Dynamic pH regulation drives Nitrosomonas for high-rate stable acidic partial nitritation

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering
• Biochemical process optimization

Background:

• Ammonia oxidation rate (AOR) intensification is crucial for acidic partial nitritation technologies.
• High free nitrous acid (FNA) levels in acidic conditions inhibit ammonia-oxidizing bacteria (AOB).
• Existing methods struggle with AOB inhibition by FNA, hindering process development.

Purpose of the Study:

• To propose and evaluate a dynamic acidic pH regulation control strategy for high-rate acidic partial nitritation.
• To investigate the long-term effects of dynamic pH on nitrifying bacterial activity in a laboratory-scale reactor.
• To enable efficient partial nitritation using the common AOB genus Nitrosomonas.

Main Methods:

• Utilized a laboratory-scale sequencing batch moving bed biofilm reactor (SBMBBR) for 700 days.
• Implemented a dynamic acidic pH regulation control strategy.
• Monitored influent ammonia concentration, nitrite accumulation ratio, AOR, and FNA levels.
• Assessed the inactivation rates of nitrite-oxidizing bacteria (NOB) and AOB by FNA.

Main Results:

• Achieved a nitrite accumulation ratio exceeding 90% with an influent NH4+-N concentration of approximately 100 mg/L.
• Reached a maximum AOR of 14.5 ± 2.6 mg N L-1h-1.
• Demonstrated that FNA at 6.5 mg HNO2N/L effectively inactivated NOB (inactivation rate 0.61 ± 0.08 h-1) while minimally affecting Nitrosomonas (inactivation rate 0.06 ± 0.01 h-1).
• Maintained effluent pH at 4.5, with periodic FNA reaching levels sufficient for NOB inactivation.

Conclusions:

• Dynamic acidic pH regulation is a viable strategy for high-rate acidic partial nitritation.
• Nitrosomonas can effectively drive partial nitritation under dynamic acidic conditions with controlled FNA exposure.
• This approach offers a pathway for stable and efficient acidic partial nitritation, overcoming AOB inhibition challenges.