Hydrophobic NADES–Biohydrogel extraction of antibiotic contaminants from primary wastewater: Integrating leaching control and mechanistic understanding

The limited efficiency of conventional wastewater treatment plants in removing antibiotic micropollutants evidences the need for advanced, yet sustainable, separation technologies. Here, we investigated the potential of hydrophobic natural deep eutectic solvents (H-NADES) as green liquid–liquid extractants for the removal of ciprofloxacin (CPX), tetracycline (TET), and sulfamethoxazole (SMZ) from primary wastewater. Three menthol-based H-NADES, with acetic acid (Men:AceA), octanoic acid (Men:OctA), and decanoic acid (Men:DecA) were prepared and tested. Initial screening in model aqueous antibiotic solutions revealed that Men:OctA and Men:DecA exhibit higher stability and removal efficiency, achieving complete extraction of CPX and SMZ at 10 ppb initial concentration, > 85% removal at 500 ppb, and > 50% TET removal at 500 ppb, though some solvent leaching was observed. The use of the biohydrogel significantly reduced H-NADES leaching into the water while preserving high extraction efficiencies. In the biohydrogel-assisted system, Men:DecA achieved extraction efficiencies of 89% for CPX, 87% for TET, and 49% for SMZ. Molecular dynamics (MD) simulations revealed that while hydrogen bonding occurs between antibiotics and H-NADES, extensive hydrophobic interactions are an important contribution to solute transfer into the H-NADES phase.