Clean water flux

The clean water flux across a membrane without any material being deposited follows Darcy s Law ... 

A study was carried out into the potential recovery of plasticiser and solvent from waste PVC plastisols using a ceramic multi-bore crossflow tube filter. The procedure employed to perform the test sequence involved clean water flux measurement, media acclimatisation, optimisation trial, concentration run, cleaning trial and final water flux measurement. Permeate samples were analysed using gas chromatography and compared with standards of diisononylphthalate(DINP)/white spirit mixtures. The ceramic membrane successfully recovered a clear mixture of DINP and white spirit. 

Alumina membranes having a mean pore diameter of 4 and 50 nm reduce the oil and grease concentration in the wastewater containing lubricating oil from 80-120 mgA in the feed to about 2-4 ppm in the p meate. This is equivalent to a retention efficiency of about 96% [Bhave and Fleming, 1988]. The attainable peimeate flux is close to about 90 L/hr-m. The permeate flaxes for the two membranes are shown in Figure 6.14 where they are compared to conesponding clean water fluxes. 

As in many other membrane separation applications, the clean water flux is essentially proportional to the transmembrane pressure difference (TMP). When solutes, macromolecules or particulates are to be separated from the solvent (e.g., water), the permeate flux is first a linear function of the TMP and is in the pressure controlled regime. Although similar to the behavior of water flux, the permeate flux is nevertheless lower. Beyond a "threshold pressure," the permeate flux is insensitive to TMP due to concentration and gel polarization near the membrane surface. This behavior is so-called mass transfer controlled. It appears that the larger pore membrane, 50 nm in pore diameter, reaches the threshold pressure sooner than the finer pore membrane, 4 nm in pore diameter. There is a significant advantage of operating the membranes at a higher... 

Field et al. [157] introduced the concept of critical flux in membrane filtration. They proposed that upon start-up, there exists a flux below which a decline of flux with time does not occur. Although a concentration polarization layer is present, solid deposition on the membrane that gives rise to cake layer formation does not take place, so that a nonfoufing or cake-free operation is achieved. This flux is the critical flux and it may either be in strong form, in which flux is identical to the clean water flux at the same TMP, or in weak form, in which flux varies linearly with TMP but the slope of the fine differs from that of clean water [6,157,161]. 

Clean waterflux It refers to the original flux of filtered deionized water with a virgin membrane. In most applications, after cleaning is performed the clean water flux is restored to approximately within 10% of its original value. It is seldom recovered to its original value after membrane cleaning due to monomolecular irreversible adsorption of foulants. 

Third, a water quality parameter (WQP), which considers colloid, organics, and salt rejection, was developed for the membranes investigated. A linear relationship beween WQP and log pore diameter was found. Finally, a partial cost analysis of various options was undertaken by evaluation of a) membrane cost as a function of clean water flux and operation at fouled conditions, b) WQP as a function of membrane cost, c) ferric chloride cost, and d) energy costs. 

Figure A 1.9 Pressure dependence of RO clean water flux before and after concentration.

The PSpM combines very high porosity with low thickness (a few 10 pm). The smallest pore size of the membranes prepared by PSpM (0.1-0.2 pm) is determined by the photolithographic technologies for manufacturing the mold. Depending on the membrane pore size and porosity, such microsieves may have clean water fluxes of about 1 million L/(m h bar). 

The membrane flux is the flow rate of permeate per unit area of membrane surface and typically proportional to the TMP. The flux for a new membrane, operating with water only, is referred to as the clean water flux, and serves as a useful benchmark. Clean water flux rates for membranes that are used for wastewater treatment may be of the order of 3—4 m /m /day. 

Gleaning. Fouling films are removed from the membrane surface by chemical and mechanical methods. Chemicals and procedures vary with the process, membrane type, system configuration, and materials of constmction. The equipment manufacturer recommends cleaning methods for specific apphcations. A system is considered clean when it has returned to >75% of its original water flux. 

Continued decline in performance indicates a membrane cleaning or compatibihty issue. The adequacy of the cleaning step is determined by the recovery of at least 80 percent of the initial normalized water flux. Although some variability in water flux is typical, any consistent dechne reflects an inadequate cleaning procedure. 

Module design Packing density (ft2/ft3) Water flux at 600 psi Salt (gal/ft2 day) rejection Water output per unit volume (gal/ft3 day) Flow channel size (in.) Ease of cleaning... 

Flush the system thoroughly with water to remove all traces of detergent measure the pure water flux through the membrane modules under standard test conditions. Even after cleaning, some degree of permanent flux loss over time is expected. If the restoration of flux is less than expected, repeat steps 1-3. 

Average permeate fluxes (normalized by the clean membrane water flux, J0) for yeast-BSA mixtures are plotted vs time in Fig. 6 for different concentrations of yeast in the primary and secondary feed reservoirs. The average flux, , was calculated by dividing the amount of net permeate collected by the time required to complete one cycle of yeast deposition, feed filtration, and backflushing (fs/+ tf + tb) the net permeate collected is... 

During reverse osmosis and ultrafiltration membrane concentration, polarization and fouling are the phenomena responsible for limiting the permeate flux during a cyclic operation (i.e., permeation followed by cleaning). That is, membrane lifetimes and permeate (i.e., pure water) fluxes are primarily affected by the phenomena of concentration polarization (i.e., solute build up) and fouling (e.g., microbial adhesion, gel layer formation, and solute adhesion) at the membrane surface [11]. 

Water Flux The permeability of a UF membrane is determined by pore size, pore density, and the thickness of the membrane active layer. Water flux is measured in the absence of solute, generally on a newly made or freshly cleaned sample. The test is simple, and involves passing water through the membrane generally in dead-end flow under carefully controlled conditions. In a water flux test, the membrane behaves as a porous medium with the flow described by Darcy s law. Adjustments for viscosity and pressure are made to correct tne results to standard conditions, typically the viscosity of water at 25°C and the pressure to 50 psi (343 kPa). The water flux will be many multiples ofthe process flux when the membrane is being used for a separation. Virgin membrane has a standard water flux of over 1 mm/sec. By the time the membrane is incorporated into a device and used in an application, that flux drops to perhaps 100 pm/s. Process fluxes are much lower. 

Module Design Packing Density (ft /ft ) Water flux at 600 psi (gal/ft -day) Salt Rejection Water Output per unit Volume (gal/ft -day) Flow Channel Size (in.) Ease of Cleaning... 

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