In　this　study,　different　concentrations　of　Fe(II)　(0,　1.00,　7.00　mg/L)　were　introduced　to　investigate　the　effect　on　the　removal　of　Mn(II)　in　the　biofilter.　Fe(II)　significantly　inhibited　the　removal　of　Mn　and　prolonged　the　start-up　of　biofilters,　the　start-up　periods　for　the　biofilters　with　different　Fe(II)　concentrations　(0,　1.00　and　7.00　mg/L)　were　24,　30　and　46　days,　respectively.　The　study　showed　that　Fe(II)　and　the　Fe(III)　oxyhydroxides　generated　from　Fe(II)　oxidation　inhibited　the　removal　of　Mn(II)　by　affecting　the　proliferation　of　manganese-oxidizing　bacteria　(MnOB)　and　the　activity　of　manganese　oxides　(MnOx)　in　the　biofilter.　On　day　20,　the　total　MnOB　genera　proportions　were　13.44　%,　13.35　%　and　20.09　%　with　different　Fe(II)　concentrations　(0,　1.00,　7.00　mg/L),　respectively.　The　addition　of　Fe(II)　significantly　impeded　the　proliferation　of　Pseudomonas,　Acinetobacter　and　Arthrobacter,　but　enhanced　the　proliferation　of　Hyphomicrobium　and　Sphingopyxis.　On　day　60,　the　abundance　of　total　MnOB　was　reduced　obviously　in　three　biofilters　(6.95　%,　6.44　%　and　9.76　%).　This　indicated　that　the　biological　oxidation　of　Mn　dominates　during　the　initial　operation　stage　of　the　filter　layer,　while　the　chemical　auto-catalytic　oxidation　of　active　MnOx　dominates　in　the　later　stages.　The　contribution　of　Mn　removal　by　biological　oxidation　was　positively　correlated　with　the　abundance　of　MnOB,　and　batch　experiments　confirmed　this　conclusion.　Moreover,　the　addition　of　Fe(II)　reduced　MnOx　activity　by　suppressing　the　production　of　high-reactivity　intermediate-Mn(III),　and　Fe(III)　oxyhydroxides　hindered　the　formation　of　mature　MnOx　films　on　the　surface　of　the　filter　media.　©　2023　Elsevier　Ltd