Azo dyes are one group of major pollutants found worldwide. Wastewater containing these dyes from the textile industry are notoriously difficult to treat. Furthermore, azo dyes make up approximately 50% of all dyes produced worldwide and are the largest class of synthetic dyes. So far, biological treatment methods are among the most promising remediation methods. Consequently, search for new species of actinobacteria capable of either biodegrading or bioabsorping azo dyes in a marine environment has been intense.
Breaking down azo dyes
A variety of microorganisms including fungi and algae have been studied and, so far, bacteria have had the most success. Bacteria use both aerobic and anaerobic pathways in processing these materials. For example, the metabolic pathway of a thermophilic bacterial strain Anoxybacillus sp. PDR2 in degrading the dye material Direct Black G has been determined using bioinformatics analysis.
Reassessing the treated waste material
Follow-up analysis of the degraded material was done using phytotoxicity studies. Germination rates of rice and mung bean seeds, known to be sensitive to environmental hazards, were tested and it was discovered that the toxicity of the treated wastewater was greatly reduced as compared to the original azo-containing wastewater. Similarly, additional test results have been produced using other bacteria and azo-dye combinations.
Waste becomes fuel
And why stop there? Even more useful biological methods may exist that can not only break down the azo dyes to less toxic substances, but also produce oils to be used as biofuels. In this way, a waste product from one industry may be used as a feedstock for production of useful product in another industry. Recently, an oil-producing enzyme found in wood-feeding termites has been explored for the additional capability of breaking down azo dyes. Subsequently, a detailed dual-process biological pathway fulfilling both objectives has been proposed.
Further research remains to find a solution to combat all of the negative impacts on human health and the environment caused by azo dye wastewater. At any rate, coupling a waste remediation process to a production process of a useful and desired product would be an ideal goal to achieve.
Chen G, An X, Li H, et al. Detoxification of azo dye Direct Black G by thermophilic Anoxybacillus sp. PDR2 and its application potential in bioremediation. Ecotoxicol Environ Saf. 2021 May;214:112084. doi: 10.1016/j.ecoenv.2921.112084. PMID: 33640726
Chittal V, Gracias M, Anu A, et al. Biodecolorization and biodegradation of azo dye Reactive Orange-16 by marine Nocardiopsis sp. Iran J Biotechnol. 2019 Sep 1;17(3):e1551. doi: 10.29252/ijb.1551. PMID: 32195279
Ali S, Al-Tohamy R, Koutra E, et al. Coupling azo dye degradation and biodiesel production by manganese-dependent peroxidase producing oleaginous yeasts isolated from wood-feeding termite gut symbionts. Biotechnol Biofuels. 2021 Mar 8;14(1):61. doi: 10.1186/s13068-021-01906-0. PMID: 33685508