Comparative study on the role of single- and double-cathode in electro-Fenton process for treatment of Reactive Orange 16 dye bearing wastewaters

Abstract

ABSTRACT The study presents the single- and dual-cathode electro-Fenton (DCEF) treatment of the Reactive Orange 16 (RO16) azo dye-bearing synthetic wastewater. Initially, the effect of operational parameters, i.e. initial [RO16] dye, [Fe+2] iron catalyst, [NaCl] electrolyte, operational pH, and current density (ρ), on the performance of the electro-Fenton (EF) process was evaluated with the application of low-cost stainless steel (SS) electrodes. At the optimum condition ([RO16] = 150 mg/L, [Fe+2] = 0.4 mM/L, [NaCl] = 0.4 M/L, pH = 3.5, ρ = 20 mA/cm2), with a total electrolysis time of 40 min, the colour (RD) and COD (RC) removals were observed to be 92.023% and 83.344%, respectively. Further, the process was upgraded by providing an additional activated graphite plate (AGP) cathode (dual cathodes), and the results indicated a significant reduction (40 min to 25 min) in the electrolysis time, with a drop in electrical energy (2.51 kW/m3 to 1.47 kW/m3). This consequently reduced the operational cost ($3.42/m3 to $1.23/m3) of the lab-scale DCEF process. The XPS analysis showed enhancement in H2O2 concentration at the surface of the additional AGP cathode. The cyclic voltammetry (CV) test confirmed the complete mineralisation of RO16 dye and the formation of intermediate products. The insight mechanism of the conventional and upgraded processes was also explored for the generated sludge and formed products using FTIR and quantum chemical (QC) analysis. The results showed that the DCEF process was highly efficient, low-cost, and an environmentally compatible technology for the treatment of dye-bearing industrial effluents.