The object of the present invention is to achieve a reciprocating sludge scraper for water purifying basins, which sludge scraper has the function of eliminating sludge collected in the basin and other materials sedimented.

Background of the invention Reciprocating sludge scrapers for water purifying basins, either for fresh water or waste water, are known from SE-C-8604573-9 (publ. no 454,140) and SE-C-9102345-7 (publ. no 507,592), which sludge scrapers intend to transport sludge precipitated in a water purifying basin towards one end of the basin, where it is collected in a sludge hopper, which is intermittently intended to be drained on its content. The scrapers described in these patent publications have a triangular cross section or a substantially triangular cross section and are fixedly arranged to a supporting frame or the like, reciprocally moving along the bottom of the basin in question, by means of a wire system or hydraulically driven drag rod.

Other reciprocating sludge scrapers comprise blades, which are collapsed towards the bottom of the basin in the transport direction, (the forward direction) and are hinged in the return direction (the rearward direction), in order not to bring the sludge backwards in the basin.

Further it is known to bring collected sludge out of a basin by means of siphons arranged side by side across the basin. However, this solution is complicated and requires a major investment, i. e. is expensive.

Suction apparatuses for sludge are also known, which are moved along the whole

bottom of the sedimentation basin, without the presence of other transport elements.

This also leads to, except for a complicated technology for handling the suction apparatuses, an out-transport of large amounts of water.

From US-A-5,047,150, it is known a sludge scraper comprising on one hand a scraper unit, which is angled against the bottom with respect to the transport direction of the scraper unit, on the other hand contains a suction box from which sludge brought-up by means of the scraper is sucked out. A number of such sludge scrapers are intended to be located after each other over a bottom of a sedimentation basin, and there transport and dispose sludge settled at the bottom by means of the intermittently reciprocally movement. The disadvantage of this sludge scraper is on one hand that it is large, which creates whirls lifting the sludge settled, on the other hand that it works over surfaces with reduced sludge precipitation (sludge falls much unequally in different parts of a sludge basin), which leads to that large amounts of water is unnecessarily transported away. Sludge occurring in tap water basins is extremely light and lifts easily at the slightest whirl formation.

Further it is known to use wire scrapers transporting sludge to a site in a basin, whereupon a separate slurry exhauster is lowered down for sucking-out sludge.

However, requirements have been raised on basins which do not require a sludge hopper, since it is more expensive to dig down and prepare a sludge hopper, and further admits a simple and preferably continuos sludge drainage, as, under certain circumstances, the sludge precipitated and collected constitutes a large volume.

Description of the preferred invention Now it has surprisingly been shown possible to solve this problem by means of the present invention, which is characterized in that, at least a suction scraper blade unit is arranged, to the reciprocating scraper unit, which suction scraper blade unit extends over the width of the basin.

Further characteristics are evident from the accompanying claims.

By means of the present invention a suction scraper unit is achieved, which is preferably used at the front end of the scraper unit, but depending on the sedimentation

situation in the actual basin, may be located in another appropriate location over the bottom, for sucking sludge settled, from there. As evident from below, the suction unit has also such a shape that whirl formation is minimized, and thereby the sludge suction is maximized with insignificant water tapping.

The invention will be described in the following more in detail with reference to the enclosed drawing, which shows an exemplified embodiment of the invention. In the drawing Fig. 1 shows a side-view of a sedimentation basin with a suction apparatus according to the present invention; Fig. 2 shows a perspective-view of a suction scraper blade according to the present invention; Fig. 3 shows a cross section-view of the suction scraper blade according to fig. 2; and Fig. 4 shows a suction scraper blade according to fig. 2 seen from its underside.

An elongated sedimentation basin is denoted 1 which is used at water purification, either of fresh water or of waste water. The basin 1 is restricted by a bottom 2, two long sides 3 and two short sides 4,5 (the rear short side is denoted 4, the front short side is denoted 5).

A web of reinforced plastic or a series of longitudinal, stainless steel bands, draw bands, linked with steel bands of the same sort along its longitudinal direction is denoted 7, which web of plastic or steel bands supports a number of transport elements 8, which are fixedly arranged to the web/band structure 7 and extend over the entire width of the basin 1, whereby they are located substantially perpendicular to the longitudinal direction of the basin, and are equally distributed along the length of the basin.

Along the web/the band structure 7, in the middle of the longitudinal direction, a draw absorbing band 12 of steel or the like runs. The band 12 may be exchanged with a lesser flexible rod or draw rod if so desired. The band or the draw rod 12 is attached to a cord 13 at its ends, which via four break rolls 14 a, b, c, d; two in each end of the basin, lead the cord to a driving device 15, which pulls the cord in one direction and the other direction, alternatively. Hereby, the driving device may be a gear engine having a cord drum or a hydraulic system with a reciprocally movement, at the ends of which ends the

cord 13 is attached. By partly placing the break rolls 14a and 14b on a level just above the bottom of the basin 2, partly by means of the tension of the cord, and partly by means of the density of the transport elements 8, the web 7 having the transport elements 8 will only very easily touch the bottom 2, which implies a minimal wear and minimal working distance. By applying gliding elements on the underside of the web, the minimum distance to the bottom 2 may also be guaranteed. A draw rod may also be reciprocally displaced directly via hydraulic effect or by means of an appropriate gear unit.

