Enhanced Nitrogen Removal from Landfill Leachate via a Two-Stage A/O–MBBR System Coupled with Anammox
Landfill leachate, characterized by high ammonia nitrogen, high organic load, complex toxic components, and low nitrogen removal efficiency, poses significant environmental challenges. To achieve efficient nitrogen removal, a continuous-flow two-stage anoxic/oxic (A/O) moving-bed biofilm reactor (MBBR) system coupled with anaerobic ammonium oxidation (Anammox) was constructed and operated for long-term treatment of actual landfill leachate. After biofilm attachment and multi-gradient acclimation, influent concentrations were gradually increased from low levels (NH4+-N ~200 mg·L−1, COD ~2500–3000 mg·L−1) to high levels (NH4+-N ~1800 mg·L−1, COD ~8500 mg·L−1). During stable operation, average removal efficiencies of NH4+-N and COD reached 97.7% and 66.8%, respectively, with total nitrogen (TN) removal efficiency improving to 93.9%. Along the reactor, the first A/O stage achieved major organic degradation and ammonia oxidation, while the second stage facilitated nitrite accumulation and promoted Anammox for synergistic nitrogen removal. High-throughput sequencing revealed Proteobacteria as the dominant phylum (>50%), with denitrifying genera such as Azoarcus and Thauera significantly enriched. Planctomycetota abundance increased from 0.6% to 3.7%, and Candidatus Kuenenia was detected, confirming successful Anammox colonization and participation in nitrogen removal. This study validates the efficient combined nitrogen removal mechanism of the A/O–MBBR system with Anammox, providing theoretical basis and technical support for engineering treatment of high-ammonia wastewater.