The effect of cyclic anaerobic–aerobic conditions on biodegradation of azo dyes

Abstract

The effect of cyclic anaerobic-aerobic conditions on the biodegradative capability of the mixed microbial culture for the azo dye Remazol Brilliant Violet 5R (RBV-5R) was investigated in the sequencing batch reactor (SBR) fed with a synthetic textile wastewater. The SBR had a 12-h cycle time with anaerobic-aerobic periods of 3/9, 6/6 and 9/3 h. General SBR performance was assessed by measurement of catabolic enzymes (catechol 2,3-dioxygenase, azo reductase), chemical oxygen demand (COD), color and amount of aromatic amines. In this study, under steady-state conditions, the anaerobic period of the cyclic SBR was found to allow the reductive decolorization of azo dye. Longer anaerobic periods resulted in higher color removal efficiencies, approximately 71% for the 3-h, 87% for 6-h and 92% for the 9-h duration. Total COD removal efficiencies were over 84% under each of the cyclic conditions and increased as the length of the anaerobic period was increased; however, the highest color removal rate was attained for the cycle with the shortest anaerobic period of 3 h. During the decolorization of RBV-5R, two sulfonated aromatic amines (benzene based and naphthalene based) were formed. Additionally, anaerobic azo reductase enzyme was found to be positively affected with the increasing duration of the anaerobic period; however; it was vice versa for the aerobic catechol 2,3-dioxygenase (C23DO) enzyme.

Destruction of azo dyes by anaerobic–aerobic sequential biological treatment: a review

“…Thus, the mixed microbial consortia can carry out tasks better than or equivalent to that of an individual pure culture without any precautions to prevent contamination. Different reactor configurations, such as the widely used upflow anaerobic sludge blanket (UASB), expanded granular sludge bed (EGSB), anaerobic/aerobic sequential batch reactor (SBR), activated sludge process (ASP), have been reported for efficient dye decolourization using mixed microbial consortia (Dos Santos et al 2007;Karatas et al 2010;Yasar et al 2012;Da Silva et al 2012). The biodegradation of azo dyes occurs in a two-step process (Rai et al 2005;Vanderzee et al 2001).…”

“…Extent of anaerobic biological colour removal has been reported to be higher than 80 % and in some cases even 100 % for a variety of azo dyes (Karatas et al 2010;Yasar et al 2012;Da Silva et al 2012). The extent and rate of anaerobic decolourization of azo dyes are influenced by various parameters such as dye structure, dye concentration, supplementation with different carbon and nitrogen sources, electron donor, and redox mediator (Vanderzee and Villaverde 2005;Da Silva et al 2012;Johnstrup et al 2011;Koupaie et al 2011;Mohanty et al 2006;Albuquerque et al 2005).…”

“…For instance, Johnstrup et al (2011) reported increase in the extent of decolourization of Remazol Red RR (initial concentration: 100 mg/L) from 85 to 98 % when HRT of anaerobic batch reactor was increased from 0.5 to 3 days. Yasar et al (2012) employed an SBR consisting of cyclic anaerobic-aerobic conditions for decolourization for Remazol Brilliant Violet 5R (RBV 5R). The authors reported that the decolourization efficiencies were 72 % for HRT of 3 h, 87 % for HRT of 6 h, and 92 % for HRT of 9 h with rest of experimental conditions being constant.…”

“…Some of the evidences of amine generation were based on quantitative direct detection of individual compounds. However, this is possible with the use of sophisticated analytical techniques like liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), highperformance liquid chromatography (HPLC), GC, and UV-Vis spectroscopy (UV-Vis) (Yasar et al 2012;Montano et al 2008;. If standards of the expected aromatic amines are not available, HPLC peaks cannot be identified and quantified directly, but the chromatographs can be useful to detect aromatic amines by comparing the retention time with standards of similar structured amines (Lourenco et al 2001).…”

“…Auto-oxidation is often a faster process than biodegradation and the compounds are usually recalcitrant and thus not suitable for biological treatment. It has been observed that aromatic amines with ortho-substituted hydroxyl groups are particularly susceptible to auto-oxidation (Vanderzee and Villaverde 2005;Johnstrup et al 2011;Yasar et al 2012;Libra et al 2004;Supaka et al 2004). Partially degraded Sen and Demierer (2003) Mechanism of biodegradation of azo dyes under sequential anaerobic-aerobic process Generally, bacterial azo dye biodegradation proceeds in two stages.…”