Membrane devices

Each of the membrane devices may be assembled by connecting the modules into combinations of series, pataUel-flow paths, or both. These assembUes ate connected to pumps, valves, tanks, heat exchangers, instmmentation, and controls to provide complete systems. 

SelF-siipported cylindrical membranes For liquid separations are made From 250 jlrn up to 6 rnrn, but there is no obvious limit to Future oFFerings. Membrane devices For liquids are almost alvvws tube-side Feed, with tw o major exceptions at the extremes oF porositv. High-pressure RO is almost always shell-side Feed, and one supplier oF verv lovv -pressiire MF also rims with shell-side Feed. 

Fouling is the term used to describe the loss of throughput of a membrane device as it becomes chemically or physically changed by the process fluid (often by a minor component or a contaminant). A manifestation of fouling in cross-flow UF is that the membrane becomes unresponsive to the hydrodynamic mass transfer which is rate-controlling for most UF. Fouling is different from concentration polarization. Both reduce output, and their resistances are additive. Raising the flow rate in a cross-flow UF will increase flux, as in Eq. 

Cassettes Cassette is a term used to describe two different cross-flow membrane devices. The less-common design is a usually large stack of membrane separated by a spacer, with flow moving in parallel across the membrane sheets. This variant is sometimes referred to as a flat spiral, since there is some similarity in the way feed and permeate are handled. The more common cassette has long been popular in the pharmaceutical and biotechnical field. It too is a stack of flat-sheet membranes, but the membrane is usually connected so that the feed flows across the membrane elements in series to achieve higher conversion per pass. Their popularity stems from easy direct sc e-up from laboratoiy to plant-scale equipment. Their hmitation is that fluid management is inherently veiy hmited and inefficient. Both types of cassette are veiy compact and capable of automated manufacture. 

While it is easy to add materials to a fermentation, removal is difficult. Membrane devices have been placed in the fermenter or in external recycle loops to dialyze away a soluble component. Cells release wastes or metabolites that can be inhibitory these are sometimes referred to as staling factors. Their removal bv dialysis has allowed cell concentrations to reach ten to one hundred times that of control cultures. 

USE OF SEMI PERMEABLE MEMBRANE DEVICES (SPMDs) TO INDOOR AIR MONITORING OF PYRETHROID INSECTICIDES... 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

Garrett and Chemburkar [15] described a membrane device which provides for steady-state conditions by continuously circulating fresh donor solution into the donor cell. 

Huckins, J.N., M.W. Tubergen, and G.K. Manuweera. 1990b. Semipermeable membrane devices containing model lipid a new approach to monitoring the bioavailability of lipophilic contaminants and estimating their bioconcentration potential. Chemosphere 20 533-552. 

Lebo, J.A., J.L. Zajicek, J.N. Huckins, J.D. Petty, and P.H. Peterman. 1992. Use of semipermeable membrane devices for in situ monitoring of polycyclic aromatic hydrocarbons in aquatic environments. Chemosphere 25 697-718. 

Meadows, J., D. Tillitt, J. Huckins, and D. Schroeder. 1993. Large-scale dialysis of sample liquids using a semipermeable membrane device. Chemosphere 26 1993-2006. 

Prest, H.F., W.M. Jarman, S.A. Bums, T. Weismuller, M. Martin, and J.N. Huckins. 1992. Passive water sampling via semipermeable membrane devices (SPMDs) in concert with bivalves in the Sacramento/San Joaquin river delta. Chemosphere 25 1811-1823. 

Semipermeable Membrane Devices and Other Membrane Processes. 57... 

Due to the predicted and previously detected low concentrations of pesticides in environmental samples (usually around the nanogram per liter level), a preconcentration step of the water samples is necessary prior to measurement. In this way, a preconcentration factor of several orders of magnitude (200-1,000-fold) is mandatory to reach the low detection limits necessary for the identification of pesticides, especially in complex wastewater samples. Also, the use of surrogate standards (e.g., triphenyl phosphate) added before the extraction step is a common practice in order to account for possible errors during the extraction process and for quantitative purposes. The commonly used extraction methods for polar compounds from water matrices involve isolation using liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which are commented on below. Other methods such as semipermeable membrane devices (SPMD) are also mentioned. 

