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[Display omitted] • Nature based redox materials can serve as electron acceptors and donors. • Complete nitrogen removal based on redox materials. • Emergence of a new pathway for anerobic ammonium oxidation. • Nature-based sustainable solutions for nitrogen management. Complete nitrogen removal depends on the requirement of oxygen as an electron acceptor and organics as electron donors. In the natural environment, these electron acceptors and donors regulate the nitrogen cycle in association with several nature-based processes, such as iron dependent (feammox), sulphur dependent (sulfammox), and nitrite dependent (annamox). These processes represent the latest discoveries in the nitrification part of the nitrogen cycle and provide the electron acceptors for anaerobic ammonium oxidation. Research findings on these processes suggest that a previously undescribed pathway is available for anaerobic ammonium oxidation, which can regulate the nitrogen cycle in natural environments. It has been shown that some redox active materials can serve simultaneously as electron acceptors and donors in the nitrogen cycle. This review provides comprehensive information of the known oxidative processes in the nitrogen cycle and highlights the emergence of a new pathway for anaerobic NH 4 + oxidation, which is dependent on insoluble redox active materials as electron donors and acceptors. This new pathway is not limited to anaerobic NH 4 + oxidation, but it also includes reductive pathways to nitrogen gas, and thus can lead to complete nitrogen removal from nitrogen environments. Recent developments and knowledge advancement in the nitrogen cycle open a new path for nature-based sustainable solutions for nitrogen management. This new knowledge can provide innovative and novel approaches for conventional NH 4 + removal processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple mediators function as electron shuttles to promote anammox process; • The EET capability of anammox bacteria can be facilitated by external mediators; • The concurrent presence of mediators triggered the activation of essential enzymes; • The application perspective should focus on the EET-enhanced anammox optimization. The anaerobic ammonium oxidation (anammox) process, transforming ammonia into nitrogen gas in oxygen-free environments using nitrite as an electron acceptor, is increasingly recognized for its potential in treating ammonium-rich wastewater. A major challenge for widespread application of this technology is the limited presence of nitrite in most wastewaters. The intrinsic electroactivity of anammox bacteria implies that the introduction of exogenous additives through the extracellular electron transfer (EET) process could effectively stimulate ammonia oxidation even in the absence of nitrite. This comprehensive review consolidates various approaches to enhance EET-dependent anammox, including the utilization of carbonaceous materials, metal ions, and humic substances. Molecular mechanisms involved in enhancing nitrogen removal performance based on extracellular electron transfer capacity are expounded. The co-occurrence of electron acceptors and exogenous electron shuttles is proposed to increase the activity of c-type cytochromes (c -Cyts) and N-acyl-homoserine lactones (AHLs) in extracellular polymeric substances (EPS), as well as enzymes such as hydrazine synthase (HZS) and hydrazine dehydrogenase (HDH), leading to stable a nitrogen removal performance. This review presents novel insights into the engineering of the EET-enhanced anammox process, providing a theoretical framework for its advancement and optimization. [ABSTRACT FROM AUTHOR]