TUBULAR TRASH NET FOR PRE-TREATING SEWAGE

Abstract: The tubular trash net is a cleaning and collecting device for pre-treatment of sewage, where the water which is to be separated from waste trash materials is led through a collecting net (8), after which the net (8) containing the separated trash is drawn through mechanically-driven rollers (10) which simultaneously de-water the trash prior to its being conveyed, together with the used net (8), to a container for disposal, while runoff pre-treated water is sent on for either further treatment or deep-water outfall.

Description: Tubular trash net for pre-treating sewage. In cleaning plants for sewage, the sewage will normally first flow through a raked bar-screen, which is designed to stop larger solid waste particles such as textiles, plastic, cigarette butts etc. which are carried in by the sewage. Such coarse waste can easily clog drain outlets, pumps and valves, etc. A typical raked bar-screen consists of flat steel strips placed parallel to each other across the sewage inlet, at an angle to the inlet flow direction. The sewage is forced through the parallel bars, where openings normally vary from 15 to 25 mm. The coarse trash material is depos¬ ited around the bars and is removed at necessary intervals by a rake, with teeth which fit between the bars, which is drawn up from the bottom of the bar-screen and rakes the trash up over the water-level and deposits it on a conveyor belt, whereas in larger installations the trash will be transported to a de-watering unit in order to press out most of the water content. There are other methods for separating trash from the sewage, e.g. by diverting the sewage over a strainer unit which has openings of approximately 1 mm. , so that the sewage water passes on through while the wet trash slides down the strain¬ er due to its own weight, and is . transported on a conveyor belt to a disposal container, in some cases being first run through a de-watering unit. If one further wishes to remove small trash particles remain¬ ing in the sewage, traditional sediment-collecting basins must be used in addition to the bar-screen or strainer. The above-mentioned screen or strainer are normally the first stages in the cleaning process, coming before the sewage * is • diverted on either to a sediment-collector or to a deep-water outfall distributor pipeline (clogging can occur if the above trash removal is neglected) . The raked bar-screen has the disadvantage that coa se trash particles, threads, string, bits of stockings,etc. can pass on through the screen, since the length of the openings is considerably greater than their width. Due to the relatively small area of the openings themselves, the average speed of the sewage through the bars—is high, which reduces the screen's effectiveness in separating solid trash from sewage. The most effective solution for the screen principle would be to use square openings in the screen, for example 10x10 mm. or 15x15mm. , etc., but this arrangement doesn't allow raking the trash away from the screen because of the limitations of current technology. Screens, strainers etc. also have the great disadvantage that they must be constructed in a series of mechanical units, each with its own separate power drive: the screen with its raking arm, a convey belt transport unit, a de-watering unit, and in many cases an additional conveyor belt leading to a disposal container. The invention described below - the tubular trash net unit for pre-treating sewage - replaces all of the above units with a single device, and in addition can achieve a much higher efficiency in removing solid trash from sewage water. Details of operation will be explained below, with numbers which refer to the enclosed drawing (see fig. 1 and 2): Sewage is pumped to the tubular trash net (8) , as indicated in fig.l, by the pump (1) through the inlet pipe (2), but may also be led into the net using gravity flow from above. A pressure gauge/pressostat (3) is placed near the inlet " and sends an electrical impulse to the mechanically-driven rollers (10/11) when pressure build-up in the inlet section exceeds the desired level. A drainage canal (4) leads runoff water from the trash net to the next stage of processing or outflow. The sewage is passed on through inlet pipe (5), which is connected to the inlet pipe (2) with a hinged joint with a water-tight gasket, which allows replacing the trash net cassette (7) when the net (8) , which is colour-coded to indicate time for replacement, must be changed (see fig.2). This can be performed by stopping the pump (1) , swinging the inlet pipe (5) on its hinge (6) so that the trash net cassette (7) can come into its replacement position, the rubber friction sleeve (9) is loosened, the cassette (7) is removed and the inlet pipe (5) is ready to receive a- ~ new trash net cassette. The friction sleeve (9) is then adjusted, the tubular trash net (8) is fastened to the end of the previous net which is still in position between the rollers(lθ), and the trash removal process is ready to proceed once again.

