Abstract
Biodegradation of azo dyes is difficult due to their complex structures and low BOD to COD ratios. In the present study, the efficiency of using Fenton’s reagent (H2O2 + Fe2+) as a pretreatment process to enhance microbial transformation of reactive black 5 (RB5) in an aqueous system was evaluated. The RB5 with an initial concentration of 250 mg/L was decolorized up to 90% in 60 h by using a bacterial consortium. Fenton’s reagent at a Fe2+ concentration of 0.5 mM and H2O2 concentration of 2.9 mM (molar ratio, 1:5.8) was most effective for decolorization at pH = 3.0. The extent of RB5 removal by the combined Fenton–biotreatment was about 2 times higher than that of biotreatment alone. The production of some aromatic amines intermediates implied partial mineralization of the RB5 in Fenton treatment alone; in addition, decreasing of GC-MS peaks suggested that dearomatization occurred in Fenton-biological process. Fenton pretreatment seems to be a cost–effective option for the biotreatment of azo dyes, due mainly to the lower doses of chemicals, lower sludge generation, and saving of time. Our results demonstrated positive effects of inoculating bacterial consortium which was capable of dye biodegradation with a Fenton’s pretreatment step as well as the benefits of low time required for the biological process. In addition, the potential of field performance of Fenton-biological process because of using bacterial consortium is an other positive effect of it.
Highlights
Textile industries produce large amounts of liquid effluents
Decolorization of different concentrations of dyes in biological treatment The bacterial consortium was chosen on the basis of its ability to form a clear zone on the plate containing Luria Broth (LB) agar and reactive black 5 (RB5)
At a dye concentration of 50 mg/L, more than 90% dye removal was achieved within 36 h; similar decolorization was observed at concentrations of 250 and 500 mg/L within 60 and 108 h, respectively
Summary
Textile industries produce large amounts of liquid effluents. More than 7 × 105 tones of synthetic dyes are produced annually by textile industries [1,2], of which 2.8 × 105 tones are discharged [3,4,5]. Discharge of wastewater containing azo dyes results in the pollution of aquatic systems and, causes adverse effects on human health [8]. Most of these dyes or their cleavage products (i.e., aromatic amines) may be mutagen or carcinogen [9,10,11]. Treatment of wastewater containing such dyes is essential to prevent deterioration of ecosystems [12,13]
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