Advancements and challenges of partial denitrification/anammox technology: Implementation strategies for plug-flow municipal wastewater treatment.

This review systematically summarizes the latest advances, key challenges, and engineering application strategies of partial denitrification/anammox (PD/A) technology, with a particular focus on plug-flow biosystems. The plug-flow process is widely used, yet its effluent often fails standards due to low C/N ratios. To address this carbon deficiency, PD/A leverages its own low-carbon metabolic feature to offer a promising upgrade pathway toward compliant discharge. Here, this review highlights latest strategies developed to enhance nitrogen removal efficiency (NRE) in plug-flow PD/A systems, including the use of biological carriers, improved temperature adaptation, and optimized suspended sludge management, and emphasizes the need for further breakthroughs to overcome microbial competition. Comprehensive studies demonstrate that through the synergistic regulation of biofilm establishment and sludge management, PD/A technology can achieve excellent autotrophic nitrogen removal in plug-flow systems, effectively mitigating the adverse effects of low temperature and carbon deficiency. However, niche competition and long-term stable contribution of autotrophic nitrogen removal remain core bottlenecks for engineering application, urgently requiring multi-process coupling control strategies.