Enhancing single-stage partial nitritation-anammox process with airlift inner-circulation and oxygen partition: A novel strategy for treating high-strength ammonium wastewater.

In the single-stage partial nitritation-anammox process for high-ammonium wastewater treatment, the presence of sufficient biomass with high activity is essential. This study developed an innovative airlift inner-circulation partition bioreactor (AIPBR) with a dual-cylinder structure. During the 362 days' operation, the AIPBR exhibited robust and stable nitrogen removal performance under diverse influent ammonium spanning from 300 to 1800 mg N/L. Notably, when the influent ammonium was 1820 ± 34 mg N/L, the nitrogen removal rate reached 3.194 ± 0.074 kg N/m³/d, accompanied by removal efficiency of 87.6 ± 1.5%. The unique design of the reactor enabled the formation of dissolved oxygen gradient, which improved the synergy of functional microorganisms by facilitating mass transfer within the sludge. Additionally, it maintained appropriate hydraulic shear in the inner cylinder to support granule formation and simultaneously reduced excessive flow in the outer cylinder to prevent sludge loss. Through the cyclic granulation, the system fostered a symbiotic consortium of flocculent and granular sludge with particle size predominantly distributed within the range of 200-400 μm, which enhanced the activity of microorganisms. These findings highlight the potential of AIPBR as a novel and effective strategy for high-ammonium wastewater treatment.