N2O and NO emissions from a partial nitrification sequencing batch reactor: exploring dynamics, sources and...

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering
• Biogeochemical cycling

Background:

• Wastewater treatment plants generate greenhouse gases like nitrous oxide (N2O).
• Partial nitrification using ammonia oxidizing bacteria (AOB) is an efficient wastewater treatment process.
• Understanding N2O emission dynamics during partial nitrification is crucial for environmental protection.

Purpose of the Study:

• To investigate nitrous oxide (N2O) and nitric oxide (NO) emissions during partial nitrification in a sequencing batch reactor (SBR).
• To identify factors contributing to N2O peaks and explore mitigation strategies.

Main Methods:

• Enrichment of a sequencing batch reactor (SBR) with ammonia oxidizing bacteria (AOB).
• Treatment of synthetic reject wastewater with high ammonia concentration (1 g NH4+ N/L).
• Monitoring of N2O and NO emissions under various operational conditions and cycle configurations.

Main Results:

• Achieved 98% conversion of NH4+ -N to NO2- -N, indicating successful partial nitrification.
• Observed a significant N2O peak (60-80% of total emissions) within the first 5 minutes of each cycle.
• Minimized N2O emissions by introducing anoxic phases, though this led to increased NO emissions.
• Identified biological reactions during the settling phase as the primary source of initial N2O.

Conclusions:

• Partial nitrification in SBRs can lead to substantial N2O emissions, particularly during the initial cycle phase.
• Optimizing aeration time to ensure complete oxidation of ammonia or hydroxylamine can minimize N2O emissions.
• Operational strategies, such as introducing anoxic phases, can reduce N2O but may increase NO, requiring careful process balancing.