A comprehensive study of biodegradation and detoxification of triazine-based azo dye (Reactive Red 120) using biofilm-mediated continuous packed-bed bioreactor

Nowadays, the presence of triazine-based azo dyes like Reactive Red 120 (RR 120) in textile wastewater poses a significant hazardous environmental impact, deteriorating the aquatic biota and requiring an effective treatment method. Compared to conventional energy-intensive and secondary waste-generating physicochemical methods, biological methods, especially microbial biodegradation, offer a sustainable, eco-friendly, and cost-effective alternative for the treatment of effluents containing dye-laden wastewater. This study evaluated the efficacy of <i>Bacillus tequilensis</i> MCC2908 for biodegradation and detoxification of RR 120 using a continuously Packed Bed Bioreactor (PBBR). The experimental findings revealed an optimum range of ILR within 75-85 mg/L.day, achieving 94.2 ± 2.71% RE and 24.1 ± 1.205 mg/L.day EC, avoiding limitations imposed by mass transfer and bioreaction, and maintaining a robust and efficient bioreactor system. Crystal Violet staining test confirmed the quantitative assessment of biofilm growth, while SEM images made it observable on the polyurethane bio-carrier. The FTIR spectra confirmed the biodegradation of RR 120, showing significant changes in the functional groups. The detoxification was demonstrated using bacterial and phytotoxicity, validating the toxicity reduction, further duly supported by photosynthetic pigment analysis. The Monod model and the Andrew-Haldane kinetics significantly described microbial growth under non-inhibitory and inhibitory conditions, respectively. Nevertheless, the present findings not only highlighted the potential of biofilm-based PBBR but also delivered an eco-friendly, sustainable solution for the remediation of textile wastewater. Future studies may explore the scaling up of this biotechnological solution for the mitigation of industrial challenges and establish hybrid approaches to further enhance biodegradation efficiency.<b>Highlights</b>PBBR significantly achieved efficient biodegradation and detoxification of RR 120.An optimum ILR of 75-85 mg/L.day exhibited the best operating conditions for PBBR.Microbial biomass and biofilm formation were quantified using the Crystal Violet Staining method.Phytotoxicity, photosynthetic pigment analysis, and bacterial toxicity unveiled the RR 120 detoxification.Moderate <i>K_i</i> and low <i>K_s</i> values depicted the resilience and high microbial activity for RR 120.