A water-repellent PVDF-HNT membrane for high and low concentrations of oxytetracycline treatment via DCMD: An experimental investigation

Oxytetracycline (OTC) is classified as contaminants of emerging concern (CEC) and has been detected in significant quantities in aquaculture wastewater in several countries. This study introduces an alternative treatment using a water-repellent poly(vinylidene fluoride)-halloysite (PHNT) membrane via direct contact membrane distillation (DCMD). The membrane was fabricated using halloysite nanotube (HNT) and poly(vinylidene fluoride) (PVDF) was used as a base polymer, which was dissolved in triethyl phosphate (TEP) via immersion precipitation. The performance of HNT as an additive was compared with montmorillonite (MMT). The water repellent properties were evaluated using a porometer, goniometer, and scanning electron microscope to meet the membrane requirements for direct contact membrane distillation (DCMD) and gain insights into the PHNT separation mechanism. The fabricated membrane obtained the desired anti-wetting properties after the addition of HNT in the PVDF matrix, where the contact angle and liquid entry pressure were 137° ± 0.79 and 2.11 ± 0.03 bar, respectively. The OTC removal by the PHNT membrane was experimentally tested for high and low OTC concentrations. The presence of HNT enhanced the permeate flux to 5.69 L/m²·h (100 ppm) and 5.35 L/m²·h (10 ppm) with 97% and 90% of OTC removal, respectively. Complete removal (100%) of 10 ppm OTC solution proved a successful separation of low OTC concentration by the 0.5% PHNT membrane.