Membrane filtrations

In comparison to above methods, concentrating suspended cells on the surface of a membrane (of porosity small enough to retain them) permits 

Presterilized membranes may be purchased from supply houses. They may be packaged individually or in units of varying numbers, they may be white or gray, and with or without grids. Prior to use, it is necessary to remove the membrane from the packaging and transfer it to the sterilized filter housing without contamination (see Sec. 6.4). 

Unwrap and insert previously sterilized filter base into appropriately sized vacuum filter flask and connect to vacuum source. 

Using a pair of sterilized forceps (see Supplemental Note 1) remove the membrane from the package and place grid-side up on filter base. Carefully unwrap and position funnel. Clamp components together. 

Where the sample is 10 mL, add 20-30 mL of sterile diluent to filter funnel prior to the addition of the sample. This technique ensures more uniform distribution of microbes. 

Concentration of juice by filtration using semipermeable membranes and high pressure (0.1-1 MPa) is known as ultrafiltration. When the membrane is permeable for water and only to a limited extent for other small molecules (Mr 500, e. g., salts, sugars, aroma compounds), the process is called reverse osmosis. Concentration of juice is possible only to about 25% dry matter content. 

When sampling from the bottling line where microorganisms are either absent or present at low populations ( 5CFU/1000mL), the volume of sample needed to provide statistically reliable results becomes important. If, by experience, recovery of 10 cells/L at bottling likely results in instability, detection limits can be calculated when only 100 mL of a 750 mL bottle is membrane filtered (Cases 1 and 2). 

Comparing cases 1 and 2, the difference between stabihty and potential refermentation is less than 1CFU per plate, a population that would probably not be recovered. Using the same acceptance levels, detection limits are far better when the entire bottle contents (750 mL) are membrane filtered (cases 3 and 4). 

Aseptically obtain a sample from either a botde or a tank. 

Flame the open neck of the bottle or sample container for a couple of seconds and immediately pour at least 250 mL into the top of a membrane filter unit. 

Apply vacuum until all of the wine has been filtered into the lower chamber. Be sure to have a trap flask located between the vacuum source and the sterile filter unit to catch additional wine. 

Membiaiie technology has e qpanded at an incredible rate over the past twenty years, and now embraces a muM-hinion dollar industry. Applications can be broadfy divided into processes fbr (a) su ended particles and (b) dissolved solids. Thus the filtration of particles in the si2ie range 0.1-10 pm, u g relativefy open membranes is described as microfiltration (MF). 

Membranes for the removal of dissolved species are necessarily tighter, in pore size terms, than the microporous variety. Table 1.5 contains information on membranes used for uhrafiltratiQn (UF) (0.001-0.02 pm) and reverse osmosis (RO) (1-10 A) 

Ultrafiltration Colloids macromolecules in solution 0.001-0.02 10-200 (or 300-3 000 MW spherical proteins  

In RO processes, the pumping s tem has to overcome the osmotic pressure of tire salt in water. This leads to the necesaty for large pressure drops (25-70 bar) across RO membranes in order to achieve accqrtable filtrate rates. In contrast, MF and UF processes op nte at rdativdy low pressures (0.07-7 bar). 

Conventional filtration involves slurry flow dead-md into the filter, ie. the flow of fluid is petpendicukr to the suifiice of the medium. The subsequent accunmlation of colloidal or suhmiarometie-sized particles are particularly difficult to filter and retention of such particles often culminates in pluming ofthe fitter medium. 

These methods may be used for liquid samples or solid samples which are soluble. They are especially useful for handling liquid samples containing only a small number of micro-organisms, when it becomes necessary to process large volumes. 

A number of companies sell the equipment and also sterile dehydrated pads of selective media for use with membrane filters. These only need the addition of sterile water before use. The most important suppliers in the UK include companies such as Gelman, Millipore, and Sartorius. 

One problem common to all cultural techniques, whether plate counting or membrane filtration, is the degree of recovery of damaged organisms. 

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Membrane filtration Membrane module Membrane permeability Membrane process Membrane processes Membrane reactor Membrane roofing Membranes... 

Methods to Detect and Quantitate Viral Agents in Fluids. In order to assess the effectiveness of membrane filtration the abihty to quantitate the amount of vims present pre- and post-filtration is critical. There are a number of techniques used. The method of choice for filter challenge studies is the plaque assay which utilizes the formation of plaques, localized areas in the cell monolayer where cell death caused by viral infection in the cell has occurred on the cell monolayer. Each plaque represents the presence of a single infectious vims. Vims quantity in a sample can be determined by serial dilution until the number of plaques can be accurately counted. The effectiveness of viral removal may be determined, as in the case of bacterial removal, by comparing the vims concentration in the input suspension to the concentration of vims in the effluent. 

