Industrial indigo dyeing wastewater purification: Effective COD removal with peroxi-AC electrocoagulation system

Direct current (DC) electrocoagulation has obvious decolorization effect on indigo dye-ing wastewater produced in actual production, while the removal rate of chemical oxygen demand (COD) was less than 40%, accompanied by serious electrode corrosion and high energy consump-tion. In order to enhance the COD removal rate, reduce the electrode loss and power consumption, a peroxi-alternating current (AC) electrocoagulation (EC) system was constructed. With COD as the main evaluation index, the effects of power type, electrode combination and process parameters on COD removal rate and decolorization rate were focused on and explored, as well as revealing the degradation mechanism of COD. The results showed that AC electrocoagulation enhanced the floc adsorption capacity by improving the floc structure, and the COD removal rate after treatment was 51.19%. The coupled system of peroxi-AC electrocoagulation further removed sulfite and residual dyes in the wastewater, and the COD removal and decolorization rate of the treated wastewater reached 78.09% and 98.47%, respectively. In addition, the specific energy consumption analysis of COD removal showed that the coupled system was far less energetic than the DC electrocoagu-lation process, with only 30% of its energy consumption. The uniform corrosion of the electrode under the action of AC weakened the passivation, which reduced the electrode loss and power con-sumption by 22.73% and 43.75%, respectively. Results from the present work indicated that the peroxi-AC EC system could be an effective method for reducing the concentration of COD in indigo dyeing wastewater.(c) 2023 The Author(s). Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Direct current (DC) electrocoagulation is effective in decolorizing indigo dyeing wastewater but has low chemical oxygen demand (COD) removal rate and high energy consumption due to electrode corrosion. To improve COD removal rate and reduce energy consumption, a peroxi-alternating current (AC) electrocoagulation (EC) system was developed. The study focused on the effects of power type, electrode combination, and process parameters on COD removal rate and decolorization rate, and investigated the COD degradation mechanism. Results showed that AC electrocoagulation enhanced floc adsorption capacity and achieved a COD removal rate of 51.19%. The coupled peroxi-AC electrocoagulation system further removed sulfite and residual dyes, reaching COD removal and decolorization rates of 78.09% and 98.47%, respectively. The system also had significantly lower energy consumption compared to DC electrocoagulation, with a reduction of 70%. Overall, the peroxi-AC EC system is an effective method for reducing COD concentration in indigo dyeing wastewater.