Initial free ammonia is critical for robust acidic partial nitrification in sequencing batch reactor

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Microbial Ecology

Background:

• Partial nitrification (PN) implementation is hindered by low influent ammonium (NH₄⁺-N) concentrations.
• Stability and inhibition boundary conditions for nitrite-oxidizing bacteria (NOB) in sequencing batch reactors (SBRs) treating low-strength wastewater are not well-defined.
• Dynamic environmental factors in SBRs complicate achieving stable PN.

Purpose of the Study:

• To identify critical factors for stable partial nitrification (PN) in SBRs.
• To extend the boundary conditions for stable PN under dynamic environmental conditions.
• To investigate the combined inhibition of free ammonia (FA) and free nitrous acid on NOB in SBRs.

Main Methods:

• Long-term operation (580 days) of a conventionally configured SBR.
• Investigation of combined inhibition by dynamic free ammonia (FA) and free nitrous acid on different NOB.
• Kinetic parameter measurement and model development for predicting PN conditions.

Main Results:

• Initial free ammonia (FA) concentration is critical for establishing PN under low-alkalinity conditions.
• Nitrospira NOB are highly sensitive to FA inhibition (K_{I_FA}=0.35 mg NH₃-N/L), reducing required FA levels.
• Lowering pH to 5.4 effectively inhibited acid-intolerant Ca. Nitrotoga NOB, crucial for maintaining PN.

Conclusions:

• Initial FA concentration is a critical factor for achieving stable and robust acidic partial nitrification (PN) in SBRs.
• Controlling FA and pH provides effective inhibition of NOB, enabling stable PN in low-strength wastewater.
• Study findings offer guidance for robust acidic PN implementation in conventional SBRs.