The current work have investigated the accumulation of soluble microbial products (SMP) and aromatic amines in anaerobic reactors followed by aerobic reactors (An1 or Ar2) during the azo dye Remazol Golden Yellow RNL (RGYRNL) degradation. One anaerobic reactor (An2) contained powdered activated carbon (PAC) in its interior, while another one (An1) was used as control. The results have shown the efficiency of COD and color removal in the combined system An1/Ar1 was higher than 70%, while in the An2/Ar2 system the COD and color removal was above 85% and 90%, respectively, in all three operational phases, The aerobic reactors were capable of removing most of the residual organic matter, volatile fatty acid (VFA) and aromatic amines, generated during the anaerobic step, and the presence of PAC inside reactor An2 ensured higher operational stability since it minimized the toxic effects caused by anaerobic degradation byproducts. The presence of PAC contributed to reduce SMP accumulation in phases 2 (CODSMP = 32.40 mg/L) and 3 (CODSMP = 21.61 mg/L) and enhanced the effluent quality. (C) 2014 Elsevier B.V. All rights reserved.