Liquid purification or separation – Processes – Separating
Patent
1982-11-24
1987-10-27
Fisher, Richard V.
Liquid purification or separation
Processes
Separating
210393, 210411, B01D 2324, B01D 2938
Patent
active
047028475
DESCRIPTION:
BRIEF SUMMARY
In the operation of modern sewage treatment plants, the separation of water and solids takes place almost exclusively in the sedimentation tank.
This type of separation is incomplete, because the solids are very light and are discharged from the sedimentation tank in large quantities by the outflowing water.
The discharge of solids is particularly great if hydraulic shocks occur, or if the biological decomposition is disturbed by a certain toxic action or by a one-sided sewage composition. These known disadvantages of the sedimentation tank are compensated by two countermeasures, namely flocculation or filtration, or the combination of both these measures.
Numerous filtering devices are already known for the filtration of the sedimentation tank. It is common to all these that they are connected downstream of the sedimentation tank.
Swiss Pat. No. 553 558 describes revolving drum filtering devices, which are incorporated directly into a biological plant. This revolving drum filter has a cleaning means constructed on the vacuum cleaner principle, which rests on the filter surface and flushes back the filter materials by suction.
In the case of such filters, mainly felt-like filter materials are used and they clog up due to microorganisms and algae. Due to the strong suction force of the pump, in the case of a clogged filter, the frictional resistance between the suction means and the filter material is so great, that the filter material is torn away from the drum.
This known filtering device has a further serious disadvantage. It is generally known that a vacuum pump never functions with a plurality of parallel-connected suction pipes, water only being sucked through the pipe where the resistance is lowest. The same applies in connection with filter cleaning. The surface of the filter is best cleaned by suction at those points where it is least clogged.
As a result of this, in the known device, the width of the filter belt to be cleaned is limited. In the case of wider suction connections, the function of such filter cleaning processes is dubious.
U.S. Pat. No. 3,575,850 describes a similar drum or revolving filter. Filter cleaning takes place by spraying the filter material surface exposed to the air. The filtered, suspended substances are removed by a gutter.
Such filtering devices are always of a large rotary type, with poor surface utilization with respect to the filter volume. They also have the disadvantage that they must always be installed in a separate tank prepared for the filter. The gradient losses in the feed and discharge pipes and in the filtering device are generally so great that the existing natural gradients are no longer sufficient. It is therefore necessary to instal an additional sewage lifting means.
In addition, a filtering device is known, in which a wide-meshed filter gauze is horizontally installed between the discharge channels. The sewage flows from bottom to top through the filter materials and over a period of time a layer of sludge builds up from the deposition side on the gauze and which acts as a filter layer. Filter cleaning takes place manually by lowering the water level and spraying the gauze with mains water.
The disadvantage of this filtering device is the manual operation. Only wide-meshed filter materials can be used, so that the cleaning intervals are as long as possible. The filter must be put out of operation for cleaning purposes.
In the sewage treatment field, numerous sand filters are also known, but they have nothing in common with the presently described filter.
Sewage filtration is relatively new, it being used as a further cleaning stage and in most cases must therefore additionally be fitted in an existing sewage treatment plant.
All the previously mentioned filter types require a separate filter tank and, if the natural gradient is not sufficient, an additional lifting means is also required.
The problem of the present invention is to provide a simple and inexpensive filtering device, which in an extremely economic manner can be installed in existing sedi
REFERENCES:
patent: 2066479 (1937-01-01), MacIsaac
patent: 2603354 (1952-07-01), Way et al.
patent: 3357566 (1967-12-01), Schmid et al.
patent: 4266953 (1981-05-01), Matthys et al.
Fux Kamil
Gresa Ludwig
Fisher Richard V.
Jones W. Gary
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