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

Abstract 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 NH 4 + -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  − 1 , manganese  − 1 and ammonia  − 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.