Fouling in membrane apparatus: The mechanisms of particle deposition

A detailed understanding of the mechanisms of particle-deposition and particle-removal during Crossflow Microfiltration (CMF) is essential for an improved design of membrane modules used in separation processes. The influence of the governing parameters filtrate flow rate, flow velocity and particle concentration on the local particle deposition is analysed both at constant transmembrane pressure and constant filtrate flow rate. For the investigation of the particle layer build-up under well-defined boundary and entrance conditions, new flat gap membrane modules are developed. Using these modules, a homogeneous plug flow profile at the entrance of the module is generated. The thickness of the cake layer received for different boundary conditions is determined by means of a stepping motor-driven laser-autofocus-sensor with high resolution. These thickness measurements allow a precise determination of the cake layer's surface topography. The net mass flow of every particle size fraction at the membrane during different time intervals and at different positions is determined. The investigations provide quantitative results of the selective particle deposition and allow an evaluation of existing models. Depending on the particle size distribution and the flow parameters, a particle-free, membrane can be achieved.