The problem of the optimization of selective treatment systems of wastewater streams contaminated with hexavalent chromium [Cr(VI)] is investigated. In order to comply with the Mexican environmental norm of Cr(VI) for treated wastewater streams at minimum cost, a nonlinear programming (NLP) model for the electrochemical reduction of hexavalent chromium to trivalent chromium was developed. The model incorporates a variable reaction rate, which is a function of the Cr(VI) concentration and the electrical current density of the electrochemical process. For this purpose, a basic superstructure of the effluent treatment is proposed. The superstructure is composed of three continuous electrochemical reactors without recirculation, and it may produce either a series and/or parallel design topology. The NLP model was used to minimize the objective function, defined as the total annual cost (TAC), which includes the capital cost of each electrochemical reactor, the electrical energy cost and the cost of the treatment of the wastewater streams. In order to investigate the solution set of the proposed NLP model, i. e., to improve the possibilities of obtaining optimum solutions based on economic criteria, a multi-start algorithm was implemented. Two example problems are used to show the versatility of the model and different local optimal solutions were obtained for each case study. The results show that a selective treatment of wastewater streams based on the search of local optimal solutions yields significant savings with respect to a centralized treatment design.
ResumenEn este trabajo, se formula un modelo de programación no lineal (PNL) para el diseño de sistemas de tratamiento selectivo de efluentes que contienen trazas de amoxicilina. La presencia de antibióticos en aguas superficiales o subterráneas representa un problema ambiental importante por su potencial bioacumulativo y el desarrollo de resistencia antibiótica. Los métodos para la eliminación de fármacos y antibióticos incluyen la oxidación química usando reactivos Fenton, floculación y fotoquímica. Sin embargo, sus eficiencias de remoción son limitadas y se requiere de estudios orientados a optimizar los costos de tratamiento. Para la degradación de la amoxicilina se incorpora en el sistema una tecnología electroquímica. El modelo de PNL desarrollado se construye con base en una superestructura básica de red que expande el espacio de alternativas posibles de tratamiento, minimizando el flujo total de efluente que es tratado. Se resuelven cuatro ejemplos para mostrar la versatilidad y la utilidad del modelo propuesto.
Palabras clave: degradación de amoxicilina; tratamiento de aguas residuales; coagulación electroquímica; diseño óptimo
Nonlinear Programming Model for the Design of Electrochemical Treatment Systems for Wastewater Streams Contaminated with Amoxicillin Traces AbstractIn this work, a nonlinear programming (NLP) model is formulated for the design of selective effluent treatment systems containing traces of amoxicillin. The presence of antibiotic in surface water bodies or groundwater generates an important environmental problem due to its bio-accumulative potential and the development of antibiotic resilient bacteria. Current methods employed in the removal of drugs and antibiotics include chemical oxidation by Fenton reagents, flocculation and photochemical treatments. However, their removal efficiencies are still limited and studies are required for the optimization of the treatment costs. An electrochemical technology is incorporated in the system for the degradation of amoxicillin. The NLP model developed is built from a basic network superstructure that expands the space of alternative treatment possibilities, minimizing the total flowrate that is sent to treatment. Four illustrative examples are solved to show the versatility and usefulness of the model proposed.
In this work, the mechanism of nucleation and growth of gold was studied on the surface of a glassy carbon electrode (GCE) modified with poly-5-Amino-1-10 phenanthroline (Poly5Aphen), from Au (III) ions, dissolved in a deep eutectic solvent (DES). For which, electrochemical techniques such as cyclic voltammetry (VC) and chronoamperometry (CA) were used. The analysis of the results of the potentiostatic electrochemical tests showed that the Au nucleation and growth mechanism on the GCE/Poly5Aphen electrode fits a theoretical model of 3D nucleation limited by diffusion and by the reduction of residual water present in the electrode (1). In addition, the potentiostatic current density transients recorded during gold electrodeposition on the modified electrode (GCE/Poly5Aphen), when presented in their dimensionless form I2/ I2
m
vs t /tm
and compared with the theoretical models described by Scharifker and Hills (2), the experimental data did not fit the progressive or instantaneous nucleation models, presenting particularly large deviations for >1.4.
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