Monitoring of Membrane Processes

Steady-state Fluorescence versus Time-resolved Fluorescence Techniques 

Steady-state Fluorescence for the Monitoring of Membrane Water Treatment Processes and Membrane Bioreactors 

Several compounds exhibit intrinsic fluorescence behavior when exposed to an excitation source. Among the molecules that exhibit fluorescence behavior we may refer to a number of compounds which are intracellular fluorophores, such as tryptophan, NAD(P)H, riboflavin and pyridoxine, as well as a number of other compounds that frequently occur in water sources, included under the generic designation of humic acids (usually poorly characterized). 

Taking into consideration that some of these intracellular fluorophores correlate well with the observed behavior of biological systems (growth, activity), a significant 

These fluorescence maps can therefore be regarded as overall fluorescence fingerprints of the system under study. They capture, in a convoluted mode, all the information that a defined system is giving, when inspected with UV/visible radiation. Each fingerprint represents the sum of responses by a series of fluorophores present in the sample and their complex interactions in their specific environment. Therefore, such fingerprints are rather sensitive to any changes, not only in terms of the fluorophore composition of the media, but also in terms of the environmental conditions the fluorophores are exposed to (pH, ionic strength, salt composition). 

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A step in the development of the acoustic technique for the monitoring of membrane processes is to choose a frequency adapted to the membrane material. Therefore, several frequencies have to be tested (usually in the range 1-10 MHz). The adapted frequency must result in a workable signal, with large amplitude and well separated waves. Some frequencies can be cut by the membrane material, that is to say totally absorbed. Usually, each material has its own adapted frequency. 

Monitoring of Membrane Processes Using Fluorescence Techniques Advances and Limitations... 

This chapter discusses the use of fluorescence techniques for the monitoring of membrane processes, making use of the intrinsic fluorescence properties of the various components involved. This chapter deals with situations where none of these components is labeled with an external reporter, a fluorescence probe, as happens in many other applications described in this book (see Chapters 3,4 and 8). 

This chapter introduces and discusses different fluorescence techniques that do not require the use of external labeling steady-state fluorescence (including 2D fluorescence), fluorescence anisotropy and time-resolved fluorescence and it provides illustrative examples showing how these techniques may be used for the monitoring of membrane processes. 

S8 I 72 Monitoring of Membrane Processes Using Fiuorescence Techniques... 

The case studies presented in this chapter are very much based on the personal experience and research interests of the authors and they should illustrate, not limit, the high potential of using natural fluorescence techniques for the monitoring of membrane processes. The examples selected reflect, however, the authors perception about the areas of membrane research where natural fluorescence techniques may contribute to a better monitoring of membrane processes and, ultimately, to a better comprehension of the phenomena taking place when complex media interact with membranes. 

The use of 2D fluorescence techniques for the monitoring of membrane processes, namely the ones involving water treatment and biological systems such cell culture/membrane bioreactors, may be adopted soon. The applications envisaged (some of them under study for which results were not shown) involve ... 

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