Dual-parameter aeration control improves post-anoxic denitrification by limiting aerobic depletion of biomass-associated carbon pools.

Aeration control in anaerobic-oxic-anoxic systems must sustain nitrification while preserving carbon for post-anoxic denitrification. The effectiveness of combining rear-zone low aeration with ammonium feedback remains insufficiently resolved. A 90 m3/d pilot system was operated for 245 d under conventional aeration (CA) and dual-parameter aeration control (DPAC). DPAC adjusted blower frequency using rear-zone dissolved oxygen (0.5-1.0 mg/L) and end-of-oxic ammonium nitrogen (0.4-0.8 mg/L), with ammonium priority. Mean effluent total nitrogen decreased from 8.32 ± 0.65 to 6.56 ± 0.36 mg/L. Same-sludge batch tests showed similar ammonium oxidation rates, while subsequent anoxic nitrite-plus-nitrate removal reached 0.86 mg N/(L·h), 36.3% above CA. Longitudinal profiles showed smaller aerobic losses and greater anoxic depletion of polyhydroxyalkanoates, bound extracellular polymeric substances, and intracellular free amino acids; glycogen changed less. These patterns support preservation of biomass-associated carbon pools for post-anoxic nitrogen removal. Modeled aeration energy decreased by 7.0% per day, 8.0% per treated volume, and 15.7% per unit total nitrogen removed. These findings support the feasibility of combining spatial aeration allocation with ammonium-prioritized feedback for post-anoxic nitrogen removal under the investigated conditions.