Petty JD, Huckins JN, Martin DB. 1995. Use of semipermeable membrane devices (SPMDS) to determine bioavailable organochlorine pesticide residues in streams receiving irrigation drainwater. Chemosphere 30(10) 1891-1903. 

Membrane devices can be classified into four main types ... 

In the following sections we highlight only selected works that have contributed toward the further development of passive samplers for SVOCs and/or HOCs. The literature related to the development and use of passive samplers for monitoring gases or VOCs in occupational environments is large. However, these publications are discussed only briefly, because lipid-containing semipermeable membrane devices (SPMDs) are primarily designed for SVOCs. 

Based on earlier work (Lieb and Stein, 1969 Chiou, 1985 Sddergren, 1987 Zabik, 1988) Huckins etal. (1989,1990a, 1993) flrstdeveloped and tested two types of lipid-containing semipermeable membrane devices (SPMDs) for in situ passive sampling of bioavailable dissolved aqueous-phase HOCs. The lipid-containing... 

Axelman, J. Ntes, K. Naf, C. Broman, D. 1999, Accumulation of polycyclic aromatic hydrocarbons in semipermeable membrane devices and caged mussels (Mvtilus edulisl in relation to water column phase distribution. Environ. Toxicol. Chem. 18 2454-2461. 

Baussant, T. Sanni, S. Jonsson, G. Skadsheim, A. Bprseth, J.F. 2001, Bioaccumulation of polycyclic aromatic compounds 1. Bioconcentration in two marine species and in semipermeable membrane devices during chronic exposure to dispersed crude oH.Erwiron. Toxicol. Chem. 20 1175—1184. 

Booij, K. Sleiderink, H.M. Smedes, F. 1998, Calibrating die uptake kinetics of semipermeable membrane devices using exposure standards. Environ. Toxicol. Chem. 17 1236—1245. 

Booij, K. Hofmans, H.E. Fischer, C.V. van Weerlee, E.M. 2003a, Temperature-dependent uptake rates of nonpolar organic compounds by semipermeable membrane devices and low-density polyediy-lene membranes.Ewviww. Sci. Technol. 37 361—366. 

Huckins, J.N. Manuweera, G.K. Petty, J.D. Mackay, D. Lebo, J.A. 1993, Lipid-containing semipermeable membrane devices for monitoring organic contaminants in water. Environ. Sci. Technol. 27 2489-2496. 

Huckins, J.N. Petty, J.D. Prest, H.F. Clark, R.C. Alvarez, D.A. Orazio, C.E. Lebo, J.A. Cranor, W.L. Johnson, B.T. 2002a, A Guide for the Use of Semipermeable Membrane Devices (SPMDs) as Samplers of Waterborne Hydrophobic Organic Contaminants Publication No. 4690 American Petroleum Institute (API) Washington, DC. 

Lefkovitz, L.F. Crecelius, E.A. Gilfcil, T.J. 1994, The Use of Semipermeable Membrane Devices to Predict Bioaccumulation of Hydrophobic Organic Contaminants. The 15 Annual meeting of Society of Environmental Toxicology and Chemistry, Denver, CO Abstract WE25. 

Moring, J.B. and Rose, D.R. 1997, Occurrence and concentration of polycyclic aromatic hydrocarbons in semipermeable membrane devices and clams in three urban streams of the Dallas-Fort Worth Metropolitan Area, Texas. Chemosphere 34 551-566. 

Ockenden, W.A. Prest, H.E. Thomas, G.O. Sweetman, A. Jones, K.C. 1998, Passive air sampling of PCBs Eield calculation of atmospheric sampling rates by triolein-containing semipermeable membrane devices. Environ. Sci. Technol. 32 1538—1543. 

Petty, J.D. and Orazio, C.E. 1996, Application of Semipermeable Membrane Devices (SPMDs) Ay Passive Monitors of the Environment of Antarctica. USGS, Midwest Science Center, Columbia, MO Unpublished report to National Science Foundation Washington, DC. 

Rantalainen, A.-L. Ikonomou, M.G. Rogers, I.H. 1998, Lipid-containing semipermeable-membrane devices (SPMDs) as concentrators of toxic chemicals in the Lower Fraser River, British Co mAA2LCheniosphere 37 1119—1138. 

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