Applications of CSLM to Membranes and Membrane Processes

The combination of a multiple staining protocol with CSLM enabled the visualization of the 3D structure ofthe main components of a biofouling layer (details are reviewed in Section 4.3.3). By applying a complex image analysis, several morphological parameters were determined, such as the porosity and fractal dimension of the fouling layer. 

Other authors [9-11] have calculated 3D parameters of the cake structure by Image structure analyzer (ISA 2). This software was particularly developed to quantify structural parameters from CSLM images [12] and has been used to measure (among others) porosity, biovolume, cake volume and average run length of the cake structure. 

The application of CSLM to membrane and membrane process characterization has been mainly developed during the past decade. The earliest applications of CSLM found in the literature were addressed to membrane characterization and the adsorption of proteins onto ion exchange membranes was the first membrane process visualized by CSLM. More recent uses of CSLM still focus on membrane characterization, but some other applications have been reported on membrane fouling characterization and some attempts to apply CSLM for online 

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The main drawbacks of CSLM are related to the fluorescent labeling of the sample and to its limited magnification capability as it is an optical microscope. Chapter 4 reviews in detail the fundamentals of CSLM and its applications to membrane processes. 

More recently, other applications of CSLM in the characterization of membrane processes have been reported, such as the studies of Hayama et al. [26, 27] who visualized the distribution of an endotoxin trapped in an endotoxin-blocking filtration dialysis membrane. In their first study [26], they found that endotoxins were practically rejected by the outer skin layer of a polyester-polymer alloy (PEPA) membrane, hence playing a vital role in endotoxin removal from the dialysate fluid. In a second work [27], CSLM contributed successfully to visualize the distribution of endotoxin fiuorescently labeled in six kinds of dialysis membranes. They concluded that a dialysis membrane favorable for endotoxin blocking should have a double skin layer structure, composed of a hydrophilic inner skin layer and a completely hydrophobic void and outer skin layers. 

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