Adsorption and Recovery of Phosphorus Using a PEI–PMVEMA Hydrogel: Performance under Batch and Continuous Conditions

The increasing demand for phosphorus, together with the finite and uneven distribution of phosphate rock reserves, has intensified the need for phosphorus recovery from secondary resources. Human urine is a promising source due to its high phosphorus content. This work investigates the performance of a PEI–PVEMA hydrogel for phosphorus recovery under batch and continuous-flow conditions using pure phosphate solutions and artificial urine. In pure phosphate solutions, the hydrogel achieved adsorption capacities of approximately 160 mg/g at pH 4.5 and 115 mg/g at pH 6.5 for an initial phosphorus concentration of 100 ppm. In artificial urine, competing ions reduced performance, but capacities of 60–80 mg/g were still obtained in batch systems. Under continuous flow with an influent phosphorus concentration of approximately 700 ppm, phosphorus uptakes of up to 135 mg/g were measured. Selectivity studies showed only moderate preference for phosphorus over sulfur, resulting in progressive phosphorus displacement during column operation. Consequently, controlled adsorption–desorption cycles were identified as the preferred operating strategy, with optimal recovery windows of approximately 1–2.5 hours for concentrated artificial urine and around 8 hours for diluted systems. Compared with conventional ion-exchange resins, the hydrogel consistently exhibited superior phosphorus recovery, particularly in complex matrices. Additional experiments showed strong albumin adsorption onto the hydrogel surface, indicating that organic matter may influence adsorption behaviour. Overall, the PEI–PVEMA hydrogel demonstrates strong potential for phosphorus recovery from urine due to its high adsorption capacity, stability, and performance under realistic conditions. Future work should focus on improving selectivity, optimizing column operation, and evaluating long-term performance using real urine.