Bottom feed

Because in the most common bottom feed version the feed suspension enters the dmm from the bottom, fast settling slurries are not suitable for most rotary dmm filters nor are very fine slurries because of inevitable penetration problems. 

Cake Thickness Control Sometimes the rate of cake formation with bottom feed-type filters is rapid enough to create a cake too thick for subsequent operations. Cake thickness may be controlled by adjusting the bridge-blocks in the filter valve to decrease the effective submergence, by reducing the slurry level in the vat, and by reducing the vacuum level in the cake formation portion of the filter valve. If these measures are inadequate, it may be necessaiy to use a toploading filter. 

Figure 18-95 also contains a schematic layout of the equipment which is required for all bottom-feed leaf tests. Note that there are no valves in the drainage line between the test leaf and the filtrate receiver, nor between the filtrate receiver and the vacuum pump. 

It is difficult to plan a filtration leaf test program until one test has been run. In the case of a bottom-feed test, the first run is normally started with the intention of using a 30-s cake formation time. However, if the filtrate rate is very high, it is usually wise to terminate the run at the end of 15 s. Should the filtrate rate be very low, the initial form period should be extended to at least 1 min. If cake washing is to... 

Bottom-Feed Procedure The procedure for coUecting data using bottom-feed leaf test techniques is as follows ... 

Top-Feed Procedure The sequence of operations with a top-feed leaf test is the same as in a bottom-feed test, except that the leaf is not immersed in the sluriy. The best method for transferring the slurry to the top-feed leaf is, of course, a function of the characteristics of the sluriy. If the particles in the sluriy do not settle rapidly, the feed can usually be transferred to the leaf from a beaker. If, however, the particles settle veiy rapidly, it is virtually impossible to pour the slurry out of a beaker satisfactorily. In this case, the best method is to make use of an Erlenmeyer flask, preferably one made of plastic. The slurry is swirled in the flask until it is completely suspended and then abruptly inverted over the leaf. This technique will ensure that all of the sohds are transferred to the leaf. 

Precoat Procedure Precoat filtration tests are run in exactly the same manner as bottom-feed tests except that the leaf must first be precoated with a bed of diatomaceous earth, perhte, or other shave-able inert sohds. Some trial and error is involved in selecting a grade of precoat material which will retain the filtered solids to be removed on the surface of the bed without any significant penetration. During this selection process, relatively thin precoat beds of I to 2 cm are satisfactory. After a grade has been selected, bench-scale tests should be... 

One of the oldest filters applied throughout the chemical processing industry is the rotary vacuum drum filter, which is illustrated in Figure 8. This machine belongs to the group of bottom feed configurations. Rotary drum filters are typically operated in the countercurrent mode of operation. The principle advantage of these machines is the continuity of their operation. 

A mixture of hydrocarbons at 80 psia is to be differentially distilled until the mols of propane is reduced to 10 mols per 100 mols of bottom feed material. A kettle with bottom coil is to be used, and no trays. 

Vicinity of Los Alamos National Laboratory, 1997, Bottom-feeding fish (n=10/site) ... 

Barbel (Barbus graellsii), a cyprinid species endemic to the Ebro River [63], is a bottom-feeding fish. Finally, the cyprinid fish, Alburnus alburnus, also known as bleak, feed mainly on plankton, including crustaceans and insects (http //www. fishbase.org). 

Maccubbin, A.E., P. Black, L. Trzeciak, and J.J. Black. 1985. Evidence for polynuclear aromatic hydrocarbons in the diet of bottom-feeding fish. Bull. Environ. Contam. Toxicol. 34 876-882. 

Bottom feed, with rotary drum vacuum filters, 11 357... 

The concentration of toxicants present in sediments is a measure of its concentration in the water over a period of time and is therefore a measure of the risk to creatures. In the case of bottom feeding creatures there is the additional risk of direct ingestion of contaminated sediments in the gills and mouth with consequent adverse effects. 

Burbot, a bottom-feeding fish, taken from remote lakes in Canada in 1985--1986, contained liver concentrations of mirex ranging between 3.7 and 17.4 pg/kg (ppb) lipid weight (detection limit, 0.5 p g/kg), while photomirex was not detected. The lowest mirex values were seen in fish from the most remote locations, suggesting that atmospheric transport of this compound was occurring (Muir et al. 1990). 

In essence, the disc filter operates in a manner similar to a bottom-feed drum filter. The principal differences to be noted are the compartments which are formed on both faces of vertical discs. These comprise eight or more segments, each of which is connected to the horizontal shaft of the machine. The filtrate and air are drawn through the filter medium, into the drainage system of the segments, and finally through passages in the rotary shaft to a valve located at one or both ends. 

Dawe, C.J., Stanton, M.F. and Schwartz, F.J. Hepatic neoplasms in native bottom-feeding fish of Deep Creek Lake, Maryland. Cancer Res. (196U) 2k, 119 -1201. 

The marine amphipod Ampelisca abdita is a suspension and deposit feeder and it often occurs as a numerically dominant member of benthic communities (Fay et al., 2000). It can also serve as an important food source for bottom-feeding fish. 4-nonylphenol is a degradation product from detergents (see Fig. 2.16). Its relevant physical-chemical properties are given in Appendix C. 

The crude C4 mixture is charged to a 70 tray extractive distillation column T-l that employs acetonitrile as solvent. Trays are numbered from the bottom. Feed enters on tray 20, solvent enters on tray 60, and reflux is returned to the top tray. Net overhead product goes beyond the battery limits. Butadiene dissolved in acetonitrile leaves at the bottom. This stream is pumped to a 25-tray solvent recovery column T-2 which it enters on tray 20. Butadiene is recovered overhead as liquid and proceeds to the BDS reactor. Acetonitrile is the bottom product which is cooled to 100°F and returned to T-l. Both columns have the usual condensing and reboiling provisions. 

Value for bottom feed filters assume no trunnion stuffing boxes, except for precoat. Consult manufacturers for availability of higher submergences. 

Fish and Wildlife. A survey of 2,3,7,8-TCDD contamination in benthic (bottom feeding) and predator fish from major U.S. watersheds was conducted for the EPA National Dioxin Study (Kuehl et al. 1989). It was observed that 17 of 90 (19%) samples collected at sites statistically selected by the EPA had detectable levels of 2,3,7,8-TCDD, whereas 95 of 305 (31%) samples from sites chosen by EPA regional laboratories had detectable levels (detection limits 0.5-2 ppt on a wet weight basis). Of the 112 sites where 2,3,7,8-TCDD was detected, 74 samples (67%) were below 5 ppt, 34 samples (32%) were between 5 and 25 ppt, and 4 samples (1%) were above 25 ppt. A subset of samples collected at sites near the discharges from pulp/paper manufacturing facilities (n=28) had a higher frequency of... 

There are three primary hypotheses for their mode of formation. The first is that they are simply sediment that has been resuspended by bottom feeding fish. The "mullet muds" in Florida Bay are probably an example of this process. The second is that they result from spontaneous precipitation of CaCC>3 which may be... 

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