One　lab-scale　biofilter　that　simultaneously　removes　Fe,　Mn　and　ammonia　from　4　degrees　C　groundwater　was　established　to　investigate　the　nitrogen　conversion　process.　The　results　showed　that　333　days　were　needed　to　achieve　the　required　standards　for　Fe,　Mn　and　ammonia　under　a　filtration　rate　of　3　m/h.　Effluent　nitrite　concentration　was　the　key　factor　determining　the　final　operation　parameters.　Both　nitrification　and　anaerobic　ammonium　oxidation　(ANAMMOX)　contributed　to　nitrogen　conversion.　The　calculation　results　demonstrated　that　autotrophic　nitrogen　removal　proportion　was　about　15.92%　in　steady　operation　period.　Meanwhile,　7　genera　of　Mn　oxidizing　bacteria　(MnOB)　were　detected;　Candidatus　Brocadia　was　the　only　detected　ANAMMOX　genera.　The　corresponding　functional　oxidizing　bacteria　could　be　acclimated　sufficiently　in　biofilter　treating　low-temperature　groundwater.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.