The enhancement of anammox by graphene-based and iron-based nanomaterials in performance and mechanisms

Anaerobic ammonium oxidation (anammox) is a cost-effective biological nitrogen removal technology, yet its time-consuming start-up and significant environmental sensitivity are major barriers to its widespread use. Nonetheless, nanotechnology could provide an innovative approach to address these challenges, and particularly, graphene-based and iron-based nanomaterials have shown remarkable results. Graphene-based nanomaterials are beneficial due to their vast specific surface area, superior electrical conductivity, and strong biocompatibility, while iron-based nanomaterials offer valuable redox potential and are readily accessible. Although many studies have investigated the role of nanomaterials in boosting anammox processes, a deeper understanding of the mechanisms through which nanomaterials promote anammox is essential for practical application. This study provided a comprehensive summary of the latest research on how graphene-based and iron-based nanomaterials improve anammox for nitrogen removal, enhance specific anammox activity (SAA), and increase the growth rate of anammox bacteria. We also discussed their role in enhancing system stability and integrating anammox with other nitrogen removal pathways. The mechanisms by which these nanomaterials enhance anammox are analyzed and compared, focusing on extracellular polymeric substances (EPS) formation, electron transfer, functional genes and enzymes, and quorum sensing (QS). Finally, the study outlined several potential directions for future development, including identifying challenges and proposing solutions.