By　embedding　immobilized　biofiller,　100%　denitrification　efficiency　was　achieved　with　nitrate　or　nitrite　as　electron　acceptors　utilizing　volatile　fatty　acids　(VFAs)　from　domestic　wastewater　after　hydrolysis　acidification.　The　consumption　patterns　of　VFAs　by　functional　bacteria　and　differences　in　nitrogen　metabolic　gene　expression　were　thoroughly　analyzed.　Total　consumption　of　acetic　and　propionic　acids　with　＞95%　VFAs　utilization　was　achieved　utilizing　nitrate,　whereas　the　consumption　of　butyric　and　valeric　acids　was　enhanced　utilizing　nitrite.　Denitrification-related　genes　were　all　upregulated,　particularly　nosZ,　indicating　systemic　N2O　emission　reduction　potential.　Electron　acceptor　changes　dynamically　shifted　microbial　dominance　from　Thauera　(19.4%)　to　Thiobacillus　(7.2%).　These　results　provide　valuable　insights　into　the　adaptability　and　ecological　niche　characterization　of　denitrifying　bacteria,　contributing　to　improving　nitrogen　removal　efficiency,　optimizing　carbon　source　utilization,　and　reducing　sludge　production.