Effects of organics concentration on the gravity-driven membrane (GDM) filtration in treating iron- and manganese-containing surface water

•Effects of organics concentration on flux stabilization and manganese removal of GDM were identified.•Moderate organics concentration endowing GDM an excellent stable flux (∼6.3 L m−2 h−1) and Mn removal (∼94.6%).•Increasing organics concentration benefited to the formation of heterogeneous and porous biocake layer.•Excessive organics would wrap the MnOx to result in reduction of manganese removal.