Two-stage partial nitritation-anammox process for high-rate mainstream deammonification

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Nitrogen Removal

Background:

• Two-stage partial nitritation (PN)-anammox processes are increasingly recognized as superior to single-stage systems for high-rate mainstream deammonification.
• Direct experimental evidence supporting the efficacy of two-stage PN-anammox for real wastewater, especially under varying winter conditions, has been limited.
• Low temperatures can significantly inhibit biological nitrogen removal processes, posing challenges for year-round wastewater treatment.

Purpose of the Study:

• To provide direct experimental evidence for the successful operation of a two-stage PN-anammox process for nitrogen removal from low-strength, anaerobically pretreated municipal wastewater during winter.
• To evaluate the impact of influent shifts and low temperatures on process performance and the stability of anammox bacteria.
• To propose a control strategy for optimizing the two-stage mainstream deammonification process.

Main Methods:

• Operation of a two-stage PN-anammox process treating anaerobically pretreated sewage under winter conditions (15-7 °C).
• Monitoring of nitrogen removal rates (NRRs), effluent total nitrogen (TN) concentrations, and chemical oxygen demand (COD) removal.
• Assessment of anammox bacteria activity and stability at low temperatures.

Main Results:

• Achieved promising NRRs of 0.28-0.07 kg N m⁻³ d⁻¹ with an average effluent TN of 5.2 mg L⁻¹.
• The first-stage PN reactor effectively removed nearly all degradable COD, protecting anammox bacteria from influent variations and temperature decreases.
• Anammox bacteria maintained high activity (76-85% of maximum potential) at low temperatures, indicating potential for higher NRRs through bioaugmentation.

Conclusions:

• The two-stage PN-anammox process is a viable and effective option for treating mainstream municipal wastewater, even in cold winter conditions.
• The process demonstrates resilience to influent changes and effectively removes COD in the first stage, safeguarding the anammox step.
• Further optimization through bioaugmentation or enrichment could significantly enhance nitrogen removal rates, making the process more efficient.