Excess nutrients in agricultural waste and municipal wastewater lead to eutrophication and impaired water quality. To address these concerns, we propose Donnan dialysis for selective recovery of ammonium from waste solutions. In Donnan dialysis, electrochemical potential gradients across an ion-exchange membrane are leveraged to recover target ions (i.e., NH4+) into acid- or salt-based draw solutions. We evaluated ammonium recovery from synthetic and real wastes by Donnan dialysis with the CMI-7000 (0.45 mm thick, 1.6 meq g-1 capacity) and Nafion-117 (0.18 mm thick, 0.9 meq g-1 capacity) membranes. The first aim compared the rate of ammonium recovery with 100 meq L-1 sodium chloride (NaCl) and hydrochloric acid (HCl) draw solutions. With the CMI-7000 membrane, the NaCl draw solution achieved 91.2% ammonium recovery in 22 h, but the HCl draw solution only required 12 h for a similar recovery (90.4%). The Nafion 117 membrane demonstrated better performance, with 91.1% ammonium recovery in 6 h with the NaCl draw solution. The second aim investigated the effects of competing monovalent (potassium) and divalent (calcium) ions on the rate of ammonium recovery from synthetic waste solutions. Given the higher membrane affinity for divalent ions, calcium exerted a stronger impact on ammonium recovery. To suppress those impacts, EDTA was added to the waste solution to complex calcium and prevent its co-recovery. The third aim assessed the effect of EDTA addition on the extent and rate of ammonium recovery from both synthetic wastes and a real poultry litter slurry. The optimal draw solution, membrane chemistry, and pretreatment strategy enabled 90% ammonium recovery from real wastes within 6 h, suggesting opportunities for further development of this sustainable nutrient recovery technique.

Evaluation of competing ion effects and EDTA on ammonium recovery by Donnan dialysis

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