Pyrite-driven　autotrophic　denitrification　(PAD)　has　been　recognized　as　a　promising　treatment　technology　for　nitrate　removal.　Although　the　occurrence　of　PAD　has　been　found　in　recent　years,　there　is　a　knowledge　gap　about　effects　of　crystal　plane　of　pyrite　on　the　performance　and　mechanism　of　PAD　system.　Here,　this　study　investigated　the　effects　of　crystal　planes　({100},　{111}　and　{210})　of　single-crystal　pyrite　on　denitrification　performance,　electron　transfer,　and　microbial　mechanism　in　PAD　system.　The　removal　efficiency　of　nitrate　in　B-{210}　reached　100%,　which　was　1.67-fold　and　2.86-fold　higher　than　that　of　B-{100}　and　B-{111},　respectively.　X-ray　photoelectron　spectroscopy　and　electrochemical　results　indicated　that　Fe-S　bonds　of　pyrite　with　{210}　crystal　plane　were　more　susceptible　to　breakage　by　Fe3+　oxidation　assault,　and　leaching　microbially　available　Fe2+　and　sulfur　intermediates　to　drive　autotrophic　denitrification.　Metagenomic　results　suggested　that　community　of　functional　pyrite-driven　denitrifiers　varied　in　response　to　crystal　plane,　and　abundances　of　N-S　transformation　and　EET-related　microbes　and　genes　in　B-{210}　notably　up-regulated　compared　to　B-{100}　and　B-{111}.　In　addition,　this　work　proposed　a　dual-mode　for　electron　transfer　pathway　during　pyrite　oxidation　and　nitrogen　transformation　in　PAD　system.　In　B-{210},　Fe(II)-　and　sulfur-driven　denitrifiers　obtained　electron　after　pyrite　oxidation-dissolution,　and　the　enrichment　of　pyrite-oxidizing　bacteria　in　B-{210}　could　enhance　the　electron　transfer　from　pyrite　through　electron　shuttles.　This　work　highlighted　that　stronger　surface　reactivity　and　electron　shuttle　effect　in　B-{210}　enhanced　electron　transfer,　leading　to　favorable　PAD　performance　in　B-{210}.　Overall,　this　study　provides　novel　insights　into　the　structure-activity　relationship　between　the　crystal　plane　structure　of　pyrite　and　denitrification　activity　in　PAD　system.　©　2024