Acetaminophen and trimethoprim batch and fixed-bed sorption on MgO/Al₂O₃-modified rice husk biochar

Pharmaceuticals' ubiquitous presence in surface and groundwater from their increased consumption and inefficient conventional wastewater treatment removal, poses a threat to flora and fauna. Pyrolyzed co-precipitated Mg/Al oxides (3:1) on rice husk biochar surfaces (MgO/Al2O3-BC700) were prepared to treat aqueous acetaminophen and trimethoprim contamination. This adsorbent, characterized for proximate and elemental compositions, crystallinity, surface area, morphology, zero-point charge and functional groups, had a higher surface area (419 m(2)/g) and pore volume (0.132 cm(3)/g) than its pristine biochar BC700 analog (surface area 182 m(2)/g and pore volume 0.062 cm(3)/g). Hybrid multiphase MgO/Al2O3-BC700 easily adsorbed aqueous acetaminophen and trimethoprim (similar to 8 h equilibrium) with capacities of 69.7-137.4 mg/g and 54.2-269 mg/g, respectively. It has excellent sorption efficiency at significant ionic strengths (10-50 mM KCl), with competing individual anions (Cl-, CO32-, HCO3-, SO42-) and cations (Ca2+, Na+, Mg2+, Al3+) and with anionic mixtures and cationic mixtures at 0.1, 1.0 and 10 mM concentrations. Column studies for both pharmaceuticals were conducted, and key sorption parameters (EBCT, column capacity, adsorbent use rate, and % saturation) were calculated. Spent MgO/Al2O3-BC700 was regenerated using optimized concentrations of EDTA, HCl, H2SO4, ethanol, and methanol. Regeneration was performed after 3-consecutive adsorption-desorption cycles. Thorough characterization and spectroscopic investigations suggested potential sorption interactions.