Membranes prefilter system

Mod i f 1 ed Mjymbrajne Viscometer Foi- the pulsed system a coil of tubing (the injection loop) was placed after the prefilter and liefore the membrane holder as shown in Figure P. Directional valves at each end of the loop controlled the flow path. Solvent or solution could be pumped directly to the UV to establish baseline absorbance or for calibration. To make P measurements the flow was directed through the membrane and then into the differential UV spectrophotometer. The flow could also be brought to the upstream portion of tlie membrane holder and then to the UV detector in an effort to measure the concentration at the membrane surface. 

Membrane filtration is useful where the usage is moderate and a continuous circulation of water can be maintained. Thus, with the exception of that drawn off for use, the water is continually being returned to the storage tank and refiltered. As many waterborne bacteria are small, it is usual to install a 0.22-pm pore-size membrane as the terminal filter and to use coarser prefilters to prolong its life. Membrane filters require regular sterilization to prevent microbial colonization and growthrough . They may be treated chemically with the remainder of the storage/distribution system or removed and treated by moist heat. The latter method is usually the most successful for heavily contaminated filters. 

The selection of the optimum prefilter/membrane combination is best done experimentally on the user s process stream. The manufacturers give some guidance as to which prefilters should be used for a given membrane pore-size, but unfortunately, there is no standard rating system for prefilters. 

A prefilter is normally used to protect the membranes and avoid excessively rapid fouling. An industrial filtration system includes a prefilter unit and a final filfrafion unit , assembled in series on the same base. 

If laboratory tests using a disc of the filter membrane indicate that the filter will have insufficient throughput or life then prefiltration ould be considered. Ideally both filters should come to the end of their service life together, i.e. the dirt holding capacity of both filters should be exhausted at the same time. This enables both filters to be replaced together. A duplex system switching over both prefilter and fine filter is available. 

Before introducing the feed into the RO system, the membrane was cleaned and wetted with deionized water. Initially feed water was passed through the micron prefilter cartridge using low-pressure pump to remove coarse solids. 

A prefilter should be used ahead of the membrane filter in order to reduce the pressure drop when filtering through the membrane, thus reducing the size of the housing needed for the filter cartridges. This will increase the life of the process system and take the load off the membrane filter that performs the removal of the finer particulates. As for the chemicals used to develop photoresists, continuous recirculation and membrane filtration are the preferred techniques. Strict temperature and atmospheric control must be maintained. Compressed air and water are two separate, but essential, tools in the production of electronic components and systems. 

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