Bioaugmentation performances with a powerful strain for nitrogen removal without N₂O accumulation

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Technologies
• Nitrogen Cycle

Background:

• Nitrous oxide (N₂O) is a significant greenhouse gas and an inevitable intermediate in conventional nitrogen removal processes.
• High N₂O emissions from wastewater treatment plants (WWTPs) necessitate improved operational strategies to mitigate environmental impact and reduce costs.

Purpose of the Study:

• To isolate and characterize a novel bacterium capable of nitrogen removal without N₂O accumulation.
• To investigate the nitrogen removal pathway, efficiency, and applicability of the isolated strain in different reactor systems.
• To assess the microbial community dynamics during the bioaugmentation process.

Main Methods:

• Isolation and identification of a novel bacterium (Citrobacter freundii XY-1).
• Analysis of nitrogen removal characteristics, including ammonium and organic carbon removal rates.
• Isotope analysis and functional gene detection to elucidate the nitrogen removal pathway.
• Bioaugmentation experiments in sequencing batch reactors (SBR) and biological aerated filters (BAF).
• Microbial diversity analysis using 16S rRNA sequencing.

Main Results:

• Citrobacter freundii XY-1 achieved 99.42% ammonium-nitrogen and 95% total organic carbon removal within 48 hours.
• High removal rates of 4.03 mg/(L·h) for ammonium-nitrogen and 39.42 mg/(L·h) for TOC were observed.
• Isotope analysis and gene detection suggested the absence of traditional denitrification and N₂O generation pathways.
• Bioaugmentation with XY-1 significantly enhanced nitrogen removal performance in both SBR and BAF reactors.
• XY-1 dominated the microbial community, with relative abundance ranging from 45% to 66%.

Conclusions:

• Citrobacter freundii XY-1 effectively removes nitrogen and organic carbon without accumulating N₂O.
• The novel nitrogen removal pathway employed by XY-1 presents a significant advancement over traditional methods.
• XY-1 is a promising candidate for enhancing the efficiency and environmental sustainability of WWTPs.