Heterogeneous microstructure induces floatation in high-rate anammox granules.

Area of Science:

• Environmental Microbiology
• Biotechnology
• Wastewater Engineering

Background:

• Anammox (anaerobic ammonium oxidation) granules are crucial for efficient wastewater treatment.
• Granule floatation is a significant operational challenge, leading to performance degradation and biomass loss.

Purpose of the Study:

• To investigate the mechanisms behind anammox granule floatation.
• To comparatively analyze floating anammox granules (F-AnGS) and settling anammox granules (S-AnGS).

Main Methods:

• Comparative analysis of F-AnGS and S-AnGS from a high-rate reactor.
• Anaerobic respirometry to quantify gas release.
• 3D X-ray microscopic imaging to reveal granule microstructure.
• Analysis of extracellular polymeric substances (EPS) accumulation and distribution.

Main Results:

• F-AnGS exhibited 1.6 times higher specific anammox activity than S-AnGS.
• Only 65% of produced gas was released from F-AnGS due to a dense EPS surface layer.
• F-AnGS showed a heterogeneous microstructure, distinct from S-AnGS.
• Increased abundance of functional genes related to anammox and partial denitrification in F-AnGS, indicating an enhanced nitrite loop.

Conclusions:

• The heterogeneous microstructure and EPS distribution, forming a dense surface layer, are the primary causes of anammox granule floatation.
• The unique microstructure of F-AnGS enhances microbial metabolic interactions and the nitrite loop.
• Findings suggest controlling granule activity is key for optimizing granule-based anammox processes.