Why AGS–SBRs Do Not Require Separate Anoxic Selector Zones

Anoxic selector zones are commonly used in Activated Sludge SBRs to compensate for biological limitations. Their absence in AGS–SBRs reflects a fundamental difference in how nutrient removal is achieved.

Selector Zones Compensate for Activated Sludge Limitations

Activated sludge flocs lack internal redox differentiation. Selector zones artificially create environments that the biomass itself cannot sustain.

Granules Create Anoxic Zones Internally

AGS granules naturally develop oxygen gradients. Denitrification occurs inside the granule without bulk anoxic conditions.

This mechanism underpins the simultaneous nutrient removal described in Article 9.

readily biodegradable carbon is limited and valuable. Its premature consumption leaves insufficient substrate for denitrification and biological phosphorus removal, resulting in partial BNR or dependence on external carbon dosing.

Internal Carbon Storage Enables Denitrification

Stored carbon within granules supports denitrification during aerobic phases, eliminating dependence on external anoxic zones.

Simplified Hydraulics, Lower Risk

AGS–SBRs avoid internal recycle streams, selector compartments, and complex controls, improving reliability and reducing failure points.