Microbial mechanisms of rapid startup in a sequencing batch biofilm reactor treating high-ammonia slaughterhouse wastewater

High-ammonia wastewater treatment performance (ammonia nitrogen/total nitrogen/chemical oxygen demand) and biofilm-microbe-gene dynamics over time. Traditional processes for treating high-ammonia slaughterhouse wastewater face challenges of long start-up periods and poor shock load resistance. This study established a sequencing batch biofilm reactor (SBBR) to achieve rapid start-up and elucidate the underlying microbial mechanisms. Through integrated analysis of reactor performance, microbial community succession, and functional gene dynamics, the system achieved stable removal of ammonia nitrogen (NH3-N) (>90%) and chemical oxygen demand (COD) within 20 days, marking a rapid functional start-up. After 50 days, the system demonstrated excellent resistance to influent fluctuations. Full biofilm maturation and microbial specialization were accomplished within 80 days, yielding high mean removal efficiencies of 93.04% for NH3-N, 79.38% for COD, and 58.47% for total nitrogen. Microbial analysis revealed a distinct ecological succession from initial Proteobacteria dominance to mature-phase specialization, characterized by significant enrichment of Thermomonas (11.06%) and Flavobacterium (10.16%) capable of heterotrophic nitrification and aerobic denitrification. Functional gene annotation showed marked upregulation of energy metabolism, lipid metabolism, and glycan biosynthesis pathways in the mature biofilm, enabling efficient degradation of complex organics and robust biofilm structure. These findings demonstrate that SBBR achieves rapid start-up through directed microbial succession and metabolic specialization, providing important insights for the optimization of high-ammonia wastewater treatment systems.