Direct filtration

The trend in the use of deep bed filters in water treatment is to eliminate conventional flocculators and sedimentation tanks, and to employ the filter as a flocculation reactor for direct filtration of low turbidity waters. The constraints of batch operation can be removed by using one of the available continuous filters which provide continuous backwashing of a portion of the medium. Such systems include moving bed filters, radial flow filters, or traveling backwash filters. Further development of continuous deep bed filters is likely. Besides clarification of Hquids, which is the most frequent use, deep bed filters can also be used to concentrate soflds into a much smaller volume of backwash, or even to wash the soflds by using a different Hquid for the backwash. Deep bed filtration has a much more limited use in the chemical industry than cake filtration (see Water, Industrial water treatment Water, Municipal WATERTREATiffiNT Water Water, pollution and Water, reuse). 

Turbidity At no time can turbidity (cloudiness of water) go above 5 nephelolometric turbidity units (NTU) systems that filter must ensure that the turbidity go no higher than 1 NTU (0.5 NTU for conventional or direct filtration) in at least 95% of the daily samples in any month. As of January 1,2002, turbidity may never exceed 1 NTU, and must not exceed 0.3 NTU in 95% of daily samples in any month... 

The viscosity of the 20 mg/mL PGA solution was too high to be filtered by the 2000 daltons cut-off membrane. In direct filtration or filtration experiments at the earliest stages of the enzymatic degradation, a gel appeared between the hollow fibers of the cartridge, which meant that we had to keep the reaction without filtration for 6 hours (until the viscosity of the system was adequate). 

Yamamoto and co-workers reported the use of scandium(lll) triflate as an esterification catalyst when acetic anhydride was used as the acetate source.5 6 While they only reported on monoalcohols (1°, 2°, and 3°) on a small scale, the submitters modified the Yamamoto procedure to suit the submitters reaction with the 1,1,2-triphenyl-1,2-ethanediol. As detailed above, the current procedure provides a yield of the HYTRA acetate that is comparable to the procedure reported by Braun and coworkers,2 1 but via simple, direct filtration for the reaction mixture. 

Direct filtration would also be employed when the solid consists of unwanted reaction products, in which case the filtrate would be treated as the single-phase... 

To a solution of 30.4 mg (0.114 mmol) of3-bis(phenylsulfonyl)methylcyclopentene in 2.4 mLofdry CH2C12 are added 16.4 mg (0.147 mmol) of trimethylamine iV-oxide dihydrate and a 2.5% solution of 0s04 (0.01 equiv, 0.00728 mL) in CCl4 in order. After stirring for 4 h, direct filtration through a small pad of silica gel (EtOAc elution) and subsequent evaporation of the eluent gives the desired product (91 %) in a 92 8 ratio as determined by H-NMR analysis (CDC13/D20). 

Chuang, C. J. and K. Y. Li (1997). Effect of coagulant dosage and grain size on the performance of direct filtration. Separation Purification Technol. 12, 3, 229-241. 

Vims filtration membranes are made of various polymers such as hydrophilized PVDF, hydrophilized PES, and cellulose. They are available in pleated cartridge and hollow-fiber formats. At present almost all vims filtration applications are performed in the direct filtration mode. 

Direct flow filtration has certain Umitations. The flux (filtration flow rate per unit membrane area) decreases over time as the process continues because the filtering media is loaded with more contaminant particles, as illustrated in Figure 14.1. Moreover, when the concentration of the contaminant in the feed stream is high, the filtering media must be replaced very frequently, which can be economically impractical. Also when the contaminant matter to be separated is small in size, requiring ultrafiltration or reverse osmosis membranes with much smaller pores, then direct filtration is less feasible as the flux declines very rapidly over time, again requiring frequent filter replacement. 

Fig. 12. Reduced efficiency of three-layer direct filtration caused by nannoplankton (Date 9 April 1985)...

Direct filtration Established All Lower cost alternative to conventional filtration... 

Conventinal filtration Direct filtration Slow sand filtration Package plant filtration Diatomaceous earth filtration Membrane filtration (reverse osmosis)... 

