Synthesis of biochar from iron-free and iron-containing microalgal biomass for the removal of pharmaceuticals from water

The contamination of natural water bodies with pharmaceutical compounds has raised significant concerns about ecological and public health safety. In this study, biochars were synthesized from iron-free microalgal biomass (harvested by centrifugation) and iron-containing microalgal biomass (harvested by coagulation) and tested for the adsorption of ciprofloxacin (CIP) and diclofenac (DIC) from water in batch and fixed-bed column continuous studies. The physicochemical properties of synthesized biochars were analyzed using Brunauer, Emmett and Teller (BET) surface area analyzer, elemental analyzer, Fourier Transformed Infrared spectroscopy (FTIR), X-ray Diffractometer (XRD), and Scanning electron microscope with energy dispersive spectroscopy (SEM-EDS). The maximum monolayer adsorption capacities of iron-containing biochar (FBC750W) and iron-free biochar (MBC750W) based on the Langmuir model were obtained as 75.97 mg/g and 39.08 mg/g for CIP, and 40.99 mg/g and 6.77 mg/g for DIC, respectively. Comparatively, maximum monolayer adsorption capacities of commercial activated carbon (C-AC) were found to be 50.97 mg/g and 46.39 mg/g for CIP and DIC, respectively. In fixed-bed column continuous adsorption studies, the effects of flow rate (1 and 2 mL/min) and the adsorbent amount (50 and 100 mg) on adsorption performance were evaluated. Column kinetic models, such as Bohart-Adams model and Fractal-like Bohart-Adams model were examined. The adsorption mechanisms were proposed as pore filling, π-π interaction, and electrostatic interaction. Overall, the results of this study revealed that microalgal biomass, harvested with FeCl3, can be used for the direct synthesis of iron-containing biochar for the removal of pharmaceuticals from water.