NEW DECLINE PATTERN OF FILTRATE FLUX IN CROSS-FLOW MICROFILTRATION OFDILUTE SUSPENSION

The cross-flow microfiltration flux is assumed to fall smoothly with a decreasing slope from startup to the steady state. Under actual opera ting conditions beyond a critical level, however, an anomalous decline pattern arises; initially cross-flow medium filtration occurs and the n thin-cake filtration. At the earlier stage, fine particles in polydi spersed suspensoids are filtered out on the surface of the membrane an d/or captured within the latter clogging the membrane pores gradually. After the membrane surface is covered by the deposit, further filtrat ion occurs by the buildup of filter cake on the initial deposit. Among the many operating variables, three major controlling factors for the earlier stage are confirmed: solids concentration, relative size of s olids and pores, and relative force of sweeping and capturing of suspe nsoids. Because suspended solids are separated by medium- and cake-law filtration in a series a method for evaluating the time dependence of flux with the new pattern is derived. Reliable flux analysis is achie ved for the transient flux of the dilute suspension forming a low comp ressibility fouling layer, which helps understand efficient flux perfo rmance.