Decolorization of synthetic Methyl Orange wastewater by electrocoagulation with periodic reversal of electrodes and optimization by RSM

Treatment of Methyl Orange (MO), an azo dye, synthetic wastewater by electrocoagulation with periodic reversal of the electrodes (PREC) was examined. Response Surface Methodology (RSM) was used to optimize the influence of experimental conditions for color removal (CR), energy consumption (ENC), electrode consumption (ELC) and sludge production (SP) per kg MO removed (kg(MOr)) with optimal conditions being found to be pH 7.4, solution conductivity (K) 9.4 mS cm(-1), cell voltage (U) 4.4V, current density (j) 185 mA cm(-2), electrocoagulation time (T) 14min, cycle of periodic reversal of electrodes (t) 15s, inter-electrode distance (d) 3.5 cm and initial MO concentration of 125 mg L-1. Under these conditions, 97 +/- 2% color was removed and ENC, ELC and SP were 44 +/- 3 kWh kg(MOr)(-1), 4.1 +/- 0.2 kg(Al) kg(MOr)(-1) and 17.2 +/- 0.9 kg(sludge)kg(MOr)(-1), respectively. With the enhanced electrochemical efficiency resulting from the periodic electrode reversal, the coefficients of increased resistance and decreased current density between the two electrodes in the PREC setup were 2.48 x 10(-4) Omega cm(-2) min(-1) and 0.29 mA cm(-2) min(-1), respectively, as compared to 7.72 x 10(-4) Omega cm(-2) min(-1) and 0.79 mA cm(-2) min(-1) as measured for the traditional electrocoagulation process. The rate constant of decolorization was also enhanced by 20.4% from 0.152 min(-1) in the traditional electrocoagulation process to 0.183 min(-1) in the PREC process. These performance characteristics indicate that the PREC approach may be more promising in terms of practical application, as a cost-effective treatment, than conventional electrocoagulation for textile dye removals. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.