Electrocoagulation for the decolorization of textile wastewater in single-channel reactor: Response surface methodology for optimization and a novel model exploitation

Abstract

This work focuses on the multi-objective optimization of the electrocoagulation process. The goal is to decolorize synthetic Reactive Black 5 wastewater using a single-channel reactor operating in a closed-circuit. Response Surface Methodology (RSM) is employed for the optimization. The Central Composite Design (CCD) is used to study the empirical relationship between two responses (decolorization efficiency (η) and energy consumption (WC)) and four independent variables (recirculation flow rate (Qv), current intensity (I), electrolysis time (τe) and active electrode area (Sa)), while the desirability function (D) is applied to determine optimal conditions. In addition, a novel approach for the exploitation of the RSM model is developed to set correlations between the limit of η (ηLim) and corresponding independent variables’ limit values (below of which η < ηLim). The developed correlations showed a good agreement between the graphical data and the estimated values (R2 > 0.99). The CCD model fits well the experimental data with a R2 of 0.94 and 0.95, for η and WC, respectively. The analysis of variance allowed to build quadratic models for both responses. For a maximal overall desirability D of 0.88, optimal conditions are Qv = 70 L h−1, I = 100 mA, τe = 34.6 min and Sa = 621 cm2. Under these conditions, η = 70.9% and WC = 4.6 Wh.m−3 were achieved. The sludge characterization using X-ray diffraction, Scanning Electron Microscopy, and Fourier Transform InfraRed reveals the formation of the amorphous Al(OH)3 without other precipitated substances and authenticates the successful sorption of RB5 onto the Aluminum hydroxide flocs.