Standard Operating Procedure - Ultrafiltration - Department of ...

DESIGN:There are many different ways to design a membrane filtration module. From the standpoint ofcleaning, some are easier to clean than others are, but all have their particular problems.The design has a bearing on the flow pattern and on the type of structural support to hold themembrane. In the case of tubular membranes and hollow fiber modules, the fibers and/or tubesare arranged in a parallel way. This is more or less identical in design to a tubular heatexchanger. The problem is that if one or more of the tubes or fibers are clogged, or offerresistance to flow-through, it is not immediately realized. The fluid chooses the easiest way outand unless noticeable deviations in flux or flow or pressure occur, one might think the module tobe clean.Different module types have different types of support structure. In tubular modules, it is mostlythe membrane in form of tubes with stainless steel casings. The cleaner must only consider themembrane itself. In plate/spacer modules and in spiral wound modules the cleaning solution canand will come into contact with the glues holding everything together, also with the spacer platesmade of plastomers, with the retaining supports for spiral wounds. The compatibility of thecleaners with these materials must also be tested, and usually imposes yet another constraint onthe composition of the cleaner.Water:Water is a good solvent, a good cleaner all by itself. For cleaning therefore we should strive touse good quality water in order to achieve the best results. Especially in membrane cleaning thequality of water is important. Whatever may be in the water could be filtered, concentrated andwould deposit on the membrane surface, clogging it and thereby defeating the whole purpose ofcleaning.The pH of water should be 6-7.5, especially when cleaning Cellulose Acetate membranes, whichare sensitive to higher pH values.The water should not contain any “chlorine” as even low concentrations may, over the longperiods of time of contact, endanger the membranes. This is particularly true of polyamide orthin film composite membranes, which are susceptible to oxidizers.There should not be any considerable amounts of solids as they will be filtered out and soil themembranes. The same is true for the bacteriological status. It is not necessary to sterilize thewater before, besides sterilization only kills, it does not remove the microorganisms themselves.Bad water can lead to bacteriological fouling if left standing for a while on membranes. Thereare bacteria, which might attack the membrane and digest it, in the case of natural derivatives(CA).62