To minimize the negative environmental outcomes associated with eutrophication and provide a sustainable supply of fertilizer products, Donnan dialysis was applied for nutrient recovery from municipal wastewater and agricultural waste. Due to their low reactivity and ineffective recovery by other processes, ammonium (NH4+) and potassium (K+) were prioritized. The objective of this work was to determine the relative importance of ion-exchange capacity, membrane thickness, separation factors, and diffusion coefficients on the rate of nutrient recovery by Donnan dialysis. The CMI-7000 and Nafion 117 cation-exchange membranes were used for all experiments. The CMI-7000 membrane had a higher cation-exchange capacity (1.6 meq g-1) than Nafion 117 (0.90 meq g-1), but the Nafion 117 membrane was thinner (183 µm) than CMI-7000 (450 µm). Separation factors were calculated for NH4+ and K+ over Na+ and H+, which are typical draw ions in Donnan dialysis systems. For 10 meq L-1 solutions, the separation factors for NH4+ over Na+ for the CMI-7000 and Nafion 117 membranes were 0.91 ± 0.11 and 2.32 ± 0.09, respectively, indicating the greater affinity of the Nafion membrane for NH4+. Donnan dialysis experiments involved waste solutions containing 1 meq L-1 and 10 meq L-1 of NH4Cl or KCl and draw solutions with 10 meq L-1 and 100 meq L-1 NaCl or HCl. The solutions were separated by flat-sheet, cation-exchange membranes. For NH4+ recovery, Donnan dialysis was conducted at pH 7, 9, and 10 to evaluate the effects of NH4+ speciation. Nutrient concentrations in the waste solution were modeled by solving for diffusion coefficients with the Nernst-Planck equation. The aggregate data were used to determine the sensitivity of the rate of nutrient removal to the ion-exchange capacity, membrane thickness, separation factors, and diffusion coefficients in order to optimize membrane selection.

Ammonium and potassium recovery by Donnan dialysis: Role of ion-exchange capacity, membrane thickness, separation factors, and diffusion coefficients on the rate of recovery

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.