If the basin 1 shows a large width several cords or draw rods be may applied side by side, if so required to obtain a smooth operation.

The device according to fig. l works with a stroke in the reciprocally movement of 50- 75 cm.

The transport elements 8 have a cross section in the embodiment shown which has a downward facing plane basis 9, a substantially inclined, convex surface 10, and a substantially vertically, concave surface 11, whereby the concave surface 11 is directed in the forward transport direction. These transport elements have been shown to give very good results at sludge transports, and even achieve a sludge concentration, thickening. The transport effect is also good in itself, and the basin contains a larger sludge pillow at normal operation in the end of the basin, which sludge pillow constitutes more than the half of the basin deep.

The transport element 8 works with all types of sludge occurring, such as primary sludge, return sludge, biological sludge, chemical precipitated sludge as well as light sludge (generally occurring at tap water purifying plants).

In the front part of the web/the band structure 7, a suction scraper unit is at least arranged, here denoted suction scraper blade 21. This suction scraper blade 21 is arranged perpendicular to the longitudinal direction of the basin 1, and extends over its entire width. The suction scraper blade 21 is a gable-provided half-moon shaped, trough-shaped unit 22, suitably manufactured in a steel or a plastic material, which unit shows the form of a semi arch or a segment of a circle in cross section with a plane bottom surface 23 towards bottom of the basin 2. The bottom surface 23 shows a large

number of through-going holes 24, which admit passage from the outside of the unit 22 to its interior. Further the unit 22 shows at least an outlet hole 25 provided with a bump 26, which bump 26 is connected to a flexible hose 27, which in its other end is connected to an outlet 28 in the short side 5 of the basin. The outlet 28 operates by means of gravity (the water level in the basin 1 lies over the outlet 28) or by means of a pump, continuously or intermittently working. The total area of the holes 24 should not exceed the area of the outlet hole/holes 25 for achieving possible best suction flow over the entire basis of the suction scraper blade through all the holes 24 and thereby the best sludge transport.

The suction scraper blade 21 is located 5-50 mm, preferably 10-25 mm over the bottom of the basin 2. Further the suction scraper blade 21 has normally a width in the cross section of approx. 300 mm and a height of 100-150 mm. These measurements are only standard values and large deviations from these values may occur, depending on the size of the basin, type of sludge and other working conditions valid. From a standard basin 150 m3/hr of water-containing-sludge is transported out by means of one or several suction scraper blades.

At larger basin widths more than one outlet should be arranged to the upper part of the suction scraper 21.

Instead of the through-going holes 24, one or several slot (s) extending along the length of the suction scraper blade 21 may be arranged. However, it is then important to notice that the suction flows to and through the suction scraper blade, so that this not only sucks in connection to its outlets, but that the flowing is equally distributed over the entire width of the suction scraper blade. This requirement may also imply that the through-going holes 24 obtain a larger diameter or cross sectional area at greater distances from the outlet, in comparison to the through-going holes 24 at a more adjacent distance. The essential thing is to obtain a smooth through flow which is distributed over the entire area of the suction scraper blade.

As the suction scraper blade 21 is provided with several outlets, these are more appropriately brought together to a collection pipe located on the inside of the basin, from which collection pipe the sludge is brought out later on via the outlet 28.

The suction scraper blade 21 is preferably located, as mentioned, in the front part of the scraper conveyor, and receives sludge transported forward from the transport element lying behind.

In another embodiment, the transport elements 8 may be placed towards each other, so that the sludge is collected for instance in the middle at the bottom of the basin, whereby the suction scraper blade 21 is located in the middle of the length of the conveyor unit 7.

By regulating the outlet velocity at gravity or the pump effect, the amount of sludge brought up may easily be adjusted. The outlet amounts should, in every moment, not exceed the sludge volumes in order to decrease the amount of unnecessary water leaving from the basin.

The suction scraper blade 21 may also be pivotally suspended at its ends, in such a way, that it turns/winds its bottom surface inclined upward toward the scraper direction.

Further the suction scraper blade 21 may in cases when very thick sludges exists, such as biological sludge, be provided with a supply of air in connection with the outlet opening (s) 25. Hereby compressed air is pressed via an number of hoses, from a compressed air source forward to the respective outlet opening 25, whereby the sludge is loosened up and is more easily pressed/pumped out.

It is obvious to the person skilled in the art that variations of the present invention may be achieved within the scope of the following claims.