Abstract:
The invention relates to a sedimentation basin for sewage treatment plants, the sedimentation basin separating materials such as sand, rocks or broken glass, from waste water, which materials settle by gravitational action. The waste water is introduced in the inlet region of the sewage treatment plant. The sedimentation basin is provided with flow guide walls having a wave or meander shape, a plurality thereof being disposed vertically adjacent to each other and parallel to the main flow direction of the sedimentation basin. The slowing of the flow caused by this arrangement results in improved sedimentation that occurs in an efficient and compact basin requiring less space.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a sedimentation basin for a sewage treatment plant for the purification of waste water collected in drain systems and transported to a sewage treatment plant. 
         [0002]    Biological, chemical and mechanical (also referred to as physical) methods are used to remove undesirable constituents from waste waters. Accordingly, modern sewage treatment plants have three stages, with special emphasis being placed on a particular method in each purification stage. 
         [0003]    The raw waste water that is fed from the drains comprises a mixture of different admixtures of organic and non-organic matter, which can be either soluble or insoluble and are carried along by the water, which forms the primary constituent. Particularly after heavy rainfall, which produces large amounts of sewage water, the waste water entrains considerable amounts of coarser, settleable impurities, such as sand, rocks and broken glass, and a variety of organic substances. This matter can result in disruption (wear, clogging) of the operation of the sewage treatment plant, and must therefore be removed in advance from the flow of waste water that is to be purified. 
         [0004]    For this purpose, the feed region of the sewage treatment plant is equipped, not only with a collection tank for receiving the untreated waste water fed from the drains, but also a first settling tank for the coarse admixtures, which settle out because the density thereof is higher than that of water. Such sedimentation basins are also known as “sand traps”. They are employed in a variety of design embodiments, such as, for example: 
         [0005]    elongate sand collectors, described in DE 41 21 392 A1; 
         [0006]    aerated sand traps, whereby oils and fats floating on the surface can be separated, as set forth in DE 35 29 760 C2; and 
         [0007]    circular sand traps, for example according to DE 100 12 379 A1. 
         [0008]    Aerating the sand trap, preferably from the bottom of the settling tank, produces a turbulent flow and lowers the density of the waste water, causing the heavy, mineral portions (primarily sand) to settle at the bottom of the tank. Such a sand trap is disclosed, for example, in DE 198 30 082 C1. With a deep sand trap, the waste water flows into the tank from above. Because of the depth, the waste water has a relatively long residence time, and thus the heavy sand can settle at the bottom of the tank. The tank bottom is usually configured as a sand funnel. In modern plants, after removal of sand from the sand trap, the sand trap material is washed, for example in order to separate organic admixtures that may be present, as set forth in DE 296 23 203 U1. This measure allows for better recycling and subsequent use, for example in road construction. 
         [0009]    Sand is separated, depending on the type of the sand trap, by gravity, such as in the elongate sand collector described in DE 41 21 392 A1, or by way of centrifugal force, such as in a circular sand trap according to DE 85 23 894 U1, or by way of a vortex sand trap, such as according to DE 198 30 082 C1 or DE 100 12 379. Rake blades or screw conveyors are frequently used for longitudinal clearing of the bottom of the settling tank. Solid matter is removed further on in the process, using a pump and grit grader; and these two parts may also be combined in one construction, in the form of a grit-grader worm. 
         [0010]    A sedimentation basin for sewage treatment plants designed as an elongate sand collector is known from DE 41 21 392 A1, wherein a plurality of vertically disposed flat metal sheets are oriented parallel to the direction of flow, in a region adjacent to the discharge of the basin. These installations are provided in a region in which sand has already settled and are intended to increase friction, so as to slow the flow. However, this measure is only used to maintain the water level approximately constant over the length of the drain channel 
         [0011]    Guiding a flow through planar installations is known from DE 36 41 365 C2, where the planar installations are disclosed as electrode plates and the flow is guided in a meander-like fashion in order to achieve a longer application time for an electrical field for floating dirt particles in the waste water. At the same time, sand entrained in the waste water is separated. The meanders formed by the installations run in the vertical direction and have no influence on deposition of the sand. 
