[Comparison of the Microbial Community Structure in Nitrifying Processes Operating with Different Dissolved Oxygen...

Area of Science:

• Environmental Microbiology
• Wastewater Treatment
• Microbial Ecology

Background:

• Nitrification is crucial for wastewater treatment, converting ammonia to nitrate.
• Dissolved oxygen (DO) levels are critical operational parameters influencing microbial community structure and function in nitrifying reactors.
• Understanding microbial community dynamics under varying DO conditions is essential for optimizing nitrification efficiency.

Purpose of the Study:

• To investigate the impact of different dissolved oxygen (DO) levels on the microbial community structure and function of nitrifying reactors.
• To compare the microbial richness, diversity, and functional organization between reactors operated under low and high DO conditions.
• To identify key microbial taxa and their relative abundance shifts in response to varying DO levels.

Main Methods:

• High-throughput sequencing was employed to analyze the microbial community structure.
• Nitrifying reactors were operated under two distinct dissolved oxygen (DO) levels: low (0.2-0.3 mg·L⁻¹) and high (2.0±0.1 mg·L⁻¹).
• Bioinformatic analyses were performed to assess microbial richness, diversity, and relative abundance of key taxa.

Main Results:

• The low DO reactor (R_L) exhibited significantly higher microbial richness and diversity compared to the high DO reactor (R_H).
• The high DO reactor (R_H) demonstrated a more functionally organized microbial community.
• While sharing over 85% genetic information, relative abundances of specific species differed; Proteobacteria, including *Nitrosomonas*, were enriched in R_H, whereas R_L showed a more diverse community including Firmicutes, Bacteroidetes, and anaerobic/anoxic functional bacteria.

Conclusions:

• Dissolved oxygen levels significantly influence the structure and diversity of microbial communities in nitrifying reactors.
• While *Nitrospira defluvii* dominated nitrite oxidation in both conditions, ammonium-oxidizing bacteria (*Nitrosomonas oligotropha*, *Nitrosomonas europaea*) showed differential enrichment.
• Ammonia and nitrite availability appear to be more critical factors than DO in the selective enrichment of specific nitrifier populations.