Methylene blue biodecolorization by Ralstonia pickettii bacterium immobilized on Sodium Alginate - Polyvinyl Alcohol - Bentonite beads

Methylene Blue (MB) is a synthetic dye commonly used in the coloring industry. Its disposal in nature can pollute the waters and cause several diseases in humans. In this study, a bacterium culture of Ralstonia pickettii (R. pickettii) was immobilized into a Sodium Alginate - Polyvinyl Alcohol - Bentonite (SA-PVA-Bentonite) matrix. The entrapment method was used, where R. pickettii cells (1 mL bacterium suspension = 2.48×108 CFU) were homogenized with the SA-PVA-Bentonite matrix. The resulting beads were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), which showed that the bacterium and matrix were successfully homogenized. The results showed that bacterium and the matrix were successfully homogenated. Furthermore, biodecolorization process was performed using free cells and immobilized R. pickettii on Mineral Salt Medium (MSM) with the final MB concentration of 50 mg/L. MB Biodecolorization solution was analyzed by UV-Vis Spectrophotometer and the metabolic products were examined by LC-TOF/MS. Immobilized R. pickettii showed better performance (96%) than the free cell (38%) after a 48 h incubation. the biodecolorization process produced 5 metabolite products identified by LC-TOF/MS. Additionally, the metabolite products generated from the process were Azure A, Thionine, C12H11N3O6S, C12H13N3O6, and C12H13N3O7. This was supported by FTIR and SEM characterization, indicating that MB was adsorbed by beads. One significant advantage of bacterium immobilized in dye decolorization was reusability. A study on immobilized R. pickettii showed that beads can be reused for up to 3 cycles of MB Biodecolorization. Furthermore, this study suggests that immobilizedR. pickettii on SA-PVA-Bentonite matrix could be used as an alternative method in MB Biodecolorization.