Biofilm growth on ion exchange membranes in electrodialysis

Biofouling in electrochemically driven water treatment processes, like electrodialysis (ED), is of critical concern due to its effect on ion fluxes and energy consumption. Biofilm formation begins with microbial adhesion to surfaces mediated by extracellular polymeric substances (EPS). In ED, ions are removed from water by external electric field through charged ion exchange membranes (IEMs). While this process is well established, the influence of the ED specific conditions on EPS adsorption remains poorly understood. Brackish water biofilms were grown on cation and anion exchange membranes (CEM & AEM) in an ED cell, with and without electric fields. Biofilm viability and EPS were analyzed by confocal laser scanning microscopy (CLSM), while EPS adhesion properties were characterized using Electrochemical Quartz Crystal Microbalance with Dissipation (E-QCMD), applying chronoamperometry (CA) and cyclic voltammetry (CV). Zeta potential analysis showed all EPS samples were negatively charged, with charge density influenced by membrane type and electric field. Positively charged AEMs accumulated more highly negative EPS, whereas less negative fractions preferentially attached to negatively charged CEMs. Applied electric fields results in EPS fractions with reduced negative zeta potentials on both membranes due to electrostatic repulsion on CEMs and selective attraction of less negative EPS to AEMs under shear. CA E-QCMD results indicated stronger electrostatic responses for AEM derived EPS, while CEM derived EPS interactions were mainly hydrophobic. CV analyses revealed that EPS from both membranes formed more compact and stable layers after exposure to negative potentials, regardless of field conditions during formation, highlighting the dominance of hydrophobic interactions. Biofouling caused greater ion flux decline on AEMs, correlating with higher EPS and biomass accumulation. These findings improve understanding of biofouling mechanisms in electrically driven membrane systems, supporting improved ion transport, membrane performance, and energy efficiency.