Ilyas, Dr. S. (Shazia)

FOULING CONTROL IN MEMBRANES USING “SACRIFICIAL LAYER” APPROACH

Fouling constitutes a major problem in membrane technology and leads to a reduced production capacity and increased operation cost. This research outlines a solution for membrane fouling based on a polymeric “Sacrificial Layer” approach. Polyelectrolyte multilayers (PEM) are coated using layer by layer (LBL) approach involving alternating sequential adsorption of polycations and polyanions onto a charged surface. The number of deposited layers determines the thickness of a PEM membrane (PEMM) and thus selectivity and flux can be tuned by the number of LBL cycles or by the chemical composition of the utilized polyelectrolytes (PEs). In this project the PE’s are chosen especially so that the polymer layers of a few nanometers thickness can be removed by simple trigger such as a change in pH or salt concentration. This so-called “sacrificial layer” approach, allows the possibility that when fouling agents gets adsorbed on the surface of the membrane, they can be removed by simply desorbing (sacrificing) the polymer coating in solution. An extra benefit might be that the polyelectrolytes that are released into solution upon destruction of the layer could well act as so-called anti-redeposition agents: by adsorbing to the released fouling agents they could prevent possible re-adsorption of the fouling agents. This concept is schematically shown in Fig. 1.

Full-size image (54 K)

Fig. 1: Schematic representation of polyelectrolyte multilayer as a sacrificial layer. Fouling agents are adsorbed to the multilayer but upon a change of the pH, the layer desorbs, taking with it the adsorbed fouling particles. Released polyelectrolytes cover the particles and prevent re-adsorption.

To give a “proof of principle” for the application of such multilayers as sacrificial layers we use polyelectrolyte multilayers in combination with silica particles. After that the membrane can be recoated with PEs. The proof of the principle of this sacrificial layer has been shown on substrate like silica wafer but on membranes it has not been tested yet. In this research poly electrolyte multilayers with different polymers will be grown on different types of ultrafiltration/microfiltration membrane surfaces and characterized with respect to the structure of the layer, its antifouling properties and the membrane performance. The research will contribute to fundamental knowledge on membrane surface modifications, but at the same time will also help tackle and alleviate the practical problem of membrane fouling.