Mainstream　anammox　still　faces　the　challenges　of　non-ideal　NO2-/NH4+　ratios　and　excess　nitrate　resulted　from　the　instability　of　partial　nitrification　(PN)　in　municipal　wastewater.　To　address　these　problems,　in　this　study,　we　developed　a　novel　two-sludge　process　that　combined　PN　with　synchronous　anammox　and　endogenous　partial　denitrification　(SAEPD);　the　process　was　tested　with　pre-treated　domestic　sewage　at　ambient　temperatures　for　205　d.　High　nitrogen　removal　efficiency　of　91.2%　was　achieved　with　an　influent　C/N　ratio　of　1.7　at　15.4　degrees　C;　the　success　was　attributed　to　the　fact　that　EPD　replenished　the　deficient　nitrite　by　reducing　nitrate　and　the　excess　nitrite　was　further　reduced　to　nitrogen　gas.　With　a　non-ideal　NO2-/NH4+　ratio　of　0.89,　the　contribution　of　the　SAEPD-sequencing　batch　reactor　(SBR)　during　the　anoxic　stage　reached　98.2%　and　the　proportional　contributions　of　the　anammox　and　denitrification　pathways　were　77.2%　and　22.8%,　respectively.　Although　the　low　nitrite　accumulation　(66.1%)　caused　10.8　mg　N/L　of　nitrate　to　be　transported　into　the　SAEPD-SBR　and　the　anammox　reaction　also　converted　20%　of　nitrite　to　nitrate,　only　1.1　mg　N/L　of　nitrate　remained　in　the　effluent.　High-throughput　sequencing　analysis　revealed　that　although　NH2OH　was　added,　some　genera　of　nitrite-oxidizing　bacteria　(0.73%)　remained　in　the　PN-SBR　and　potentially　resulted　in　the　oxidation　of　nitrite　to　nitrate.　In　the　SAEPD-SBR,　anammox　and　endogenous　denitrifying　bacteria　co-existed　and　synergistically　achieved　the　removal　of　ammonium,　nitrite,　and　nitrate.　Overall,　the　PN-SAEPD　process　has　great　potential　for　achieving　cost-effective　and　energy-efficient　municipal　wastewater　treatment.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.