Carbon　capture　performance　is　a　key　factor　determining　the　chemical　energy　recovery　potential　of　the　high-rate　contact　stabilization　(HiCS)　process.　However,　the　mechanisms　of　organic　carbon　capture　are　complex,　involving　surface　adsorption,　extracellular　adsorption,　and　intracellular　storage.　A　unique　characteristic　of　the　HiCS　process　is　its　low　sludge　residence　time　(SRT).　Unfortunately,　the　influence　of　SRT　on　carbon　capture　has　not　been　thoroughly　studied,　especially　in　terms　of　the　underlying　mechanisms.　In　this　study,　the　microscopic　changes　in　carbon　capture　performance　during　the　transition　from　a　conventional　contact　stabilized　(CS)　system　to　a　highrate　mode　of　operation　were　demonstrated　using　intracellular　carbon　sources,　extracellular　polymeric　substances　(EPS),　signaling　molecules,　and　microbial　community　assays.　The　results　showed　that　the　extracellular　carbon　adsorption　and　intracellular　carbon　storage　performance　increased,　and　the　microbial　community　structure　changed　significantly　with　converting　the　CS　system　to　the　high-rate　operation　mode.　The　enhancement　of　extracellular　carbon　adsorption　performance　mainly　relied　on　the　growth　of　EPS,　which　was　accomplished　by　the　strong　growth　of　the　relative　abundance　of　the　dominant　bacterial　group　Cloacibacterium　within　the　HiCS　system,　offsetting　the　negative　effect　produced　by　the　decline　of　acyl-homoserine　lactones.　98　mgCOD/gSS,　343　mgCOD/　gSS,　and　500　mgCOD/gSS　of　polyhydroxyalkanoates　(PHAs)　per　sludge　unit　were　obtained　at　SRT-24d,　8d,　and　2d,　respectively,　suggesting　that　the　HiCS　system　is　more　advantageous　for　rapid　PHAs　production.