In membrane distillation (MD), the permeation of volatile components is traditionally driven by partial vapor pressure gradient set up by a transmembrane temperature differential. Conventional MD can be employed for the separation of volatile components, e.g., soluble gases such as ammonia, from aqueous feed streams and collected on the sweep side. However, the process suffers from undesired simultaneous water permeation that dilutes the collector stream and incurs large energy losses due to the enthalpy of vaporizing water. In this study we present a novel operation of MD, termed isothermal membrane distillation with acid collector (IMD-AC), for the separation and recovery of ammonia from aqueous solutions, while suppressing water transport. The innovative operating features of IMD-AC that distinguish it from conventional MD are: i) same temperature on both the feed and collector sides and ii) acidic solution on the collector side. High ammonia flux with minimal water permeation for isothermal membrane distillation was realized with 500 mM total ammonia nitrogen (TAN) feed solution to simulate hydrolyzed urine, and either 100 mM acetic acid or deionized (DI) water as the collector. Traditional MD operating at feed and collector temperatures of 40 and 20 °C, respectively, exhibited ammonia flux of 9.3 mol/m2h with water flux at 8.3 kg/m2h, while IASMD was enhanced ammonia flux to 13.9 mol/m2h, while diminishing water flux to effectively zero. Ammonia permeation in isothermal MD is enhanced 1.5-fold when acidic sweep solution is used compared to DI water. IMD-AC operation from 20 to 60 °C demonstrates that ammonia flux increases with increasing temperature, from 5.6 to 22.8 mol/m2h, while suppressing water flux across all temperatures. Furthermore, IMD-AC is substantially more energy efficient than traditional MD, achieving energy savings of 96.2%. IMD-AC has promising potential for the selective and energy efficiency removal and recovery of volatile contaminants from aqueous wastestreams.

Novel isothermal membrane distillation with acid collector for selective and energy efficient removal and recovery of ammonia

2019 Fall National Meeting

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