Indigenous Bacteria Synergistically Degrade Indigo Dye in Textile Wastewater via Enzymes and EPS

Cost-Effective and Sustainable Microbial Strategies for the Bioremediation of Textile Dyes: A Review

Integrated Enzymatic–Microbial Systems for Textile Wastewater Detoxification: Mechanisms, Synergies and Industrial Perspectives

The textile industry generates dye-containing wastewater characterized by intense coloration, high salinity, elevated oxygen demand, and recalcitrant pollutants. Although conventional treatment technologies can remove color and reduce organic load, decolorization alone does not guarantee detoxification because toxic transformation products may persist or be generated during incomplete degradation. This review emphasizes the synergistic interaction between oxidative and reductive enzymes and microorganisms as a promising strategy for promoting extensive pollutant transformation and potentially enhancing mineralization. Particular attention is given to the complementary roles of laccases (LAC), azoreductases (AZOR), ligninolytic peroxidases, bacteria, fungi, and microbial consortia in sequential degradation pathways that can improve detoxification efficiency. Mechanisms including azo bond cleavage, aromatic amine transformation, and subsequent microbial degradation are discussed to demonstrate how integrated systems can overcome the limitations of enzyme- or microorganism-based treatments alone and may facilitate complete pollutant removal under appropriate conditions. The review also explores biomass-derived biocatalysts produced through solid-state fermentation of agro-industrial residues, demonstrating opportunities to integrate wastewater remediation with biomass valorization and circular bioeconomy principles. Finally, operational challenges, toxicity assessment, reactor design, enzyme immobilization, scale-up, and techno-economic considerations are discussed, and future research priorities are identified to support the development of sustainable and industrially applicable enzymatic–microbial detoxification technologies.

Multifunctional Membrane for Dyes Removal and Pathogen Inactivation in Textile Effluent

Water pollution has become a global health threat. According to WHO estimates, unsafe water is responsible for approximately 1.4–3.5 million deaths annually. Microbial pollutants and resistant organic dyes are frequently not successfully removed by conventional wastewater treatment methods. In addition, coliform bacterial pollution can turn water into a vector for disease transmission, increase organic and nutrient loads, and accelerate antimicrobial resistance. Therefore, to overcome these problems, we present the synthesis of a new copper‐metal‐ion‐based co‐crystal (CuCoXtal), which exhibits the ability to reduce dyes and 99% antibacterial efficacy against Staphylococcus aureus and Escherichia coli. When exposed to UV light, this cocrystal shows exceptional photocatalytic activity, efficiently degrading a range of dyes from textile effluents, including methylene blue, methyl orange, trypan blue, and congo red. At pH 8.5, degradation efficiency increases significantly, indicating that alkaline media generate more reactive oxygen species (ROS), than neutral (pH 7) or acidic (pH 5.5) conditions. Furthermore, a CuCoAXtal@PAM polyamide membrane was successfully fabricated and degraded methylene blue under UV light within 30 min. In addition to its photocatalytic activity, the fabricated membrane serves as an advanced wastewater treatment material that degrades dyes, disinfects, and detoxifies wastewater in a single step.

Sustainable Approach to the Degradation of Azo Dyes by Bacteria: A Review

Azo dyes account for the majority of synthetic colorants discharged by the textile, leather, paper and food industries, and their recalcitrant azo bonds, together with the carcinogenic and mutagenic aromatic amines that can arise from their reductive cleavage, make them a persistent environmental and public health concern. Physicochemical treatments reduce colour but rarely achieve complete mineralisation and often generate secondary waste streams, which has sustained interest in bacterial bioremediation as a comparatively low-cost and potentially complete alternative. This review critically synthesises the literature on bacterial degradation of azo dyes, with particular attention to the enzymatic basis of decolorisation, the ecological and genomic organisation of degrading consortia, process engineering strategies that couple reductive and oxidative steps, the performance of extremophilic and genetically engineered strains under conditions representative of real effluents, and the analytical and computational tools now used to verify detoxification and optimise operation. The literature indicates broad agreement that azoreductase-mediated reductive cleavage under anaerobic or microaerophilic conditions is the obligatory first step in bacterial metabolism of most azo dyes, and that subsequent oxidative transformation of the resulting aromatic amines, whether by laccases, peroxidases or aerobic ring-cleavage pathways, is required for adequate detoxification. Evidence is more heterogeneous, and confidence correspondingly lower, regarding the generalisability of consortium performance across dye structures and salinities, the scalability of genetically modified strains beyond laboratory conditions, and the extent to which decolorisation percentages reported in isolated batch assays translate into demonstrable reductions in ecotoxicological endpoints. Methodological heterogeneity in dye concentration, inoculum history and toxicity assay selection substantially limits cross-study comparison. The review identifies specific priorities for future work, including standardised detoxification reporting, longer-term and mixed-dye continuous-flow trials, and closer integration of genomic characterisation with process design. Overall, bacterial systems offer a mechanistically well-understood and practically promising route to azo dye remediation, but their translation to industrial-scale, sustainable wastewater treatment remains constrained by inconsistent evidence on robustness, detoxification completeness and long-term operational stability.

