Single-stage autotrophic nitrogen removal process at high loading rate: granular reactor performance, kinetics, and...

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Biogeochemical cycles

Background:

• The partial nitritation/anammox (PNA) process is crucial for efficient autotrophic nitrogen removal from wastewater.
• Optimizing PNA performance requires understanding the interplay between operational parameters and microbial community dynamics.

Purpose of the Study:

• To achieve the highest possible performance in a single-stage PNA process using a continuous complete-mix granular reactor.
• To investigate the relationship between reactor performance and the abundance of functional microorganisms through bacterial community analysis.

Main Methods:

• Operation of a continuous complete-mix granular reactor at increasing nitrogen loading rates.
• Characterization of bacterial community structure in granules using high-throughput pyrosequencing.
• Kinetic modeling to determine specific substrate utilization rates.

Main Results:

• A stable total nitrogen (TN) removal rate exceeding 3.9 kg N/(m3/day) was achieved at 1.9 mg/L dissolved oxygen.
• Nitrosomonas dominated the granule surface, facilitating the enrichment of anammox bacteria (Candidatus Kuenenia) in the inner layers.
• Heterotrophic organisms involved in fermentation and denitrification were also present and significant.
• Excess ammonium in bulk liquid was identified as key to suppressing nitrite-oxidizing bacteria and maintaining stability.

Conclusions:

• The study demonstrates a high-performance PNA process with optimized operational conditions and microbial community structure.
• The spatial distribution of Nitrosomonas and anammox bacteria within granules is critical for efficient nitrogen removal.
• Maintaining an ammonium excess is a viable strategy for enhancing PNA process stability.