         [0012]    DE 297 12 469 U1 describes an apparatus for separating granular matter from a fluid, particularly, a coolant enriched with chips, in the metal-working industry. In this apparatus the fluid flow is alternately reversed from the bottom to the top by guide plates arranged in a zig-zagging arrangement, whereby heavy particles are deposited on the bottom and can be removed by a sliding scraper. 
         [0013]    The sedimentation rate for granular material such as sand or rocks is dependent, in a complicated manner, on the specific radius of the material particles. If the radius is small, the sedimentation rate is low, and varies according to the square of the particle radius. If the particles are larger, the sedimentation rate is high, and is proportional to the root of the particle radius. In general terms, waste water carries settleable materials having a wide range of grain sizes, which should be separated in the sedimentation basin as completely as possible. Because of the different settling rates for the individual grain sizes, it is necessary to ensure a sufficiently long waste water residence time in the sedimentation basin. Since the residence time depends on the flow rate of the waste water and the length of the basin, the sedimentation basin must be relatively long in order to achieve sufficient sedimentation, even with smaller grain sizes, which is shown in DE 41 21 393 A1, for example. The space requirements and material costs involved in building such a sedimentation basin can be problematic. 
       SUMMARY OF THE INVENTION 
       [0014]    It is an object of the invention to provide a more efficient sedimentation basin for sand, rocks and other settleable matter entrained by waste water, which has a high waste water throughput rate and reduced space requirements. 
         [0015]    The present invention uses an advantageously slow waste water flow for sedimenting entrained matter having higher specific weights, and employs structure that effects forced directional changes of the flow, resulting in alternating turbulent and stagnating zones, which promote the sedimentation process. 
         [0016]    Such directional changes occur in natural bodies of flowing water that entrain bed loads, such as sand, gravel and rocks, in regions having low gradients and therefore low flow rates. Rivers of this sort are referred to as “meanders,” taking the name from a river in Asia Minor. In general, they develop in the lower course of the body of water. The cause of the meander shape is the effect of the inertia of the water, as a result of which the outside radius of the river bend, which is referred to as the cut bank, is subject to greater erosion than the inside radius of the river bend, which is known as the point bar. Once a bend has been formed, it therefore continues to become more pronounced. Once the channel line has been diverted from the center of the river to one of the banks, a cut bank forms, which continually recedes due to erosion of the side. Opposite the cut bank, the point bar is formed, from which the river moves away depositing sediments. As a result of the meandering course of the river, the flow rate is reduced, which generally promotes sedimentation. 
         [0017]    According to the invention, installations are introduced into the sedimentation basin which are configured as flow guide walls for the fluid, that is, the waste water to be purified, which flow guide walls provide a structured path for the fluid to flow though. “Structure” here shall be understood to mean that, contrary to the prior art according to DE 41 21 392 A1, the flow guide walls are not designed as flat metal sheets, but instead have a wave-like or meandering curved shape. Hereinafter, the terms “wave” and “meander” are used in a substantially synonymous manner. That is, the terms “wave” and “meander” generally define a surface having alternating elevations and depressions, as, for example, shown in  FIG. 4  of the present specification. The terms can be used interchangeably. That is, no difference in the meaning of the terms is intended herein. The individual waves and/or meanders, of which the flow guide walls will have a plurality, do not have to be identical to each other. For example, they can differ in the distances from each other, the heights (amplitude), the curvatures, or angles, one or combinations thereof can result in a change in flow direction and/or flow properties. 
