Modeling MIC copper release from drinking water pipes.

Copper is used for household drinking water distribution systems given its physical and chemical properties that make it resistant to corrosion. However, there is evidence that, under certain conditions, it can corrode and release unsafe concentrations of copper to the water. Research on drinking water copper pipes has developed conceptual models that include several physical-chemical mechanisms. Nevertheless, there is still a necessity for the development of mathematical models of this phenomenon, which consider the interaction among physical-chemical processes at different spatial scales. We developed a conceptual and a mathematical model that reproduces the main processes in copper release from copper pipes subject to stagnation and flow cycles, and corrosion is associated with biofilm growth on the surface of the pipes. We discuss the influence of the reactive surface and the copper release curves observed. The modeling and experimental observations indicated that after 10h stagnation, the main concentration of copper is located close to the surface of the pipe. This copper is associated with the reactive surface, which acts as a reservoir of labile copper. Thus, for pipes with the presence of biofilm the complexation of copper with the biomass and the hydrodynamics are the main mechanisms for copper release.

Enhanced copper release from pipes by alternating stagnation and flow events.

Traditional studies of copper release in plumbing systems assume that the water extracted from a pipe follows a plug-type flow and that the pipe surface does not interact with the bulk water under flow conditions. We characterized actual stagnation-flushing cycles in a household pipe undergoing corrosion in the presence of a microbial biofilm. The mass of copper released in 10 experiments was on average 8 times the value estimated by using the plug-flow assumption. The experimental copper release pattern was explained by an advection-diffusion model only if a high copper concentration occurs near the pipe surface after stagnation. Microscopic examination of the pipe surface showed a complex assemblage of biotic and abiotic features. X-ray diffraction analyses identified only malachite, while X-ray absorption spectroscopy also revealed cupric hydroxide and cuprite. These results indicate that the surface serves as a storage compartment of labile copper that may be released under flow conditions. Thus, the diffusive transport from the pipe surface to the bulk during stagnation is not the only control of the flux of copper to the tap water when porous reactive microstructures cover the pipe. Our results highlight the need for models that consider the interaction between the hydrodynamics, chemistry, and structure at the solid-water interface to predict the release of corrosion byproducts into drinking water.