Emerging contaminants modulate phosphorus recovery in batch and fluidized-bed systems: Kinetic modeling and mechanistic insights

Struvite crystallization is a sustainable strategy for phosphorus (P) recovery, yet the presence of emerging contaminants (ECs) poses significant obstacles by disrupting crystallization kinetics and compromising product purity. This study systematically investigates the impacts of tetracycline (TC), Cu²⁺, polyethylene terephthalate (PET), and humic acid (HA) on struvite formation using both the batch (BR) and the fluidized-bed reactors (FBR). Batch experiments revealed that HA and Cu+TC act as potent inhibitors through Mg²⁺ complexation. Conversely, FBR results demonstrated that optimized hydraulic conditions can mitigate the kinetic inhibition of Cu+TC, yielding larger pellets with superior Cu²⁺ encapsulation. Trials with real swine wastewater verified that excessive dissolved organic matter and Ca²⁺ favor the formation of amorphous phases rather than crystalline struvite. Density functional theory (DFT) calculations indicated that EC-Mg²⁺ interactions are primarily governed by non-covalent ion-dipole (Mg-O) forces. Ternary complexes bridged by either Mg²⁺ or Cu²⁺ were identified as the most stable species within complex matrices. These findings provide critical mechanistic insights into ECmediated crystallization and propose an integrated framework, i.e., combining targeted pre-treatment with optimized reactor hydraulics, to enhance phosphorus recovery efficiency and product agronomic safety. This work advances the molecularscale understanding of struvite formation in multi-contaminant environments, facilitating the development of more robust P recovery strategies from complex waste streams.