Autotrophic　nitrogen　removal　via　anaerobic　ammonium　oxidation　(anammox)　technology　currently　faces　significant　challenges　in　treating　low-strength　wastewater　due　to　inefficient　retention　of　bacteria　and　unstable　activity　under　fluctuating　conditions.　This　study　demonstrates　enhanced　resilience　and　stability　of　anammox　coupled　with　partial　denitrification　(PD)　in　granular　sludge,　assisted　by　ferric　iron　(Fe(III))　and　nano　zero-valent　iron　(nZVI).　The　systems　treated　wastewater　with　low　concentrations　of　ammonia　(NH4+-N　of　50　∼　80　mg/L)　and　nitrate　(NO3−-N　of　60　∼　100　mg/L).　Fe(III)　and　nZVI　were　intermittently　added　to　two　PD　coupled　with　anammox　(PD/A)　systems,　which　were　subjected　to　increasing　nitrogen　loading　rates　(NLRs)　and　decreasing　temperature.　Remarkably,　both　Fe(III)-　and　nZVI-assisted　systems　achieved　satisfactory　total　nitrogen　(TN)　removal　efficiencies　of　98.1　%　and　96.6　%,　respectively,　even　as　the　temperature　dropped　from　28.5℃　to　13.4℃　and　the　NLR　increased　from　0.22　to　0.72　kgN/m3/d.　Significantly,　these　two　systems　exhibited　pronounced　resilience　under　the　shocking　effect　of　excessive　organic　load,　extremely　low　pH,　and　high　salinity.　The　presence　of　iron,　acting　as　an　accelerated　electron　transporter,　enhanced　anammox　activity　and　microbial　NH4+-N　oxidation.　Additionally,　iron　reduced　the　requirement　for　an　organic　carbon　source,　further　stimulating　the　competitiveness　of　anammox　for　nitrite　(NO2−-N)　against　denitrification.　Interestingly,　metagenomic　analysis　revealed　that　the　functional　bacteria　Thauera,　responsible　for　PD,　employed　versatile　metabolic　pathways　for　NO3−-N　reduction　to　NO2−-N　using　Fe(II)　as　an　electron　donor.　Overall,　this　study　provides　new　insights　into　microbial　interactions　and　versatile　metabolism　in　iron-assisted　anammox　systems,　contributing　to　more　energy-efficient　wastewater　treatment.　©　2024