The　production　of　volatile　fatty　acids　(VFAs)　from　primary　sludge　and　the　subsequent　application　to　improve　biological　nutrient　removal　has　drawn　much　attention.　In　this　study,　a　novel　approach　of　using　primary　sludge　as　an　additional　carbon　source　was　conducted　in　batch　tests.　The　nitritation　effluent　was　directly　injected　into　the　sludge　fermentation　reactor　to　achieve　nitrogen　removal.　Complete　denitrification　could　be　realized　in　the　combined　reactor.　Moreover,　injecting　nitrite　not　only　promoted　the　sludge　stabilization　process,　but　also　reduced　the　release　of　phosphate　and　ammonium　during　sludge　stabilization.　The　novel　process　was　further　evaluated　in　a　continuous　system　by　treating　sludge　dewatering　liquors.　Under　optimum　conditions,　85%　removal　of　ammonium　and　75%　of　total　nitrogen　could　be　obtained　using　primary　sludge,　resulting　in　the　suitable　effluent　for　recycling　into　the　inlet　of　the　waste-water　treatment　plant.　(c)　2013　Elsevier　Ltd.　All　rights　reserved.