Phosphorus recovery from aqueous solutions via phase separation using bioinspired coacervates.

Phosphorus (P) is crucial for crop growth. However, in waters, P is considered as contaminant due to its role in causing eutrophication and algae blooms. Therefore, recovering P from wastewater is essential for sustainable P management. This study investigated the removal of P from aqueous solutions using bioinspired poly(ethylenimine)-poly(acrylamide-co-acrylic acid) (PEI-PAMcoAA) coacervates. In detail, we investigated various parameters affecting P removal, including the ratio of PEI to PAMcoAA (ranging from 1:2 to 3:1, stoichiometry ratio of NH to COOH), pH (5.0-8.0) of P-containing solutions, initial P concentration (0.05-5 mmol/L), and the addition of calcium (Ca, 0.1-5 mmol/L). We found that increasing the PEI:PAMcoAA ratio from 1:2 to 3:1 significantly enhanced P removal efficiency, increasing from 47.21 % to 95.44 %. Under neutral pH conditions without calcium (Ca), PEI-PAMcoAA coacervates demonstrated optimal P removal capabilities (achieving an efficiency of 77.96 %) through electrostatic adsorption. In contrast, the addition of Ca under alkaline conditions markedly improved P removal efficiency, increasing it from 64.16 % to 82.42 %. Detailed analyses of P within the coacervates indicated that Ca facilitates P precipitation and provides additional binding sites. These findings demonstrated that PEI-(Ca)-PAMcoAA coacervates show promise for efficiently removing P, particularly at low P concentrations. After the P-removal, the immobilized P can potentially be reused directly, as P able to be released from the reacted products. Therefore, the reacted coacervates could serve as a non-toxic fertilizer. Given its simplicity, high efficiency, and environmental friendliness, P removal based on bioinspired coacervates represents a low-hanging fruit in the pursuit of sustainable P management.