A critical review of impact and synergistic mechanisms of iron and co-elements in anammox

Abstract

Iron has a significant role in the anaerobic ammonia oxidation (anammox) process. Studying iron and its synergies with other elements is essential for optimizing and improving anammox technology. To this end, this paper systematically reviews the impacts of iron in three distinct forms: iron ions, iron minerals, and zero-valent iron on the anammox process, and further explores the effects of combinations of iron with elements such as manganese, sulfur, and carbon on the anammox and the mechanisms of their effects. Firstly, iron itself can markedly augment the nitrogen removal efficiency in the anammox process, and at the same time can provide an electron donor and influence bacterial activity. Additionally, in the synergy between iron and other elements, Fe-Mn synergism can provide additional electron acceptors and promote Fe (II) regeneration through Mn4+ reduction, enhancing microenvironmental conditions, bacterial growth, activity, and nitrogen removal, thereby improving treatment efficiency and system stability. Next, in the iron-sulfur synergy, sulfide acts as an electron donor, enhances nitrogen removal, and reduces nitrate and nitrite accumulation, thereby optimizing the reaction conditions and the stability of the anammox colony. Finally, the iron-carbon synergy optimizes the equilibrium between electron donors and acceptors by supplementing the carbon source, markedly boosting the efficiency of nitrogen removal and the diversity of anammox colonies. This review underscores the various functions of iron within the anammox process and its synergistic effects with other elements, aiming to provide insights for future research and practical applications.