Biodegradation and detoxification of Congo red by thermophilic Bacillus smithii AMPNK.

Congo red (CR) is a widely used azo dye in the textile industry and is known for its carcinogenic properties. The discharge of CR-containing textile effluents necessitates efficient and sustainable treatment strategies before environmental release. In this study, the ability of the thermophilic bacterium Bacillus smithii AMPNK to biodegrade CR under different physicochemical conditions was evaluated. A maximum CR decolorization of approximately 95% was achieved at 55 °C when maltose was used as the carbon source, while beef extract was the most effective nitrogen source, yielding approximately 87.17% decolorization. The optimum pH for dye degradation was 7.0, with approximately 90% decolorization. UV-Vis, FT-IR, and GC-MS analyses confirmed the occurrence of azo bond cleavage and the formation of lower-molecular-weight degradation metabolites, indicating efficient biodegradation of CR. Laccase activity and total protein analysis further demonstrated that enzymatic degradation was closely associated with the active growth phase of B. smithii AMPNK. Phytotoxicity assays using Vigna radiata and Trigonella foenum-graecum revealed that untreated CR markedly inhibited seedling growth, reducing root length to 2.2 ± 1.23 cm and 2.1 ± 0.81 cm, respectively, whereas treatment with biodegraded metabolites restored root growth to 5.4 ± 1.50 cm and 4.7 ± 1.34 cm, respectively, indicating substantial detoxification. Overall, these findings demonstrate that thermophilic B. smithii AMPNK is a promising biocatalyst for the biodegradation and detoxification of Congo red in high-temperature textile wastewater.

Bioremediation of Brilliant Red Azo Dye Toxicity in Vigna radiata Using Encapsulated Bacillus subtilis SC9

The discharge of azo dye‐containing wastewater threatens soil microbial activity, plant growth, and ecosystem health because of the persistence and toxicity of synthetic dyes. However, the potential of immobilized siderophore‐producing bacteria for simultaneous dye decolorization and mitigation of dye‐associated phytotoxicity remains unexplored. This study highlights the decolorization and bioremediation potential of viable free cells and calcium‐alginate immobilized Bacillus subtilis SC 9 against brilliant red (BR) dye. Among ten previously identified siderophore producing bacteria (SPB), B. subtilis SC 9 exhibited the highest decolorization efficiency (88.5%). Under optimized conditions, free and immobilized cells achieved 88.5% and 94.86% decolorization, respectively, within 9 days. FTIR and GC‐MS analyses confirmed structural transformation of BR dye into simpler degradation intermediates, indicating biodegradation rather than adsorption. Greenhouse studies demonstrated that immobilized B. subtilis SC9 alleviated BR dye phytotoxicity by increasing root length (142.16%), shoot length (160.91%), soil dehydrogenase activity (192.37 µg TPF g−1 soil), FDA hydrolysis (33.71 µg fluorescein g−1 soil), alkaline phosphatase activity (852.20 µg pNP g−1 soil), and siderophore production (331.53%) compared with untreated dye stress. Overall, calcium‐alginate immobilized B. subtilis SC 9 is a promising eco‐friendly bioinoculant for azo dye bioremediation. Future studies should validate its performance under pilot‐scale and field conditions.