3D Printed Photocatalytic Spacers Integrated with Membrane Filtration for Degradation of Persistent Organic Micropollutants

Sammanfattning

Certain organic micropollutants and emerging contaminants are increasingly detected in wastewater effluents due to enhancement of detection techniques and new technological processes or household items being introduced. Some of them can accumulate in food chains and/or pose health risks for humans, wildlife and ecosystems. Often, these are very difficult or impossible to sufficiently remove using conventional wastewater treatment technologies, hence calling for the use of advanced and hybrid processes. This study aims to explore the possibility of developing an integrated system combining ozonation, 3D-printed photocatalytic spacers and nanofiltration for removal of model contaminants – caffeine, which is found in beverages or medication and can cause anxiety at elevated concentrations, and iohexol, an X-ray contrast agent that can transform into toxic by-products. The study first focuses on evaluating several nanofiltration membranes (NF, NF90, NF270) for their permeability and rejection of the target products. NF90 demonstrated the best performance with 93% and 21% rejection of iohexol and caffeine respectively, hence it was chosen for further testing. Next, the behaviour of the two compounds during ozonation was studied, appropriate dose and reaction time are investigated, and kinetic constants aligning with literature were estimated. Following that, several photocatalysts were tested for the purpose of micropollutant degradation, including commercial and synthesized ZnO2, ZnO, g-C₃N₄, and a ZnO₂/g-C₃N₄ composite – the selected materials were characterized using FTIR and the kinetics of degradation under 365 nm LED light system were studied for iohexol and caffeine, demonstrating that while the latter can be efficiently degraded via photocatalysis, iohexol due to its more complex structures undergoes transformation into a by-product. In order for the photocatalysts to be integrated into a filtration system using a commercial membrane while avoiding the need for frequent cleaning from using their powder forms, different 3D-printed spacer configurations were investigated – such as photocatalysts blended with PLA, polycaprolactone or coated on top of fabricated spacers. Among them, PLA spacers coated with ZnO demonstrated high photocatalytic activity, achieving up to 89.6% caffeine degradation. The combination of advanced oxidation processes (AOPs) and membrane filtra-tion resulted in a synergistic effect, enhancing the overall removal efficiency with up to 96.1% caffeine removal. The study demonstrates the potential of using additive manufacturing to produce photocatalytic components that can be tailored for integration into existing membrane filtration setups. While the tests were carried out using model solutions and only UV-Vis detection of contaminants was available, the findings provide a foundation for future development of customizable AOP-membrane hybrid systems, including work with real wastewater matrices and expanded contaminant categories.