A critical review of comammox and synergistic nitrogen removal coupling anammox: Mechanisms and regulatory strategies

• Published in: The Science of the total environment 2024-10, Vol.948, p.174855, Article 174855
• Main Authors: Jin, Da, Zhang, Xiaonong, Zhang, Xingxing, Zhou, Li, Zhu, Zixuan, Deogratias, Ufoymungu Kisa, Wu, Zhiqiang, Zhang, Kangyu, Ji, Xu, Ju, Ting, Zhu, Xurui, Gao, Bo, Ji, Luomiao, Zhao, Rui, Ruth, Guerra, Wu, Peng
• Format: Article
• Language: English
• Subjects: ammonia; anaerobic ammonium oxidation; Anammox; Biological nitrogen removal; Comammox; ecophysiology; environment; Environmental factors; greenhouse gases; Hydroxylamine; intermediate product; nitrogen; nitrogen cycle; oxidation; sludge; wastewater treatment
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.174855

Nitrification is highly crucial for both anammox systems and the global nitrogen cycle. The discovery of complete ammonia oxidation (comammox) challenges the inherent concept of nitrification as a two-step process. Its wide distribution, adaptability to low substrate environments, low sludge production, and low greenhouse gas emissions may make it a promising new nitrogen removal treatment process. Meanwhile, anammox technology is considered the most suitable process for future wastewater treatment. The diverse metabolic capabilities and similar ecological niches of comammox bacteria and anammox bacteria are expected to achieve synergistic nitrogen removal within a single system. However, previous studies have overlooked the existence of comammox, and it is necessary to re-evaluate the conclusions drawn. This paper outlined the ecophysiological characteristics of comammox bacteria and summarized the environmental factors affecting their growth. Furthermore, it focused on the enrichment, regulatory strategies, and nitrogen removal mechanisms of comammox and anammox, with a comparative analysis of hydroxylamine, a particular intermediate product. Overall, this is the first critical overview of the conclusions drawn from the last few years of research on comammox-anammox, highlighting possible next steps for research. [Display omitted] •The ecophysiological characteristics of comammox bacteria were reviewed.•The enrichment strategies of comammox bacteria were summarized.•The synergy of comammox and anammox is a promising strategy for nitrogen removal.•Hydroxylamine-mediated is effective in regulating the gene expression of comammmox.•Future challenges in physiology and application of comammox bacteria were proposed.