Combined Use of the Two Methods Approach

The goal of the study was to obtain several kinds of information (thickness, porosity) about a deposit. Therefore, two characterization methods were developed. First, the acoustic method gives time variations from a complex signal, which are qualitative variations. Second, the optical method gives thickness measurements, which are quantitative variations. Adaptation of the two methods on the same apparatus, a confined channel, enables a complete deposit characterization to be obtained. 

It appears that the two methods measure the same relative thickness variations. Nonetheless, there is a shift between the absolute thickness values. This shift 

In situ local characterization of cake formation is a key step towards a better understanding of filtration processes. Some non-invasive characterization methods have shown their efficiency for cake investigation on flat-sheet membranes but they give only one kind of information. Few studies concern cake characterization in a confined geometry like an inside-out hollow fiber membrane. 

This chapter presents two original characterization methods that were developed in our laboratory (LISPB). Both allow the characterization of in situ fouling on organic membranes during filtration. Their common use on the same filtration apparatus could give complete characterization of filtration deposits. 

The first innovative method (LSGI) is based on the use of laser sheet at grazing incidence. It enables the deposit thickness at several locations in the vertical direction to be measured and the deposit thickness profile in a channel cross-section (z) to be obtained. Moreover, with this method it is possible to follow the deposit kinetics in relation to flow rate variations. First results were obtained with day suspensions and showed good reproducibility. Local measurements in conjunction with global measurements (flux or pressure) enable the deposit structure to be studied. It is now a tool that is used in our laboratory to study the suspension of 

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