Chemical properties and optimisation of bioflocculant from Klebsiella michiganensis: Elucidation of dye decolourisation efficacy and mechanisms

Flocculants derived from bacteria are considered as promising alternatives to chemical flocculants in wastewater treatment. However, few studies have applied them in dye decolourisation and evaluated their flocculation mechanisms. Therefore, in this study, flocculant BF–PX353943 derived from Klebsiella michiganensis was characterised, optimised and applied in dye decolourisation. Scanning Electron Microscopy (SEM), High-Performance Liquid Chromatography (HPLC), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR) were used to characterise the material’s morphology, carbohydrate composition, crystallinity, thermal stability (pyrolytic behaviour), and functional groups, respectively. Response Surface Methodology (RSM) was employed to optimise the operational parameters, including pH, CaCl 2, sedimentation time and dosage. Jar test experiments and zeta potential analysis were conducted to evaluate dye removal efficiency and mechanisms of action. The bioflocculant exhibited a rod-shaped morphology and was predominantly composed of sucrose (31.90%) and fructose (17.77%). Sharp diffraction peaks at 2θ = 45° and 84° indicated its crystalline nature. TGA demonstrated good thermal stability, with less than 40% weight loss after thermal treatment up to 600°C. FTIR revealed hydroxyl, carboxyl, carbonyl, and amino groups as the main functional groups. The bioflocculant achieved decolourisation efficiencies of 71.82% for Congo red and 82.17% for methylene blue under optimal conditions of pH 6.8, 5% CaCl₂, 10 minutes of sedimentation time and a dosage of 1 mg/mL. BF–PX353943 utilised a cation-mediated bridging mechanism for flocculation. Overall, this study demonstrates that BF–PX353943 is an effective and environmentally friendly bioflocculant with strong potential for application in dye-contaminated wastewater treatment, thus contributing to the development of sustainable water treatment technologies.