Nitrous Oxide Emissions from Nitritation Reactors under Hypersaline Conditions

Area of Science:

• Environmental microbiology
• Wastewater treatment
• Greenhouse gas emissions

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas.
• Nitritation and nitrification are key processes in wastewater treatment.
• Hypersaline conditions present unique challenges for microbial processes.

Purpose of the Study:

• To investigate N₂O emissions during hypersaline nitritation.
• To identify factors controlling N₂O production in fixed bed reactors.
• To evaluate strategies for mitigating N₂O emissions.

Main Methods:

• Continuous feeding and mixed fixed bed reactors were used.
• Experiments were conducted at 4% salinity.
• Dissolved oxygen (DO), ammonium, and nitrite concentrations were monitored.

Main Results:

• N₂O emissions decreased with increasing DO, but persisted even at 15 mg/L.
• Bulk ammonium concentration was the primary factor controlling N₂O emissions.
• Reducing ammonium below 1 mg N/L reduced N₂O by ~90%.
• Reducing nitrite below 0.3 mg N/L reduced N₂O by ~60% under full nitrification.

Conclusions:

• Bulk ammonium concentration is a critical control point for N₂O emissions in nitritation and nitrification.
• Targeted reduction of ammonium and nitrite can significantly mitigate N₂O production in hypersaline wastewater treatment.