A one-pot approach: Oxychloride radicals enhanced electrochemical oxidation for the treatment of textile dye wastewater trailed by mixed salts recycling

Abstract

Abstract The efficacy of a photo-assisted electrochemical oxidation for the mineralization of real textile effluents (wash water and dye-bath effluent) was investigated by employing a non-photoactive dimensionally stable anode in a tubular flow cell. Under optimized conditions, the photo-assisted electrochemical oxidation was performed at a pH of 2, with a chloride concentration of 2 g L−1, a current density of 10 mA cm−2, and a flow rate of 50 mL min−1. The process efficiency was assessed through ultraviolet–visible spectroscopy, high performance liquid chromatography, Fourier transform-Infra red spectroscopy, nuclear magnetic resonance spectroscopy, chemical oxygen demand and total organic carbon analyses. The results obtained have shown that, in case of wash water effluent, 96% of chemical oxygen demand and 68% of total organic carbon were removed in 180 min of photo-assisted electrochemical oxidation, whereas a simple electrochemical oxidation removed only 70% of chemical oxygen demand and 27% of total organic carbon, in the same time. The energy consumptions were about to 29.8 and 39.5 Wh g−1 of chemical oxygen demand in photo-assisted electrochemical oxidation and electrochemical oxidation. The higher efficiency of photo-assisted electrochemical oxidation is attributed to the formation of oxychloride radicals at acidic pH, as confirmed by electron paramagnetic resonance analysis. The analytical results revealed that the degradation mechanism of photo-assisted electrochemical oxidation is entirely different from that of electrochemical oxidation; in particular, the byproducts formed in the photo-assisted process are free from chlorinated organic compounds and exhibit zero toxicity towards Lemna minor. The photo-assisted electrochemical oxidation proved to be effective also in the case of dye bath effluents with a high organic load: about 90% of the chemical oxygen demand was removed within 5 h at 10 mA cm−1. The recovered salts from the color-free dye-bath effluent were recycled for further dyeing purposes.