Surface-loaded Fe₂O₃-biochar for the abatement of antibiotics from pharmaceutical wastewater

A significant amount of antibiotics are discharged with pharmaceutical effluents into the aquatic environment. These pose human health risks, hence their removal is important. This study aimed at using biomass-based adsorbents to remove ciprofloxacin, sulfamethoxazole, and trimethoprim from pharmaceutical wastewater. Biochar was synthesized using a custom-made Elsa stove, and a portion was impregnated with ferric chloride solution and further pyrolyzed to obtain Fe₂O₃ modified biochar. Fourier-transform infrared and energy-dispersive X-ray spectroscopy data confirmed the incorporation of iron into the biochar matrix. The antibiotics removal efficiency was pH-dependent and increased with dosage and contact time until saturation. The adsorption of ciprofloxacin, sulfamethoxazole, and trimethoprim on Fe₂O₃ modified biochar followed the Freundlich model (R ² = 0.86, 0.91, and 0.91, respectively), and the adsorption processes were better described by pseudo-second-order kinetics. For all the antibiotics, there was a decrease of Gibbs free energy with increasing temperature, showing that the adsorption process was spontaneous. The positive values ΔH of ciprofloxacin on biochar (9.0) and Fe₂O₃ modified biochar (12.8) indicated that the adsorption process was endothermic, while the negative enthalpy changes for the adsorption of sulfamethoxazole, and trimethoprim indicated exothermic adsorption processes. All adsorbents exhibited negative entropy change, indicating a decrease in the degree of freedom of the antibiotics. Overall, this study demonstrated an effective, versatile, environmentally friendly, and sustainable strategy for pharmaceutical wastewater treatment and ensure environmental protection.