The　presence　of　fluoride　ions　(F-)　in　nitrogen-rich　wastewater　from　photovoltaic　and　semiconductor　industries　introduces　a　significant　challenge　to　biological　treatment　processes,　particularly　for　the　innovative　partial　denitrification　(PD)　process,　which　supplies　nitrite　for　anaerobic　ammonium　oxidation　(Anammox).　This　study　provides　the　first　comprehensive　and　systematic　investigation　of　the　effects　of　F-　stress　on　the　granule-based　PD　process　through　batch　tests　and　long-term　operation.　Results　indicate　that　PD　activity　remains　resilient　to　F-　shock　up　to　1.5　g/L　but　is　markedly　impaired　at　concentrations　of　2.0–3.0　g/L,　despite　maintaining　a　nitrate-to-nitrite　transformation　ratio　(NTR)　of　approximately　80　%.　Under　long-term　F-　stress　at　0.5　g/L,　NTR　gradually　reduces　to　50　%,　but　subsequently　recovers　to　and　maintains　at　70　%.　The　increased　secretion　of　loosely　bound　extracellular　polymeric　substances　and　proteins　likely　enhances　the　resistance　of　PD　granules　to　F-　stress,　though　excessive　amounts　degrade　their　settling　properties.　F--induced　microbial　community　succession　shapes　a　predominance　of　medium　granules　(1.0　＜　d　＜　2.0　mm　of　60.2　%)　by　enhancing　aggregation　of　smaller　granules　and　disintegration　of　larger　ones.　This　enhances　the　mechanical　strength　and　microbial　activity　of　PD　granules,　aiding　in　resistance　to　F-　stress　to　sustain　microbial　metabolism.　Thauera　is　selectively　enriched　under　long-term　F-　stress,　with　upregulated　nirBDS　genes　contributing　to　the　reduced　NTR.　Additionally,　increased　electron　metabolism　activity　and　a　robust　antioxidative　response　help　to　maintain　higher　microbial　metabolic　activity,　mitigating　F--induced　oxidative　stress.　These　findings　advance　our　understanding　of　the　resilience　and　adaptability　of　the　PD　process　under　F-　stress,　providing　critical　insights　for　optimizing　biological　wastewater　treatment　systems　in　challenging　environments.　©　2025