Research on Enhancing Domestic Wastewater Treatment in the Heterotrophic Nitrification–Aerobic Denitrification-Based Anaerobic/Oxic Biofilm System

Traditional wastewater treatment processes still encounter challenges such as the limited treatment efficiency and excessive greenhouse gas emissions, which restrict their application in environmentally sustainable practices. This study developed an A/O biofilm system and assessed the impact of inoculating the system with the heterotrophic nitrification–aerobic denitrification (HN–AD) strain Alcaligenes faecalis WT14 on pollutant removal efficiency and greenhouse gas emissions. A continuous monitoring experiment was conducted over 140 days, comparing the system inoculated with WT14 (the TWT14 system) and the non-inoculated system (the CK system). The results demonstrated that the TWT14 system outperformed the CK system in pollutant removal, with higher NH₄⁺-N, TN, and COD removal efficiencies of 11.22%, 21.96%, and 12.51%, respectively, and the quality of discharge water from TWT14 maintaining compliance with national discharge standards. This improvement underscores the positive impact of inoculation with the WT14 strain on enhancing the pollutant removal performance of the A/O biofilm system. Regarding greenhouse gas emissions, the TWT14 system exhibited a significantly higher N₂O emission flux in the aeration tank compared with the CK system, while CO₂ and CH₄ emissions were predominantly concentrated in the anaerobic tank. Global warming potential (GWP) analysis showed no significant difference in the total average GWP between the two systems. However, the TWT14 system demonstrated a lower GWP per unit of TN removed, highlighting its superior ecological benefits. Environmental factor analysis revealed that the temperature, pH, humidity, and salinity had significant impacts on both pollutant removal efficiency and greenhouse gas emissions. Additionally, microbial community analysis indicated that inoculation with the WT14 strain enhanced microbial diversity and richness within the A/O biofilm system, with Alcaligenes and norank_f_JD30-KF-CM45 playing key roles in nitrogen removal. This study provides valuable insights for optimizing A/O biofilm system design and offers scientific guidance for the sustainable upgrading of wastewater treatment technologies.