Microbial Aggregation Effect by Micron-Sized Carriers in Sewage Treatment: Insights into Interfacial Thermodynamics and Microbial Metabolism

Understanding the characteristics and mechanisms underlying microbial aggregation induced by carriers is essential for advancing biofilm technology. This study investigated the microbial aggregation effect driven by micrometer-scale carriers, focusing on the interfacial interaction mechanisms and microbial metabolic characteristics. Based on variations in carrier size, three structural models of bioaggregates were proposed. The results demonstrated that the total nitrogen removal efficiency of the carrier-connected structure (83.1 ± 1.9%) significantly exceeded that of both the carrier-embedded structure (76.0 ± 2.8%) and the surface-attached structure (69.4 ± 3.9%). Biofilm formation on carriers had a threshold (40–60 μm), and the carrier-connected bioaggregates exhibited higher hydrophobicity and lower surface free energy (−17.5 ± 0.5 mJ/m2). Notably, the enrichment of specific bacteria, such as Candidatus_Competibacter (9.1%), norank_Comamonadaceae (2.9%), and Terrimonas (2.0%), in carrier-connected bioaggregates enhanced both endogenous denitrification and aerobic denitrification processes. Moreover, significant enhancements in metabolic pathways, including the TCA cycle, glycolysis, ABC transporters, and nitrogen metabolism, indicated that micrometer-sized carriers facilitated the coupling of hydrolytic fermentation and denitrification. Upregulation of fatty acid biosynthesis and quorum sensing metabolic pathways contributed to the establishment of hydrophobic microenvironments and efficient information and material transfer within the microbial community. These findings offer deeper insights into the development of biofilm technology.