The decolorization of azo dye Acid Orange 7 (AO7) was studied in a sequential anaerobic/aerobic reactor system; the anaerobic stage was carried out in a continuous upflow stirred packed-bed reactor (USPBR) filled with biological sludge carbonaceous material (BSCM) and aerobic stage took place in an aerobic membrane bioreactor (aerobic MBR). In a continuous USPBR-BSCM system, azo dye bioconversion rates were about 99% at very short space times (tau) 1.02-16 min. In the sequential aerobic stage, hydraulic retention times (HRTs) were determined on removal efficiencies of chemical oxygen demand (COD), resulting about 66% at 48 h. Total organic carbon (TOC) assay showed a removal efficiency about 54.37%, suggesting the degradation of the aromatic amines produced in the anaerobic reactor. Total aromatic amine (TAA) values were 45.30 and 8.97 mg L-1 in USPBR and aerobic MBR respectively, resulting in about 80.28% removal efficiency. These results indicate that anaerobic sequential USPBR/aerobic MBR reactor system seems to be an effective and promising system for complete azo dye biodegradation. (C) 2015 Elsevier B.V. All rights reserved.