[N₂O Production Pathways in Partial Nitrification Based on Isotope Technology].

Area of Science:

• Environmental Science
• Environmental Chemistry
• Microbiology

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas.
• Partial nitrification is a key wastewater treatment process.
• Understanding N₂O production pathways is crucial for mitigation.

Purpose of the Study:

• To investigate N₂O generation during partial nitrification under varying dissolved oxygen (DO) concentrations.
• To elucidate the specific pathways of N₂O production influenced by DO levels.

Main Methods:

• Batch experiments were conducted at normal temperatures.
• Dissolved oxygen concentrations were systematically varied (0.5, 1.5, 2.5 mg·L⁻¹).
• Isotope measurements were used to determine N₂O production pathways.

Main Results:

• N₂O emissions decreased as DO increased (4.35% at 0.5 mg·L⁻¹ to 2.63% at 2.5 mg·L⁻¹).
• At 0.5 mg·L⁻¹ DO, N₂O was solely from ammonia-oxidizing bacteria (AOB) denitrification.
• At higher DO (1.5 and 2.5 mg·L⁻¹), hydroxylamine oxidation contributed significantly to N₂O production (4.52%–9.11%), alongside AOB denitrification.

Conclusions:

• Dissolved oxygen concentration critically influences N₂O production pathways in short-cut nitrification.
• Elevated DO promotes N₂O generation via hydroxylamine oxidation.
• Minimizing nitrite accumulation is key to reducing N₂O emissions in this process.