Hydrodynamic Regulation of Anodic Biocake in AnEMBRs: from Community Assembly and Spatial Structure to “Cell Filter” Engineering

Abstract

Transitioning the biocake of anaerobic electrochemical membrane bioreactors (AnEMBRs) into a functional “cell filter” presents an ideal paradigm for simultaneous fouling mitigation and deep effluent purification. However, the strategic orchestration for the precision regulation of the biointerface remains unresolved. This study investigated the effect of hydrodynamics on the community assembly, spatial structure, and metabolic activity of anodic biocakes. AnEMBRs were operated under gradient flux (8.5–34 LMH) and shear (0.13–2.12 Pa) regimes. Ecological analysis revealed that under the interplay of deterministic anodic selection and stochastic hydrodynamic deposition, low-flux operation (8.5 LMH) amplified the homogeneous selection of the anodic potential, maximizing the enrichment of core electroactive genera (e.g., Geobacter, Desulfovibrio) to 24.7%, forwarding an enhanced synergetic metabolism of “acetogenesis-anode respiration.” Meanwhile, unconstrained thickening of biocakes triggered an “active-outer/decayed-inner” stratification, where Methanosaeta-mediated occlusion starved the inner exoelectrogens due to limited substrate diffusion. Crucially, the application of moderate shear (0.87 Pa) effectively constrained thickness of biocake (<50 μm) to suppress methanogens colonization. The formed “cell filter” exhibited superior permeability with improved porosity and reduced resistance, while maintaining robust metabolic activity for the discharged DOM. This research provided a strategic framework for the directional assembly of “cell filter,” advancing the precision engineering of biointerfaces for sustainable wastewater treatment.