Recently,　the　production　of　short-chain　fatty　acids　(SCFAs)　from　waste　activated　sludge　(WAS)　has　received　increasing　attention.　Although　several　pretreatment　methods　had　been　investigated,　sludge　hydrolysis　through　depletion　of　multivalent　cations　has　rarely　been　reported.　In　this　work,　cation　exchange　resin　(CER)　was　used　for　enhancing　WAS　hydrolysis　and　subsequent　SCFAs　production　at　various　dosages　of　0　to　3.5　g/g　SS.　With　the　addition　of　CER,　the　multivalent　cations　and　trace　metal　elements　(e.g.　Ca2+,　Mg2+,　Fe3+,　Zn2+,　etc.)　were　removed　from　sludge　through　CER-mediated　ion　exchange,　leading　to　disruption　of　extracellular　polymeric　substance　(EPS),　while　triggering　cell　lysis　which　was　evidenced　by　remarkable　leakage　of　cellular　DNA.　This　CER-mediated　cyclic　release-removal　of　multivalent　cations　resulted　in　substantial　sludge　hydrolysis　with　release　of　biodegradable　organic　matters.　At　the　optimal　CER　dosage　of　1.75　g/g　SS,　soluble　COD　(SCOD)　was　dramatically　increased　to　5944　mg/L　(SCOD/TCOD　=　34.7%)　against　1440　mg/L　in　the　control　after　2-day　fermentation.　Meanwhile,　a　considerable　SCFAs　of　334.5　mg　COD/g　VSS　was　produced　within　the　first　4　days　of　anaerobic　fermentation,　which　was　3.3　times　higher　than　that　in　the　control.　It　was　found　that　the　acetic　and　propionic　acids　accounted　for　57.4–65.4%　of　SCFAs　produced　in　CER-assisted　anaerobic　fermentation.　Compared　to　pretreatment　with　potassium　ferrate,　surfactant　and　enzymes,　a　much　higher　SCFAs　concentration　was　obtained　in　this　study　with　CER.　In　fact,　used　CER　could　be　recovered　and　reused,　without　harsh　chemicals　left　in　fermented　sludge.　This　indeed　created　an　environmentally　and　economically　beneficial　situation　with　considerably　saved　pretreatment　agents.　©　2020　Elsevier　B.V.