Lanthanum-quaternized chitosan-modified zeolite for long-lasting operation of constructed wetland: A bifunctional...

Saturation adsorption capacity and clogging pose persistent challenges to phosphorus (P) removal in constructed wetlands. Developing substrates capable of efficient and sustained P sequestration is therefore critical. However, few existing substrates achieve both high performance and long-term stability. Here, we report a novel engineered substrate, Lanthanum-quaternized chitosan modified zeolite (LCZ), synthesized from natural zeolite via an impregnation method. LCZ exhibits a maximum phosphate adsorption capacity of 46.69 ± 0.93 mg/g in a 100 mg P/L solution-representing a 16-fold enhancement over pristine zeolite (2.89 ± 0.01 mg/g). The adsorption mechanism involves synergistic effects of electrostatic attraction, ligand/ion exchange, and surface precipitation. Notably, the synergistic action of lanthanum and quaternized chitosan imparts LCZ with potent antibacterial properties, significantly reducing bacterial adhesion compared to natural zeolite. Granulation with cement yields the wetland substrate LCZ-C, which features a porous surface morphology with sharp-edged, nanoflower-like architectures. These architectures, with their ultra-high surface area, are highly effective for phosphorus fixation, enhancing P availability. Concurrently, the inherent sharp edges of these nanomaterials provide a powerful physical mechanism for antibacterial activity, mechanically disrupting pathogenic bacterial cell membranes. LCZ-C effectively reduced P levels in actual lake water to consistently below 0.05 mg/L, and the removal efficiency was close to 80 %. Hedley sequential P fractionation revealed that HCl-extractable P, representing a stable P pool, constitutes the dominant fraction (67.64 %) of the adsorbed P, indicating superior long-term P immobilization potential in eutrophic waters. Crucially, coculture experiments demonstrated that LCZ-C could efficiently kill Escherichia coli through the "breaking-cell-wall" effect, which disrupts bacterial cells on its surface and exerts durable antibacterial effects. This translates to significant resistance to biofilm formation, suggesting a potential solution to mitigate substrate clogging. This work offers a sustainable solution that ensures stable, long-term performance in enhanced phosphorus removal within constructed wetlands.