Revisiting the interplay between Comammox and Anammox: cooperative or competitive?

Complete ammonia oxidation (Comammox) has challenged the traditional two-step nitrification paradigm and reshaped the understanding of nitrogen removal in wastewater treatment. Anaerobic ammonia oxidation (Anammox) technology is considered as a suitable process for future wastewater treatment. However, the limited availability of substrates for Anammox has consistently hindered its broader application. The Comammox process has often been neglected in previous studies of Anammox. However, as far as the current study is concerned, Comammox may contribute to the advancement of wastewater treatment in the future with its wide distribution, strong environmental adaptability and low greenhouse-gas emissions. Recent studies have shown that Comammox may have the ability of nitrite leakage during ammonia oxidation, which provides a new pathway for substrate acquisition for the Anammox process. In this study, the relationship between Comammox and Anammox was elaborated based on their functions by comparing the distribution of both, as well as the similarity and specificity of the effects of different environmental factors on them. It was noted that the synergistic effects of Comammox and Anammox should be further explored. A possible strategy to achieve a fast nitrite supply by Comammox is proposed and the optimization of kinetic parameters is suggested.