Polyurethane biocarrier drives simultaneous nitrification–denitrification and phosphorus removal in IFAS by enriching Pseudomonas and Aeromonas

BACKGROUND The effective removal of nitrogen and phosphorus from municipal wastewater with low carbon‐to‐nitrogen ratios remains a significant challenge for conventional biological processes. This study aimed to evaluate the enhancement of nutrient removal using an integrated fixed‐film activated sludge (IFAS) equipped with a commercial polyurethane biocarrier (PUB) and to elucidate the underlying microbial mechanisms. RESULTS A field‐scale anaerobic–anoxic–oxic system (48 m 3 d −1 ) was operated for 190 days, with 20% PUB added to the aerobic zone for the final 130 days. The addition of PUB significantly improved system performance, increasing the total nitrogen removal efficiency from 50.4% to 69.5% and enhancing the stability of phosphorus removal. Microbial analysis revealed the unique enrichment of key genera such as Pseudomonas and Aeromonas on the PUB biofilm. Functional gene sequencing demonstrated that nitrogen removal was achieved through a synergistic effect between conventional nitrification–denitrification and simultaneous nitrification–denitrification (SND) pathways. The porous structure of PUB promoted robust biofilm development with abundant extracellular polymeric substances. CONCLUSION The PUB created a favorable microenvironment that selectively enriched functional microorganisms, enabling efficient simultaneous nitrogen and phosphorus removal, particularly via SND. These findings provide crucial mechanistic insights into PUB‐enhanced systems and support their practical application for upgrading wastewater treatment plants to achieve stricter nutrient discharge standards.