The present research emphasizes on degradation of azo dyes from simulated textile wastewater using down flow microaerophilic fixed film reactor. Degradation of simulated textile wastewater (COD 7200 mg/L and dye concentration 300 mg/L) was studied in a microaerophilic fixed film reactor using pumice stone as a support material under varying hydraulic retention time (HRT) and organic loading rate (OLR). The intense metabolic activity of the inoculated bacterial consortium in the reactor led to 97.5% COD reduction and 99.5% decolorization of simulated wastewater operated under OLR of 7.2 kg COD m(3)/d and 24 h of HRT. FTIR, H-1 NMR and GC-MS studies revealed the formation of lower molecular weight aliphatic compounds under 24 h of HRT, leading to complete mineralization of simulated wastewater. The detection of oxido-reductive enzyme activities suggested the enzymatic reduction of azo bonds prior to mineralization. Toxicity studies indicated that microbial treatment favors detoxification of simulated wastewater. (C) 2014 Elsevier Ltd. All rights reserved.