Biodegradation of Textile Azo Dyes by a Bacterial Consortium From Contaminated Soil

Abstract

Azo dyes are the largest chemical class of synthetic colorants, and a good share of what is applied in textile mills leaves in the wastewater. Bacterial consortia isolated from dye-contaminated soil are often proposed as a cheap way to clean it up, and reports of rapid decolorization are common. This narrative review asks what such reports can and cannot show. It draws on published work on azo dye chemistry, the enzymes that cleave the azo bond, the aerobic fate of the aromatic amines that result, and the design of consortium studies, and it reports no new data and no local measurements. Loss of colour is best read as the first step of a longer pathway: reductive cleavage is usually fast under low-oxygen conditions, but the amines it releases can be as worrying as the dye and need a second, oxidative stage that colour readings do not track. Consortia often outperform single isolates because the members divide the work, yet that same division makes them hard to reproduce, to describe and to scale. Many reports rely on colour alone, on single dyes in clean media, and on communities that are never characterised. The review concludes that consortium treatment is plausible and sometimes impressive, that complete detoxification is far less often shown than complete decolorization, and it sets out the controls, chemistry and toxicity tests that a convincing study would contain.