T. D. Brock, Membrane Filtration, Sci. Tech. Inc. Publishing, Madison, Wis., 1983. 

Membrane filtration has been used in the laboratory for over a century. The earliest membranes were homogeneous stmctures of purified coUagen or 2ein. The first synthetic membranes were nitrocellulose (collodion) cast from ether in the 1850s. By the early 1900s, standard graded nitrocellulose membranes were commercially available (1). Their utihty was limited to laboratory research because of low transport rates and susceptibiUty to internal plugging. They did, however, serve a useflil role in the separation and purification of coUoids, proteins, blood sera, enzymes, toxins, bacteria, and vimses (2). 

Membrane Filtration. Membrane filtration describes a number of weU-known processes including reverse osmosis, ultrafiltration, nanofiltration, microfiltration, and electro dialysis. The basic principle behind this technology is the use of a driving force (electricity or pressure) to filter... 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Optimized modern dry scrubbing systems for incinerator gas cleaning are much more effective (and expensive) than their counterparts used so far for utility boiler flue gas cleaning. Brinckman and Maresca [ASME Med. Waste Symp. (1992)] describe the use of dry hydrated lime or sodium bicarbonate injection followed by membrane filtration as preferred treatment technology for control of acid gas and particulate matter emissions from modular medical waste incinerators, which have especially high dioxin emissions. 

Polymer Membranes These are used in filtration applications for fine-particle separations such as microfiltration and ultrafiltration (clarification involving the removal of l- Im and smaller particles). The membranes are made from a variety of materials, the commonest being cellulose acetates and polyamides. Membrane filtration, discussed in Sec. 22, has been well covered by Porter (in Schweitzer, op. cit., sec. 2.1). 

Economics Microfiltratiou may be the triumph of the Lilliputians nonetheless, there are a few large-industrial applications. Dextrose plants are veiy large, and as membrane filtration displaces the precoat filters now standard in the industry, very large membrane microfiltratiou equipment will be built. 

Emerging Membrane Control Technologies The recent improvements in membrane technology have spawned several potentially commercial membrane filtration uses. 

In this work ion-exchange and gel-permeation chromatography coupled with membrane filtration, photochemical oxidation of organic metal complexes and CL detection were applied to the study of the speciation of cobalt, copper, iron and vanadium in water from the Dnieper reservoirs and some rivers of Ukraine. The role of various groups of organic matters in the complexation of metals is established. 

Instead, membrane filtration may be used to sterilise the nutrient in this experiment. This can be accomplished by drawing the nutrient from a mixing jar and forcing it through an in-line filter (0.2 p,m pore size) either by gravity or with a peristaltic pump. The sterilised medium is fed into an autoclaved nutrient jar with a rubber stopper fitted with a filtered vent and a hooded sampling port. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

Intensive technologies are derived from the processes used for the treatment of potable water. Chemical methods include chlorination, peracetic acid, ozonation. Ultra-violet irradiation is becoming a popular photo-biochemical process. Membrane filtration processes, particularly the combination microfiltration/ultrafiltra-tion are rapidly developing (Fig. 3). Membrane bioreactors, a relatively new technology, look very promising as they combine the oxidation of the organic matter with microbial decontamination. Each intensive technique is used alone or in combination with another intensive technique or an extensive one. Extensive... 

Fig. 3 Treatment train including membrane filtration for microbial decontamination...

Tertiary treatment is required often to meet the industry or irrigation standards, especially when disinfection is needed. This step is known as water regeneration. Typical tertiary treatment proposed in the literature [23] is composed of the following stages low pressure membrane filtration (e.g., MF) followed by disinfection stage and finally high pressure membrane filtration (e.g., RO). Industrial... 

Table 4 summarizes the efficiency of membrane filtration as preliminary treatment in the hybrid process to obtain regenerated water for industrial reuse. Working with the adequate cleaning cycle to avoid fouling and to keep a constant flux (10 1 min ) important reduction in suspended solids (90%) and turbidity (60%) of the wastewaters is achieved but there is no significant reduction of other chemical or physical parameters, e.g., conductivity, alkalinity or TDS, or inactivation of E. coli. 

Kim SL, Chen JP, Ting YP (2002) Study on feed pre-treatment for membrane filtration of secondary effluent. Sep Purif Technol 29 171-179... 

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