Development of a regeneration technique for aluminum-rich and iron-rich phosphorus sorption materials

Preventing dissolved phosphorus (P) accumulation in soils and its transport to water bodies has been subject of many studies. However, despite the continuous efforts and advances, excessive P is still a concern and it is especially problematic in freshwater systems: excessive dissolved P leads to eutrophic conditions, a threat for water quality and aquatic life. P removal structures are a novel technology used in urban and rural settings to intercept dissolved P in surface and subsurface flows. P sorption materials (PSMs), active media with high affinity for dissolved P, are the core components of these structures. Once the PSMs reach service life, replacing the spent media can be costly. The objective of this research is to assess potential regeneration techniques that will extend the lifetime of Aluminum (Al)/Iron (Fe)-rich PSMs. We are proposing a regeneration involving a continuous circulation of 1M KOH aiming to restore unavailable sorption sites on the PSMs. A series of flow-through experiments was conducted alternating between P sorption (0.5 and 50 mg/L input solution) and desorption with KOH (5 or 20 pore volumes), varying residence times (0.5 min and 10 min) and number of recirculations (0, 6 and 24). We tested the treatments in 3 manufactured PSMs, Alcan, Biomax and PhosRedeem. Across two cycles of sorption-desorption, Alcan, Biomax and PhosRedeem showed an average P recovery of 81%, 79% and 7%, respectively.  The comparative investigation of the tested treatments revealed that the most effective regeneration treatment is characterized by a larger KOH volume (20 pore volumes) and no recirculation, with up to 100% reported P recovery. This research demonstrates the ability of Al/Fe-rich PSMs regeneration to contribute to a circular economy of P, as P recovery enables a more sustainable P cycle in both terrestrial and aquatic environments.