Hydrophobic PVDF-HNT membrane for oxytetracycline removal via DCMD: The influence of fabrication parameters on permeability, selectivity and antifouling properties

Abstract

Halloysite nanotube (HNT) was incorporated in poly(vinylidene fluoride) (PVDF) membrane to remove contaminants of emerging concern (CEC) known as oxytetracycline (OTC), which is extensively used in the aquaculture industry. The presence of HNT in the PVDF matrix has improved the characteristics and separation of the pristine membrane. This study evaluated the effectiveness of low concentration of HNT loading for treating OTC molecules via direct contact membrane distillation (DCMD), which produced high flux recovery after ethanol cleaning. The performance of PVDF-HNT (PHNT) membrane with 0.5 % HNT loading was compared using immersion time of 5 and 15 s. Further improvement was carried out by reducing 500 μm of the membrane thickness to 250 and 100 μm. The wetting characteristics were determined to achieve the desired properties of DCMD membrane and gain insights into the antifouling mechanism of PHNT membrane. The modified membrane using 5 s immersion time obtained a high liquid entry pressure and contact angle (CA) of 2.13 bar ±0.34 and 140° ± 3.10, respectively. This membrane had removed 95 % of OTC molecules with a permeate flux of 5.52 L/m2h. A 38.4 % increment in flux permeation with 98 % removal was obtained after reducing the membrane thickness to 250 μm (7.64 L/m2h). The total and irreversible flux decline of this membrane was significantly low; as a result, the flux recovery obtained above 90 % after ethanol cleaning including for membrane regeneration and long-term operation investigation. OTC removal from the feed solution improved from 98 % to 100 % after the regeneration and long-term operation.