From Waste to Resource: Overcoming Osmotic Distillation in Membrane Contactors for High-Efficiency Ammonia Recovery and Concentration

This study developed an integrated membrane contactor–membrane distillation (MC–MD) process using polytetrafluoroethylene (PTFE) membranes to recover ammonia from a highly saline, ammonium-rich blend of landfill leachate and food waste digestate. To overcome osmotic distillation (OD) and rapid membrane fouling, a thermodynamic control strategy established an isopiestic equilibrium by coupling near-isothermal conditions (Δ T ≤ 10 °C) with a critical absorbent concentration of ∼4.9 wt % sulfuric acid. This nullified the transmembrane vapor pressure difference, suppressing OD and mitigating the convective drag of foulants. Under these balanced conditions, the MC process achieved >97% ammonia removal. A simple deionized water rinse between cycles removed reversible foulants, sustaining operational stability over 13 cycles with a stable average transmembrane ammonia flux of 39.1–41.1 g m –2 h –1 following an initial peak flux of 98.8 g m –2 h –1 . Finally, a vacuum MD unit concentrated the dilute ammonium sulfate product from 5.86 to 17.5–18.0 wt % with >99.9% solute rejection and a 67% volume reduction. This closed-loop pathway transforms hazardous wastewater into a concentrated, reusable product, advancing sustainable resource management.