Aerobic decolorization of Acid Brilliant Scarlet GR by microbial community and the community dynamics during sequencing batch processes

Bioremediation of reactive orange 16 by industrial effluent-adapted bacterial consortium VITPBC6: process optimization using response surface methodology (RSM), enzyme kinetics, pathway elucidation, and detoxification

Textile effluent is one of the most hazardous industrial pollutant sources. It is generated in huge volumes and contains a wide array of toxicants. Reactive azo dyes, which are xenobiotic compounds, are predominantly utilized by textile industries for dyeing cotton, viscose, wool, and silk. The conventional physicochemical treatments used by industrial effluent treatment plants are ineffective in dye degradation. The present study thus attempted to find a potential treatment for reactive azo dyes. A novel bacterial consortium VITPBC6 was constructed with the most potent and compatible reactive orange 16 (RO-16) decolorizing isolates of tannery and textile effluents, and the isolates were identified as Bacillus flexus VITSP6, Bacillus paraflexus VITSPB7, Bacillus megaterium VITSPB9, Bacillus firmus VITEPB1, B. flexus VITEPB2, and Bacillus aryabhattai VITEPB3. The physicochemical factors of RO-16 decolorization were optimized by response surface methodology. Consortium VITPBC6 was able to tolerate a high concentration of RO-16 up to 800 mg L^-1. A cocktail of enzymes including azoreductase, tyrosinase, laccase, lignin peroxidase, and manganese peroxidase was involved in RO-16 degradation by VITPBC6. Consortium VITPBC6 degraded RO-16 following zero-order reaction. The enzymes of consortium VITPBC6 had a V_max of 352 mg L^-1 day^-1 for RO-16 degradation; however, the K_m value was high. VITPBC6 biodegraded RO-16 resulting in the formation of small aromatic compounds. Lastly, different toxicity assays conducted with untreated RO-16 and its corresponding biodegraded metabolite revealed that the toxicity of biodegraded metabolites was significantly lower than the untreated dye.

Performance of a newly enriched bacterial consortium for degrading and detoxifying azo dyes

To obtain a bacterial consortium that can degrade azo dyes effectively, a bacterial consortium was enriched that can degrade Metanil yellow effectively. After 6 h, 96.25% Metanil yellow was degraded under static conditions by the bacterial consortium, which was mainly composed of Pseudomonas, Lysinibacillus, Lactococcus, and Dysgonomonas. In particular, Pseudomonas played a main role in the decolorization process. Co-substrate increased the decolorization rate, and yeast powder, peptone, and urea demonstrated excellent effects. The optimal pH value and salinity for the decolorization of azo dyes is 4-7 and 1% salinity respectively. The bacterial consortium can directly degrade many azo dyes, such as direct fast black G and acid brilliant scarlet GR. Azo reductase activity, laccase activity, and lignin peroxidase activity were estimated as the key reductase for decolorization, and Metanil yellow can be degraded into less toxic degradation products through synergistic effects. The degradation pathway of Metanil yellow was analyzed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry, which demonstrated that Metanil yellow was cleaved at the azo bond, producing p-aminodiphenylamine and diphenylamine. These findings improved our knowledge of azo-dye-decolorizing microbial resources and provided efficient candidates for the treatment of dye-polluted wastewaters.

454-Pyrosequencing analysis of highly adapted azo dye-degrading microbial communities in a two-stage anaerobic-aerobic bioreactor treating textile effluent

Azo dyes, which are widely used in the textile industry, exhibit significant toxic characteristics for the environment and the human population. Sequential anaerobic-aerobic reactor systems are efficient for the degradation of dyes and the mineralization of intermediate compounds; however, little is known about the composition of the microbial communities responsible for dye degradation in these systems. 454-Pyrosequencing of the 16S rRNA gene was employed to assess the bacterial biodiversity and composition of a two-stage (anaerobic-aerobic) pilot-scale reactor that treats effluent from a denim factory. The anaerobic reactor was inoculated with anaerobic sludge from a domestic sewage treatment plant. Due to the selective composition of the textile wastewater, after 210 days of operation, the anaerobic reactor was dominated by the single genus Clostridium, affiliated with the Firmicutes phylum. The aerobic biofilter harbored a diverse bacterial community. The most abundant phylum in the aerobic biofilter was Proteobacteria, which was primarily represented by the Gamma, Delta and Epsilon classes followed by Firmicutes and other phyla. Several bacterial genera were identified that most likely played an essential role in azo dye degradation in the investigated system.