Efficient removal and recovery of phosphorus (P) from wastewater is critical for addressing both phosphate rock depletion and eutrophication-related deterioration of surface water quality. Herein, we present a promising platform approach integrating cerium-doped NH 2 -MIL-101(Fe) with melamine sponge (MS) scaffolds for rapid and high-efficiency recovery of P from wastewater. The as-prepared MIL-101@sponge composites (denoted as MIL-101@CS, MIL-101@PVDF, and MIL-101@ SDBS, respectively) are featured by flexibility and stability according to many characterization techniques. Batch adsorption of P over these composite adsorbents indicates that these MIL-101@sponge composites exhibit a maximum adsorption capacity (e.g., 253.66 mg g −1 for MIL-101@CS) at the optimum pH of 6.0 and that adsorption equilibrium can be attained within 150 min and well described by the pseudo-second-order kinetic model. In addition, these composites show a high selectivity for P over carbonate and other common monovalent anions under environmentally relevant conditions. The results of desorption and recycling tests indicate that MIL-101@CS retains good adsorption and desorption efficiency even in a much short operating time (i.e., 5 min), which allows such a composite to be applied in enriching and recovering P efficiently from wastewater via a rapid adsorption/desorption operation. Moreover, the high feasibility of MIL-101@CS in actual scenarios was validated by efficiently enriching the P from a sludge dewatering liquid. Furthermore, the main mechanisms for P adsorption are elucidated from various microstructural characterizations. Overall, this work presents a strategy of integrating MIL-101 with sponge scaffolds for rapidly and efficiently recovering P from wastewater, which may be potentially extended to the recovery of other value-added elements of interest from waste streams.

Adsorption represents a well-documented, effective and reliable means for phosphorus (P) recovery from waste streams, and is often followed by chemical precipitation for attaining value-added fertilizers or feedstocks. To assess the feasibility of recovering P from water by combining batch adsorption enrichment with struvite crystallization, we prepared four ternary layered double hydroxides (LDHs) with P-preferring elements (i.e., zirconium (Zr) or lanthanum (La)) via a facile coprecipitation method, and then evaluated their performance in capturing P from water, particularly in enriching P from a low-level P solution. We find that P adsorption on all ternary LDHs is pH-dependent and ionic strength-independent, showing a maximum adsorption efficiency at pH ~5 regardless of the ionic strength. Besides, all ternary LDHs demonstrate remarkably high P adsorption capacities, i.e., 842.2, 958.8, 499.6 and 1029.3 mg P g−1 under a certain condition for ZnFeZr, ZnFeLa, ZnAlZr and ZnAlLa, respectively, outperforming other LDHs reported so far. Microstructural analyses show that all ternary LDHs have high stability against the acidic or basic solution, and that the P uptake mechanisms are attributable to anion exchange between P and intercalated nitrate ions, complexation at both the edge of LDHs and the surface of metal (hydr)oxides co-occurred, and electrostatic attraction. Results of recycling tests indicate that all ternary LDHs present good enrichment for P, with enrichment factors above 2.6 after only five adsorption-desorption cycles. In addition, more than 96% of the phosphorus in the P-enriched eluates can be efficiently reclaimed via struvite crystallization in a fluidized bed reactor at an Mg:N:P ratio of 2:5:1 in the feed solution. These findings demonstrate the feasibility of combining adsorption enrichment with struvite crystallization for P recovery.

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