3. Results and discussion
3.1. Removal of the selected antibiotics by NF
Removal efficiencies of the four antibiotics through NF were investigated with different feed solutions at varied operation pressures. Fig. 2 shows the removal behaviour at the pressure of 0.2 MPa in the first set of experiments, in which background organics were not added. Rejections of the four antibiotics were above 98%. Higher rejections were obtained at 0.4 MPa (>99%). The results indicated that NFX membrane was efficient in removing the selected antibiotics. As molecular weights of the four antibiotics are higher than the MWCO of NFX membrane, steric exclusion is bound to play a predominant role in the rejection.