Bioelectrochemical decolorization of a reactive diazo dye: Kinetics, optimization with a response surface methodology, and proposed degradation pathway.

Bioelectrochemical systems (BESs) have shown great potential for azo dye removal. However, comprehensive evaluation of the bioelectrochemical decolorization performance for reactive diazo dyes remains limited, particularly the kinetics and operation parameter optimization. This study evaluated the decolorization of the diazo dye Reactive Black 5 (RB5) in BESs, particularly with regard to kinetics, parameter optimization using response surface methodology (RSM), and the degradation pathway. The results indicated that the pseudo-first-order kinetic rate constant of RB5 decolorization increased from 0.023 ± 0.001 to 0.146 ± 0.008 h-1 with a decrease in cathode potential from -400 mV to -500 mV. RSM optimization suggested that the linear effects of RB5 concentration, cathode potential and hydraulic retention time (HRT), interaction of RB5 concentration with cathodic HRT, and the quadratic effect of cathodic HRT were most influential on the bioelectrochemical decolorization of RB5. Further, the decolorized RB5 products in the BESs were characterized by ultraviolet-visible spectrophotometry, Fourier-transform infrared spectroscopy, and liquid chromatograph-mass spectrometry. From this, a potential decolorization mechanism is proposed based on cleavage of azo bonds.