Unravelling colloid filter cake motions in membrane cleaning procedures

Abstract

The filtration performance of soft colloid suspensions suffers from the agglomeration of the colloids on the membrane surface as filter cakes. Backflushing of fluid through the membrane and cross-flow flushing across the membrane are widely used methods to temporally remove the filter cake and restore the flux through the membrane. However, the phenomena occurring during the recovery of the filtration performance are not yet fully described. In this study, we filtrate poly(N-isopropylacrylamide) microgels and analyze the filter cake in terms of its composition and its dynamic mobility during removal using on-line laser scanning confocal microscopy. First, we observe uniform cake build-up that displays highly ordered and amorphous regions in the cake layer. Second, backflushing removes the cake in coherent pieces and their sizes depend on the previous cake build-up. And third, cross-flow flushing along the cake induces a pattern of longitudinal ridges on the cake surface, which depends on the cross-flow velocity and accelerates cake removal. These observations give insight into soft colloid filter cake arrangement and reveal the cake’s unique behaviour exposed to shear-stress.

Automated tangential-flow diafiltration device

“…In this flushing step, we remove the filter cake from the membrane by suppressing permeation by closing the permeate stopcock and removing the cake by tangential crossflow flushing. This method was proven in a previous study [21]. Flushing times of 5 min with a maximum feed flow rate are recommended.…”

Geometrical Influence on Particle Transport in Cross-Flow Ultrafiltration: Cylindrical and Flat Sheet Membranes

“…The ratio, Π /TMP, of length-averaged transmembrane osmotic pressure and TMP equals 0.34 and 0.18 in Figure 6a,b, respectively. It reflects the strong influence of the CP layer on the permeate flux v w , exerted through the (length-averaged) Darcy-Starling law in Equation (13). Notice further that for extreme parameter values not considered here where the longitudinal pressure drop across the channel length is comparable to the TMP, the according profiles for φ w (z) can be non-monotonic in z, with maximum concentration attained for z < L. As discussed in [15], in the context of the CM geometry, a criterion for a strictly monotonic increase in φ w (z) is that TMP > 3 P(0) − P L .…”

“…Moreover, flat sheet membranes can be operated at larger TMP, since they are commonly supported mechanically by plates or rigid porous spacers on the permeate side [8][9][10]. The FMS module with a transparent substrate sheet is also useful for monitoring flow behavior and fouling [11][12][13][14].…”

Particle Movements Provoke Avalanche-like Compaction in Soft Colloid Filter Cakes

“…Different studies investigate the influence of the cake morphology on permeation, 30,31 the deformation of single microgels during cake compression, 11 and the relaxation and removal of filter cakes by backflushing. 25,32,33 These microfluidic studies display the complexity of the phenomena influencing single particles' behavior during micro-and ultrafiltration by studying single events during pore blocking, cake formation, or cake compression. However, transferring single colloid phenomena to real membrane processes lacks the description of how single colloid events, such as colloid deformation, affect the overall cake morphology and its properties.…”