Energy Efficient and Robust Shortcut Nitrogen Removal via Novel Acidic Partial Nitrification Coupling Anammox for Actual Municipal Wastewater Treatment

Acidic partial nitrification (a-PN) has great potential for efficient nitrite accumulation but may hinder subsequent anammox coupling due to its associated low pH. This study developed an acidic partial nitrification coupling anammox (a-PNA) in a single reactor to elucidate the metabolic interactions. As a prerequisite for anammox, a-PN driven by both Candidatus Nitrosoglobus and Nitrosomonas, maintains a pH below 6, achieving nondiscriminatory suppression of NOBs. Results demonstrate that a-PN is highly reproducible and has been demonstrated in biomass from four wastewater plants across China. During the a-PNA phase, 94.5% nitrogen removal efficiency (NRE) was realized, with effluent quality of 2.7 mg/L NH₄⁺–N, 0.4 mg/L NO₂^––N, and 1.1 mg/L NO₃^––N. The a-PNA could adapt to various stresses by evolving community structure, reconfiguring metabolic pathways, and regulating gene expression. Notably, the anammox community was drastically altered, with Candidatus Brocadia (4.9%), which has weak acid tolerance, being the only detectable genus. Under substrate-limited conditions, a-PNA greatly enhanced organic carbon utilization, energy metabolism, and denitrification capacity, ensuring community stability and metabolic function sustainability. Consequently, even as influent ammonia decreased to 24.2 mg/L, a robust nitrogen removal rate of 0.19 kg/m³/d and NRE of 89.3% was demonstrated. This study presents a novel, sustainable wastewater treatment approach, contributing to environmental sustainability.