The　sulfur‑iron　(II)　autotrophic　denitrification　(SIAD)　technology　can　achieve　simultaneous　nitrogen　and　phosphorus　removal　from　wastewater　with　a　low　C/N　ratio　without　an　organic　carbon　source.　However,　the　low　nutrient　removal　load　limits　its　large-scale　application.　To　enhance　N　removal　load　and　decrease　the　effluent　SO42−　concentration,　we　propose　a　novel　bioaugmentation　technology　by　adding　magnetite　to　a　sulfur‑iron　(II)　biofilter　to　generate　an　endogenous　magnetic　field　(EMF).　The　treatment　characteristics　of　two　biofilters　with　sulfur‑iron　(II)　(S1)　and　sulfur‑iron　(II)-magnetite　(S2)　were　comparatively　studied　in　long-term　experiments.　The　maximum　nitrate　removal　load　of　the　S2　system　was　1.02　±　0.04　kg　N/(m3·d),　1.27　times　higher　than　that　of　S1.　The　S2　system　also　showed　a　40　%　higher　PO43−　removal　efficiency　compared　to　S1.　The　production　of　SO42−　was　reduced　by　＞12.34　%　in　S2　with　5.40　g　SO42−/g　N.　The　EMF　significantly　increased　nitrate　reductase　activity　by　3.50　times　and　enhanced　the　size　of　the　attached　microbial　bacterial　population　by　30　%–50　%.　Functional　gene　prediction　indicated　that　amino　acid　metabolism,　cell　activity,　N/S　metabolism　were　improved　under　the　EMF,　and　the　genera　Ferritrophicum　and　Thiobacillus　were　the　predominant　autotrophic　bacteria,　forming　a　symbiotic　relationship.　Our　study　demonstrates　a　novel　solution　to　resolve　the　limits　of　high　sulfate　byproduct　and　low　nutrient　removal　load　in　SIAD　biofilters,　which　could　promote　large-scale　application　of　SIAD　process　as　a　highly　efficient　and　low-cost　postdenitrification　process.　©　2023　Elsevier　Ltd