Enhanced wastewater treatment via a hybrid biofilm carrier: Sulfidized nano zero-valent iron-loaded polyurethane foam for synergistic nutrients and organics removal.

Polyurethane foam (PUF) is widely used as a biofilm carrier in water treatment due to its three-dimensional porous structure and large specific surface area. However, inert nature of PUF limits its active involvement in biological processes. This study developed a novel composite carrier by integrating sulfidized nano zero-valent iron (SnZVI) containing hydrogel into PUF (SnZVI-PUF), aiming to improve its function in nutrients and organic matter removal. The SnZVI-PUF carrier exhibited enhanced phosphorus adsorption capacity (17.10 mg/g), prolonged iron release kinetics and better anti-aging properties than nZVI. The biofilm reactor packed with the SnZVI-PUF carrier outperformed that with control PUF, achieving a higher average removal percentage of PO43⁻-P, NO3⁻-N, TN and COD by 28.8 %, 17.9 %, 14.2 % and 31.3 %, respectively, under aerobic operation at the influent containing 3.0 mg/L PO43⁻-P, 15.0 mg/L NO3⁻-N and 90 mg/L COD. The hydrogel layer allowed SnZVI to adhere stably to PUF surfaces, preventing rapid aggregation and passivation of nZVI while enabling controlled release of Fe2+/Fe3+. Phosphate could be removed via adsorption by SnZVI, binding with oxidized Fe species (Fe2+/Fe3+) or coprecipitation with iron hydroxides. The SnZVI-PUF carrier promoted the enrichment of specific functional microorganisms (e.g., Acinetobacter for phosphorus accumulation, Comamonas for nitrate reduction, Comamonas and Raoultella for Fe(III) reduction and Acidovorax for Fe(II) oxidization), which may also contribute greatly to the enhanced phosphorus and nitrate removal. The study highlights the potential of SnZVI-PUF as a multifunctional biofilm carrier in advanced wastewater treatment and offers a sustainable solution for simultaneous nutrient and organic pollutant removal.