In　this　study,　partial　denitrification　(PD,　nitrate → nitrite)　using　dissolved　slowly-biodegradable　organic　matter　(DSBOM)　was　effectively　established　by　introducing　biosorption　and　hydrolytic　acidification　(HA)　as　a　pretreatment　for　carbon　capture　and　conversion.　After　119 days　of　optimized　operation,　an　efficient　nitrate　to　nitrite　transformation　of　80%　was　achieved,　with　an　influent　nitrate　level　of　40 mg/L　and　DSBOM　level　of　183.8 mg/L.　There　was　a　significant　shift　from　exogenous　PD　to　endogenous　PD,　with　energy　supplied　by　HA　products　of　captured　DSBOM,　i.e.,　acetate,　saccharide　and　intracellular　poly-hydroxyalkanoates　(PHAs),　jointly　facilitating　nitrite　production.　This　was　well　explained　by　that　genera　Dechloromonas　(26.7%),　possibly　responsible　for　carbon　HA　and　nitrite　production,　were　enriched;　while　abundant　enzymes　for　glycolysis,　acetate　fermentation　and　PHAs　storage,　and　2.6　times　more　nitrate　reductases　than　nitrite　reductases　were　identified.　These　results　highlight　a　novel　carbon　capture　reuse　and　PD-based　anammox　strategy　to　cost-effectively　treat　nitrogen.