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Ammonia Recovery from Wastewater as a Fuel: Effects of Supporting Electrolyte on Ammonium Permeation through a Cation-Exchange Membrane

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posted on 2022-06-07, 14:06 authored by Linji Xu, Dingyang Liu, Wenzong Liu, Jixiang Yang, Jiansheng Huang, Xinzhu Wang, Qiang He
Electrodeionization (EDI) is used to recover ammonia from wastewater as a fuel, but how its performance for ammonia recovery is affected by the supporting electrolyte is not very clear. This study involved experimental tests and theoretical calculations on NH3 recovery, NH4+ permeation, and NH4+ and Na+ interacting with the functional groups in a cation exchange membrane (CEM) using Na2SO4 as the supporting electrolyte. The results demonstrated that a low concentration (≤0.250 mol L–1 of Na2SO4) was conducive to NH4+ permeation, while the a concentration (0.750 mol L–1 of Na2SO4) hindered NH4+ permeation. A maximum recovery efficiency of ammonia of 80.00%, a current efficiency of 70.10%, and an energy balance ratio of 0.66 were obtained at 0.250 mol L–1 of Na2SO4. Numerical results indicated that an increase in Na2SO4 concentration caused severe concentration polarization that resisted NH4+ migration in the CEM. The DFT results demonstrated that competitive adsorption of Na+ to the CEM hindered NH4+ migration. The weaker interacting force between NH4+ and the sulfonate functional group (−SOH3) in comparison to that between Na+ and −SOH3 might be related to the geometric and orientation effects, which generated an additional energy barrier for NH4+ transport. Therefore, this study suggests that the supporting electrolyte concentration should be matched with that of the desalted ions.

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