This　study　aimed　at　exploring　the　potential　of　volatile　fatty　acids　(VFAs)　produced　from　excess　sludge　(ES)　as　a　new　cost-effective　internal　carbon　source　in　wastewater　treatment　processes.　The　optimal　condition　for　VFA　accumulation　and　the　bacterial　community　structure　in　the　bio-production　of　VFAs　from　ES　were　investigated　at　different　pH　conditions.　Denaturing　gradient　gel　electrophoresis　(DGGE)　was　performed　to　characterize　the　bacterial　community　structure　of　ES.　The　results　showed　that　the　optimal　pH　was　10.0　for　VFA　production,　and　acetic　and　propionic　acids　were　the　dominant　acid　species.　Pseudomonas　sp.　was　identified　as　the　major　bacteria　capable　of　utilizing　organic　carbon　at　all　pHs.　Uncultured　bacterium　(AB658278)　adapted　well　at　high　pH.　Uncultured　bacteria　(KC633537　and　JN596370)　were　mainly　responsible　for　anaerobic　degradation　of　ES.　The　study　demonstrated　the　variation　of　bacterial　community　structures　at　pHs　and　the　close　correlation　with　the　VFA　accumulation.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.