[High-rate Nitrogen Removal in a Two-stage Partial Nitritation-ANAMMOX Process Under Mainstream Conditions]

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biotechnology

Background:

• Low-strength ammonia wastewater presents treatment challenges, especially at ambient/low temperatures.
• Conventional nitrogen removal processes can be energy-intensive and less efficient under cold conditions.
• The partial nitritation (PN)-ANAMMOX process offers a promising alternative for efficient nitrogen removal.

Purpose of the Study:

• To evaluate the performance of a two-stage PN-ANAMMOX process for treating low-strength ammonia wastewater at low temperatures (10-20°C).
• To investigate the impact of temperature on the PN and ANAMMOX reactions and identify rate-limiting steps.
• To propose a control strategy for optimizing nitrogen removal in the PN-ANAMMOX process.

Main Methods:

• Implementation and operation of a two-stage PN-ANAMMOX reactor system.
• Monitoring of key parameters including ammonium, nitrite, nitrate, and total nitrogen concentrations.
• Temperature variation experiments (10-20°C) to assess process kinetics and activity-temperature coefficients.
• Analysis of PN and ANAMMOX sludge characteristics and performance.

Main Results:

• The two-stage PN-ANAMMOX process achieved total nitrogen removal rates >0.6 kg·(m³·d)⁻¹ and efficiencies >80% between 20°C and 14°C.
• Anammox reaction was identified as the rate-limiting step at 12°C, while PN reaction remained unaffected.
• Anammox bacteria exhibited higher temperature sensitivity (θ=1.172) compared to ammonium oxidizing bacteria (AOB) (θ=1.056).
• Nitrogen removal loading rate was primarily controlled by anammox biomass quantity and activity, while efficiency depended on PN performance.

Conclusions:

• The two-stage PN-ANAMMOX process is effective for low-strength ammonia wastewater treatment at low temperatures.
• Anammox biomass is critical for maintaining high nitrogen removal rates, and its temperature sensitivity influences process performance.
• A hierarchically separate control strategy is proposed for optimizing high-rate nitrogen removal in mainstream PN-ANAMMOX systems.