Selective adsorption of antibiotics from human urine using biochar modified by dimethyl sulfoxide, deep eutectic...

Antibiotics present in human urine pose significant challenges for the use of urine-based fertilizers in agriculture. This study introduces a novel two-stage approach utilizing distinct biochar types to mitigate this concern. Initially, a modified biochar selectively adsorbed azithromycin (AZ), ciprofloxacin (CPX), sulfamethoxazole (SMX), trimethoprim (TMP), and tetracycline (TC) from human urine. Subsequently, a separate pristine biochar was employed to capture nutrients. Biochar, derived from sewage sludge and pyrolyzed at 550 and 700 °C, was modified using dimethyl sulfoxide, deep eutectic solvent, and ionic liquid to enhance antibiotic removal in the first stage. The modifications introduced hydrophilic functional groups (-OH/-COOH), which favor antibiotic adsorption. Adsorption kinetics followed the pseudo-second-order model, with the Langmuir isotherm model best describing the adsorption data. The maximum adsorption capacities for AZ, CPX, SMX, TMP, and TC after the modification were 196.08, 263.16, 81.30, 370.37, and 833.33 μg/g, respectively. Pristine biochar exhibited a superior ammonia adsorption capacity compared to the modified biochar. Hydrogen bonding, electrostatic attraction, and chemisorption drove antibiotic adsorption on the modified biochar. Regeneration efficiency declined due to solvent accumulation and potential byproduct formation on the biochar surface (<30% removal capacity after three cycles). This study presents innovative biochar modification strategies for selective antibiotic adsorption, laying the groundwork for environmentally friendly urine-based fertilizers in agriculture.