Integrated fixed-film activated sludge and the derivative process: a review of carrier design, microbial regulation, and enhanced nitrogen removal in wastewater treatment

The integrated fixed-film activated sludge (IFAS) process has demonstrated excellent performance and stability in wastewater treatment due to its dual advantages of biofilm and suspended sludge. This article systematically reviews the principles and configuration of the IFAS process, and summarizes the key criteria for carrier selection and characteristics of common carriers in IFAS based on the characteristics, types, and biofilm formation process on carriers. At the level of the pollutant-enhanced removal mechanism, the role of the biofilm-established microenvironment in multi-pathway synergistic denitrification was explored, as well as the value of extracellular polymeric substances and quorum sensing in functional bacterial enrichment and system regulation. Due to the limitations of suboptimal mass transfer efficiency, intensive energy consumption, and constrained functional microbial enrichment posed by larger-sized IFAS carriers, the high concentration powder carrier bio-fluidized bed (HPB) was introduced as a derivative process of IFAS. By incorporating micron-sized powder carriers instead of conventional millimeter-scale carriers, HPB can significantly improve mass transfer efficiency, carrier biological affinity and regulation of functional microbial populations by constructing a fully fluidized dual sludge age system. Even under complex conditions such as high loading or low C/N ratio, efficient synchronous nitrogen and phosphorus removal can be achieved. IFAS and its derived process have shown significant advantages in biomass enrichment, microbial community structure optimization and engineering applications, with broad application prospects and technological extension space. • IFAS boosts N removal via biofilm-sludge synergy and multi-path denitrification. • EPS and quorum sensing promote biofilm stability and functional bacteria regulation. • Micron-sized carriers enhance fluidization and microbial regulation in N removal. • Carrier recycling enhances stability, phosphorus removal, and microbial renewal.