Simultaneous autotrophic denitrification and nitrification in a low-oxygen reaction environment

Area of Science:

• Environmental microbiology
• Biotechnology
• Wastewater treatment

Background:

• Autotrophic denitrification and nitrification are key processes in nitrogen removal.
• Understanding these processes under low dissolved oxygen (DO) is crucial for optimizing bioreactor performance.
• Ammonia-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB) play vital roles.

Purpose of the Study:

• To investigate the occurrence and efficiency of simultaneous autotrophic denitrification and nitrification in a bioreactor.
• To determine the impact of varying oxygen influx rates and low DO levels on these processes.
• To identify optimal conditions for nitrogen removal via autotrophic pathways.

Main Methods:

• Utilized a bioreactor system with controlled oxygen influx and DO levels.
• Fed the bioreactor with a specific loading of ammonia nitrogen (NH4(+)-N).
• Monitored nitrogen removal rates, including autotrophic denitrification and nitrification, under different oxygen conditions.

Main Results:

• Simultaneous autotrophic denitrification and nitrification effectively removed NH4(+)-N at low DO (<0.5 mg/L) and oxygen influxes of 2-14 mg O2/h.
• Maximum nitrogen removal rates were observed within a narrow oxygen influx band (3-5 mg O2/h), accounting for up to 36% of NH4(+)-N removal.
• Autotrophic denitrification ceased at higher oxygen influxes (>16 mg O2/h), leading to increased oxidation of NH4(+)-N to NOX(-)-N.

Conclusions:

• Autotrophic denitrification and nitrification are viable processes for nitrogen removal in bioreactors, even at low DO.
• Oxygen influx is a critical parameter controlling the balance between nitrification and denitrification.
• The study provides insights for optimizing bioreactor design and operation for efficient nitrogen removal.