Novel insights into carbon nanomaterials enhancing anammox for nitrogen removal: Effects and mechanisms

Carbon nanomaterials (CNMs) possess the properties including large specific surface area, high porosity, and stable chemical structures, presenting significant application advantages in wastewater treatment. Indeed, CNMs are considered to be added to anammox systems to strengthen anammox function, especially to resolve the challenge of anammox technology, i.e., the slow growth rate of anammox bacteria, as well as its high environmental sensitivity. This paper systematically reviews the promotion effects and mechanisms of CNMs on the nitrogen removal performance of anammox system. Among the zero-, one-, and two-dimensional CNMs, two-dimensional CNMs have best promoting effect on the nitrogen removal performance of anammox system due to its excellent conductivity and abundant functional groups. Then, the promotion effects of CNMs on anammox process are summarized from the perspective of anammox activity and bacteria abundance. Furthermore, CNMs not only enhance the anammox process, but also stimulate the coupling of denitrification pathways with anammox, as well as the improvement of system operational stability (alleviating the inhibitions of low temperature and pH fluctuation), thus contributing to the promoted nitrogen removal performance. Essentially, CNMs are capable of facilitating microbial immobilization and electron transfer, which favor to improve the efficiency and stability of anammox process. Finally, this review highlights the gap in knowledge and future work, aiming to provide a deeper understanding of how CNMs can strengthen the anammox system and provide a novel perspective for the engineering of the anammox process.