule. Copper pipes and copper levels were sampled from drinking water taps of 16 buildings with pipes ranging in age from less than 1 to 48 years. Water samples from each building were collected before and following a 16-hour stagnation period. A piece of domestic cold water pipe was cut from each building and analyzed to determine the mineralogy of the copper scale present using x-ray diffraction (XRD) and x- ray photoelectron spectroscopy (XPS) technologies. Results were compared to the predictions of the 'cupric hydroxide model,' developed by the Environmental Protection Agency. The samples showed remarkable variation in scale appearance and mineralogy, demonstrating the diversity of pipe scales present within a single distribution system. A mix of highly soluble and relatively insoluble copper phases were identified in the real world scale. Both stable scales, such as malachite, and relatively instable solids, such as cupric hydroxide appear in pipes irrespective of age. In many samples cupric hydroxide and cuprite appeared on the surface of the scale while malachite was in the bulk. Copper cyanide was also identified in two pipe scales. XPS and XRD are shown to be complimentary techniques for characterizing complex scales made up of a mixture of amorphous and crystalline solids.