Membrane filters flux reduction

Many studies have pointed out that a CR ultrafilter can operate at a flux level of 300-400 L/(m h) when white waters are filtered. The reduction in organic compounds (COD, UV absorption at 280 nm, or sugar) using a UF membrane (cutoff 30-200 kg/mol) has been from 10% to 40% depending on the process water. The reduction of anionic trash is usually better (30%-90%) [48]. A pilot study showed that a high-shear filter (CR-nanofiltration unit) could operate without any pretreatment at a flux level of 50-120 L/(m h) when paper null clear filtrate was filtered. Mechanical erosion was a problem with some of the NF membranes used [18]. 

Fane et al. (1982) discussed the possibility of UF flux enhancement by particulates. It was found that rigid particles larger than 1 pm could enhance flux. Cohesive and compressible particles, even if large, would cause flux reduction. Milonjic et al. (1996) filtered hematite suspensions and found that increased pressure and stirring lead to a increased flux. Chudacek and Fane (1984) measured deposit layers of several pm on UF membrane by macrosolutes and silica colloids. 

Process Concept The application of a direct elec tric field of appropriate polarity when filtering should cause a net charged-particle migration away from the filter medium. This electrophoretic migration will prevent filter-cake formation and the subsequent reduction of filter performance. An additional benefit derived from the imposed electric field is an electroosmotic flux. The presence of this flux in the membrane and in any particulate accumulation may further enhance the filtration rate. 

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