Discerning the biodegradation of binary dyes in microbial fuel cell: Interactive effects of dyes, electron transport behaviour, autocatalytic mechanism, and degradation pathways

This research presented the first attempt to investigate the effect of biodegradation of binary Acid Orange 7 (AO7) and Reactive Green 19 (RG19) on the performances of wastewater treatment and bioelectricity generation, using anti-gravity flow microbial fuel cell (AGF-MFC) system. The influences of initial dye concentration, substrate loading, sulphate concentration and application of quinones on system performances were comprehensively evaluated. The decolourization efficiencies of AO7 were higher than RG19 in binary solutions, at every tested concentrations. The addition of higher concentration of RG19 in binary solution was also found to have increased the overall performances of MFC, owing to electron mediating characteristics of its decolourized intermediates. However, the power density declined with the addition in dye concentration. Further increase of substrate loading by 3-folds (2.43 g/L) improved the decolourization efficiency approximately by 7%, but deteriorated power performance by 42%, to 63.40 ± 0.07 mW/m2. Increasing sulphate concentration from 20 to 400 mg/L had resulted in a high decolourization extent of binary dyes ascribed to sulphide-mediated dye degradation, whereas the power generation was reduced. The increase of sulphate to 800 mg/L led to decrease in decolourization and power density of the system. These outcomes deciphered the competitions of electrons between different electron acceptors in the anodic compartment. Moreover, the autocatalytic mechanism of RG19 decolourized intermediates, 1-amino-2-naphthol-3,6-disulphonate (1A2N36S) as electronophore was thoroughly unearthed. Detailed degradation pathways of dyes were proposed based on UV-Visible spectra and gas chromatograph-mass spectrometer (GC-MS) analyses.