Optimizing nitrogen removal in PD/A reactors: Effects of influent composition and temperature on system stability and...

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biogeochemical Cycles

Background:

• Partial denitrification/anammox (PD/A) is a key process for nitrogen removal in wastewater treatment.
• Temperature fluctuations can significantly impact the efficiency and stability of PD/A systems.
• Understanding microbial community dynamics is crucial for optimizing PD/A performance under varying conditions.

Purpose of the Study:

• To investigate the performance and microbial community shifts in PD/A reactors with different influent compositions under a decreasing temperature gradient.
• To evaluate the impact of influent nitrogen ratios on nitrogen removal efficiency and stability.
• To identify microbial mechanisms responsible for stable PD/A performance during temperature reduction.

Main Methods:

• Operation of two lab-scale PD/A reactors (R1 and R2) with distinct influent nitrogen and COD/NO3- ratios.
• Controlled reduction of temperature from 30°C to 20.92°C over 76 days.
• Monitoring of nitrogen removal performance, specific anammox activity (SAA), and microbial community composition (anammox bacteria abundance and key gene expression).

Main Results:

• A 3:3:1 NH4+/NO2-/NO3- ratio (R1) resulted in more stable nitrogen removal compared to R2 during temperature decrease.
• Specific anammox activity declined linearly with temperature, but the relative abundance of Ca. Brocadia increased in R1.
• R1 exhibited a higher percentage of anammox-related key genes, indicating a robust microbial community structure.

Conclusions:

• Influent nitrogen composition critically influences PD/A system stability under thermal gradients.
• Optimizing influent ratios, particularly the NH4+/NO2-/NO3- ratio, is essential for robust nitrogen removal.
• Microbial community structure, specifically the abundance of anammox bacteria and related genes, underpins system stability.