The physicochemical properties of membranes (e.g., hydrophobicity, charge, pore size distribution, surface roughness) strongly determine the removal of bacteria through ultrafiltration membranes. The removal efficiency of membranes against bacteria is affected by fouling, which is, among other factors, caused by pore blocking and abiotic gel layers. Biotic processes on the membrane (e.g., biofilm formation) also influence the removal efficiency of the membrane for bacteria. An promissing method to influence the physical properties of such membranes, and thus biofilm growth on the membrane, is the coating of membranes with different materials. Optical coherence tomography (OCT), as a non-invasive method for characterizing the biofilm growth, is promising and subject of this conbribution.

Here, a continuously operated cylindrical cross-flow cell with a relatively small diameter (around 3 cm) is used to generate biofilms of diverse properties on different ultrafiltration membranes. The bacterial strain used is E. coli MG1655 cultivated in a lysogeny broth medium. OCT is used to characterize the fouling layers, which allows the simultaneous determination of the thickness, surface roughness, and porosity of fouling layers (Pratofi-orito, Horn & Saravia, 2022), (Im, Fortunato & Jang, 2021). The ultrafiltration membranes used are: an uncoated polyether sulfone (PES) membrane, a PES membrane embedded with Bismuth oxyiodide nanoparticles (BiOX), a Carboxylated Polyether Sulfone (CPES) coated membrane with polyelectrolyte (PE) (in our case we use Poly-(diallyl-dimethylammoniumchlorid): PDADMAC and Polyacrylic Acid: PAA), and a CPES PE-BiOX coated membrane.

The results of the optical OCT measurements are presented in this contribution. Different membrane coatings affect the characteristics of the biofilm. These coatings with diverse properties will subsequently be used to determine which membranes have the best conditions to minimize biofouling.


References
Im, S. J., Fortunato, L., & Jang, A. (2021). Real-time fouling monitoring and membrane autopsy analysis in forward osmosis for wastewater reuse. Water Research, 197, 117098.
Pratofiorito, G., Horn, H., & Saravia, F. (2022). Differentiating fouling on the membrane and on the spacer in low-pressure reverse-osmosis under high organic load using optical coherence tomography. Separation and Purification Technology, 291, 120885.