article · RSC Advances
Treating toxic dye waste such as methyl orange is critical for environmental protection. Successful bio-decolorisation of methyl orange was accomplished using the bacterium Ralstonia pickettii immobilised within a polyvinyl alcohol (PVA), alginate, and hectorite bead matrix, designated as BHec-RP. Optimal degradation conditions occurred with 10 percent PVA and 1 percent hectorite under static incubation at 40 °C and pH 7. Comparative testing showed that beads containing dead cells removed the dye through physical monolayer adsorption following pseudo-first-order kinetics. In contrast, living immobilised cells actively degraded the dye at 0.025 milligrams per litre per hour at an initial concentration of 50 milligrams per litre, significantly outperforming free bacterial cells, which achieved 0.015 milligrams per litre per hour. The breakdown process involved enzymes including azoreductase, NADH-DCIP reductase, and laccase, successfully cleaving the dye into five distinct molecular fragments.
Azo dyes like methyl orange are toxic pollutants commonly found in industrial wastewater that resist conventional breakdown. Developing effective biological solutions to neutralise these hazardous chemicals protects aquatic environments and public health. Immobilising beneficial bacteria inside protective mineral-polymer beads improves their degradation efficiency compared to free-floating cells, demonstrating a viable biological approach for breaking down persistent chemical pollutants.
This technology could support biological wastewater treatment processes for industrial dye users and textile effluent processors. The immobilised bead system provides an alternative to conventional bioreactors by combining adsorption with active microbial degradation. At present, this represents early-stage laboratory research focused on kinetic modelling, optimal parameter identification, and metabolite fragmentation, with no pilot-scale testing or field implementation demonstrated in the abstract.
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Biological methods are widely used to treat dye waste, particularly methyl orange (MO) dye. The importance of MO degradation stems from its classification as a toxic dye. Within the scope of this research, successful bio-decolorization of MO was achieved through the use of <i>Ralstonia pickettii</i> bacteria immobilized in a PVA-alginate-hectorite matrix (BHec-RP). The optimum conditions for the degradation were observed at a composition of PVA (10%), hectorite (1%), static incubation, 40 °C, and pH 7. Subsequently, the adsorption kinetics of BHec-RP (dead cells) as well as the degradation kinetics of BHec-RP (live cells) and MO using free <i>R. pickettii</i> cells were evaluated. The decolorization of MO using BHec-RP (dead cells) is an adsorption process following pseudo-first-order kinetics (0.6918 mg g<sup>-1</sup> beads) and occurs in a monolayer or physical process. Meanwhile, the adoption of BHec-RP (live cells) and free <i>R. pickettii</i> cells shows a degradation process under pseudo-first-order kinetics, with the highest rates at an initial MO concentration of 50 mg L<sup>-1</sup> being 0.025 mg L<sup>-1</sup> h<sup>-1</sup> and 0.015 mg L<sup>-1</sup> h<sup>-1</sup>, respectively. These results show that the immobilization system is superior compared to free <i>R. pickettii</i> cells. Furthermore, the degradation process shows the inclusion of several enzymes, such as azoreductase, NADH-DCIP reductase, and laccase, presumed to be included in the fragmentation of molecules. This results in five fragments based on LC-QTOF/MS analysis, with <i>m</i>/<i>z</i> values of 267.12; 189.09; 179.07; 169.09; and 165.05.
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DOI: 10.1039/d3ra08692e
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