Performance assessment of a bio-electro-Fenton system for azo-dye removal from synthetic wastewater

This investigation aimed to evaluate the application of a bio-electro-Fenton (BEF) system for Remazol brilliant violet – 5R (RBV-5R) removal. Three experimental runs were conducted under varied conditions using RBV-5R concentrations of 5, 10, and 20 mg L⁻¹, external resistances (R_ext) of 1000, 100, and 10 Ω, and a hydraulic retention time (HRT) of 12 h. At 20 mg L⁻¹ RBV-5R and 10 Ω, removal efficiencies for color, aromatic groups, and chemical oxygen demand (COD) reached 95.5 ± 0.25 %, 73.6 ± 0.4 %, and 82.4 ± 0.3 %, respectively. A residual hydrogen peroxide (H₂O₂) concentration of 12.25 ± 0.17 mg L⁻¹ was measured at a maximum power density of 69.4 mW m⁻², with Coulomb and Faraday efficiencies of 7.2 ± 0.4 % and 5.81 ± 0.1 %. Phytotoxicity assays showed that the germination index (GI) for L. sativa and R. sativus increased from approximately 6 – 39 % after 12 h. A strong positive correlation (r = 0.926, p < 0.01) between residual H₂O₂ and the microbial community suggests that the anodic biofilm may enhance H₂O₂ generation at the cathode for the Fenton reaction. These results support BEF systems as a promising technology for azo dye removal without external energy or H₂O₂ addition.