Browsing by Author "Pizarro, Gonzalo E."

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    Distributed simulation with cellular automata using the multispin coding technique
    (ASCE-AMER SOC CIVIL ENGINEERS, 2008) Sepulveda, Marcos; Moreno, Rolando; Pizarro, Gonzalo E.
    Cellular automata (CA) are discrete dynamical mathematical systems that have been used for modeling many physical and engineering systems. Usually they are used as an alternative to more complex models based on partial differential equations. CA models can be implemented efficiently in parallel hardware due to the properties of locality, uniformity, and spatial regularity of the rules that govern their behavior. At the same time, CA simulations make intensive use of memory and processing time. For a widespread use of these models, implementations able to run in short periods of time without requiring specialized hardware are needed. This work presents a generic library able to simulate efficiently CA models, using the multispin coding technique and parallel processing on a network of conventional personal computers. Results of three different models tested show that it is possible to obtain a linear speedup. The observed speedup improves as the domain size increases or the simulated models become more complex, as in the case of a heterogeneous biofilm model used for designing wastewater treatment systems.
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    Empirical model for dissolved oxygen depletion during corrosion of drinking water copper pipes
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) Vargas, Ignacio T.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Predictive models characterizing the evolution and interaction of key parameters of water chemistry are needed to better understand corrosion events in drinking water pipes. We performed experiments with new copper pipes under combinations of pH, dissolved oxygen (DO), temperature, chlorine, and dissolved inorganic carbon. We found that DO consumption during 24 h of stagnation was not limited by diffusion, thus the DO consumption rate in the bulk water could be used to probe the processes occurring at the pipe surface. We propose a quantitative dependency of the DO consumption rate on a rather limited set of physicochemical parameters. (C) 2010 Elsevier Ltd. All rights reserved.
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    Enhanced copper release from pipes by alternating stagnation and flow events
    (AMER CHEMICAL SOC, 2007) Calle, Gustavo R.; Vargas, Ignacio T.; Alsina, Marco A.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Traditional studies of copper release in plumbing systems assume that the water extracted from a pipefollows 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.
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    Increase of the concentration of dissolved copper in drinking water systems due to flow-induced nanoparticle release from surface corrosion by-products
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) Vargas, Ignacio T.; Pavissich, Juan P.; Olivares, Tomas E.; Jeria, Gustavo A.; Cienfuegos, Rodrigo A.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Standard measurements of dissolved copper are made by filtering water samples through 0.45 mu m pore-size membranes. However, the surface of corroding metallic surfaces may be covered by topographic features < 0.2 mu m and structures that can be detached into the bulk water as nano-sized particles. A SEM, EDX, and AFM characterization of a corroding pipe after flow events revealed surface cavities, detached particles and attached particles with sizes between 0.05 and 0.2 mu m. Our findings show that the release of colloidal and nanoparticles of corrosion by-products into the water can result in an increase of the dissolved copper measurements. (C) 2010 Elsevier Ltd. All rights reserved.
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    Influence of solid corrosion by-products on the consumption of dissolved oxygen in copper pipes
    (PERGAMON-ELSEVIER SCIENCE LTD, 2009) Vargas, Ignacio T.; Alsina, Marco A.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Research on corrosion of copper pipes has given little consideration to the influence of solid corrosion by products on the processes occurring at the metal-liquid interface. Consequently, the effect of such solid phases on the rate of dissolved oxygen (DO) consumption remains poorly understood. In-situ experiments were performed in copper pipes under different carbonate concentrations and ageing times. Our results show that the amount of solid corrosion by-products and concentration of hydrogen ions affect the rate of DO consumption during stagnation. Furthermore, our findings support the existing hypothesis that the available concentration of hydrogen ions, rather than DO, is the limiting factor for copper release into drinking water. (C) 2009 Elsevier Ltd. All rights reserved.