Granular Stratification Enables Stable and Efficient Nitrogen Removal in Anammox Sludge Bed Reactors

Area of Science:

• Environmental biotechnology
• Microbial ecology
• Wastewater treatment

Background:

• The granule-based anammox process is a key technology for nitrogen removal.
• Simultaneously achieving high rates and efficiency in anammox processes remains a challenge.

Purpose of the Study:

• To enhance nitrogen removal performance by coupling two granule types with complementary kinetics in an anammox sludge bed reactor.
• To investigate the self-organization and stability of stratified granules.

Main Methods:

• Coupling bright red granules (high activity, low affinity) and yellow-brown granules (low activity, high affinity) in a sludge bed reactor.
• Analyzing physicochemical properties and microbial communities of stratified granules.
• Implementing a sludge withdrawal strategy to maintain stratification.

Main Results:

• Self-organized stratification of granules based on substrate affinity and concentration gradients was achieved.
• The stratified reactor demonstrated a high nitrogen removal rate (14.5 kg-N/(m³·d)) and efficiency (90.2%).
• Granule stratification was primarily governed by structure and mass transfer, not intrinsic microbial differences.

Conclusions:

• Granule stratification is a viable strategy for optimizing anammox bioreactor performance.
• Understanding granule heterogeneity and mass transfer is crucial for designing efficient nitrogen removal systems.
• Active sludge management can maintain stable stratification for sustained high performance.