Using　internal　carbon　source　contained　in　waste　activated　sludge　(WAS)　is　beneficial　for　nitrogen　removal　from　wastewater　with　low　carbon/nitrogen　ratio,　but　it　is　usually　limited　by　sludge　disintegration.　This　study　presented　a　novel　strategy　based　on　free　nitrous　acid　(FNA)　pretreatment　to　intensify　the　release　of　organic　matters　from　WAS　for　enhanced　denitrification.　During　FNA　pretreatment,　soluble　chemical　oxygen　demand　(SCOD)　production　kept　increasing　when　FNA　increased　from　0　to　2.04　mg　HNO2-N/L.　Compared　with　untreated　WAS,　the　internal　carbon　source　production　increased　by　50%　in　a　simultaneous　fermentation　and　denitrification　reactor　fed　with　WAS　pretreated　by　FNA　for　24　h　at　2.04　mg　HNO2-N/L.　This　also　increased　denitrification　efficiency　by　76%　and　sludge　reduction　by　87.5%.　More　importantly,　greenhouse　gas　nitrous　oxide　production　in　denitrification　was　alleviated　since　more　electrons　could　be　provided　by　FNA　pretreated　WAS.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.