         [0018]    By designing the flow guide walls in the form of a plurality of waves or meanders, the flow rate of the waste water being purified is reduced. Stagnation zones and vortices are created. The sediments can therefore settle quicker, and over shorter distances. Additionally, the sediments are preferably deposited on the back side of the waves or meanders, relative to the flow direction. This process is promoted by the bottom of the basin being designed in an ascending manner toward the outlet region. That is, the vertical distance over which the sediment must travel in order to be deposited is progressively reduced. The efficiency of sedimentation is increased by these attributes, and as a result the sedimentation basin can be designed and constructed considerably smaller than under the state of the art. 
         [0019]    In order to further lower the flow rate, different surface configurations can be employed for the flow guide walls. For example, in addition to the wave or meander shape discussed above, the flow guide walls may be provided with additional relatively finer structuring, for example, nubs or dimples, or other structures protruding from the surface. For this purpose, structures directed counter to the flow, providing a “shark skin” quality, can be used. Such finer structuring can be applied, for example, by way of embossing with dies, by chemically applied coatings, or by way of thermal processes such as brazing, welding or flame spraying. 
         [0020]    A plurality of flow guide walls are disposed in the basin, substantially parallel to each other in the main flow direction, that is, the straight path between the inlet region and the outlet region. Due to the aligned, parallel arrangement, flow channels having a substantially constant width are formed between adjoining flow guide walls. The flow channels, and therefore the waste water flows, run in a meandering fashion with alternating directional changes, resulting in the formation of flow regions which correspond to the conditions of a cut bank and a point bar. In the region of the point bar, the flow rate is considerably reduced, resulting in particularly effective sedimentation. 
         [0021]    The distances of the individual waves or meanders from each other, and the length of the wave, can be established in different ways. The distances can be, for example, constant both in the horizontal direction and in the vertical direction. However, the distances can also be varied with respect to one or both of these directions. For example, the length of the wave in the main flow direction, that is, the horizontal direction, can increase, or alternatively, it can decrease. Likewise, the length of the wave can increase in a downward direction (i.e., toward the basin bottom). The amplitudes of the waves or meanders, that is, the distances of the crests from an imaginary center line of the flow guide walls, can be dimensioned as appropriate. 
         [0022]    A particularly preferred design for elongate basins are trapezoidal basins, wherein the width of the basin continuously increases in the main flow direction. The inlet region is located at the narrow end, while the outlet region is disposed at the opposite wide end. This basin shape further slows the flow rate of the waste water in the main flow direction, since the flow cross-section continuously increases. The reduction in the throughput rate as a result of widening the flow paths favors sedimentation because finer grains of sand having a lower sedimentation rate also have the opportunity to settle. 
         [0023]    The trapezoidal design of the basin also provides for compensation of the influence of the bottom that ascends in the longitudinal direction of the basin. This design variant is also conducive to the sedimentation of finer grains of sand, since the vertical distance over which the settling sand grains must travel before they reach the bottom of the basin is progressively reduced. 
         [0024]    In one embodiment, the sedimentation basin is a circular basin having an inlet region preferably located in the central region of the basin, where the sludge or sand collecting chamber, which is typically funnel-shaped, is also disposed. The outlet region is provided at the edge of the basin, for example, in the form of an overflow outlet having a duct for the waste water, from which waste water sediments have been separated, and resulting in a partially purified waste water. In this embodiment, the flow guide walls substantially originate in the inlet region and extend in the radial direction to the edge of the basin. In the case of larger basins, additional, shorter flow guide walls in the outer region can be provided, in order to compensate for the divergence of the adjoining radially extending flow guide walls, in order to maintain a constant channel width. The additional flow guide walls do not have to be oriented exactly in the radial direction. Also, it is possible to use additional flow guide walls having different lengths. 
