Tetramethylammonium　hydroxide　(TMAH),　an　extensively　utilized　photoresist　developer,　is　frequently　present　in　ammonium-rich　wastewater　from　semiconductor　manufacturing,　and　its　substantial　ecotoxicity　should　not　be　underestimated.　This　study　systematically　investigated　the　effects　of　TMAH　on　the　anammox　granular　sludge　(AnGS)　system　and　elucidated　its　inhibitory　mechanisms.　The　results　demonstrated　that　the　median　inhibitory　concentration　of　TMAH　for　anammox　was　84.85　mg/L.　The　nitrogen　removal　performance　of　the　system　was　significantly　decreased　after　long-term　exposure　to　TMAH　(0–200　mg/L)　for　30　days　(p　＜　0.05),　but　it　showed　adaptability　to　certain　concentrations　(≤50　mg/L).　Concurrently,　the　stability　of　the　granules　decreased　dramatically,　resulting　in　the　breakdown　of　AnGS.　Further　investigations　indicated　that　TMAH　exposure　increased　the　secretion　of　extracellular　polymeric　substances　but　weakened　their　defense　function.　The　increase　in　reactive　oxygen　species　resulted　in　damage　to　the　cell　membrane.　Reduced　activity　of　anammox　bacteria,　impeded　electron　transfer,　and　changes　in　enzyme　activity　suggested　that　TMAH　affected　the　metabolic　activity.　Microbiological　analysis　revealed　that　TMAH　caused　a　decrease　in　the　abundance　of　anammox　bacteria　and　a　weakening　of　symbiotic　interactions　within　the　microbial　community.　These　results　provide　valuable　guidance　for　the　AnGS　system　application　in　chip　wastewater　treatment.　©　2024　Elsevier　Inc.