Feammox, a “green” nitrogen removal process: Microorganism communities, related factors, benefits and challenges in wastewater treatment

Nitrogen removal from low C/N wastewater is a significant challenge, as conventional denitrification requires the addition of external carbon, thereby increasing operational costs. Feammox, an anaerobic process, is emerging as a “green” alternative for nitrogen removal. While numerous reviews on this topic exist, this paper provides several new contributions, including a comprehensive synthesis of Feammox coupling pathways, a quantitative overview of the microbial communities involved, and a critical evaluation of the process's benefits versus its drawbacks. This process offers significant benefits, including reduced energy consumption, no organic carbon requirement, and lower greenhouse gas emissions. However, its primary drawback remains a low nitrogen removal rate, linked to unresolved issues like unclear enzymatic mechanisms and unidentified key functional microorganisms. Overcoming this limitation through strategies like microbial enrichment and reactor optimization is critical to realizing the potential of Feammox for sustainable wastewater treatment. • Mechanisms, key enzymes, microbial communities, and factors affecting Feammox were reviewed. • The controversial effect of pH and carbon source on Feammox was discussed. • Feammox can occur in microaeration (DO < 1.0 mg/L), with intermittent aeration extending the iron cycle. • The Feammox process is energy-efficient with lower N 2 O and CH 4 emissions. • Low nitrogen removal rate (1.14 – 16.8 mgN/gVSS.d) is Feammox's main challenge.