Nitrate removal from contaminated groundwater by micellar-enhanced ultrafiltration using a polyacrylonitrile membrane with a hydrogel-stabilized ZIF-L layer.

Contamination of groundwater by nitrate from intensive agriculture is a serious problem globally. Excessive fertilization has led to nitrate contamination of the Coastal Aquifer in Israel. Here we report the efficient removal of nitrate from contaminated groundwater by micellar-enhanced ultrafiltration (MEUF) using a specially tailored membrane. Graft polymerization with hydrophilic poly(methacrylate) and incorporation of porous zeolitic imidazole framework ZIF-L nanoparticles imparted antifouling properties to the membrane. The resulting modified membrane showed high water permeance (82.2 ± 1.7 L·m·h·bar). The efficiency of nitrate removal by MEUF was tested using cetylpyridinium chloride as a surfactant in nitrate-contaminated groundwater collected from the Coastal Aquifer of Israel. The membrane reduced nitrate levels from 40-70 to levels of 6.8-29.5 mg·L, depending on the groundwater composition; further reduction to 6.1-24.1 mg·L with complete surfactant rejection was achieved via two-stage membrane filtration, which showed high permeate flux (between 32.1 ± 0.9 and 45.9 ± 0.6 L·m·h) at 2 bar. The membrane maintained stable separation performance during multiple cycles, and the flux recovery ratio was >93 %. Nitrate concentrations fell well below the acceptable limit for drinking water, allowing the treated water to be used without restriction. Overall, the membrane has the potential to allow efficient removal by MEUF of nitrate from contaminated groundwater.