Organic rejection Ultrafiltration

Common membrane processes include ultrafiltration (UF), reverse osmosis (RO), electro dialysis (ED), and electro dialysis reversal (EDR). These processes (with the exception of UF) remove most ions RO and UF systems also provide efficient removal of nonionized organics and particulates. Because UF membrane porosity is too large for ion rejection, the UF process is used to remove contaminants, such as oil and grease, and suspended soHds. 

In ultrafiltration, the effluent is passed across a semiper-meable membrane (see Chapter 10). Water passes through the membrane, while submicron particles and large molecules are rejected from the membrane and concentrated. The membrane is supported on a porous medium for strength, as discussed in Chapter 10. Ultrafiltration is used to separate very fine particles (typically in the range 0.001 to 0.02 xm), microorganisms and organic components with molar mass down to 1000 kg kmol. Pressure drops are usually in the range 1.5 to 10 bar. 

Reverse osmosis is essentially the same process as ultrafiltration with low salt rejection. Kopfler and co-workers (12) used reverse osmosis in combination with solvent extraction and XAD adsorption. Solvent extraction with pentane and methylene chloride was used to remove organics from the reverse-osmosis concentrate (i.e., for desalting), and XAD was used for adsorption of the intractables from the extracted... 

The goal of most of the early work on reverse osmosis was to produce desalination membranes with sodium chloride rejections greater than 98 %. More recently membranes with lower sodium chloride rejections but much higher water permeabilities have been produced. These membranes, which fall into a transition region between pure reverse osmosis membranes and pure ultrafiltration membranes, are called loose reverse osmosis, low-pressure reverse osmosis, or more commonly, nanofiltration membranes. Typically, nanofiltration membranes have sodium chloride rejections between 20 and 80 % and molecular weight cutoffs for dissolved organic solutes of 200-1000 dalton. These properties are intermediate between reverse osmosis membranes with a salt rejection of more than 90 % and molecular weight cut-off of less than 50 and ultrafiltration membranes with a salt rejection of less than 5 %. 

The ultrafiltration or microfiltration membrane used in the described submerged membrane photoreactors showed high fluxes and a good removal efficiency of organic molecules, nevertheless, they are not able to reject compounds with low molecular weight. 

Replacing the ultrafiltration, nanofiltration pretreatment and reverse osmosis by BAHLM processes in desalination industry is the main idea of this proposal. Rejection characteristics of natural organic matters and inorganic salts in a low pressure nanofiltration (e.g., >99% at 1.5 MPa [115]) and capacity of polyanions to complex monovalent and especially bivalent cations [92, 95, 115-117] make this idea promising. 

The large number of papers necessitated publishing the symposium in two volumes. Volume I describes the desalination and salt-rejecting hyperfiltration membranes. Volume II covers hyper- and ultrafiltration membrane utilization in the following areas food, medicine, pulp, paper, and textile industries, oily waste stream purification, and in the separation of gases, polymers, organic solutes, and biopolymers. 

To assess microbial rejections, sterile membranes were challenged with P. diminuta, B. coagulans, S. cerevisiae, and P. roqueforti spores suspended in apple puree or 0.1% peptone. Reductions achieved by ultrafiltration of cells in peptone at normal operating pressure (300 psi) were 5.1, 6.0, 7.6, and >9.0 logs for smallest to largest organisms (Table III). 

Substances that are solubilized in surfactant micelles can be separated by ultrafiltration through membranes whose pores are smaller in diameter than the micelle size. For a membrane molecular weight cutoff from 1 to 50kDa, the rejections are 98%. The stream of water-containing monomeric molecules of surfactant (permeate) flows through the membrane. The remaining solution (retentate) contains solutes solubilized in micelles. The MEUF process is used for the separation of organic substances and various ions, the latter after their previous complexation. 

Cho, J., Amy, G., and Pallegrino, J. (1999). Membrane filtration of natural organic matter Initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes. Water Res. 35(18), 4455 4463. 

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