Mineralization of reactive azo dyes present in simulated textile waste water using down flow microaerophilic fixed film bioreactor

• BDN mineralize all six azo dyes of simulated wastewater in fixed film bioreactor.
• Nearly 97% of initial COD and BOD were removed at an optimum HRT of 24 h.
• Synergistic action of oxido-reductive enzymes is shown at an optimum HRT.
• At an optimum HRT toxicity of dye and its intermediates decreased significantly.

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 m3/d and 24 h of HRT. FTIR, 1H 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.