Molecular insights into dye decolorization performance and mechanisms under carbon limited conditions in a membrane...

Bioelectrochemical systems (BES) is a promising strategy for azo dyes decolorization enhancement in carbon-limited condition, but decolorization products need further aerobic mineralization. Here, a counter-diffusion biofilm-supported BES (E-MABR) was designed to achieve the decolorization, mineralization and denitrogenation of Alizarin Yellow R (AYR) in electron-deficient wastewater. The introduction of electrodes facilitated the secretion of extracellular polymeric substances (EPS), particularly proteins (PN), whose content in the cathodic biofilm was 2.5 ± 0.2 times higher than that in the MABR. Additionally, electrical stimulation enriched electroactivity bacteria (e.g. Geobacter) and azo dyes metabolism contributor (e.g., Thauera and Dechloromonas), and significantly upregulated the expression of decolorization-related genes, particularly azoR (1.2 log₂) in the cathodic biofilm. The increased β-sheet proportions of protein structures in the anode (22.2 ± 1.5 %) and cathode (20.1 ± 1.7 %) promoted the exposure of hydrophobic groups in amino acid; consequently, more hydrogen bonds formed, leading to stronger hydrophobic interactions in molecular dynamic simulations. Under the electric field stress, the total binding free energy between azoR and AYR declined to -32.6 kJ·mol⁻¹, enhancing the stability of the complex and creating a favourable environment for AYR degradation. Finally, under carbon-limiting conditions, E-MABR significantly promoted AYR decolorization efficiency, mineralization efficiency, and total nitrogen removal by 32.4 ± 2.3 %, 29.4 ± 3.6 %, and 18.4 ± 2.0 %, respectively, compared to MABR.