Optimization of a Treatment System of Wastewater Streams for Electrochemical Cr(VI) Reduction: Selective versus Centralized Treatment

Abstract

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.

Synthesis and optimization of a selective treatment network of wastewater streams contaminated with paracetamol

“…The combination of effluents of different concentrations and flows, increases the pollutant concentrations in the more diluted streams increasing the treatment costs. In contrast, distributed or decentralized treatment systems allow to treat contaminated effluents separately and more selectively, reducing thus the effluent flows to be treated, and consequently the costs of the treatment system (Wang et al, 1994;Gálan et al, 1999;Zamora et al, 2004;López-Yañez et al, 2018).…”