(658e) Utilizing MOF-808 Grafted NF-Membrane for Selective Removal of Selenium from Produced Water

Oil extraction produced water, with high salinity (~35000 ppm) and elevated selenium (Se) levels (500 ppm-300 ppt), presents challenges for reuse. Selenium, with bioaccumulation risks, can be harmful when ingested at levels exceeding 0.05 ppm, affecting aquatic life, wildlife, and humans. Nanofiltration (NF) membranes have been explored for produced water treatment, demonstrating the effective removal of Se oxyanions at more than 93%. However, NF membranes reject pollutants that stay in the retentate stream, demanding an extra step for safe recycling. Adsorptive membranes with Se selectivity adsorb selenate and selenite during filtration, removing the need for additional separation. This study introduces MOF-adsorptive membranes, utilizing the advanced properties of metal-organic frameworks (MOFs) to selectively remove selenate and selenite from high salinity (35000 ppm NaCl) and oily waste streams like produced water. Based on the acceptable removal performance of MOF-808 (~75 mg/g selenite) and Fe-MOF (~60 mg/g selenite), they were selected for grafting on the TFC membrane for the generation of MOF-adsorptive membranes. The mentioned MOFs were grafted on the polyamide layer through chemical grafting. The effect of different operation conditions (MOF dosage, temperature, pH and varying ionic strength) on the physicochemical properties of MOF-NF membrane were studied. The MOF-membrane was also tested to investigate the oil fouling mechanism. The blank TFC membrane exhibited rejection rates of ~85%, ~50%, and ~10% for 2000 ppm Na₂SO₄ and NaCl, and 35000 ppm NaCl. In contrast, the MOF-808-membrane showed ~70%, ~20%, and ~10% rejection for the same concentrations. The water permeability of the blank TFC membrane, and MOF-808-membrane was observed to be ~15 LMH/bar, and ~20 LMH/bar respectively. The blank TFC membrane rejected approximately 90% and 92% of 3 ppm selenite and selenate. While the MOF-808-membrane removed around 45% and 40% of selenite and selenate at 3 ppm from which about 85% of selenite and a negligible amount of selenate was adsorbed within 60 minutes at a permeance of 20 LMH/bar. The MOF-membrane demonstrated outstanding regenerability, maintaining a constant adsorption efficiency even after undergoing five adsorption cycles.