Study on the Aerobic Denitrification Nitrogen Removal Characteristics and Microbial Degradation Mechanism of the Air-Lift Multistage Integrated Reactor

Abstract

This study evaluates an air-lift multistage integrated reactor designed for township wastewater treatment. Under controlled aeration, the reactor established distinct dissolved oxygen zones (1.06, 1.46, and 1.89 mg/L from bottom to top) and maintained high mixed liquor suspended solids (MLSS), which together promoted both aerobic and anaerobic denitrification. During extended operation, the system achieved average removal efficiencies of 93.3% for chemical oxygen demand (COD), 96.2% for NH4+-N, 74.9% for total nitrogen (TN), and 92.9% for total phosphorus (TP). Concurrently, the evolution of extracellular polymeric substances (EPS) and enhanced sludge activity─as shown by increases in dehydrogenase activity (DHA) and specific oxygen uptake rate (SOUR)─contributed to the formation of microenvironments favorable for nutrient removal. High-throughput sequencing revealed a dynamic shift in microbial community composition, marked by enrichment of functional genera such as Pseudomonas, Flavobacterium, and Acinetobacter, and by a significant increase in the abundance of the napA gene linked to aerobic denitrification. The above results indicate that the air-lift multistage integrated reactor process has significant application potential in rural sewage treatment.