Hyperfiltration

Hyperfiltration, particularly RO, was the first membrane process to be run on an industrial scale, as early as the 1960s [1,3]. The great breakthroughs here were the invention in the early sixties by Loeb and Sourirajan [4] of asymmetric membranes prepared via phase inversion and the development of membranes prepared via interfacial polymerization [5]. The membranes appHed are densified even more than those for UF and a Hmit is reached membranes may get so dense that the 

Sometimes considered as another pressure-driven membrane process, diafiltration (dilution mode) is in fact nothing other than an improved design for a more enhanced purification (Fig. 3.6-2) [1, 5]. It has, for instance, appHcations in the pharmaceutical, biotech and food industries where a complete separation of high MW compounds from low MW compounds is required. After a first separation, the retentate is diluted again before the next separation purifies the stream further. This process can be repeated as often as desired. Without the dilution, the filtration would stop at a certain point when still too much of the unwanted compound would be present because of fouHng or an excessive increase in osmotic pressure. 

The main problem with pressure-driven membrane processes is the flux decline as a function of filtration time (Fig. 3.6-3) due, most importantly, to concentration polarization (remaining constant once estabhshed) and membrane fouling (worsening as a function of time). These cause extra resistances on top of the membrane resistance and thus slow down the transport This reduction can be as severe as 99% of the initial flux value in M F. Reviews are available on these matters [7], some focusing in more detail on in situ monitoring techniques [8], some only on concentration polarization [9] others only on fouling [10-12]. 

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Hyper compressors Hypercube topology Hyperfiltration Hyperglycemia... 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Ultrafiltration separations range from ca 1 to 100 nm. Above ca 50 nm, the process is often known as microfiltration. Transport through ultrafiltration and microfiltration membranes is described by pore-flow models. Below ca 2 nm, interactions between the membrane material and the solute and solvent become significant. That process, called reverse osmosis or hyperfiltration, is best described by solution—diffusion mechanisms. 

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

Because renal vasodilatation and hyperfiltration are often associated with a natriuretic response, a number of activators or inhibitors of endogenous vasoactive systems can cause increased NaCl excretion, and some of these may be developed into compounds of clinical interest in special situations. Such agents include natriuretic pqDtides most notably B-type natriuretic peptide (nesiritide), neutral endopeptidase (NEP) inhibitors (thiorphan, phosphoramidon), mixed NEP and ACE inhibitors (omapatrilat), guanylin and uroguanylin, kinins, prostaglandins of the E series, adrenomedullin, relaxin, prolactin, and others. 

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. 

Roels H, Lauwerys R, Konings J, et al. 1994. Renal function and hyperfiltration capacity in lead smelter workers with high bone lead. Occup Environ Med 51 505-512. 

Middaugh, D.P., R.L. Thomas, S.E. Lantz, C.S. Heard, and J.G. Mueller. 1994b. Field scale testing of a hyperfiltration unit for removal of creosote and pentachlorophenol from ground water chemical and biological assessment. Arch. Environ. Contam. Toxicol. 26 309-319. 

Hyperdispersants, 3 677 Hyperfiltration, 25 890 Hyperglycemia, as cause of age-related conditions, 2 813 Hyperhomocysteinemia, 2 822... 

Separation and concentration by means of hyperfiltration (reverse osmosis). 

A bottleneck in all membrane processes, applied in practice, is fouling and scaling of the membranes. These processes cause a decrease in water flux through the membrane and a decrease in retention. Much attention is paid, especially in case of nanofiltration and hyperfiltration, to prevent fouling of the membrane by an intensive pretreatment and the regular removal of fouling and scaling layers by means of mechanical, physical or chemical treatment. 

Membrane processes, such as hyperfiltration, can also reduce the health risks caused by the presence of pollutants such as pesticides, heavy metals, endocrine disrupters, pathogens and viruses. This is especially important in case where human beings can get in contact with reclaimed water. 

Reverse osmosis (hyperfiltration) Pressure gradient <1 nm Dissolved salts, small organics... 

Spiegler, K. S. and Kedem, O. Desalination 1 (1966) 311. Thermodynamics of hyperfiltration (reverse osmosis) criteria for efficient membranes. 

Belfort, G. In Synthetic Membrane Processes, Belfort, G. (ed.) (Academic Press, Orlando, 1984). Desalting experience by hyperfiltration (reverse osmosis) in the United States. 

Kraus, K. A. and J. S. Johnson. 1966. Colloidal hydrous oxide hyperfiltration membrane. U.S. Patent 3,413,219. 

Ballou, E. V., M. I. Leban and T. Wydeven. 1973. Solute rejection by porous glass membranes. III. Reduced silica dissolution and prolonged hyperfiltration service with feed additive. J. Appl. Chem. Biotechnol. 23 119-30. 

Leenaars, A. F. M. and A. J. Burggraaf. 1985b. The preparation and characterization of alumina membranes with ultrafine pores. Part 4. Ultrafiltration and hyperfiltration experiments. J. Membrane Sci. 24 261-70. 

Twenty years ago two researchers laboring diligently at the University of California at Los Angeles developed the first modified asymmetric membranes which seemed to have commercial potential for what was to become the exciting field that today is known as hyperfiltration or reverse osmosis. Since that time, these dedicated scientists have given freely of themselves and their talents not only to further contribute technically, but also to help guide, teach, and train others to grow in this frontier area. 

In conclusion, it can be claimed that a combination of kinetic and equilibrium conductance and membrane potential measurements provides a powerful method for investigating the permselective properties of membranes of low fixed charge density. Such methods should be applicable also to other polymers useful in hyperfiltration if they can be prepared in the form of homogeneous membranes. 

Thomas, D.G., and Mixon, W.R., "Effect of Axial Velocity and Initial Flux on Flux Decline of Cellulose Acetate Membrane in Hyperfiltration of Primary Sewage Effluents," I EC Process Design and Development 11, 339-343 (1972). 

Sheppard, J.D., Thomas, D.G., and Channabasappa, K.C., "Membrane Fouling Part IV Parallel Operation of Four Tubular Hyperfiltration Modules at Different Velocities with Feeds of High Fouling Potential," Desalination 11, 385-398 (1972). 

Intrinsic Membrane Compaction and Aqueous Solute Studies of Hyperfiltration (Reverse-Osmosis) Membranes Using Interferometry ... 

The major significance of this work is that yinth-ini c. compaction for one solute and aqucoui iotwtion c i )Cct6 for different solutes are measured for a commercial hyperfiltration membrane as a function of applied differential pressure. The results are obtained via simulation of the steady state concentration profile adjacent to the planar surface of the membrane for... 

Mahlab, D., Ben-Yosef N. and Belfort G, "Concentration Polarization Profile for Dissolved Species in Unstirred Batch Hyperfiltration (Reverse Osmosis) - II Transient Case." Desalination, 24, 297-303 (1978)... 

Thomas, D.G. and Watson, J.S., "Reduction of Concentration Polarization of Dynamically Formed Hyperfiltration Membranes by Detached Turbulence Promoters", I EC Process Design and Develop., 1968, T, July, 397. 

The SBP membrane filtration system concentrates contaminants and reduces the volume of contaminated groundwater, surface water, storm water, landfill leachates, and industrial process water. This hyperfiltration system consists of stainless steel tubes coated with a multilayered membrane, which is formed in-place using proprietary chemicals. The membrane filtration system can be used with an SBP bioremediation system or another technology as part of a treatment train. 

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