Percolation filtering

Percolation filter and/or sub-surface irrigation may be required to provide aeration and final purification ... 

This one-stage scrubber worked on the principle of the percolating filter technique. 

Percolating filter installations consist of installations with a large specific surface over which the scrubbing water to be purified is distributed. The efficiency of the percolating filter depends on the size of the biological mat an is expressed in m2 area... 

A lateral percolation filter was fabricated on quartz (see Figure 8.2). The filter elements, which were located near the entry port of a channel, had 1.5 im channel width and 10 im depth. They were anisotropically etched with an aspect ratio greater than 30 1 [828], In contrast to the usual axial slit filter, in which the filter area is dictated by the channel area, the fluid flow in the lateral percolation filter... 

Finally, microfilters are described as part of the microchannel system in order to assist sample preparation. Channels with diameters less than 30 /rm can easily be blocked by particulates in the sample, or crystals formed in solutions held in a micro-reservoir. While prefiltration outside of the microchannel system can separate most particles out of the sample solution prior to addition to the biosensor system, volumes required for macrofiltration are much larger than the volume finally applied to the biosensor. In addition, crystal or aggregate formation inside the channel cannot be avoided. Thus, the use of microfilters inside the microchannel system will be an important element in miniaturized biosensors. Filters have been described for trapping cells from blood [53], percolation filters for filtering solvents containing particulate materials ranging from dust to cells [54], and nanofilters that can separate particles as small as 44 nm [55]. 

The sulfur content of an oil is to be reduced by percolation through a b l of adsorbent clay. Laboratoiy tests with the clay and oil in a representative percolation filter show the foUomng instantaneous sulfur contents of the effluent oil as a function of the total oil passing through the filter adapted from Kaufman, Chem. Met. Eng., 30, 153 (1924 ] ... 

In general, the hydrocarbons are adsorbed in the following order unsaturates, aromatics, naphthenes, and paraffins. In each series the high-molecular-weight hydrocarbons are adsorbed more readily, and this doubtless accounts for most of the decolorizing action. Thus the specific gravity, viscosity, and color of the stream of oil from a percolation filter increase as more and more oil flows through the filter, and the first oil... 

The process is practiced at 220 to 650 F, but most refiners contact diluted cylinder stocks at 475 F and neutral oils at 220 to 320°F. Occasionally lower temperatures are used, but such an operation should be classed as neutralization. The acid-stage oil is mixed with 200 or 200 to 300 mesh clay, and the mixture is heated in a pipestill to the aforementioned temperatures. The hot oil is then allowed to settle for a short time, and the fines (clay dust) are filtered from the oil in Sweetland or similar presses. Sometimes a short percolation filter is used to aid in the removal of the fine clay. R. C. Davidson has made a complete summary of the methods of applying contact treating. The clay is usually not recovered, but Chenault and Miller report the commercial use at 90 to 100 F of a 20 per cent acetone (naphtha) solution for extracting impurities from contact clay. A low contact temperature is employed so that the adsorbed materials will not be too tightly attached to the clay. The reactivated clay has an efficiency of 80 to 85 per cent. Spent clay is mixed with solvent, filtered in a closed rotary-type filter, and washed on the filter with naphtha. The recovery of acetone by distillation from the naphtha and from water constitutes a major part of the process. 

Reeves and Turkleson, Cycle Washing of Percolation Filters, Pet. Refiner, March, 1949, p. 135. 

The results of the laboratory experiments were confirmed in various, sometimes very extensive investigations in treatment plants and water-courses. Earlier reviews were published by Heinz and Fischer [77] in 1962, and by Husmann, Malz and Jendreyko [78] in 1963. Full-scale tests on percolating filter plants confirmed the values found in the laboratory for the degradation of linear alkylbenzenesul-fonate [79]. During these tests, it was also observed that a part of the surfactant is already degraded, before it reaches the treatment plant, while the effluent runs along the sewer system [80]. 

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