0501_Microscopy for fouling analysis

Title: Microscopy as a tool for analyzing of membrane failure and fouling
Journal: Desalination
Authors: Emond W.F. de Roeever, Ingmar H. Huisman
Corresponding author:Emond W.F. de Roeever
Institute: Nalco Europe BV, Ir.G. Tjalmaweg 1, 2342BV Oegstgeest, The Natherlands 
The original and creativity of paper: This study point out the optional way to identify fouling and failure using microscopy tools
Membrane autopsy is destructive analysis of membrane. It includes observation of the degree of fouling, collection of deposit for chemical and microbiological analysis, and tests of the integrity of membrane surface. Optical microscopy can identify many foulants by their color, size, crystalline structure, or other characteristic. Anyway, the depth of focus and the limited magnification reduce the usefulness of optical microscopy. Therefore, scanning electron microscopy (SEM) is more adequate technique for membrane autopsies. SEM provides increased depth of focus and higher magnification compared to optical microscopy. Moreover, SEM can easily be combined with an energy-dispersive X-ray spectrometer (EDS), which enables one to obtain the elemental composition of area being imaged by the SEM. More recently, atomic force microscopy (AFM) has been deployed for membrane characterization. AFM can reach similar or better magnification than SEM, and has the advantage that it is more appropriate for measuring surface roughness.  
Summary: This paper employed autopsy method to investigate membrane failure and fouling. They show how autopsy techniques revealed two unique phenomena on membranes, which provide essential clues on performance restriction and reduced membrane life time. Fouled membranes were used to examine and compare the results with clean membrane. The summary of results is explained following;
1.Permeate spacer imprints under high pressure of operation enhances membrane fouling, hampers cleaning, and cause leaking of membrane.
2.The imprints of permeate spacer cause roughness of membrane surface. Roughness with valleys and deeper spots in the valleys, facilitates accumulation of fouling, which ultimately decreases the permeate flux.
3.SEM image detected large particles on membrane surface frequently; sooner or later these particles will damage membrane. Therefore, adequate pretreatment is needed.
4.SEM also showed that large sharp particles, which are the root cause of membrane failure, could damage membrane surface. Large sharp particles could press deep into the sensitive and vulnerable membrane surface layer, which is less than a few microns thick.
5.An empty pits and imprints also found on membrane surface, using SEM, where most probably such particles had been located.

To enhance the efficiency of reverse osmosis membrane process, an adequate pretreatment is needed to remove large shape particles which could damage membrane surface.  
By Monruedee Moonkhum
Email: moon@gist.ac.kr

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