Controlling nitritation in a continuous split-feed/aeration biofilm nitrifying bioreactor

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Bioreactor engineering

Background:

• Anammox processes require stable partial ammonium oxidation for efficient nitrogen removal.
• Low ammonium concentrations pose challenges for achieving stable nitritation in biofilm reactors.
• Controlling dissolved oxygen is crucial for selective ammonium oxidation.

Purpose of the Study:

• To investigate the stability of partial ammonium oxidation at low feed concentrations (50 g N/m³).
• To evaluate the performance of continuous fixed-bed up-flow biofilm reactors with recirculation-aeration for nitritation.
• To develop and validate a numerical model for predicting nitrogen species and dissolved oxygen dynamics.

Main Methods:

• Utilized continuous fixed-bed up-flow biofilm reactors with crushed basalt.
• Controlled dissolved oxygen levels via recirculation ratio (R) in synthetic medium.
• Employed quantitative Polymerase Chain Reaction (q-PCR) for microbial community analysis.
• Formulated a numerical model to simulate nitrogen species and dissolved oxygen concentrations.

Main Results:

• Achieved stable nitritation at recirculation ratios of approximately 4-6.
• Observed ~50% ammonium oxidation to nitrite with minimal nitrate accumulation (<5%).
• Ammonia-oxidizing bacteria dominated nitrifying communities; denitrifiers were negligible, and ammonium-oxidizing archaea were absent.
• The numerical model accurately predicted experimental results and showed sensitivity to oxygen uptake parameters.

Conclusions:

• Partial ammonium oxidation is stable at low concentrations in the studied biofilm reactor setup.
• The developed numerical model is a valuable tool for designing and operating such bioreactors.
• Understanding microbial community structure aids in optimizing anammox process performance.