Azo dye wastewater treatment in a bioelectrochemical-aerobic integrated system: effect of initial azo dye concentration and aerobic sludge concentration

An integrated system that consisted of a bioelectrochemical reactor (BER) and an aerobic completely stirred tank reactor (ACSTR) was constructed to treat simulated wastewater mixed with azo dye Acid Orange 7 (AO7) and real municipal wastewater. It was found that AO7 could be efficiently decolorized in BER within 6 h while initial concentration fluctuated from 25 to 100 mg/L. With an initial AO7 concentration of 75 mg/L, BER reached a decolorization efficiency of 93.65 +/- 2.45% at 6 h and contributed 26.56 +/- 8.91% of chemical oxygen demand (COD) removal. Coulombic efficiency (CE) of current generation varied from 23.19 +/- 6.96 to 37.23 +/- 3.48% and CE for AO7 decolorization decreased from 30.45 +/- 3.19 to 14.59 +/- 1.21% at the initial AO7 concentration of 50 mg/L, which illustrated the important contribution of electrochemical reduction on AO7 decolorization. The effluent of BERs can be subsequently refined by ACSTR, the residual COD was 72 +/- 10 mg/L after 6 h treatment with an activated sludge concentration of 6000 mg/L. Further increasing the sludge concentration to 9000 mg/L, final COD concentration decreased to 62 +/- 7 mg/L. Results showed that the bioelectrochemical-aerobic integrated system effectively treated the mixed azo dye containing wastewater.