Bacterial biofilm formation on ion exchange membranes

Ion exchange membranes (IEMs) often suffer from biofouling, which reduces ion exchange rates and increases energy consumption in water treatment processes, such as electrodialysis, reverse electrodialysis, membrane capacitive deionization, and Donnan dialysis, and in energy devices, such as microbial fuel cells. In the present study, microbial biofilm formation was studied on anion exchange membranes (AEMs) and a cation exchange membranes (CEMs) of the homogeneous and heterogeneous types. Biofilm formation of Pseudomonas aeruginosa PAO1 on the IEMs was higher on the CEMs than on the AEMs, although more dead cells were found on the AEMs, likely due to the presence of quaternary ammonium moieties on the AEM surface, which are bactericidal. An XTT assay and NPN uptake tests confirmed the antimicrobial properties of the AEM surface. The results also suggested that the surface roughness of the membranes affected interactions between bacteria and the IEMs, being more pronounced on the heterogeneous IEMs than on the homogeneous IEMs. Counter-ion transport properties were studied under the Donnan exchange regime for both pristine and biofouled IEMs. The reduction of counter-ion transport due to biofouling was more pronounced for heterogeneous CEMs and AEMs than for their homogeneous counterparts, while it was more noticeable for the AEMs than for the CEMs. The latter result is explained based on the preferential adsorption of the negatively charged EPS components to the positively charged AEMs.