Parametric optimization of hexavalent chromium removal by electrocoagulation technology with vertical rotating cylindrical aluminum electrodes using Taguchi and ANN model

Abstract

This study aims to evaluate the performance of rotating aluminum electrodes in the electrocoagulation reactor for removing hexavalent chromium (Cr⁶⁺⁾ from synthetic tannery wastewater. Taguchi and Artificial Neural Network (ANN) based models were developed to obtain the optimum condition for maximum Cr⁶⁺ removal. The optimum working condition obtained by Taguchi approach for the maximum Cr⁶⁺ removal (94%) was: Initial Cr⁶⁺ concentration (Cr⁶⁺_i) = 15 mg/L; Current Density (CD) = 14.25 mA/cm²; Intial pH = 5; Rotational Speed of Electrode (RSE) = 70 rpm. In contrast, the optimal condition for maximum Cr⁶⁺ ions removal (98.83%) obtained from the BR-ANN model was: Cr⁶⁺_i = 15 mg/L; CD = 14.36 mA/cm²; pHi = 5.2; RSE = 73 rpm. Compared to the Taguchi model, the BR-ANN model outperformed in terms of providing higher Cr⁶⁺ removal (+ 4.83%); reduced energy demand (-0.035 KWh/gm Cr⁶⁺ remove); lower error function value (χ² = -7.9674 and RMSE = -3.5414); and highest R² value (0.9991). The data for the conditions 91,007 < Re < 227,517 and Sc = 102.834 were found to fit the equation for the initial Cr⁶⁺ concentration of 15 mg/l; Sh = 3.143Re^0.125 Sc^0.33. The Cr⁶⁺ removal kinetics was best described by Pseudo 2^nd Order model, as validated by high R² and lower error functions value. The SEM and XRF analysis confirmed that Cr⁶⁺ was adsorbed and precipitated along with metal hydroxide sludge. The rotating electrode led to lower SEEC (10.25 kWh/m³), as well as maximum Cr⁶⁺ removal (98.83%), compared to EC process with stationary electrodes.