'Protector' DNRA bacteria, shielding anammox systems from perfluorooctanoic acid by mitigating nitrite accumulation

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Bioreactor engineering

Background:

• The anaerobic ammonium oxidation (anammox) process is crucial for nitrogen removal in wastewater treatment.
• Perfluorooctanoic acid (PFOA) is a contaminant that can inhibit anammox process efficiency.
• Understanding protective mechanisms against PFOA toxicity is vital for maintaining anammox performance.

Purpose of the Study:

• To investigate the protective role of dissimilatory nitrate reduction to ammonium (DNRA) against PFOA toxicity in an anammox-AnMBR.
• To analyze the microbial community dynamics and defense responses under PFOA exposure.
• To elucidate the mechanisms by which DNRA mitigates PFOA's impact on anammox bacteria.

Main Methods:

• Operation of a lab-scale anaerobic membrane bioreactor (anammox-AnMBR) for over 100 days.
• Stepwise exposure to increasing concentrations of PFOA (0.25, 0.5, 0.75 mg/L).
• Monitoring of nitrogen removal efficiency, extracellular polymeric substance (EPS) production, and microbial community dynamics via metagenomic sequencing.

Main Results:

• DNRA bacteria exhibited greater tolerance to PFOA than anammox bacteria, even at high concentrations.
• Anammox functional gene abundances (hzs, hdh) initially increased then declined with rising PFOA levels.
• Significant increases in EPS (polysaccharides and proteins) indicated a defense response by the microbial community.

Conclusions:

• DNRA plays a protective role in mitigating PFOA toxicity towards anammox bacteria in an anammox-AnMBR.
• The microbial community employs EPS production as a defense mechanism against PFOA stress.
• DNRA's resilience suggests its potential utility in enhancing the stability of anammox systems facing PFOA contamination.