Microfiltration ultrapure water

Depth membrane filters are usually preferred for in-line filtration. As particles are trapped within the membrane, the permeability falls, and the pressure required to maintain a useful filtrate flow increases until, at some point, the membrane must be replaced. The useful life of the membrane is proportional to the particle loading of the feed solution. A typical application of in-line depth microfiltration membranes is final polishing of ultrapure water just prior to use. Screen membrane filters are preferred for the cross-flow microfiltration systems shown in Figure 7.1(b). Because screen filters collect the retained particles on the surface of the membrane, the recirculating fluid helps to keep the filter clean. 

The primary market for the disposable cartridge is sterile filtration for the pharmaceutical industry and final point-of-use polishing of ultrapure water for the microelectronics industry. Both industries require very high-quality, particle-free water. The cost of microfiltration compared to the value of the products is small so these markets have driven the microfiltration industry for the past 15 years. 

M. Mierzejewski, D. Guendert, Industrial appHcations using microfiltration as RO pretreatment, Ultrapure Water 21 (7) (2004) 29-35. 

As will always be the case, the actual purity achieved for a given purpose will be a compromise between the desire for absolute purity and the cost of achieving it. The appearance on the technical scene of membranes first of all, and now microfiltration and ultrafiltration membranes of reasonable cost, has made ultrapure water a practical goal. 

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