Adsorptive Metal–Organic Framework-Grafted Membranes for Selective Removal of Selenium from Highly Saline Produced Water

Produced water from oil extraction, with high salinity (∼35000 ppm) and selenium (Se) levels (500 ppm–300 ppt), poses challenges for reuse. Se above 0.05 ppm impacts aquatic life, wildlife, and humans. Nanofiltration (NF) membranes remove Se (>93%) but require additional steps for safe recycling, while adsorptive membranes with Se selectivity eliminate further separation needs. This study presents grafted metal–organic frameworks (MOFs) on thin-film composite (TFC) membranes using MOF-808 to extract Se from high-salinity oily waste streams. The MOF-808–TFC membrane exhibited salt rejection rates of 89%, 9%, and 5% for 2000 ppm of Na2SO4, 2000 ppm of NaCl, and 35,000 ppm of NaCl solutions, respectively. The MOF-808–TFC membrane exhibited higher water permeability (∼12.5 LMH/bar) than the bare TFC membrane (∼4.7 LMH/bar). The membrane removed (adsorbed + rejected) 46% selenite and 63% selenate at 3 ppm from a highly saline oil–water emulsion in 1 h. The MOF-808-TFC membrane maintained stable performance over five adsorption–desorption cycles. It showed 75% adsorption of 0.6 ppm of selenite from water in 9 h and achieved 85% selenite adsorption in series configuration. MOF-808-TFC membranes showed an 11 mg/g selenite adsorption capacity from modeled produced water (MPW) in both filtration setups. Breakthrough analysis confirmed the membrane’s effectiveness in selenite retention without concentration polarization during filtration.