4,4-Diaminostilbene-2,2'disulfonic acid (DSD acid) wastewater from a reduction process is characterized by slow biodegradation. With a coagulation step as pretreatment, the contaminant can be efficiently removed by a cometabolism sequencing batch reactor (SBR) in the presence of glucose. Since a part of COD from DSD acid wastewater was colloidal and refractory, coagulation was applied as the pretreatment process, which demonstrated that the optimal concentration of aluminum sulfate was 90 mg/L In the biological section, reduction efficiencies for COD, chromaticity and NH4+-N were 84%, 93% and 92%, respectively, when working with 10 h and pH 7.0. In addition, dehydrogenase activity was proven to be a good parameter which can characterize the microorganism activity in this study. (C) 2009 Elsevier B.V. All rights reserved.