Technical kidney – bio-inspired membranes for water treatment

As a microscopic cell wall in organs, membranes are an essential prerequisite for efficient metabolic functions in living nature. They do not only enable substance transport, but often regulate it in a self-learning way. In the “Technical Kidney” project, Fraunhofer IKTS, the University of Applied Sciences Jena (EAH Jena) and the University Clinic Jena will, for the first time, use these principles of nature to develop new technical membranes and membrane modules that are significantly better than already existing technical membranes in terms of flow and selectivity, energy consumption and membrane surface.

The model is based on the human kidney, which first filters blood in order to selectively reabsorb molecules and ions with an energy consumption of 0.8 kWh/m³ and a volume-specific membrane surface of 20,000 m²/m³. In comparison, the best reverse osmosis systems require an energy quantity of 2.0 kWh/m³ at 1000 m²/m³. In addition, the aim is to exploit opportunities to optimize flow and mixing, to integrate heat exchangers and combine several separation processes and substance flows in one single module.

The new bio-inspired, complex membrane structures are to be produced through additive manufacturing and then coated and tested with regard to their separation traits.

Based on the membrane experience at Fraunhofer IKTS and the know-how of additive manufacturing at EAH Jena, first complex membrane structures in the form of gyroids were selected, their CAD models created and prepared for production (Fig. 1). To test lithography-based (LCM) and thermo-plastic (FLM) additive processes, the researchers produced suitable suspensions from Al2 O3 powders and photosensitive resins while also developing filaments. Samples of up to 65 wt % Al2 O3 in the suspension liquid have already been realized. Complex ceramic support structures (Fig. 2) as well as even fine pore distribution following sintering and coating processes (Fig. 3) were also achieved with the FLM process. 

Larger components, by contrast, have often shown cracks, calling for increased green density and optimizations in the firing process.

The objective in the further course of the project is to obtain membrane coatings that can perform micro-, ultra- or nanofiltration tasks depending on their pore size. Furthermore, the surfaces will be modified so that interactions of the surface with the water contents allow for selective separation. The aim is to selectively separate recyclable materials and pollutants for further use or chemical degradation.

The project is funded by the German Federal Ministry of Education and Research BMBF within the Thüringer Wasser-Innovationscluster ThWIC.