Groundwater-borne nitrate removal within heterogeneous sediments under interactions between hydraulics, nutrients, and biofilms

•Biofilm growth promotes groundwater-borne nitrate removal in heterogeneous sediment.•Hotspots of denitrification can develop in both coarse and fine facies.•More nitrate may be removed in organic-scarce coarse than organic-rich fine facies.•Poor representations of biofilms may significantly underestimate nitrate removal.