         [0025]    The flow guide walls according to the invention preferably extend over the entire length of the sedimentation basin, with the exception of the inlet region, which should be freely accessible from above for removing the collected sediment from the sludge collection chamber. The flow guide walls preferably extend at least from the upper edge of the basin to approximately the bottom thereof, following the contour of the bottom, and spaced at a constant distance from the bottom. According to the invention, the free space is used for the installation of purification apparatuses, such as rake blades, slides or scrapers, which can be used to feed the sediment deposited on the bottom to a sludge or sand collection chamber. The sludge or sand collection chamber typically represents the lowest region of the basin. It can be provided with a discharge line which opens into an orifice at the bottom of the basin. The discharge line is used for sand/sludge removal, such as, for example, by a spiral conveyor. In the case of circular basins, the rake blades are preferably disposed offset with respect to the radial direction and rotationally driven. In the case of rectangular elongate basins, rake blades which can be displaced in the longitudinal direction of the basin are preferred. 
         [0026]    In a preferred embodiment, the flow guide walls can be displaced, individually or together, in the vertical direction. For this purpose, supporting apparatuses are provided for the flow guide walls, which advantageously span the sedimentation basin. These make it possible to move the flow guide walls up and down using manual or motor drives, for example, in order to set the distance to the bottom of the guide walls to the bottom of the sedimentation basin. It is advantageous to make the travel path long enough that the lower edges of the flow guide walls can at least reach over the upper edge of the sedimentation basin. In this way, the basin is freely accessible, if needed. In addition, this makes it possible to reach the flow guide walls for inspection or cleaning purposes, without having to drain the sedimentation basin. This prevents interruption of operations, particularly if maintenance work is scheduled in a period of low waste water accumulation. 
         [0027]    Steel is the preferred material for the flow guide walls, as it has the mechanical stability and strength necessary for operations under harsh conditions in the inlet region of sewage treatment plants, and can be molded to the desired shape without difficulty. As an alternative, it is also possible to use glass fiber reinforced plastics or semi-permeable plastic membranes, for example, in the form of large-pore, reinforced non-woven fabrics, which produce a further increase in sedimentation, due to a filtration effect. 
         [0028]    In order to increase the wear resistance, or as protection against rusting, the material employed can also be coated. If the flow guide walls are permanently installed, or if the side walls of the sedimentation basin are appropriately designed, these walls can also be made of concrete, preferably in the form of armored concrete or fiber reinforced concrete. 
         [0029]    The shape of the sedimentation basin can be selected by the artisan. Preferred shapes include rectangular or trapezoidal elongate basins, wherein the inlet and outlet regions are disposed at smaller-sized faces, or circular basins having a central inlet region. In the case of elongate basins, the flow guide walls preferably run parallel to the longer side walls, that is, parallel to the main flow direction between the inlet and outlet regions. In the case of circular basins or circle sector shaped basins, the flow guide walls are located substantially in the radial direction. 
         [0030]    When operating a sedimentation basin according to the invention, sedimentation can be promoted by additional measures. This includes electrical, thermal or chemical influencing of sedimentation, which can be achieved with a suitable design or by treating the flow guide walls. 
         [0031]    Within the scope of the invention, the flow guide walls can, for example, be provided with electrostatic charges. The walls can be heated to different temperatures, or they can be chemically coated. 
