Flux recovery

According to the vendor, a key advantage of the SpinTek system is that the membranes are less likely to foul compared to static membrane systems. This feature results in less downtime for the system. The system also allows continuous operation during changes in influent waste stream characteristics, eliminating downtime for flux recovery. In addition, SpinTek requires a relatively small area for operations. The vendor states that the system is ideal for operation in hostile environments, including high temperature, pH, radioactive waste, chemical solutions, and solvent solutions. 

For the conditions in Fig. 9, improvements of 35-50% in the permeate flux were observed when a secondary membrane was used, owing to a reduction in the protein fouling of the primary membrane. Little or no flux recovery was observed with each backpulse, as might be expected from the relatively low resistance of the yeast layer and the irreversible nature of the protein fouling. The flux continuously declined with time owing to irreversible fouling, though the rate of decline was reduced by the SMY. 

Bird MR and Bartlett M. Measuring and modelling flux recovery during the chemical cleaning of MF membranes for the processing of whey protein concentrate. J. Food Eng. 2002 53 143-152. 

Juang RS and Lin KH, Flux recovery in the ultrafiltration of suspended solution with ultrasound, J. Membr. Sci. 2004 243 115-124. 

FIGURE 22.10 Dynamics profile of the flux recovery in cleaning WPC-fouled PVDF MF membranes using NaOH solution at pFI 13 and 30°C, and at crossflow velocity of 0.45 m s and 350 kPa TMP. (From Mercade-Prieto, R. and Chen, X.D., J. Membr. Sci., 254, 157, 2(X)5. With permission.)... 

MF and UF used in pretreatment to RO are more frequently cleaned by physical cleaning and less frequently by chemical cleaning. Cleaning frequencies reported in ht-erahire varied widely. Physical cleaning frequency is approximately every 40 min with a chemical clean scheduled every 6 mo (98). An air backwash frequency of 15-20 min is sufficient for hollow-fiber MF membranes (77). In a UF evaluation study, backwashing was able to achieve an average flux recovery of 86.5% (99). It was observed in the same study that flux restoration could be achieved even when backwash was reduced from 10 to 1 min. 

Based on measurements of water flux data, the polysulfone hollow fibers proved difficult to clean. Flux recovery from run to run was inconsistent, and the membrane occasionally required extra effort to clean. 

Notable is the Diaflo M ultrafilter s ease-of-cleaning. The spiral showed 100% flux recovery after cleaning in every cycle (up to 10 cycles) of use and cleaning. 

Hollow fiber membrane modules have minimum hold-up volumes and can operate without blockage of the fibers if the l.d. of the fiber is substantially larger than the maximum cell aggregate. Until recently, hollow fiber modules were only available with UF membranes. The advent of polysulfone MF hollow fibers makes possible cleaning with acid and base and even autoclaving at 121° in some instances. Since MF membranes are prone to internal pore fouling, membrane cleanability with flux recovery is particularly important. 

The membrane fabricated from the copolymer with 50 wt% PEO exhibited 100% flux recovery, indicating its low irreversible fouling. Further increasing the PEO content in the copolymer could affect severely the membrane performance. 

Al-Obeidani et al. [93] reported on the development of more effective and economical procedures for cleaning polyethylene hollow fiber MF membranes that have been used for removing oil from contaminated seawater. In their study, alkaline cleaning showed higher recovery of operating cycle time but lower permeate flux recovery than acid cleaning. 

Although the effectiveness of multistep cleaning processes using surfactants, enzymes, or surfactant-enzyme systan in flux recovery is well estabUshed, the economic impact of these... 

Figure 2.41 Membrane flux recovery with successive cleaning steps. Source Schafer et al.

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