New insight and enhancement mechanisms for Feammox process by electron shuttles in wastewater treatment — A systematic review

Anammox with alternative electron acceptors: perspectives for nitrogen removal from wastewaters

“…Its relevance is the connection between the biogeochemical cycles of Fe and N, which contributes to nitrogen loss in ecosystems as diverse as paddy soils, wetland soils, riparian zones, anaerobic tropical soils, agricultural drainage ditches, eutrophic lakes, and marine sediments (Shrestha et al 2009 ; Wang et al 2018 ; Rios-Del Toro et al 2018a ; Ding et al 2021 ). Feammox is a type of extracellular respiration because, as solid electron acceptors, Fe(III) oxides cannot diffuse into the cells to receive electrons from NH 4 + -N oxidation to reduce ferric iron (Sun et al 2023 ).…”

“…Among them, direct electron transfer occurs when microorganisms and iron oxides are in direct contact through the cell membrane or, more precisely, a redox-active membrane organelle ( e.g ., cytochromes), forming an extracellular electron transfer pathway between the intracellular respiratory chain and external iron (Harnisch et al 2011 ; Xia et al 2022 ). Indirect electron transfer via exogenous compounds happens once redox active electron shuttles ( e.g ., biochar, humic substances, activated carbon, and quinones) reversibly carry the electrons released by ammonium oxidation and transfer them to solid Fe(III) oxides, resulting in their microbial reduction (Xia et al 2022 ; Sun et al 2023 ). The last mechanism of Fe(III) reduction is via chelating agents or protein nanowires, in which the chelating agent promotes the iron dissolution and facilitates the interactions between Fe(III) oxides and the microbes (Chakraborty et al 2011 ).…”

“…The last mechanism of Fe(III) reduction is via chelating agents or protein nanowires, in which the chelating agent promotes the iron dissolution and facilitates the interactions between Fe(III) oxides and the microbes (Chakraborty et al 2011 ). The last mechanism implies that protein nanowires carry out a long-range electron transfer to Fe(III) oxides by conductive filaments synthesized by microorganisms (Malvankar and Lovley 2014 ; Xia et al 2022 ; Sun et al 2023 ).…”

“…Feammox has great potential advantages for wastewater treatment: (1) It could treat industrial wastewater with high content of heavy metals, as microorganisms involved in this reaction could also reduce additional elements besides Fe (Huang and Jaffé 2015 ; Weng et al 2017 ; Xiu et al 2020 ); (2) it does not require aeration, reducing energy consumption and wastewater treatment costs (Liang et al 2022 ; Hu et al 2022 ); (3) it can be carried out in a wide pH range, especially under acidic conditions; (4) its main product is N 2 , which is harmless to humans and the environment. Furthermore, if NO 2 − -N and NO 3 − -N are formed, they can be treated by anammox and nitrate-dependent Fe(II) oxidation, respectively (Yang 2020 ; Zhu et al 2022 ; Sun et al 2023 ); and finally, 5) the generated Fe(II) can be removed by conventional techniques, such as electrocoagulation and oxidation-precipitation-filtration processes (Zhu et al 2021 ).…”

Feammox Bacterial Biofilms as an Alternative Biological Process for the Removal of Nitrogen from Agricultural Wastewater

“…Therefore, it is possible that both pathways are engaged by the consortia of bacteria that are selected with Feammox media, because it has been observed that the oxidation of ammonium to nitrate and/or nitrite by Feammox is followed by the denitrification process in an anoxic environment [35]. For this reason, a consensus has been reached that several routes of the nitrogen cycle will be favored at a neutral pH [36]. carbon limitation may be the main reason for the dramatic decrease in the growth a activity of nitrifying bacteria below a neutral pH [37].…”