Membrane　bioreactors　(MBRs)　are　typically　used　to　dispose　landfill　leachate,　but　they　are　challenged　by　the　low　removal　of　refractory　organic　substances.　To　address　this　challenge,　in　this　study,　we　replaced　the　commonly　used　microfiltration　(MF)　membranes　in　conventional　MBRs　with　nanofiltration　(NF)　membranes,　i.e.,　MBRNF.　We　operated　a　one-step　MBRNF　for　127　days　and　benchmarked　against　a　conventional　MBRMF　in　terms　of　membrane　fouling,　pollutants　removal,　and　bulk　solution　properties.　The　results　showed　that　the　NF　membrane　could　effectively　reject　refractory　organic　substances,　leading　to　a　longer　organic　retention　time　(ORT)　and　a　higher　concentration　of　refractory　organic　substances　in　the　bioreactor.　Consequently,　the　MBRNF　outperformed　MBRMF　by　20　%–30　%　in　removing　of　refractory　organic　substances,　mainly　by　the　enhanced　biodegradation　of　refractory　organic　substances　with　low　molecular　weight.　Further　investigation　suggested　that　the　enhanced　biodegradation　in　the　MBRNF　could　be　ascribed　to　1)　more　biomass　in　the　bioreactor;　2)　higher　concentration　of　refractory　organic　substances　in　the　bioreactor;　and　3)　the　enrichment　of　dominant　bacteria　such　as　Chloroflexi.　These　findings　highlight　the　potential　of　MBRNF　in　removing　refractory　organic　substances　from　landfill　leachate　and　other　wastewaters　with　poor　biodegradability.　©　2024　Elsevier　B.V.