The performance of each filter type depends on the quality of the influent and proper design and operation. The range of influent characteristics for which various filters are effective has been provided by the US EPA (3) in Tables 5 and 6. According to the two tables, DE filtration is an established process mostly for small water systems with good influent quality (less than 5 NTU turbidity, less than 5 color units, and less than 50/100-mL conform count) and low influent capacity (below 100 MGD). The removal capacities for Giardia cysts and viruses of the above seven filter systems are presented in Table 7. It is important to note that DE filtration is better than conventional filtration and direct filtration in terms of removal efficiency of Giardia cyst and viruses. 

Conventional treatment, which includes coagulation, flocculation, clarification (sedimentation or flotation), and filtration, along with disinfection, can achieve 99.9% inactivation of Giardia cysts and 99.99% inactivation of enteric viruses when properly designed and operated. Direct filtration, slow sand filtration, and diatomaceous earth filtration systems, each combined with disinfection, have also achieved these reductions. 

When direct filtration is included in the water treatment process, disinfection credit can be taken by the filtration step for a 2-log inactivation of Giardia cysts and a 1-log inactivation of viruses. This means that the primary disinfectant must provide an additional 1-log inactivation of Giardia cysts and 3-log inactivation of viruses. In the specific instance of a conventional treatment process that includes coagulation, flocculation, sedimentation, and filtration, an inactivation credit of 2.5-logs for Giardia cysts and 2-logs for viruses may be taken. This means that the primary disinfectant must provide an additional 0.5-log inactivation of Giardia cysts but a 2-log inactivation of viruses. 

The largest area of polyelectrolytes application is potable and waste water treatment by filtration [108]. Here the anionic, nonionic, and cationic poly electrolytes are used. The USA, France, Germany, Japan, and other countries are widely use polyelectrolytes in direct water and wastewater filtration. Large quantities of ultra-high quality water are produced by suitably designed direct filtration equipment employing polyelectrolytes [109]. Polyelectrolytes strongly improve removal of color, oil, asbestos at treatment of water by filtration [110]. 

The use of nanofiltration membranes as supporting membranes have been also reported [28]. In this case, direct filtration of ionic liquids through the nanofiltration membrane was not possible at a gas pressure up to 7 bars. The ionic liquids with cations associated with straight or branched hydrocarbon chains were easily absorbed into the polymeric membrane allowing the nanoporous structure saturated with the ionic liquids. 

The term nutsche is derived from the German word for sucking. Vacuum is applied at the bottom of a vessel that contains a perforated plate. A filter cloth, screen, perforated plate, or porous ceramic plate may be the direct filtration medium (see Fig. 8). Subsequently, products should have lower cake resistances and well-defined crystal structures to facilitate separation. The driving force for the separation is vacuum and/or pressure. 

The usefulness of such supported carbodiimides is clearly illustrated in the application of resin 11 for the formation of Mosher amides 13 in deuteriochloro-form as solvent, as shown in the general procedure involving the (,S )-Mosher acid (12) depicted in Scheme 7.4. This procedure allowed a clean, fast determination of the optical purity of amines by NM R analysis after direct filtration of the residual polymer-supported urea 14 [26]. 

In the domain below a mass concentration of about 50 mg/L and Zxv < 30 /xm, granular-media filtration without flocculation as a pretreatment step (direct filtration) easily satisfies the performance criteria for a 90% removal. Although removal efficiency appears to be a minimum in the size range 0.2 to 2 /xm (17,24), a, proper selection of media size and depth will ensure satisfactory removals, provided that particulates are destabilized (17). Filters will tolerate mass concentrations higher than 50 mg/L if particulate density and shear strength are increased. 

The boundaries of the process selection regions are guidelines only they can be used for a preliminary assessment of technically feasible separation processes and pretreatment requirements (using particle size data). Lake waters typically contain low mass concentrations (< 10 mg/L) of particulates with number counts of 10 to 10 mL S and Zxv between 5 and 20 /xm (14,16,18). Thus direct filtration may satisfy particulate removal requirements. However, particulate concentrations in... 

The data in Figure 5, as well as data not shown indicated that by locating the raw water intake structure of the treatment plant below the average depth of the thermocline, the direct filtration process could be used for particulate removal. Particulate counts of approximately 10 mL (Zmin = 0.8/xm) with Zxv 10/xm or less fall in the direct filtration region shown in Figure 4. 

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