Fluidization PAC- MnOx combined ceramic membrane reactor for manganese removal: In-situ growth pathway of MnOx and supersession of water flux

Groundwater containing dissolved manganese (II) poses a significant challenge to the drinking water treatment process. Ceramic membrane technology enhances manganese removal, but its low permeate flux constrains its practical implementation. To improve efficiency, an integral aeration-MnOx fluidized bed system coupled with ceramic membrane filtration (A-MFB-CF) was developed and operated continuously for 176 days. It demonstrated efficient manganese removal, reducing Mn 2+ concentrations from 0.5–1.5 mg/L to <0.02 mg/L while maintaining a high water flux (60–120 LMH). Mn-oxidizing bacteria (MnOBs), including Ralstonia, Hyphomicrobium, and Pseudomonas , in PAC-MnOx particles, were identified using microbial community analysis. An increased abundance of MnOBs led to stronger resistance to Mn(II) shock loading. Continuous operation of A-MFB-CF filtration accelerated the conversion of MnOx, as evidenced by surface morphology evolution showing dynamic restructuring and bio-chemical synergy. The MnOx transformation pathway transitioned from dissolved Mn(II) species, to small 3D particles [Mn(III)/Mn(IV)] and large-sized 3D aggregates, eventually evolving into 2D layered sheets. The presence of birnessite with low crystallinity was confirmed using Raman and X-ray diffraction (XRD) analysis, and this structure contributes to its superb catalytic oxidation efficiency and high Mn(II) adsorption capacity. X-ray photoelectron spectroscopy (XPS) analysis further demonstrated the formation of catalytically active birnessite, characterized by mixed valence states of Mn (III) and Mn (IV). Electron Paramagnetic Resonance (EPR) indicated that MnOx formation was initially dominated by biologically mediated conversion, followed by a shift to physicochemical processes during prolonged operation. Additionally, PAC-MnOx fluidization in ceramic membrane tank effectively mitigated cake layer deposition and thus reduce membrane fouling. Our findings demonstrate an effective and space-efficient water treatment strategy, particularly suitable for decentralized water supply scenarios with stringent footprint constraints.