Anti-fouling Janus membrane for effective ammonia recovery from high-strength wastewater

With growing interest in hydrogen energy, liquid ammonia has emerged as a promising hydrogen carrier due to its low boiling point and high volumetric energy density. In addition to green and brown ammonia, white ammonia, produced through waste recycling, has gained attention. This study explored the use of a Janus membrane in a membrane contactor system for white ammonia recovery from high-strength wastewater, such as anaerobic digestion effluent, which is prone to membrane fouling owing to its complex organic and inorganic constituents. To address the challenge, a Janus membrane with asymmetric wettability, combining a hydrophilic surface and a superhydrophobic layer, was used to enhance interfacial stability and ammonia transport. The Janus membrane achieved a mass transfer coefficient (MTC) of 0.039 m/h, which was 8.3 % higher than that of the SHPO-only membrane and exhibited only a 5.13 % MTC reduction after extended fouling, compared to a 20.93 % reduction for the virgin membrane. Postoperative Fourier transform-infrared and X-ray photoelectron spectroscopy analyses confirmed the chemical integrity of both layers, and scanning electron microscopy imaging revealed limited surface deposition. In addition, the Janus configuration enabled directional vapor flow and reduced interfacial mass transfer resistance compared with symmetric membranes. The findings demonstrate that the Janus membrane provides a robust and scalable platform for stable ammonia separation in the presence of severe fouling and complex wastewater matrices.