Claims: AMENDED CLAIMS [received by the International Bureau on 01 October 1985 (01.10.85). original claims 1 and 2 replaced by new claims 1 ,2,3 and 4; original claim 3 cancelled (2 pages)] Claim 1 Method for separating, transporting and dewatering coarse solid particles suspended in water c h a r a c t e r i z e d b y leading the water through the active screening section of a submerged tubular net (8) , located between the replaceable storage cassette (7) from which the large-mesh net (8) is drawn out, and the point where the net (8) with its trapped coarse solid particles is pulled up above the water surface at a speed which is regulated by a system of rotating rollers (10) above the water surface that continuously or in stages draw the net (8) forward to provide new and unrestricted screening area, the rollers (10) at the same time transporting the net (8) with its water-soaked contents and dewatering them by pressure, prior to disposal of the net (8) and its collected solids. Claim 2 The method described in Claim 1 c h a r a c t e r i z e d b y the fact that the submerged tubular net (8) has such a large mesh-size that the pressure head loss of the water flowing through is negligible, but as the solids collect inside the tubular net (8) they will fill up the mesh openings and increase the head loss to 0-0.3 bar, and although the net (8) is open at both ends, the build-up of solids will tend to close the end above the water surface nearest to the rollers (10), forcing inflowing water to circulate back and be screened in the least restricted section of the net (8) nearest to the water inlet section (5) . Claim 3 Device for separating, transporting and dewatering coarse solid particles suspended in water, of which the method of operation is described in claims 1 and 2 c h a r a c t e r i z e d b y its consisting of a replaceable storage cassette (7) packed with a considerable length of a tubular net (8) \<ith square mesh openings varying from 5 x 5mm to 25 x 25mm, which is drawn out through a variable friction sleeve (9) at the open end of the cassette (7) to form an unfolded tubular screening area for unrestricted throughflow of water, and a system of two or three mechanically-driven rollers (10) that draw the net out automatically from the cassette (7) through signals from a pressure gauge (3) in the inlet section which monitors water inflow pressure, the rollers simultaneously dewatering the suspended solids trapped inside the tubular net (8) due to the low rotating speed and variable pressure applied to the net (8) by the rollers (10) . Claim 4 The device described in claim 3 c h a r a c t e r i z e d b y the fact that the water pipe (5) in the inlet section also functions as the support for the replaceable net-storage cassette (7) , through which water is led into the tubular screening net (8) in its horizontal, submerged position, and which can be hoisted up at a vertical angle due to a hinged joint (6) so that the cassette (7) is pulled up ' over the water level, while water inflow is temporarily stopped by cutting off the water pump (1) , and the nearly empty cassette (7) can easily be replaced by a new one. ) STATEMENTUNDERARTICLE 19 Because of the results of the International Search Report, in which the Searching Bureau evaluates ' the EP,A1,9738 (Hoechst Aktiengesellschaft Kalle) of April 16, 1980 as being relevant vs. our claim 1, we hereby amend our original patent claims. We have now limited our claim to separating coarse suspended solid particles from water. We have also emphasized that our unit consists of a replaceable cassette containing a considerable length of a tubular net (to be used as a screen for solids only once, in a fill and waste system) . We have stated that the tubular net has a mesh size with square openings limited from 5 x 5mm to 25 x 25mm. This means that the net itself makes almost no restrictions for throughflow of water. During operation, the trapped solids inside the net build up to a more effective screen by reducing the size of the openings, thus increasing the pressure loss to the area of 0 to 0.3 bar. We have also emphasized that the net is open at both ends, with the build-up of solid materials in the net eventually closing the end opposite to the water inlet. Recent experience has indicated that the active screening part of the tubular net must be submerged under the surface of the screened water, in a canal or tank carrying this water away from the unit (in our original patent application, int'l. filing date 1985-05-31. we merely proposed in claim 2 that the net "normally" would be submerged. Although the water surface level in the canal is not indicated in Figure 1 of our drawings, the level will always be on a horizontal line drawn along the top of the submerged storage cassette. The submerged position is imperative for effectively utilizing the total screening area (total circumference) of the tubular net, and for attaining maximum volumetric capacity. If the water were led into the net while it was positioned over the water surface, the water would pass only through a limited section of the net at a high specific loading rate (in 1/s per m screening area), resulting in poor utilization of screening capacity and reduced efficiency in removing solids from the wastewater. We have therefore amended our patent claims to incorporate these limitations (mesh size, operating pressure and submerged position), and we have separated our new claims in two sections: Claim 1 and 2 describe the function (hoλv the device operates) , while the new claims 3 and 4 describe the device itself with its various parts. Since the EP 9738 (Al/820416) clearly describes the use of semipermeable membranes which remove (by ultrafiltration, hyper- filtration etc.) small dispensed and dissolved particles with sizes as small as 1-0.001 micron, we have eliminated our origina claim 2 (..."the use of other forms for textile, artificial or natural cloth or collecting membrane)

Inventors: FROM JAN ODDVAR, SONDOV STEN Y, FROM, JAN, ODDVAR, SONDOV, STEN, Y.
Applicants: INTERPUBLIC AS, INTERPUBLIC A.S.
Application year: 1985
Main classification: C02F1
IPC codes: B01D29, B01D35, E03F5