         [0032]    In order to promote sedimentation, or for rinsing the sedimentation basin and the flow guide walls, openings and/or feed lines can be provided in the region of the bottom of the sedimentation basin, by way of which gases, such as compressed air or fluids, can be introduced into the basin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The invention will be described in more detail based on the figures. Shown are: 
           [0034]      FIG. 1 : a schematic illustration of a sewage treatment plant having a sedimentation basin; 
           [0035]      FIG. 2 : a schematic cross-sectional side view of a rectangular sedimentation basin according to the invention; 
           [0036]      FIG. 3 : a schematic top view of a rectangular sedimentation basin according to the invention from  FIG. 2 ; 
           [0037]      FIG. 4 : a perspective view of a separating wall/flow guide wall according to the invention; 
           [0038]      FIG. 5 : a schematic cross-sectional side view of a sedimentation basin according to the invention, which is configured as a circular basin; 
           [0039]      FIG. 6 : a schematic top view of the circular basin from  FIG. 5 ; 
           [0040]      FIG. 7 : a schematic top view of a circle sector shaped or trapezoidal basin according to the invention; 
           [0041]      FIG. 8 : a schematic longitudinal section of a rectangular or trapezoidal basin according to a further variant of the invention; 
           [0042]      FIG. 9 : a schematic cross-section of a rectangular or trapezoidal basin from  FIG. 3 ; 
           [0043]      FIG. 10 : a schematic cross-section of a rectangular or trapezoidal basin according to a further embodiment of the invention; and 
           [0044]      FIG. 11 : a schematic cross-section of a pipe having flow guide walls according to a further variant of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]      FIG. 1  shows a schematic illustration of a municipal sewage treatment plant  1 , which is used to purify waste water  3  collected from drains and transported to the treatment plant. An inlet  14   a  leads to a collection tank  6  and then a grill  7 , for sorting coarse, buoyant material, and then to a sedimentation basin  2 . The purpose of the basin  2   10  is to remove coarse, settleable matter, such as sand, from the waste water. The raw waste water from which this matter has been separated enters an activated sludge basin  8 , where organic and inorganic compounds are degraded by the action of microorganisms. In the secondary settling tank  9 , suspended matter and other settleable impurities are precipitated as sewage sludge before the purified water flows via an outlet  15   a  into receiving water, typically a flowing body of water. 
         [0046]      FIG. 2  shows a schematic illustration of a side view of a sedimentation basin  2 , 10  for sand according to the invention, configured as a rectangular elongate collection basin, which typically is recessed into the ground  26 . At a face wall  11 , the basin  10  comprises an inlet region  14  for the waste water  3  arriving from the grill  7  (see  FIG. 1 ). The waste water  3  can generally be considered a fluid having admixtures  5 , such as buoyant materials and settleable, non-buoyant materials. The waste water flows from the bottom  13  and, to a limited extent, from the side walls  12  of the basin  10  in the main flow direction  21  to the face wall  11   a  of the basin  10 , opposite the inlet region  14 . At face wall  11   a , it flows via an overflow outlet  18  into a drain duct  19  and from there to an activated sludge basin  8  (see  FIG. 1 ). 
         [0047]    According to  FIG. 3 , several installations are disposed in the basin  10  as flow guide walls  20 , which substantially run in the main flow direction  21 . Flow guide walls  20  have a wave  22  or meander  23  structure, as seen in  FIG. 4 . The crests  24  of the individual waves  22  or meanders  23 , that is, the regions of the flow guide walls  20  protruding farthest from the surface, can be oriented substantially perpendicular to the ground  26  (see  FIGS. 3 ,  6 ,  7 , and  9 ) or, alternatively, parallel thereto (see  FIGS. 8 and 10 ). The flow guide walls  20  extend in the longitudinal direction of the basin  10 , that is, in the main flow direction  21 , substantially from the inlet region  14  to the outlet region  15 , thereby defining settling region  30  of the basin  10 . In the vertical direction, the upper edges  25  of the flow guide walls  20  reach from a position above the target waste water level in the basin  10  to the position of the lower edges  27 , which extends approximately to the bottom  13  of the basin  10 . If the bottom  13  of the basin  10  is raised in the settling region, which is depicted in  FIG. 2 , the lower edges  27  of the flow guide walls  20  follow the contour of the bottom  13 . 
         [0048]    A purification apparatus  42  is provided between the lower edge  27  of the flow guide walls  20  and the bottom  13  of the basin  10 , and can be used to deliver the sediment  31 , which is present on the bottom  13  of the settling region  30 , into a sludge collection chamber  41 . The purification apparatus  42  is configured, for example, as an arrangement of rake blades  43 , which are installed displaceably in the purification region  35  of the basin  10 . One or more of the basin bottom  13 , the face walls  11 ,  11   a , and the side walls  12  can be provided with openings for feed lines, which are not shown here, by way of which gases or fluids can be introduced into the basin  10 . 
