Establishing a switchable dual-mode membrane bioreactor with functionalized PAC-MnOx filters to treat manganese-contaminated groundwater: autocatalytic manganese removal cycle, improved shear force distribution and rapid startup

Decentralized water supply is threatened by manganese pollution, especially in rural areas where groundwater is used as the main water source. This study aimed to establish a novel dual-mode membrane bioreactor (DMBR) with functionalized PAC-MnOx filters to effectively treat manganese-contaminated groundwater. DMBR operation modes could be switched by applying different filter fluidization strategies. In general, DMBR without filter fluidization (FIX-MBR) achieved 43 % better manganese removal than that with filter fluidization (FLU-MBR). Additional carbon sources stimulated manganese oxidizing bacteria (MnOB) activities for biologically oxidizing manganese, after which lamella-like structure birnessite with abundant active sites for concentrating and oxidizing manganese gradually formed. These processes facilitated the transformation of MnOx into birnessite, establishing a virtuous circle for autocatalytically oxidizing manganese. In FLU-MBR, dynamic stirring induced pulsed upwelling and enhanced membrane shear force (max = 2.20 Pa). Cake layer was timely removed and membrane flux was notably increased from 0.71 L/m 2 ·h to 12.57 L/m 2 ·h. As evidenced by increasing membrane permeability (37 L/m 2 ·h) and stable manganese removal (83.73 %), DMBR further benefited from increasing TMP from 0.01 MPa to 0.07 MPa. Exogenous mature birnessite enabled the rapid startup of DMBR, which effluent manganese fully satisfied the Standard for drinking water quality in China (GB5749-2022).