Integrated air cathode microbial fuel cell-aerobic bioreactor set-up for enhanced bioelectrodegradation of azo dye Acid Blue 29

In this study, an azo dye (Acid Blue 29 or AB29) was efficiently degraded with acetate as co-substrate into less contaminated biodegraded products using an integrated single chamber microbial fuel cell (SMFC)-aerobic bioreactor set-up. The decolorization efficiencies were varied from 91 ± 2% to 94 ± 1.9% and more than 85% of chemical oxygen demand (COD) removal was achieved for all dye concentrations after different operating time. The highest coulombic efficiency (CE) and cell potential were 3.18 ± 0.45% and 287.2 mV, respectively, for SMFC treating 100 mg L⁻¹ of AB29. Electrochemical impedance spectroscopy (EIS) revealed that the anode resistance was 0.3 Ω representing an entirely grown biofilm on the anode surface resulted in higher electron transfer rate. Gas chromatography coupled mass spectrometry (GC–MS) investigation demonstrated that initially biodegradation of AB29 started with the cleavage of the azo bond (-N=N-), resulted the biotransformation into aromatic amines. In successive aerobic treatment stage, these amines were biodegraded into lower molecular weight compounds. The 16S rRNA microbial community analysis indicated that at phylum level, both inoculum and dye acclimated cultures were mainly consisting of Proteobacteria which was 27.9, 53.6 and 68.9% in inoculum, suspension and anodic biofilm, respectively. At genus level, both suspension and biofilm contained decolorization as well as electrochemically active bacteria. The outcomes exhibited that the AB29 decolorization would contest with electrogenic bacteria for electrons.