Removal of iron, manganese and ammonia from groundwater using a PAC-MBR system: The anti-pollution ability, microbial population and membrane fouling

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 Mn^{2 +} 1.2 mg·L^{− 1}, Fe^{2 +} = 15.0 mg·L^{− 1} and NH₄⁺-N = 2.2 mg·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·L^{− 1} and 6 mg·L^{− 1}) before filtration. The results showed that an excellent MBR effluent (iron < 0.2 mg·L^{− 1}, manganese < 0.1 mg·L^{− 1} and ammonia < 0.05 mg·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.