Chromium (VI) removal by magnetite nanoparticles immobilized with extracellular polymeric substances extracted from <i>Lysinibacillus</i> sp. WH

Magnetite nanoparticles (nano-Fe₃O₄) and nano-Fe₃O₄ immobilized with bacterial extracellular polymeric substances (EPSs) extracted from Lysinibacillus sp. WH (Fe₃O₄/bact) were comparatively studied for the removal of Cr (VI) ions from aqueous solution in batch study. The objectives were to explore the removal of Cr (VI) efficiency by nano-Fe₃O₄ and Fe₃O₄/bact under varying bacterial concentrations at a range of acidic pH. Results indicated that 150 ppm Cr (VI) could be effectively removed by 5 g/L of nano-Fe₃O₄ at pH 4, with the efficiency of 89.2 ± 12%. The equilibrium time, determined by a pseudo-second-order model (R² = 0.9983), was after 5 h, indicating chemical adsorption. The Cr (VI) removal by the nano-Fe₃O₄ immobilized with bacterial EPS was effective and steady under a wide range of acidic conditions although bacterial EPS has an alkaline nature. Here, we are the first to demonstrate that Cr (VI) removal efficiency by different concentrations of EPS was not significantly different, suggesting EPS concentration is possibly not the most crucial factor to be optimized for Cr (VI) removal in the future. This study shows the potential application of nano-Fe₃O₄ immobilized with bacterial EPS for wastewater treatment. PRACTITIONER POINTS: The equilibrium time for magnetite nanoparticles to remove Cr (VI) is 5 h, suggesting chemical adsorption. The Cr (VI) removal efficiency of either magnetite nanoparticles or bacterial EPS is stable under a wide range of acidic conditions. Magnetite nanoparticles immobilized with bacterial EPS extracted from Lysinibacillus sp. WH has a potential application for Cr (VI) removal in wastewater.