Currently,　it　is　a　major　challenge　for　waste　water　treatment　plants　(WWTPs)　to　achieve　enhanced　nitrogen　removal　economically　and　effectively　from　carbon-limited　sewage　to　meet　gradually　stringent　discharge　quality　standards.　Enhanced　nitrogen　removal　can　be　achieved　by　endogenous　denitrification　(ED)　treatment　of　low　C/N　municipal　sewage,　but　its　application　is　limited　by　the　slow　reaction　rate.　In　this　study,　a　novel　process　of　Sludge　Double　Recirculation-Anaerobic/Aerobic/Anoxic　(SDR-AOA)　was　developed　to　improve　nitrogen　removal　efficiency　via　ED.　ED　was　successfully　enhanced　by　an　extra　sludge　recirculation　to　post-anoxic　zone　and　the　denitrification　rate　increased　from　0.1　to　0.17　kgN/(m(3).d).　Moreover,　the　pre-anaerobic　zone　enhanced　the　intracellular　carbon　storage,　which　might　also　favor　the　ED　process.　Overall,　under　an　influent　C/N　of　2.67,　nitrogen　removal　efficiency　of　97.7%　was　achieved　with　effluent　total　inorganic　nitrogen　(TIN)　of　1.56　+/-　1.77　mg/L　and　nitrogen　removal　rate　(NRR)　of　0.14　kgN/(m(3).d).　Therefore,　this　study　provides　a　convenient　approach　to　improve　the　nitrogen　removal　efficiency　of　municipal　sewage　with　low　C/N.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.