[Characteristics of Partial Denitrification in Biofilm System]

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biogeochemical Cycles

Background:

• Nitrite is a crucial intermediate in microbial denitrification and a substrate for anaerobic ammonium oxidation (ANAMMOX).
• Coupling partial denitrification (PD) with ANAMMOX offers a potential strategy for enhanced nitrogen removal in aquatic systems.

Purpose of the Study:

• To investigate the characteristics of partial denitrification (PD) in a biofilm system.
• To assess the feasibility of coupling PD with ANAMMOX for total nitrogen removal.

Main Methods:

• A moving bed biofilm reactor was operated for 120 days.
• Enzymatic assays were performed to measure nitrate and nitrite reductase activities.
• Illumina high-throughput sequencing analyzed microbial community composition.

Main Results:

• The nitrate-to-nitrite transformation ratio (NTR) reached 69.38±3.53% after 40 days.
• Nitrate reductase (NAR) activity increased significantly, while nitrite reductase (NIR) activity decreased.
• The abundance of *Thauera* bacteria increased from 0.3% to 37.27%.
• A total nitrogen removal ratio of 88.16±2.71% was achieved, with effluent TN concentration of 6.41±1.50 mg·L⁻¹.

Conclusions:

• Partial denitrification (PD) can be effectively achieved in a biofilm system.
• The coupling of PD and ANAMMOX is feasible and highly efficient for total nitrogen removal.
• The microbial community structure, particularly the enrichment of *Thauera*, supports the coupled process.