Reduction　and　reclamation　of　waste　activated　sludge　can　be　achieved　through　digested　sludge　supernatant　as　a　carbon　source　for　biological　nutrient　removal　from　wastewater.Under　microaerobic　conditions,the　effect　of　pH　values　on　hydrolysis　and　acidfication　of　sludge　and　microbial　community　structures　was　investigated　in　this　study.Results　indicate　that　at　alkalic　conditions,the　concentrations　of　volatile　fatty　acids　(VFAs),soluble　COD,protein　and　polysaccharide　in　digestion　supernatant　are　higher　than　those　at　acidic　conditions.The　optimal　pH　value　is　10.0,The　maximal　total　volatile　fatty　acid　(TVFA)　concentration　reaches　4　156.4mg　COD/L,among　which　acetic　acid　is　the　main　component,accounting　for　52%　of　TVFA.Protein　content　is　three　to　four　times　of　polysaccharide.Ammonia　concentrations　under　alkalic　and　microaerobic　conditions　are　much　lower　than　those　at　acidic　conditions.The　outcomes　suggest　digested　sludge　supernatant　as　a　carbon　source　for　biological　nutrient　removal　is　feasible.Proteobacteria　was　dominant　at　raw　sludge　and　pH　of　4.0,with　a　percentage　of　59.9%　and　38.6%,respectively;　Whereas　Firmicutes　become　dominant　at　pH　of　10.0,accounting　for　70.9%.The　percentage　of　Clostridia　affiliated　with　Firmicutes　is　the　highest,up　to　63.4%.At　different　pH　values,changes　of　microbial　community　structures　and　dominant　species　lead　to　the　difference　of　sewage　sludge　microaerobic　digestibility.　©　2018,　Science　Press.　All　right　reserved.