Modeling nitrogen removal with partial nitritation and anammox in one floc-based sequencing batch reactor

Area of Science:

• Environmental Engineering
• Microbial Ecology
• Wastewater Treatment

Background:

• Full-scale application of partial nitritation and anammox in floc-based sequencing batch reactors (SBRs) enables high-rate nitrogen removal.
• Mechanisms ensuring reliable operation and out-competition of nitrite-oxidizing bacteria (NOB) remain poorly understood.
• Understanding microbial dynamics is crucial for optimizing nitrogen removal processes.

Purpose of the Study:

• To calibrate and validate a mathematical model for evaluating operating conditions in partial nitritation/anammox SBRs.
• To identify conditions that out-compete NOB and maintain high anammox activity during long-term operation.
• To gain insights into microbial population dynamics and nitrogen removal performance.

Main Methods:

• A mathematical model was developed and validated using experimental data from two full-scale floc-based SBRs.
• The model simulated SBR cycle profiles and long-term dynamic data under continuous and intermittent aeration strategies.
• Analysis focused on dissolved oxygen (DO) levels, sludge age, and microbial population shifts.

Main Results:

• Simultaneous ammonium oxidation and anammox occurred at DO levels of 0.15-0.3 mg O2 L⁻¹ under continuous aeration.
• Excess oxygen supply beyond ammonium oxidizer (AOB) demand promoted NOB growth, competing with anammox for nitrite.
• High anammox fractions were maintained by controlling sludge age (>40 days) and DO (~0.2 mg O2 L⁻¹), facilitating NOB washout.

Conclusions:

• The model accurately described SBR performance and provided insights into microbial dynamics.
• Continuous aeration simplifies process control compared to intermittent aeration for nitrogen removal.
• Nitrogen removal in SBRs can occur via alternating or simultaneous nitritation/anammox, suggesting flexible SBR-cycle configurations.