Comparison of homogeneous and heterogeneous electrochemical advanced oxidation processes for treatment of textile industry wastewater

This study aimed at understanding the influence of the generation of oxidants in a heterogeneous way at boron-doped diamond (BDD) anode (anodic oxidation (AO)) or homogeneously in the bulk (electro-Fenton (EF)) during treatment of a textile industry wastewater. Both processes achieved high TOC removal. A yield of 95 % was obtained by combining EF with BDD anode during 6 h of treatment. The EF process was found to be faster and more efficient for discoloration of the effluent, whereas AO was more effective to limit the formation of degradation by-products in the bulk. An advantage of AO was to treat this alkaline effluent without any pH adjustment. Operating these processes under current limitation allowed optimizing energy consumption in both cases. However, using BDD anode led to the formation of very high concentration of ClO3-/ClO4- from Cl- oxidation (even at low current density), which appears as a key challenge for treatment of such effluent by AO. By comparison, EF with Pt anode strongly reduced the formation of ClO3-/ClO4-. Operating EF at low current density even maintained these concentrations below 0.5 % of the initial Cl- concentration. A trade-off should be considered between TOC removal and formation of toxic chlorinated by-products.

Automated summary

This study compared the generation of oxidants in a heterogeneous way and a homogeneous way for the treatment of textile industry wastewater. Both approaches achieved high TOC removal, with the electro-Fenton process being faster and more efficient for effluent discoloration, and the anodic oxidation process more effective in limiting the formation of degradation by-products. An advantage of anodic oxidation was its ability to treat alkaline effluent without pH adjustment. However, using a boron-doped diamond anode led to high concentrations of ClO3-/ClO4- formation, which poses a challenge for effluent treatment. By comparison, the electro-Fenton process with a Pt anode significantly reduced the formation of ClO3-/ClO4-. Further research is needed to find a balance between TOC removal and the formation of toxic chlorinated by-products.