A comprehensive root cause analysis of anammox bioreactor performance decline

Area of Science:

• Environmental microbiology
• Bioreactor engineering
• Wastewater treatment

Background:

• Anaerobic ammonia oxidizing bacteria (anammox) are crucial for nitrogen removal in wastewater treatment.
• Despite advances, anammox bioreactor failures are common, necessitating a deeper understanding of decline mechanisms.

Purpose of the Study:

• To investigate the sequence of events leading to an anammox bioreactor performance decline.
• To identify early warning signals of process deterioration for timely intervention.

Main Methods:

• Utilized a lab-scale anammox-sequencing batch reactor (SBR).
• Employed various measurement techniques to monitor bioreactor performance under increasing nitrogen loading rates (NLR).
• Analyzed changes in free ammonia (FA), free nitrous acid (FNA), N2 production, specific nitrogen removal rate (SNRR), and extracellular polymeric substances (EPS).

Main Results:

• Bioreactor failure occurred at an NLR of 2.01 kg-N·m⁻³·d⁻¹, following stable operation up to 1.669 kg-N·m⁻³·d⁻¹.
• Elevated NLR caused significant increases in FA and FNA, leading to reduced N2 production and SNRR.
• Microbial activity shifted, with increased syntrophic decomposer activity, CO2 production, pH decrease, and higher EPS secretion by anammox bacteria.

Conclusions:

• The study elucidates the complex cascade of biochemical and microbial changes during an anammox bioreactor failure.
• Understanding these signals allows for proactive management strategies to prevent or mitigate performance loss in anammox systems.