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

Abstract

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.

Popular Abstract

Every day, chemicals from factories, hospitals, households, and individuals make their way into wastewater – these compounds can be very different in terms of their compositions, origins and concentrations. While treatment plants do their best to clean this water, some persistent pollutants can still pass through and harm humans, animals, and ecosystems, especially when they accumulate over time. Specific technologies, called advanced oxidation processes can be used in order to remove these chemicals more effectively, but even just them alone sometimes if not enough.
This project explored how integrating different solutions into a single system can affect wastewater treatment efficiency. Two specific advanced oxidation methods were tested: adding ozone, a powerful oxidant, and using special materials that react under light (photocatalysts). These were then combined with membrane filtration – a method that physically separates harmful compounds without adding extra chemicals – to see if such a combination can be feasible and allow to better remove the contaminants. The study looked at how well these different combinations could remove two common pollutants: caffeine (a stimulant found in beverages and medication) and iohexol (a contrast agent used in X-ray imaging).

This work contains three sections for the separate parts of the future integrated process and finally their combination. The sections are dedicated to:

1) Testing different nanofiltration membranes with pore sizes about 100,000 smaller than human hair to see how well they can separate the selected chemicals – based on the screening results one membrane (NF90) was able to catch the most caffeine and iohexol molecules and, therefore, was selected for future tests.

2) Evaluating how the amount of added ozone and the time during which the selected chemical was in contact with ozone affected its degradation. Because of the different structures of caffeine and iohexol, they reacted in different ways to the addition of ozone.
3) Selecting and producing different light reactive materials, testing out their effective-ness in degrading caffeine and iohexol and researching ways of how these materials could be fitted into a membrane filtration system. Normally these materials would be added to the membrane itself or added to the system as a powder, but that requires making a fully new membrane or cleaning the membrane very often as powders can clog the pores. To make this system more efficient and adaptable to commercially produced membranes, photocatalysts were 3D-printed into custom shapes and tested.

Finally, the combined system of using membrane filtration after performing advanced oxidation showed that this way the contaminants can be removed a higher rate than by just using the techniques separately. For example, up to 96% of caffeine can be removed when the initial solution was first subjected to a reaction with a light-sensitive 3D-printed spacer and then to nanofiltration, compared to 21% removal with just nanofiltration. As a result, a system that showed the best results and potential to be used in bigger wastewater treatment installations was identified.

• author: Romanenko, Elizaveta
• supervisor: Frank Lipnizki; Ahmet Halil Avci
• organization: Chemical Engineering (M.Sc.Eng.)
• course: METM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Membrane engineering and technology, hybrid water treatment, organic micropollutants, 3D printing, photocatalysis, ozonation
• language: English
• id: 9205695
• date added to LUP: 2025-06-25 14:06:00
• date last changed: 2025-06-25 14:06:00