This study investigates the synergistic denitrification mechanism of aerobic denitrifying bacteria in low-temperature municipal wastewater treatment using an air-lift micro-pressure internal circulation integrated reactor (AMICIR). The AMICIR creates alternating aerobic and anaerobic environments by controlling aeration and dissolved oxygen (DO) levels, enabling the enrichment of aerobic denitrifying bacteria. Experimental results show high removal efficiencies for NH4+-N (93.85%), COD (89.30%), TP (92.75%), and TN (75.4%). The system enriches a wide range of microorganisms, including Flavobacterium, Rhodofera, and Pseudomonas, with Flavobacterium as the dominant species. Functional gene analysis indicates high abundance of aerobic denitrification genes, such as napA, supporting the efficient removal of nitrogen at low temperatures. The system's unique structure and DO gradient promote the growth of aerobic denitrifying bacteria, enhancing nitrogen removal. Microbial communities and gene analysis reveal the presence of anaerobic phyla and the enrichment of functional bacteria, contributing to improved denitrification. The study highlights the potential of aerobic denitrifying bacteria in low-temperature wastewater treatment, offering a theoretical basis for synergistic denitrification with anaerobic bacteria. The results demonstrate the effectiveness of the AMICIR in achieving high pollutant removal rates under low-temperature conditions.This study investigates the synergistic denitrification mechanism of aerobic denitrifying bacteria in low-temperature municipal wastewater treatment using an air-lift micro-pressure internal circulation integrated reactor (AMICIR). The AMICIR creates alternating aerobic and anaerobic environments by controlling aeration and dissolved oxygen (DO) levels, enabling the enrichment of aerobic denitrifying bacteria. Experimental results show high removal efficiencies for NH4+-N (93.85%), COD (89.30%), TP (92.75%), and TN (75.4%). The system enriches a wide range of microorganisms, including Flavobacterium, Rhodofera, and Pseudomonas, with Flavobacterium as the dominant species. Functional gene analysis indicates high abundance of aerobic denitrification genes, such as napA, supporting the efficient removal of nitrogen at low temperatures. The system's unique structure and DO gradient promote the growth of aerobic denitrifying bacteria, enhancing nitrogen removal. Microbial communities and gene analysis reveal the presence of anaerobic phyla and the enrichment of functional bacteria, contributing to improved denitrification. The study highlights the potential of aerobic denitrifying bacteria in low-temperature wastewater treatment, offering a theoretical basis for synergistic denitrification with anaerobic bacteria. The results demonstrate the effectiveness of the AMICIR in achieving high pollutant removal rates under low-temperature conditions.