One of the critical issues in the successful development of the ultrafiltration (UF) processes is the fouling,which arises from specific interactions between the membrane and various components present in thewater. Many parameters impacting the fouling have been already studied. They can be classified into twocategories: membrane chemical and structural parameters and water characteristics. The structuralproperties of membranes (roughness, porosity...) are specially studied to develop a fouling controlmethod. In this work, several microscopic and optical methods are used to characterise, first virginorganic membranes and secondly fouled organic membranes after operation.In this work, information obtained for organic UF PES clean and fouled flat sheet membranes accordingto the cut-off (10, 30, 100 and 300 kDa) and for PVDF hollow fibers (100 kDa) are compared. For that,different techniques were used.- A scanning electron microscopy (SEM) is used to probe the general structure of the membranes andto determine the porosity of the skin layer using image analysis software. It allows magnificationsranged from × 25 to × 650,000 with resolution of 1.2 to 2.5 nm. Energy Dispersive X-rayspectrometry (EDX) can be combined to SEM observation.- An optical profilometer through white light interferometry (WLI) and an atomic force microscopy(AFM) are used in order to assess the surface state of membranes (roughness spectrum). WLI allowsobtaining image sizes from 360x360 μm~2 to 900×900 μm~2. Moreover, the AFM technique is used onsurfaces whose scan tip allows the study of zones ranging from 10x10 μm~2 to 40×40 μm~2. These twotechniques are complementary of each other for size scale observation.The structural properties of virgin flat sheet PES membrane were determined as a function ofcharacteristics of molecular weight cut-off (MWCO). The characteristics of surface determined by SEMshowed an increasing trend with MWCO. The use of WLI and AFM with different observation scalesshowed that the determination of the roughness of a membrane significantly depends on the observationscale. The AFM was able to differentiate membrane according to their MWCO as well as to the method ofmanufacturing. Structural characterizations by SEM/EDX and AFM techniques are particularly adapted tothe study of hollow fibers (in/out or out/in configuration): comparison of observations for virgin, fouledand cleaned membranes after operation on industrial site can give information about efficacy of cleaningprocedure, irreversible fouling (decrease in pore size, increase in surface roughness), ageing of membrane(increase of pore size linked to active skin deterioration or chemical degradation of polymer).These optical and microscopic techniques combined with others such as chemical observation of surface(FTIR), or hydraulic-dynamic tests (filtration tests, molecules or micro-organisms retention) can help toimprove the understanding of fouling and/or ageing phenomena occurring during drinking waterproduction in order to manage and minimize them. These methods of microscopic analysis requirecomplex equipments associated to expenses of maintenance. They require expert staff trained specificallyin the use of these tools, in the data processing and in the interpretation of the results.These methods can be used, as complementary tool to the services proposed by the dedicated laboratoryon the membrane testing platform of CIRSEE, called “Memlab" through collaboration with expert academic laboratories in Marseille and Paris Universities. This platform is oriented on the assessment ofall the MF/UF products of the market. It aims at evaluating membrane quality and durability for varioustreatment applications.
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