Biodecolorization of Methylene Blue by Using Bacillus subtilis Immobilized into SA-PVA-Bentonite Matrix in Mineral Salt Medium and Non-nutritious Medium

Industrial dye wastewater can potentially cause significant harm to organisms and the environment across the world. Methylene blue (MB) is a synthetic dye that can be found in wastewater. Immobilizing clay material and degradative bacteria into a carrier is the best way to remove MB. Therefore, this study aimed to immobilize Bacillus subtilis in sodium alginate (SA)-polyvinyl alcohol (PVA)-Bentonite for adsorption and degrading MB in nutritious mineral salt medium (MSM) and non-nutritious media. The result showed that SA-PVA-Bentonite-non-living B. subtilis beads (SPB-nBS) had the highest result in non-nutritious medium, approximately 88.89%. While in nutritious MSM, living B. subtilis addition into beads (SPB-BS) reached the highest MB removal, which was 94.31%. Nutritious MSM had a role as the sole carbon and energy for living B. subtilis. So, it could adsorb and degrade MB by its enzymatic system. The degradation products were predicted as C₇H₁₀ N₂O₄ S, C₈H₁₀ N₂O₂ and C₆H₈ N₂O₃ S. Hence, this study indicated that a nutritious medium was the suitable medium for MB degradation. According to the SEM result, the bacteria spread and covered the beads. Furthermore, the adsorption kinetics and isotherms were also analyzed; SPB beads followed the pseudo-second order kinetic model and Langmuir isotherm.