Colored effluents are one of the most important environmental pollutants in the world . This study focused on the removal of dye Reactive Black5 (RB5) using a combination of an anaerobic digester and an Integrated Fixed-film Activated Sludge (IFAS) reactor. The effects of Hydraulic Retention Times (HRT), temperature and filling ratio in the anaerobic digester, the effect of hydraulic retention time and filling ratio in IFAS, and also the effect of initial dye concentration on color removal and Chemical Oxygen Demand (COD) reduction efficiencies were investigated. The Maximum efficiency of color removal and COD reduction in the anaerobic digester at HRT of 2.5 days, 35 °C and 50% of filling ratio was 81% and 99%, respectively, and in IFAS at HRT of 6 h and 70% of filling ratio was 25% and 100%, respectively. According to the Scanning Electron Microscope (SEM) photographs of the microbial community, there were morphological differences in the microorganisms of the two reactors. The Stover–Kincannon and Monod models were used to describe kinetic data. The results showed that Stover–Kincannon model follows the experimental data well. Maximum utilization rate constant and Saturation value constant of Stover–Kincannon model for dye and COD were determined as Umax = 0.15 g / (l day), KB = 0.165 g / (l day) and Umax = 11.31 g / (l day), KB = 11.31g (l day) respectively
