Low-dissolved-oxygen nitrifying systems exploit ammonia-oxidizing bacteria with unusually high yields.

Area of Science:

• Environmental Science
• Microbiology
• Environmental Engineering

Background:

• Nitrifying systems in wastewater treatment typically use high aeration, increasing operational costs and carbon footprint.
• Elevated aeration is commonly employed to prevent nitrification failures.

Purpose of the Study:

• To investigate the impact of reduced aeration rates on nitrification efficiency.
• To correlate ammonia oxidation rates with ammonia-oxidizing bacterial (AOB) community structure and abundance under varying aeration levels.

Main Methods:

• Four parallel continuous-flow reactors were operated for 43 days under low (0.1 L/min) and high (4 L/min) constant airflow rates.
• Ammonia oxidation rates, AOB community structure (via denaturing gel electrophoresis and 16S rRNA gene sequencing), and AOB abundance were monitored.
• Dissolved oxygen (DO) levels were measured in all reactor configurations.

Main Results:

• Complete nitrification was achieved in all reactors, including those with low aeration (0.5 ± 0.3 mg/L DO).
• Low-DO systems showed efficient nitrification, potentially due to higher AOB levels and/or development of mixotrophic AOB communities.
• The AOB community in low-DO systems was a subset of the high-DO systems, with *Nitrosomonas oligotropha* dominating in both.

Conclusions:

• Complete nitrification is feasible at low aeration rates in laboratory-scale reactors.
• Reduced aeration can potentially lower operational costs and greenhouse gas emissions in wastewater treatment.
• Further research is needed to validate these findings in full-scale wastewater treatment plants.