Efficiency and microbial mechanism of iron minerals in enhancing the anammox: a review

Abstract:

As the nitrogen cycle is cross-linked with the iron cycle in the nature, the metabolism and activity of anaerobic ammonia oxidation (anammox) bacteria involved in the nitrogen cycle are also closely related to the iron element. Being ubiquitous in the nature, iron minerals have been widely used for wastewater treatment, owing to the advantages of low operating cost, good stability, and low secondary pollution. The addition of a moderate amount of iron minerals not only can promote the enrichment of anammox bacteria and iron-reducing bacteria in the anammox system, and increase the abundance of functional genes and the activities of related enzymes, but also can regulate the sludge concentration, heme c content, extracellular polymeric substance (EPS) content, and granulation degree to improve the sludge properties and the anammox system stability. Meanwhile, iron minerals have the potential to promote the coupling of multiple nitrogen transformation pathways, such as the anammox, nitrate-dependent Fe(II) oxidation (NDFO), ferric ammonium oxidation (Feammox), dissimilatory nitrate reduction to ammonia (DNRA), and denitrification, which can improve the total nitrogen removal efficiency for the anammox system. Focusing on the good performance of iron minerals in promoting biological denitrification of wastewater and their varieties in the anammox system, the mechanism of iron minerals in enhancing the anammox system is systematically summarized in this study from nitrogen removal efficiency, sludge properties, microbial community characteristics, and enzymes activities. Moreover, the future research directions are prospected from the perspectives of the utilization of iron minerals and the uptake of the iron element by anammox bacteria, aiming to provide theoretical and technical guidance for the application of iron minerals in the anammox system.