LAUSR

Abstract Although a capacitive membrane stripping system (CapAmm) has been demonstrated to be an efficient approach for ammonia removal and recovery in our previous reports, the influence of the ammonia absorbent used on CapAmm performance is not well understood. In this study, we clarify the role of particular ammonia absorbents (H2SO4, H3PO4, HNO3, HCl, H2CO3* and H2O) in the CapAmm process with regard to water desalination, ammonia removal and recovery and mass flux. While results of bench-scale studies indicated that absorbent type has little impact on salt removal efficiency, the majority of ammonia flowed to the recovery chamber followed by fixation as ammonium salts when acidic absorbents were used, with the application of the non-volatile absorbents, H2SO4 and H3PO4, resulting in maximum ammonia recovery (>70%). In the case of volatile acidic absorbents (HNO3 and HCl), inferior ammonia recovery efficiency was observed with the reduced recovery attributed mainly to water transfer across the hydrophobic gas membrane as a result of the water vapor partial pressure difference between catholyte and acid receiving solution. When H2CO3* and H2O were used as absorbents, back-diffusion of CO2 and NH3 occurred, most likely as a result of both competitive occupation of the gas membrane pores and a decrease in catholyte pH, with this back diffusion leading to a deterioration in net ammonia flux. In contrast to the unsatisfying recovery performance, economic evaluation suggests that use of H2CO3* and H2O as ammonia absorbents is more cost-effective compared to strong acid adsorbents as a result of the lower chemical costs and higher product revenues.