Novel insights into Feammox coupled with the NDFO: A critical review

Ammonium oxidation coupled with Fe(III) reduction, known as Feammox, and nitrate-dependent ferrous oxidation (NDFO) are two processes that can be synergistically achieved through the Fe(III)/Fe(II) cycle. This integrated approach enables the simultaneous removal of ammonia nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) from wastewater, representing a novel method for complete nitrogen removal. This study presents a systematic and exhaustive examination of the Feammox-NDFO coupled process. An initial thorough exploration of the underlying mechanisms behind the coupling process is conducted, highlighting how the Fe(III)/Fe(II) cycle enables the concurrent occurrence of these reactions. Further, the functional microorganisms associated with and playing a crucial role in the Feammox-NDFO process are summarized. Next, the key influencing factors that govern the efficiency of the Feammox-NDFO process are explored. These include parameters such as pH, temperature, carbon source, iron source, nitrogen source, and various electron shuttles that may mediate electron transfer. Understanding the impact of these factors is essential for optimizing the process. The most recent trends and endeavors on the Feammox-NDFO coupling technology in wastewater treatment applications are also examined. This includes examining both laboratory-scale studies and field trials, highlighting their successes and challenges. Finally, an outlook is presented regarding the future advancement of the Feammox-NDFO technology. Areas of improvement and novel strategies that could further enhance the efficiency of simultaneous nitrogen removal from the iron cycle are discussed. In summary, this study aspires to offer a thorough comprehension of the Feammox-NDFO coupled process, with a focus on its mechanisms, influencing factors, applications, and prospects. It is anticipated to yield invaluable insights for the advancement of process optimization, thus sparking fresh ideas and strategies aimed at accomplishing the thorough elimination of nitrogen from wastewater via the iron cycle.