Antibiotics separation from saline wastewater by nanofiltration membrane based on tannic acid-ferric ions coordination complexes

Excessive discharge of saline antibiotics wastewater into aquatic ecosystem is one crucial environmental issue facing the world today. Herein, an eco-friendly nanofiltration (NF) membrane was fabricated based on coordination complexes of tannic acid and ferric ions (TA-Fe) to selectively separate antibiotic and monovalent salt. Optimal membrane with Fe/TA molar ratio of 3/1 and coordination time of 60 s exhibited Zeta potential of −26.0 mV (pH = 7), water contact angle of 45.5 o and pore radius of 0.36 nm. Consequently, TA-Fe@M3-T60 membrane showed high ciprofloxacin/NaCl rejection ratio of ~5.9 and considerable water permeability of 20.6 ± 1.2 LMH. Besides, relatively high rejection rates were obtained for ofloxacin (94.1 ± 2.2 %) and ciprofloxacin (91.9 ± 2.5 %), while rejection rate for trimethoprim was much lower (68.2 ± 4.1 %). Effects of static/dynamic membrane adsorption of antibiotics on subsequent removal performance were investigated for the first time. Rejection rate improvements of 7.4–15.2 % were observed on pristine membrane compared with pre-adsorbed membrane in short-term NF process. Electrostatic shielding experiment and rejection rate prediction further distinguished the contributions of steric hindrance , electrostatic interaction and membrane adsorption on antibiotics removal, especially antibiotics in zwitterionic form at pH = 7. The findings of this work imply that this newly developed NF membrane has great potential for efficient treatment of antibiotics-contaminated wastewater.