Low-dose Ultraviolet-A irradiation selectively eliminates nitrite oxidizing bacteria for mainstream nitritation

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Technologies
• Bioreactor Engineering

Background:

• Nitritation is a critical but often challenging step in nitrogen removal processes.
• Current methods for achieving partial nitritation/anammox (PN/A) face bottlenecks, particularly in controlling nitrite oxidizing bacteria (NOB).
• Selective elimination of NOB is crucial for stable mainstream nitritation.

Purpose of the Study:

• To introduce and evaluate a novel approach using low-dose ultraviolet-A (UVA) irradiation for selective NOB elimination.
• To achieve reliable mainstream nitritation by inhibiting NOB activity.
• To understand the mechanisms behind NOB suppression by UVA irradiation.

Main Methods:

• Application of low-dose UVA irradiation (0.87 μE L⁻¹ s⁻¹) in a lab-scale reactor.
• Monitoring of nitritation efficiency and nitrite accumulation ratio.
• Microbial community analysis (targeting NOB and AOB populations).
• Intracellular reactive oxygen species (ROS) analysis.
• Observation of microalgae presence and activity.

Main Results:

• Mainstream nitritation was achieved within 10 days of UVA irradiation.
• Nitrite accumulation ratio stabilized above 80%.
• UVA irradiation efficiently suppressed key NOB populations (Nitrospira, Ca. Nitrotoga) while maintaining Nitrosomonas (AOB) levels.
• NOB-dominant sludge generated more intracellular ROS under UVA, leading to inactivation.
• Microalgae in the UVA reactor contributed to NOB suppression via ROS generation during photosynthesis.

Conclusions:

• Low-dose UVA irradiation is a promising and rapid method for selective NOB suppression.
• This approach facilitates reliable mainstream nitritation, overcoming previous bottlenecks.
• The mechanism involves UVA-induced ROS generation, affecting NOB more than AOB, potentially enhanced by microalgae.