The　innovative　Complete　Ammonium　and　Nitrate　removal　via　Denitratation-Anammox　over　Nitrite　(CANDAN)　process　represents　a　promising　low-carbon　technology　for　wastewater　treatment,　has　been　widely　studied　in　sequential　batch　reactors　(SBRs)　treating　synthetic　wastewaters.　This　work　focuses　on　the　development　of　the　CANDAN　process　within　a　continuous-flow　Upflow　Anaerobic　Sludge　Blanket　(UASB)　reactor　for　nitrate　sewage　treatment　(NO3–-N:　100–1000　mg　N/L),　featuring　varying　proportions　of　real　municipal　wastewater　as　a　co-substrate　(61.3　mg　NH4+-N/L,　191.5　mg　COD/L).　The　results　demonstrate　consistently　high　N　removal　performance,　with　over　84.0　%　of　total　nitrogen　(TN)　removed　from　the　mixed　wastewaters　at　a　rate　of　approximately　0.6　Kg　N/m3/d.　As　the　proportion　of　municipal　wastewater　in　the　feed　increased,　the　activity　of　denitrifying　microorganisms　improved.　However,　their　growth　was　constrained　by　exacerbated　endogenous　respiration　resulting　from　prolonged　Hydraulic　Retention　Time　(HRT)　under　a　constant　loading　rate.　The　ideal　nitrite　production　with　the　nitrate-to-nitrite　transformation　ratio　(NTR)　of　above　84.6　%　was　always　obtained.　This　sustained　the　dominance　of　the　anammox　pathway　at　around　80　%　throughout　the　operation,　underscoring　its　pivotal　role　in　supporting　the　exceptional　performance　of　the　CANDAN　process　within　the　UASB　reactor.　Microbial　analysis　revealed　an　increase　in　species　richness　and　diversity　with　higher　proportions　of　municipal　wastewater,　while　anammox　functional　bacteria　exhibited　slight　enrichment　in　the　later　stages,　further　emphasizing　the　sustainability　of　the　CANDAN　process　even　with　increased　proportions　of　municipal　wastewater.　The　outcomes　of　this　study　provide　valuable　insights　into　the　successful　development　of　a　continuous-flow　CANDAN　process　for　highly　efficient　nitrate　sewage　treatment　by　incorporating　real　municipal　wastewater　as　a　co-substrate,　advancing　the　goal　of　achieving　carbon–neutral　wastewater　treatment　practices.　©　2024　Elsevier　B.V.