         [0049]      FIG. 3  shows a schematic illustration of a top view of a sedimentation basin  2  according to the invention. As with the sedimentation basin  2  of  FIG. 2 , it is a substantially rectangular elongate collection basin. The main flow direction  21  runs from the face wall  11  of the basin  10 , which is located on the inlet side, which forms a narrow side, to the opposing face wall  11   a . The perpendicularly disposed flow guide walls  20  are shown in a top view, so that it is shown how the crests of the waves  22  or meanders  23  extend. The arrangement of the flow guide walls  20  is such that the waves  22  or meanders  23  run substantially parallel to those of the respectively adjoining flow guide wall  20 . In this way, the waste water that is guided between two flow guide walls  20  flows through a meandering, yet substantially uniformly large, cross-section. The distances of the crests  24  of the waves  22  or meanders  23  can be regular or irregular with respect to the longitudinal extension of the flow guide walls  20 . As is apparent from  FIG. 3 , the side walls  12  of the basin  10  can also be provided with structures, which are preferably matched to the shape of the flow guide walls  20 . 
         [0050]      FIG. 4  shows a flow guide wall  20  in a schematic perspective view. The waves  22  or meanders  23 —and therefore the crests  24  thereof—extend in the vertical direction with respect to the ground  26 , not shown. The wave trough corresponds to the cut bank  32 , and the wave crest forms the point bar  33 . Incidentally, a wave crest on one side of a flow guide wall  20  appears as a wave trough on the other side. 
         [0051]    Depending on the course of the bottom  13  of the basin  10 , the distance between the upper edge  25  and the lower edge  27  of the flow guide walls  20  can be constant or change in the longitudinal direction. The distance is the smallest, having the value A′, in the vicinity of the outlet region  15  of the basin  10 . The flow guide walls  20  have holding apparatuses, not shown, which suspend and hold the walls in the basin. The holding apparatuses are preferably mounted on devices which provide for the adjustment and varying of the immersion depth of the flow guide walls  20  in the basin  10 . 
         [0052]      FIG. 5  shows a schematic illustration of a different design of a sedimentation basin  2  according to the invention. The basin  10  is a circular basin, with the inlet region  14  located in the central region  50 . The preferably conical or funnel-shaped sludge collection chamber  41  is disposed beneath the inlet region  14 . The settling region  30  extends from the central inlet region  14  to the edge  51  of the basin  10 , where the overflow outlet  18  for the waste water  3 , from which the sediment  31  has been separated, feeds a duct  19 . In the settling region  30  of the basin  10 , the flow guide walls  20  are disposed in a suspended manner such that the lower edges  27  thereof maintain a fixed distance from the bottom  13  of the basin  10 , with the bottom ascending toward the edge  51 . The space provided serves as purification zone  35 , in which rotating rake blades  43  or other wiper apparatuses feed the sediment  31  deposited on the bottom  13  to the sludge collection chamber  41 . A discharge line  44  having an opening  45 , which constitutes part of a sludge extractor  46 , opens into the sludge collection chamber  41 . The sediment  31  present in the sludge collection chamber  41  can be removed by sludge extractor  64 , for example using a spiral conveyor, which is not shown here. 
         [0053]    The arrangement of the flow guide walls  20  in a circular basin is substantially radial, which is shown in the schematic top view of  FIG. 6 . Here, as in the previous figures, the waves  22  or meanders  23  run perpendicular to the ground  26 . Since the flow guide walls  20  diverge toward the outside, an arrangement including long flow guide walls  20 , which run substantially from the inlet region  14  to the edge  51  of the basin  10 , and shorter flow guide walls  20 , having different lengths, are provided. In this manner, an at least approximately constant cross-section of flow can be achieved between adjoining flow guide walls  20 . Here, the orientations of the individual flow guide walls  20  extend only in the radial main flow direction  21 , as is shown in  FIG. 6 . 
