Synthesis of Fe3O4@activated carbon to treat metronidazole effluents by adsorption and heterogeneous Fenton with effluent bioassay

Metronidazole (MNZ), widely used to treat human bacterial infections, enters surface water and groundwater through sewage effluent that endangers the aqueous environment. In this study, MNZ is removed from real and synthetic wastewater through adsorption and heterogeneous Fenton processes. The Fe3O4 magnetic-activated carbon (AC) nanocomposite (Fe3O4@AC) was synthesized by coprecipitation and characterized by Fourier transform infrared spectroscopy, Field emission scanning electron microscope, Energy dispersive spectroscopy, Brunauer-Emmett-Teller, X-ray powder diffraction and Vibrating sample magnetometer analyzes. MNZ removal efficiency was studied under the influence of several parameters such as pH (3-11), Fe3O4@AC dose (0.1-1 g/L), H2O2 concentration (5-30 mmol/L), initial MNZ concentration (5-30 mg/L), contact time (5-60 min) and temperature (20-60 degrees C). Bioassay of treated effluents was evaluated by the germination index. Fe3O4@AC was synthesized with high magnetic strength (43.48 emu/g) and large surface area (210.95 m(2)/g) at nanoscale with a pseudo spherical structure. The maximum MNZ removal efficiency from real and synthetic wastewater by adsorption was 73.77% and 97.6% at pH 7, respectively; whereas, 74.75% and 98.03% at pH 5, respectively, was obtained by the heterogeneous Fenton process. MNZ adsorption is an exothermic process, it follows pseudo second order kinetics, Langmuir and Freundlich isotherms. Whilst, MNZ oxidation follows pseudo-first order kinetics. Finally, the MNZ removal efficiency during the recovery and regeneration of Fe3O4@AC nanocomposite in the adsorption and heterogeneous Fenton processes was 86.88% and 78.34%, respectively. Bioassay results showed significant reductions in effluent toxicity after treatment with both processes. Clearly, the Fe3O4@AC nanocomposite produced a high efficiency in the treatment of wastewater containing antibiotics.