Temperature effects on nitrogen removal and N₂O emissions in anammox reactors

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Greenhouse gas emissions

Background:

• Mainstream anammox processes struggle with temperature fluctuations and nitrous oxide (N2O) emissions.
• Attached-growth systems offer potential for enhanced microbial stability in wastewater treatment.

Purpose of the Study:

• To investigate the impact of rapid temperature shifts (15-55°C) on nitrogen removal and N2O emissions in attached-growth anammox reactors.
• To identify optimal temperature ranges for anammox process efficiency and minimal greenhouse gas release.

Main Methods:

• Utilized attached-growth anammox reactors subjected to controlled temperature variations from 15°C to 55°C.
• Monitored nitrogen removal rates and quantified N2O emissions under different thermal conditions.
• Analyzed anammox bacterial populations and overall bioactivity in response to temperature stress.

Main Results:

• Nitrogen removal rates were sustained at lower temperatures (15-25°C) but significantly decreased at higher temperatures (45-55°C) due to reduced anammox biomass and bioactivity.
• The reactor operated at 35°C demonstrated the lowest N2O emissions (<1.0 mgN/(L·d)).
• Elevated N2O emissions were observed at 15°C (approx. 5.0 mgN/(L·d)) and 55°C (approx. 3.4 mgN/(L·d)), attributed to concurrent denitrification.

Conclusions:

• Attached-growth anammox processes exhibit varying temperature adaptability, with performance degradation at temperatures above 40°C.
• Temperature management is crucial for mitigating N2O emissions, with 35°C identified as a favorable operating point.
• Findings support the optimization of mainstream anammox applications by considering thermal resilience and greenhouse gas management.