         [0054]    The arrangement of the flow guide walls  20  in the basin  10  can also be carried out using flow guide walls  20  that all have the same length, as is shown in  FIG. 11 . Here, the widening of the flow cross-sections between adjoining flow guide walls  20  is shown, which is caused by the substantially radial orientation of the flow guide walls  20 . The widening of the cross-section of flow results in a slowing of the flow toward the outside. 
         [0055]      FIG. 7  shows a schematic illustration of a further embodiment of a sedimentation basin  2  according to the invention. Here, the basin  10  is configured as a sector of a circle or a trapezoid. The inlet region  14  is located on the narrow side  16 , while the outlet region  15 , including the overflow outlet  18  and the duct  19 , is disposed at the opposing edge  51  or at the wider face wall  11   a . The sludge collection chamber  41  is preferably located beneath the inlet region  14 . In principle, the arrangement of the flow guide walls  20  is the same as that of  FIG. 6 , that is, the flow guide walls  20  run substantially in the main flow direction  21 , i.e., radial direction. The side walls  12  of the basin  10  may be smooth, or they can be matched to the shape of the flow guide walls  20 , previously described in the embodiment shown in  FIG. 3 . 
         [0056]      FIG. 8  shows a schematic longitudinal section of a rectangular or trapezoidal basin according to a further embodiment of the invention. The flow guide walls  20  are positioned in a stacked arrangement, transverse to the main flow direction  21 , such that the flow is diverted substantially vertically. The sediment here preferably settles in the wave troughs or ducts extending transverse to the main flow direction. The sediment is delivered laterally by the ducts to a side wall, by way of gravity. Thus, a sufficient slope is provided in the flow guide walls  20  in the direction of the side wall. It is also possible to use a plurality, for example two, separate arrangements of this type, for example in such a way that the slope of each arrangement is toward the center line of the basin  10 . In this embodiment, the sediment collects on the center line of the bottom of the basin, from where it is delivered through the purification apparatus into the sludge collection chamber. 
         [0057]      FIG. 9  shows a schematic cross-section of a rectangular or trapezoidal basin, as shown in  FIG. 3 . The crests  24  of the waves  22  or meanders  23  run in the vertical direction, which is indicated by the vertical lines  20 . The distance between the lines corresponds to the width of each individual flow duct. 
         [0058]      FIG. 10  shows a schematic cross-section of a rectangular or trapezoidal basin  10  according to a further embodiment of the invention. The crests  24  of the waves  22  or meanders  23  run substantially horizontally and parallel to the main flow direction  21 . 
         [0059]    In a further embodiment of the invention, it is possible to combine the designs of the flow guide walls  20  according to  FIGS. 9 and 10 , that is, to run the meanders or waves both vertically and horizontally. In this way, a profile in the manner of a “mogul slope”, which is familiar to skiers, is obtained for the flow guide walls  20 . This shape allows for a wide variety of variations when it comes to the arrangement and dimensions of the structures according to the invention on the flow guide walls  20 . The basic principle, however, is to reduce the flow rate of the waste water  3  in the basin  10  as a result of the shape of the flow guide walls  20 . 
         [0060]      FIG. 11  shows a schematic cross-section of a pipe  53  having flow guide walls according to a further embodiment of the invention. Taking into consideration the configuration of a circular basin having meanders  23  running substantially in the radial direction, such an arrangement can also be employed in the form of a pipe  53  for water procurement. For this purpose, the fluid can flow through the pipe  53  from the exterior to the interior, or vice versa. Because of the meander-shaped flow guide walls  20  inside the pipe  53 , solid matter, which settles, is separated from the fluid. This arrangement can be used, for example, to obtain drinking water from a river. In a further modification of this variant, (not shown), the meandering flow guide walls  20  run in the longitudinal direction of the pipe  53 , which is the same direction in which flow is provided. The pipe  53  is preferably oriented in a vertically or obliquely ascending manner and fluid flows through the pipe from the bottom upward. The sediment then settles predominantly in the lower region of the pipe  53  and can be removed therefrom.