Through　dedicated　batch　tests　using　the　enriched　sludge　dominated　by　sulfur-oxidizing　bacteria　(SOB),　the　potential　transformation　of　hydroxylamine　(NH2OH)　by　SOB　and　the　effects　of　NH2OH　on　the　rate-limiting　sequential　reduction　processes　of　sulfur-driven　autotrophic　denitrification　(SDAD)　were　systematically　explored　in　this　study.　The　results　indicated　that　NH2OH　might　be　first　converted　to　NO　by　SOB　and　then　participate　in　the　SDAD　process,　thus　accelerating　the　utilization　of　S2-　and　contributing　to　the　formation　of　N2O.　Up　to　3.5　mg-N/L　NH2OH　didn＇t　affect　the　NO3-　or　NO2-　reduction　of　SDAD,　during　which　no　significant　changes　were　observed　for　the　NH2OH　concentration.　Comparatively,　even　though　NH2OH　had　no　direct　impact　on　the　N2O　reduction　of　SDAD,　it　could　be　consumed　and　therefore　affect　the　depletion　of　N2O　indirectly　by　regulating　the　toxic　effect　and　electron　supply　of　S2-.　These　findings　provide　novel　implications　for　applying　NH2OH　to　SDAD-based　integrated　processes　for　biological　nitrogen　removal.　©　2024　Elsevier　Ltd