Anaerobic and hydrogen peroxide decolourisation of azo dyes: a comparative evaluation

Efficient decolourisation of azo dyes by anaerobic biological process and chemical oxidation (ozone, Fenton and R!O) process has been chaimed by both the methods. A comparative evaluation of chemical oxidation (H202 and Fenton's reagent) and anaerobic process for their efficacy for azo dye decolourisation has been done. Azo dyes namely, Orange-II (C.I. Acid Orange 7), Reactive Blue-H􀆁R (C.I. Reactive Blue 13), Reactive Red-HE7B (CJ.Reactive Red 141) and Reactive Black-3HN (CI.Reactive Black 8) were selected for the study. Anaerobic decolourisation experiments were conducted for a period of more than 50 days with a hydraulic retention time (HRT) of 10 days and at ambient temperatures. Oxidative decolourisation studies were conducted with varying peroxide dosage of 1.5 to 50 mM H202 concentrations. Decolourisation efficiencies achieved during anaerobic process was more than 99% for all the dyes evaluated. In case of hydrogen peroxide (SO mM H202 cone.) treated dye solutions, decolourisation efficiencies observed were 37, 12, 5 and 10% for orange, blue, red and black dye respectively. Fenton's reagent (Fe(II) + 50 mM H20) achieved 99 % decolourisation for dyes Orange-II and Reactive BlueH3R. Therefore it seems that anaerobic process would be economical for decolourisation of azo dyes m comparison to chemical oxidation processess.