Achieving　enhanced　biological　phosphorus　removal　dominated　by　Tetrasphaera　utilizing　waste　activated　sludge　(WAS)　as　carbon　source　could　solve　the　problems　of　insufficient　carbon　source　and　excessive　discharge　of　WAS　in　biological　phosphorus　removal.　Up　to　now,　the　sludge　reduction　ability　of　Tetrasphaera　remained　largely　unknown.　Furthermore,　the　difference　between　traditional　sludge　fermentation　and　sludge　fermentation　dominated　by　Tetrasphaera　was　still　unclear.　In　this　study,　two　different　sequencing　batch　reactors　(SBRs)　were　operated.　WAS　fromSBR-parent　was　utilized　as　sole　carbon　source　to　enrich　Tetrasphaera　with　the　relative　abundance　of　91.9%　in　SBR-Tetrasphaera.　PO43--P　removal　and　sludge　reduction　could　simultaneously　be　achieved.　The　effluent　concentration　of　PO43　--P　was　0,　and　the　sludge　reduction　efficiency　reached　about　44.14%　without　pretreatment　of　sludge.　Cell　integrity　detected　by　flow　cytometry,　the　increase　of　DNA　concentration　in　the　sludge　supernatant　and　decrease　of　particle　size　of　activated　sludge　indicated　that　cell　death　and　lysis　occurred　in　sludge　reduction　dominated　by　Tetrasphaera.　Stable　structure　of　activated　sludge　was　also　damaged　in　this　process,　which　led　to　the　sludge　reduction.　By　analyzing　the　excitation-emission　matrix　spectra　of　extracellular　polymeric　substances　and　the　changes　of　carbohydrate　and　protein　concentration,　this　study　proved　that　slowly　biodegradable　organics　(e.g.,　soluble　microbial　byproduct,　tyrosine　and　tryptophan　aromatic　protein)　could　be　better　hydrolyzed　and　acidized　to　volatile　fatty　acids　(VFAs)　in　sludge　fermentation　dominated　by　Tetrasphaera　than　traditional　sludge　fermentation,　which　provided　carbon　source　for　biological　nutrients　removal　and　saved　operation　cost　in　wastewater　treatment.　(C)　2021　Elsevier　B.V.　All　rights　reserved.