Super-Hydrophilic and Positive Charged Pressure Retarded Osmosis Membrane for Efficient Ammonia Recovery and Energy Production

Pressure retarded osmosis (PRO) is an emerging technology platform that harnesses the natural phenomenon of osmosis to address natural resources and energy scarcity. However, ammonia rejection and mechanical strength have been generally regarded as critical criteria. In this study, a new tailored, reinforced amine-rich pressure retarded osmosis (RaPRO) membrane is fabricated. The membrane support layer is strengthened by integrating it with tricot fabric, while the active layer is coated with polyethylenimine (PEI). The results indicate that RaPRO with 1% PEI coated under a polymerization time of 15 min creates a super-hydrophilic (contact angle –71°), low roughness (6.8 µm), and high positive charged (zeta potential –20 mV at pH 7) membrane. This new RaPRO membrane allows high water flux (33 LMH) and minimizes ammonia permeate (1.9 GMH at a feed concentration of 500 mg/L). In addition, osmotic power is generated at the remarkable value of 7 W/m2 under the optimal applied pressure of 10 bar. This is expected to support the fit-for-future system that facilitates efficient water, ammonia, and energy recovery.