Destruction of azo dyes by anaerobic–aerobic sequential biological treatment: a review|
Popli, S. & Patel, Upendra D.
Dyes are synthetic organic compounds widely
used in various industries such as, textile, leather, plastic,
food, pharmaceutical, and paints manufacturing industries.
Coloured effluents are highly toxic to the aquatic life and
mutagenic to humans. Wastewater containing dyes has
become an important issue demanding serious attention.
Among the synthetic dyes, azo dyes are the largest and most
widely used dyes and account for more than half of the
annually produced dyes. The biodegradation of azo dyes is
difficult due to their complex structure and synthetic nature.
Several treatments have been proposed for efficient azo dye
removal, most of them presenting some limitations such as
generation of waste sludge, high operational costs, poor
efficiency, and incomplete mineralization. Biological treatment
is a cost-effective and eco-friendly process for dye
degradation. Sequential anaerobic–aerobic biological treatment
is considered as one of the most cost-effective methods
for the complete mineralization of azo dyes. The anaerobic
stage yields decolourization through reductive cleavage of
the dye’s azo linkages, resulting in the formation of generally
colourless but potentially hazardous aromatic amines. The
aerobic stage involves degradation of the aromatic amines. It
is the most logical step for removing the azo dyes from the
wastewater. Several factors can influence the microbial
activity and consequently the efficacy and effectiveness of
the complete biodegradation processes. This paper
summarizes the results of biological decolourization of azo
dyes using various types of reactors, elaborates biochemical
mechanisms involved, and discusses influence of various
operational parameters on decolourization based on reports
published in the last decade.
Azo dyes; Biodegradation; Anaerobic decolourization; Aromatic amines; Operating parameters; Toxicity