Layer-by-layer coated ceramic membranes for the resource-efficient production of drinking and process water
New membrane process for resource-efficient water treatment
In water purification, membranes are used for the removal of water constituents, known as filtration. The separation efficiency of filtration depends on the separation properties of the membranes used. Conventional nanofiltration membrane systems (NF) have pore sizes of a maximum of two nanometres by definition and are generally subject to the problem of fouling in water treatment, i.e. organic and inorganic dirt particles are deposited on the membranes with increasing operating time. To remove these deposits, which form on the membrane surfaces during the filtration process, the membranes are rinsed against the direction of filtration. In NF wound membrane modules, where the membrane layers are wound around a pipe to collect the purified water, backwashing by reversing the water flow is not possible; also, only part of the deposit layer can be removed again. As a result, the energy requirement for filtration increases over the operating time with increasing fouling, up to the point at which the membrane modules have to be replaced.
The “KeraRes” project aims to solve this problem. The aim is to develop a new membrane process for resource-efficient water treatment. By modifying the structure, several layers (layer-by-layer) of certain molecular chains (polyelectrolytes), a ceramic NF membrane with unique separation and material properties is to be created. After a corresponding decrease in filtration performance due to fouling, the separating layer of the ceramic membrane should be able to be completely renewed in a simple process step. The old polyelectrolyte layer applied should be dissolved by increasing the pH value and then reapplied so that the NF filtration system is then fully restored and can continue to be used for filtration. This means that the membrane modules do not have to be disposed of. This results in a significant reduction in manufacturing chemicals, operational chemicals and waste streams associated with commercial NF systems.
The system is designed to enable the safe treatment of even difficult-to-treat water resources (e.g. river water, wastewater, rainwater) without microfiltration units, which should greatly simplify the process. Particles (e.g. microplastics, bacteria and viruses) as well as dissolved water constituents such as polyvalent ions (hardness formers) and organic molecules (including persistent compounds, e.g. PFAS) are to be retained. Compared to commercially available polymeric NF membranes, the developed system should be backwashable, regenerable and durable. The membrane modules resulting from the project are to be implemented in existing water treatment systems and used in the field of decentralised drinking and process water supply.
