Chemical characterization of deposits associated with microbiologically influenced copper corrosion in potable water systems

Abstract

The internal surfaces of copper tubes, removed from potable water distribution systems in Australia and New Zealand, which experienced episodes of copper by-product release or "blue water," were evaluated by x-ray photoelectron spectroscopy (XPS) and dynamic secondary ion spectrometry (SIMS). Visual and microscopic inspection of the internal tube surface revealed a mosaic of deposits. Three distinct deposits were identified on the surface of tube recovered from a Grahamtown system in the Hunter Valley (HV) of Australia, whereas two distinct deposits were detected on the surface of tube retrieved from the Defense Scientific Establishment (DSE) facility in Auckland, NZ. XPSanalysis revealed the presence of organic nitrogen, with a C/N similar to living biomass, concentrated on the yellow green-surface deposit and the deposit-free area of tube from the HVsystem. In contrast, deposits and deposit-free areas on the tube from the DSE system contained no significant quantities of organic nitrogen. A secondary ion mass spectrometer (SIMS) depth profile of a corrosion deposit on the surface of tube from the HV system revealed a multi-layer structure, consisting of an organic carbon-enriched Cu(OH)2, Cu(OH)2CuCO3 layer on top of an organic carbon-depleted Cu2O layer. The structure and chemistry of the surface deposits on the HV tube were consistent with a mechanistic model involving growth of a copper oxide film under neutral or alkaline conditions modified by the presence and activities of surface-associated microorganisms. An alternative mechanism may be responsible for the copper by-product release from the tube in the DSE system, since significant quantities of organic nitrogen were not detected in deposits on tubes from this source. Based on the surface chemical data presented here, it is difficult to determine whether similar mechanisms were responsible for the copper by-product release associated with copper tube from these two different distribution systems. The results do suggests that previous models of copper surface film structure may not describe the range of reactions required to adequately explain copper by-product release under certain conditions.