Combined nitritation-anammox: advances in understanding process stability.

Area of Science:

• Environmental Microbiology
• Wastewater Treatment Engineering
• Biogeochemical Cycles

Background:

• The nitritation-anammox process efficiently removes ammonium from wastewater with limited organic matter.
• Process instabilities can lead to temporary failures in full-scale applications.
• Understanding the causes of instability is crucial for optimizing nitrogen removal.

Purpose of the Study:

• To evaluate conditions causing instability in the nitritation-anammox process.
• To identify strategies for regaining efficient operation after instability.
• To investigate the roles of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in process stability.

Main Methods:

• Analysis of full-scale operational data, including ammonium and nitrite levels.
• Laboratory-scale experiments to simulate and test inhibition effects on AOB and anammox bacteria.
• Comparison of parallel full-scale reactors to assess factors influencing NOB abundance.

Main Results:

• Partial AOB inhibition was identified as a primary cause of instability, leading to secondary anammox inhibition due to oxygen depletion.
• Anammox bacteria inhibition is reversible, occurring at 0.2 mg O(2) · L(-1) but recovering rapidly.
• Increased NOB abundance, potentially linked to excessive oxygen supply, competes with anammox bacteria for nitrite.

Conclusions:

• Variable AOB activity is critical for reactor stability; monitoring ammonium signals can indirectly detect imbalances.
• Managing oxygen supply in relation to AOB activity is essential to prevent NOB overgrowth.
• Strategies like maintaining a sludge age of 45 days and controlling air supply based on nitrate levels can mitigate NOB proliferation; molecular methods are suggested for early detection.