Spacer fabric supported flat-sheet membranes: A new era of flat-sheet membrane technology

Current flat sheet MBR membranes are sandwich constructions containing at least 3 different layers. These membranes have no or only very backwash-ability and their envelope construction is a very labour-intensive multi-step operation.In this paper an innovative single method for constructing a prior-to-art back-washable flat sheet membrane envelope is described. The key element of this concept is the use of a 3D spacer-fabric as a membrane support stucture. Spacer-textiles can be made by a knitting or weaving process and they are normally used for the construction of all kind of light-weight composite materials. They basically consist of two faces (their outer layers), which are connected with each other by a multitude of monofilament spacer yarns. As a result a solid three dimentional structure is obtained which contains three distinguishable layers: the two faces (each e.g. 0.5 mm thick), and a hollow space in between them formed by the monofilament spacer yarns. In our concept the hollow space of the spacer fabric is used as the permeate drainage channel, whereas its faces are used for membrane anchoring. The interesting spacer fabrics for use as a membrane support have a thickness in between 2 and 10 mm. In our manufacturing process both faces of the spacer-fabric are directly and simultaneously coated with membrane dope in a vertical set-up. The pore size of both membrane layers is controlled by a combined VIPS and LIPS process. A membrane envelope has been realized with 0.3 μm pores having a pure water permeability of 1500 l/hm2 bar. A membrane adhesion test revealed that the membrane layers are attached well to the spacer fabric and can simply be back-washed with a TMP of 1 bar. Application tests showed that the critical flux of the IPC membrane is similar to a commercial MBR membrane type.