Iron, manganese and ammonia are common inorganic pollutants in groundwater. In the current study, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) was designed for the treatment of groundwater (approximately Mn2+ 1.2 mg-L-1, Fe2+ = 15.0 mg center dot L-1 and NH4+-N = 2.2 mg center dot L-1). Two lab-scale PAC-MBR systems were implemented to operate for 220 d to purify three influents that had different levels of pollutants, including raw water and the effluent of conventional bio-sand filters with different dissolved oxygen levels (i.e., 9 mg center dot L-1 and 6 mg center dot L-1) before filtration. The results showed that an excellent MBR effluent (iron <0.2 mg-L-1, manganese < 0.1 mg center dot L-1 and ammonia < 0.05 mg center dot L-1) was obtained irrespective of the amount of pollutants, but the start-up period varied (20-49 d). With respect to the trans-membrane pressure (TMP) evolution, system I (PVDF) exhibited good performance with a slight TMP increase from 7.0 to 17.0 kpa, whereas system II (PVC) exhibited a sharp rise from 20.0 to 60.0 kPa. In brief, a cake layer containing PAC and oxides was the main reason for membrane fouling. High-throughput sequencing analysis revealed that Mn-oxidizing bacteria (MnOB) (i.e., Leptothrix, Pseudomonas, Hyphomicrobium and Planctomyces) and ammonia oxidizing bacteria (AOB) (i.e., Nitrospira, Nitrosomonas) played major roles in the PAC-MBR systems. (C) 2016 Elsevier B.V. All rights reserved.