Filter dirt-load capacity

The use of positively-charged open-pore membranes as prefilters for a final "absolute" membrane has already been mentioned. In general, a prefilter serves to take the load off the final filter. The best prefilters will have a high internal surface area (high dirt-loading capacity). 

It is well known that fibrous depth filters provide enormous dirt loading capacity compared with membrane filters. Using this kind of filter media as a prefilter for the final membrane filter often provides an ideal combination (see Fig-... 

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