Standard Operating Procedure - Ultrafiltration - Department of ...

Cleaning TheoryTHE CHEMISTRY OF MEMBRANE CLEANINGThe use of membranes in many fields (food industry, water treatment, pharmaceuticals,biotechnology, and industrial waste treatment) is on the increase. As more and more applicationsare found, more and more membrane systems are devised, thus, the difficulties in cleaning theseplants increase and become more complex. We know that regulatory agencies such as FDA,USDA etc. are getting more involved by the day in inspection of new technologies andprocesses, and membrane filtration is one of them.What is so different about membrane cleaning as compared to tank cleaning or evaporator ortankers? In most processing or engineering fields, the material we encounter is metal, stainlesssteel or maybe sophisticated, complex blends of alloys and the like. Membranes for the mostpart are made of different material and because of the manufacturing process, the particularcharacteristics, membranes are simply much more expensive per unit area than normal material.When damaged, they cannot be repaired, they have to be replaced at great cost. They are muchmore fragile and more sensitive to all sorts of influences.Ecolab, having been involved in the cleaning of membranes from the beginning of theirintroduction into the food processing field, thought that in view of the many inquiries comingfrom the membrane manufacturers and users alike, a session on theoretical and practical aspectsof membrane cleaning would allow us to clear up some important points. While membranecleaning is different, it is not necessarily difficult or scary.There are many membrane filtration systems in use today. It is not our purpose to list them all,to explain their differences, advantages or disadvantages. The literature available by most of themanufacturers will provide some idea of new developments. We must define a few basic termsas a starting point of our discussion.Filtration techniques can be classified according to the molecular or particle size that isseparated.Microfiltration, also called cross flow filtration is in the range of 1/100 to 1/10,000 of amillimeter. Small particles, living cells, i.e. bacteria and large colloids fall into this category.Ultrafiltration goes beyond the particle size. Here we filter molecules, which are dissolved insolution (it may be a perfectly clear solution with no visible cloudiness). Those molecules arecalled MACROMOLECULES; they are usually long chains composed of smaller links (protein,starch, and oily substances). Smaller molecules such as sugar, salts, etc., go through a UFmembrane. UF membranes are pore-membranes with transition paths of varying size, therebyeffectively selecting different molecular sizes.56