The　challenge　of　sludge　digester　liquor　treatment　is　its　high　ammonium　nitrogen　(NH4+-N)　concentration.　Early　reports　found　that　complete　ammonia　oxidation　(comammox)　was　not　present　and　anaerobic　ammonia　oxidation　(anammox)　was　difficult　to　achieve　in　most　sludge　digester　liquor　treatments.　In　this　study,　NH4+-N　removal　by　cooperation　between　partial-nitrification,　comammox,　and　anammox　processes　was　achieved　in　a　sequencing　batch　reactor　(SBR)　for　sludge　digester　liquor　treatment.　The　results　showed　that　2100-2200　mg/L　of　NH4+-N　was　removed　in　the　SBR　with　98.82%　removal　efficiency.　In　addition,　55.11%　of　NH4+-N　was　converted　to　nitrite　nitrogen　(NO2--N)　by　partial-nitrification,　25.43%　of　NH4+-N　was　converted　to　nitrate　nitrogen　(NO3--N)　by　comammox,　and　18.28%　of　NH4+-N　was　removed　by　anammox.　During　the　operation,　in　the　SBR,　the　relative　abundance　of　the　dominant　ammonia-oxidizing　bacteria　(Chitinophagaceae)　was　18.89%,　that　of　the　dominant　anammox　bacteria　(Candidates　Kuenenia)　was　0.10%,　and　that　of　the　dominant　comammox　bacteria　(Nitrospira)　was　0.20%.　Therefore,　the　high　nitrogen　removal　efficiency　in　this　system　was　considered　the　result　of　the　combination　of　the　three　processes.　These　results　showed　that　comammox　and　anammox　could　play　very　important　roles　in　nitrogen　transformation　and　energy-saving　in　nitrogen　removal　systems.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.