Partial　nitrification　has　the　advantages　of　saving　energy　and　reducing　the　need　for　carbon　sources　in　municipal　wastewater　treatment.　However,　for　municipal　wastewater　with　low　ammonia,　start-up　and　maintenance　of　partial　nitrification　is　a　worldwide　challenge.　Here　we　developed　a　pilot-scale　double　sludge　system　consisting　of　two　sequencing　batch　reactors　for　partial　nitrification　(12　m2)　and　denitrification/anaerobic　ammonium　oxidation　(denitrification/anammox,　8.4　m2)　to　treat　municipal　wastewater.　Partial　nitrification　was　maintained　at　no　ammonium　remaining　with　a　nitrite　accumulation　rate　of　87.7%.　This　study　found　that　partial　nitrification　system　effluent　chemical　oxygen　demand　increased　from　24.8　mg　L−1　to　64.9　mg　L−1　accompanied　by　transformation　from　complete　nitrification　to　partial　nitrification.　In　the　denitrification/anammox　system,　the　reduction　of　nitrite　to　nitrogen　required　about　40%　less　carbon　consumption　than　nitrate.　High　nitrogen　removal　was　achieved　with　effluent　total　inorganic　nitrogen　of　2.7　mg　L−1　without　carbon　addition.　This　work　provided　a　pilot-scale　demonstration　of　low-carbon　high-nitrogen　removal.　©　The　Author(s)　2025.