Waste prosperity: Mandarin (Citrus reticulata) peels inspired SPION for enhancing diesel oil biodesulfurization efficiency by Rhodococcus erythropolis HN2

To enrich the activity and the lifetime of the selective desulfurizing Rhodococcus erythropolis HN2, a novel unipot eco-friendly, rapid, energy-saving, sustainable, simple, and green hydrothermal precipitation is applied to prepare superparamagnetic iron oxide nanoparticles (SPION) using the widely abundant and costless mandarin (Citrus reticulata) peels agro/domestic waste. X-ray diffraction, dynamic light scattering, zeta potential measurement, vibrating sample magnetometer, scanning electron microscope, high-resolution transmission electron microscope, and X-ray photoelectron spectroscopy revealed crystalline, highly stable spherical shaped Fe3O4 NPs with 11.58 nm average size and 51.12 emu/g magnetic saturation. The green biofunctionalized SPION proved to be non-toxic for HN2 and used for its magnetization, recording 24.97 emu/g at the optimum SPION/biomass ratio of 0.9 g/g. The first-order kinetic model described well the biodesulfurization profile of thiophenic model oil. The magnetized HN2 gained the advantage of tolerance for relatively high oil feed concentrations, higher BDS efficiency, and easier separation by applying an external magnetic field beside its efficient reusability for six consecutive times keeping approximately 80% of its initial activity. In a 120 h biphasic batch BDS process (30% v/v oil/water), the green magnetized HN2 removed approximately 86% and 96% of the 500 mg/L and 690 mg/L total sulfur content of a thiophenic model oil and a hydrodesulfurized diesel oil under mild operating conditions, respectively.

Automated summary

A novel method using superparamagnetic iron oxide nanoparticles prepared from mandarin peels was applied to enhance the desulfurizing activity of Rhodococcus erythropolis HN2. The biofunctionalized nanoparticles proved to be non-toxic for HN2 and improved its desulfurization efficiency at high oil feed concentrations, with easy separability.