Suspended materials, membranes

Suspended materials and macromolecules can be separated from a waste stream using a membrane and pressure differential, called Ultrafiltration. This method uses a lower pressure differential than reverse osmosis and doesn t rely on overcoming... 

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Suspended Material. The material retained by the 0.45-pm membrane filters during filtration of the water samples collected from Ralston Creek and Reservoir was classified as suspended solids concentrations are shown in figure 4. The 226r3 content of suspended sediment in the mine effluent was 1,300 pCi/g U content of suspended sediment was 2,400 pg/g. Suspended-material load for this sample was 6 mg/L during the sample collection. Total release of both radionuclides (dissolved and suspended) was then calculated to be 8.4 pCi/L for 226r3 and 1,710 pg/L for U. Assuming an average daily... 

Prior to toxicity testing, an appropriate volume of each composite sample is vacuum-filtered (0.45 p membrane) to remove suspended material which would otherwise interfere with the conduct of some of the bioassays employed. In removing particulates from effluent samples, it is important to note that the PEEP scale only evaluates their soluble toxicity. This issue is further discussed in Section 6.3. 

In addition to acid or caustic, cleaners will sometimes have other compounds that are effective in removing and suspending materials off of the membrane. These compounds include metal chelating agents, surfactants, and enzymes. These compounds clean a membrane by one of three mechanisms 4... 

Biologicals, colloids and macromolecules Membrane-impermeable gases and vapors Virtually all suspended and dissolved materials Dissolved and suspended materials with molecular weight >1,000 All non-ionic and macromolecular species ... 

Cortinas et al. [89] eliminated colloidal suspended material (pitch) from kraft black liquors and partly recycled the liquor to the digester to reduce the consumption of chemicals. The colloidal pitch is formed by wood extractives. In particular, compounds such as waxes, sterols, and sterol esters that do not form soluble salts or dissolve during cooking form colloidal particles. The concentrated liquors (14%-15% solids) were filtered at high temperature using a 0.2 xm alumina membrane (USF Shumacher, Crailsheim, Germany). The pitch was almost completely retained (>99.9%), but the flux was sensitive to the black liquor composition and sometimes decreased to less than 100 L/(m h). 

Conventional or passive dialysis. The driving force is the analyte concentration gradient across the membrane, which reflects the concentration difference between the donor and acceptor solutions. Ions and low-molecular-weight compounds are transferred, whereas dissolved and suspended material with high molecular mass is retained. 

Microfiltration refers to the separation of suspended material such as bacteria by using a membrane with pore sizes of 0.02 to 10 /rm. If the pore size is further decreased so that the separation can be achieved at the molecular level, it is called ultrafiltration. The typical molecular weight cutoff for ultrafiltration is in the range of 300 to... 

The sample to be analyzed should first be filtered through a micropore membrane filter of 0.45 micron average pore diameter. This eflFec-tively removes suspended matter and insures subsequent determination of only that material considered to be in true solution. The suspended material may then be examined by x-ray analysis. If the thioacetamide method were used to analyze the unfiltered sample, some of the suspended sediment might not dissolve and would remain to contaminate the sulfide precipitate. The amount of sample taken for analysis must provide adequate amounts of the trace elements being determined. A 100-ml. aliquot is a convenient volume in which to make the precipita-... 

The lifetime of the membrane will also depend on the sample species. With relatively clean water samples a membrane could last for months under continuous operation, whereas the membrane may have to be changed everyday if the sample contains appreciable amounts of suspended materials. 

Turbidity A measure of the extent to which hght is scattered by particulate matter in the water. It is caused by a wide variety of suspended materials ranging in size from colloidal to coarse dispersions. Municipal water supplies normally have a turbidity level of less than 1 NTU indicating a content of less than 0.5 ppm of suspended soHds. The mrbidity should be less than 1 NTU to avoid particulate fouling of RO/NF membrane elements. 

The membrane, even in the absence of any suspended material, will have a natural flow resistance that may be determined during a clean liquid flow test. During filtration suspended matter might become attached to the pore channel of the membrane thereby reducing the flow channel dimension, or pores may become blocked off altogedier. These last two effects lead to re ance terms that are due to adsorption and pore blocking. It is not usual to be able to quantify these two resistances when filtering suspensions... 

Lead may exist in many forms in waters, both dissolved and suspended. As indicated in Chapter 3 there is no clear cut-off point between dissolved and suspended material and the arbitrary standard of a 0.45 jJim membrane filter is usually adopted to separate filterable and non-filterable lead. 

Reverse osmosis Semipermeable membrane Dissolved and suspended materials (ionic) saline 1-80 nm... 

Particles should be suspended in membrane-filtered sea water by shaking, and left for 24 hr to separate and become uniformly hydrated. The diameter of the material employed by calibration should be checked under a microscope and t.he procedure carried out as follows ... 

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