Biodegradation of Azo Dyes in Anaerobic–Aerobic Sequencing Batch Reactors

Abstract

Effluent discharge from textile and dyestuff industries to neighboring water bodies is currently causing significant health concerns to environmental regulatory agencies due to the toxicity, mutagenicity, and carcinogenicity of the dyes and their breakdown products. Therefore, considerable attention has been given to evaluate the removal of dyes during wastewater treatment and in the natural environment. The most widely used dyes in industries are azo dyes, which require an anaerobic and aerobic phases for their complete biodegradation. Anaerobic stage is the first step of the treatment process in which azo dyes are reduced, resulting in toxic and colorless aromatic amines. Since breakdown products of azo dyes, which are formed when the azo bond is cleaved and color is removed, are resistant to anaerobic biodegradation, aerobic phase is therefore essential for complete biodegradation of colored effluents. Biological treatment has long been known, and the use of sequencing batch reactors (SBRs) for treating textile wastewater has attracted interest. The cyclic operations of SBR provide both color removal in anaerobic stage and aromatic amine removal in aerobic stage.

Decolorization and partial mineralization of a polyazo dye by Bacillus firmus immobilized within tubular polymeric gel

“…This fact is probably related to the electron-withdrawing nature of the azo bond and their resistance to oxygenases attack. As anaerobic color removal occurs by the way of reduction of the azo dye, which acts a final electron acceptor in the microbial electron transport chain, existing and more effective electron acceptors like oxygen in the medium could act as a limiting factor for dye removal (Çinar and Demiröz 2010 ). Similar results were obtained in studies on pure bacterial strains such as Pseudomonas luteola, Pseudomonas sp.…”

Factors Affecting the Simultaneous Removal of Nitrate and Reactive Black 5 Dye via Hydrogen-Based Denitrification

“…Therefore, the denitrification process occurred during the first stage, after which RB-5 was reduced, resulting in the incomplete removal of the dye color. However, a previous study reported that the sparging rate of air and H 2 is a significant parameter for achieving high color removal rates in combined systems [37]. This is because the functioning of the anaerobic azo reductase enzyme, which plays a key role in the cleavage of azo bonds, is limited under aerobic conditions, resulting in an insufficient color removal rate.…”

Draft Genome Sequences of Two Textile Azo Dye-Degrading Shewanella sp. Strains Isolated from a Textile Effluent in Peru

“…Moreover, the presence of a dye-decolorizing peroxidase (DyP) shows the potential of the strains to degrade not only azo but also high-redox anthraquinone-based dyes (11). Furthermore, genes were found for deamination, nitrate reduction, desulfonation, and sulfate assimilation, as well as for the degradation of benzoate, catechol, protocatechuate, and gentisate, which play a key role in the aerobic degradation of aromatic compounds (12). These characteristics support the capability of Shewanella sp.…”