Electrostimulation for promoted microbial community and enhanced biodegradation of refractory azo dyes

Excess azo dyes are detrimental to natural water systems and human health. To effectively treat dye wastewater, two-dimensional cylindrical electrodes were introduced into traditional biofilm reactor (BR), and thus a novel two-dimensional biofilm electrode reactor (2D-BER) was developed. In the 2D-BER, at low current density from 0.53 ± 0.05 mA m-2 to 12.61 ± 1.24 mA m-2, the electrostimulation increased microbial growth; while at higher current density above 12.61 ± 1.24 mA m-2, the electrostimulation exhibited an inhibition effect to microorganisms. Microbial decolorization in the 2D-BER demanded the participation of co-substrate as carbon source, and the order of decolorization with different co-substrates was glucose > sucrose > starch. An appropriate concentration of glucose improved dye decolorization, but high level of glucose (1 g/L) resulted in a slight decline of decolorization. UV-Vis, FT-IR and GC-MS analysis showed that azo dye was firstly decomposed into various aromatic anilines and then degraded into small molecules. By analyzing the differences in the microbial communities in the 2D-BER and BR, it was found that the electrostimulation prompted the growth and proliferation of electroactive decolorization bacteria, such as Bellilinea, Desulfobulbus, Geobacter and Desulfovibrio, thus leading to high decolorization rate constant of 0.0313 h-1 in the 2D-BER. Considering the excellent decolorization due to the synergism of bioelectrochemistry and microbial catalysis, the electrostimulation technology shows good application prospects in azo dye wastewater treatment.