Ion exchange membrane-based technologies have not been explored for phosphorus recovery, but these distinct membranes offer significant advantages that may help address food security issues associated with rapidly declining global phosphorus reserves. In this study, the Donnan membrane principle was applied to recover phosphorus from wastewater by establishing an electrochemical potential gradient across anion exchange membranes using high-strength salt (draw) solutions. Tests were conducted in two distinct systems: batch reactors with waste and draw solutions separated by an anion exchange membrane; and, a continuous flow reactor containing wastewater and tubular cation/anion exchange membranes with draw solution flowing through the membrane modules. The specific objectives were as follows: (1) to determine the effects of P(V) concentration, draw solution concentration, and draw salt composition on phosphorus recovery; (2) to investigate interference from other anions in wastewater; and, (3) to demonstrate continuous recovery of P(V) and cations (e.g., Mg2+, NH4+ and K+) from wastewater using the tubular ion exchange system. Over 95% P(V) recovery was achieved in environmental solutions (1 mg/L), municipal wastewater (10 mg/L), and agricultural wastewater (100 mg/L), demonstrating the widespread applicability of the Donnan membrane principle. Draw solutions with monovalent anions like chloride (Cl-) recovered over 90% P(V), but sulfate (SO42-)-based draw solutions only achieved 60% P(V) recovery. These results stemmed from both kinetic limitations and differences in Donnan equilibrium for monovalent-divalent and divalent-divalent systems. In the presence of other relevant anions, such as SO42- and NO3-, P(V) flux across the membrane decreased due to competition for ion exchange sites. Membrane affinity followed the order: P(V) &gt; SO42- &gt; NO3-. The continuous flow, tubular ion exchange system achieved high P(V) recovery as struvite; furthermore, the precipitation of struvite reestablished the electrochemical potential gradient allowing continuous P(V) recovery without high chemical or energy costs.

Using ion exchange membranes to recover phosphorus from wastewater

255th National Meeting (2018)

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