Phosphate Recovery and Selective Desorption with a PEI/PMVEMA Hydrogel in a Column Study

The continuous depletion of nonrenewable phosphate rock reserves as a sole source of fertilizers and ineffective agricultural practices undermine efforts to achieve the goal of global food security. The existing practices to address sustainable nutrient management fall short due to the complex nature of inorganic phosphorus recovery. This study reports on an advanced phosphate capture and release system based on a polyethylenimine/poly(methylvinylether-alt-maleic anhydride) (PEI/PMVEMA) cross-linked hydrogel. This system enables inorganic phosphate binding with a maximum capturing capacity of ∼100 mg of phosphate per gram of hydrogel in a broad pH range between 3 and 8 in a packed-bed configuration under continuous flow conditions. Upon exposure to mild alkaline conditions (∼pH 11), the phosphate-loaded hydrogel instantaneously releases bound phosphate, allowing for a complete sorbent regeneration (97–99%). The released phosphate can be converted readily into an agriculture-ready fertilizer during regeneration. The studied system retaines its performance over three capture–regeneration cycles under various flow conditions and phosphate loading. Additionally, we investigate the selectivity of the system in mixed anion flows. Anion affinity followes the SO42– ≥ H2PO4– ≫ NO3– trend at various pH conditions of the flow, with a competitive displacement of phosphate anions with sulfate at the later stages of sorbent saturation. Adjusting the effluent pH from 13 to 11 improves the temporal separation of sulfate and phosphate during the hydrogel recovery. The studied hydrogel system delivers a continuous, efficient, selective, and stable platform to address current challenges in sustainable phosphate recovery from wastewater and surface eutrophic water while reclaiming nutrients for fertilizer use in a circular economy framework.