Biomineralisation of azo dyes and their breakdown products in anaerobic-aerobic hybrid and UASB reactors

Abstract

Batch toxicity and biodegradability of two azo dyes (Siriusgelb and Siriuslichtbraun) has been investigated. It was found that the former azo dye was significantly less toxic to methanogenic sludge than the latter one (IC50 are equal to 3.55 and 0.41 g COD/l, respectively). Neither of the azo dyes was biodegradable under aerobic conditions but both dyes were readily decolourised and slowly mineralised in anaerobic environments. In order to optimise the treatment strategy, the anaerobic and aerobic phases were combined into one single unit called the anaerobic-aerobic hybrid reactor. The performance of this innovative reactor was tested with a synthetic wastewater containing Siriusgelb and ethanol at 30°C and 56% removal of azo dye COD was achieved at volumetric load of 0.3 g azo dye COD/l/day. The effluent COD content could be attributed to the presence of non-biodegradable autooxidation products of Siriusgelb breakdown intermediates. A continuous biomineralisation of 2-aminobenzoic acid (2-ABA) – intermediate of the anaerobic decomposition of Siriuslichtbraun – was studied in a UASB reactor at 30°C. A high (>90%) removal of 2-ABA was achieved under volumetric loads of 1.5 g 2-ABA COD/l/day. However, a further increase in volumetric load led to a decrease in 2-ABA removal, probably due to low attachment ability of the bacteria responsible for primary decomposition of 2-ABA.

Influence of the Applied Organic Load (Olr) on Textile Wastewater Treatment Using Submerged Anaerobic Membrane Bioreactors (Sambr) in the Presence of Redox Mediator and Powdered Activated Carbon (Pac)

“…These contaminants may cause unpleasant aesthetic aspects; increase biochemical oxygen demand; compromise algal photosynthetic activity; reduce the amount of dissolved oxygen (DO); as well as cause aquatic toxicity and mortality of aquatic species (Weisburger, 2002). In addition, textile dyes damage the environment and pose a threat to human health, since some of them or their byproducts are known carcinogenic or mutagenic compounds (Kalyuzhnyi and Sklyar, 2000). It is estimated that there are more than 3,000 types of dyes and that the azo type, characterized by the presence of one or more -N=N-bond, represents ~70% of the colorants commercialized worldwide (Hunger et al, 2004).…”

Kinetics of anaerobic biodecolourisation of azo dyes

“…The presence of such compounds in the industrial wastewater may create serious environmental problems due to toxicity for aquatic life and mutagenecity to humans (Hildenbrand et al, 1999). In spite of persistence to biodegradation under aerobic conditions (Pearce et al, 2003;Yemashova and Kalyuzhnyi, 2005), azo dyes undergo reductive splitting of the azo bond relatively easily under anaerobic conditions (Kalyuzhnyi and Sklyar, 2000;Pearce et al, 2003;Yemashova et al, 2004) releasing corresponding aromatic amines. The extensive investigations with a wide range of azo dye structures revealed that anaerobic decolourisation is a microbiologically non-specific process (Pearce et al, 2003;Yemashova and Kalyuzhnyi, 2006); moreover, it seems to be a common property of any anaerobic and even aerobic (Bromley-Challenor et al, 2000) sludge.…”

Biodegradation of Azo Dyes in Anaerobic–Aerobic Sequencing Batch Reactors

“…Since aromatic amines can be easily biodegraded aerobically through hydroxylation and ring opening of the aromatic ring, it is suggested to combine the anaerobic cleavage of the azo dyes with the aerobic biodegradation of the accumulated amines [62][63][64]. However, it was reported that some aromatic amines are readily autoxidized in the presence of oxygen [20,65].That is why researches focus on the determination of specialized cultures, which can mineralize aromatic amines under anaerobic conditions.…”