Feasibility of simultaneous optimization of Anammox start-up and nitrogen removal performance by intermittent dosing of nanoscale zero-valent iron

[Display omitted] •Fast start-up of Anammox was achieved by intermittent dosing of zero-valent iron (nZVI).•nZVI polished effluent nitrogen concentrations with up to 91.07% nitrogen removal.•Feammox, NDFO and abiotic reactions assisted the nitrogen removal process.•nZVI contributed to the enrichment of Anammox bacteria and its functional genes.•nZVI enhanced electron transfer, heme C synthesis and iron metabolism. The long acclimation period and sensitivity to environmental conditions of Anammox are the bottlenecks for its promotion and application. An innovative strategy was adopted to accelerate functional microbial enhancement and improve nitrogen removal performance by inoculating cryopreserved Anammox sludge and activated sludge with intermittent dosing of nanoscale zero-valent iron (nZVI). The acclimation time was shortened by 76 days with nitrogen removal efficiency (NRE) reaching up to 91.07 %. Anammox, NDFO (nitrate/nitrite-dependent Fe(II) oxidation), Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) and abiotic reactions were coupled in the system with nZVI, contributing to 69.79 %, 15.14 %, 9.84 % and 0.25 % of nitrogen removal, respectively. Further microbial analysis demonstrated significant enrichment of functional microorganisms, such as Candidatus Jettenia, Acidovorax and Comamonas. High-efficient nitrogen removal was attribute to the increase of functional genes involved in Anammox, electronic transfer, heme C synthesis and iron metabolism. This work provides an inspiring idea for the mainstream Anammox application.