Wastewater filtration system for non-collective sanitation installation

Abstract

Title: Wastewater Filtration Device for Individual Wastewater Treatment Systems. The invention relates to a filtration device (1) for filtering wastewater, the device (1) comprising: - a prefabricated filtration tank (2) including a bottom (21) having an internal surface (210) within the tank (2); - at least one filtration stage (4) located within the filtration tank (2); - a lift pump (6) installed within the filtration tank (2); wherein the internal surface of the bottom (21) includes: - a lift section (212) on which the lift pump (6) is installed; - a collection section (211) including at least one gravity flow channel (5) extending longitudinally towards the lift section (212), the lift section (212) being located at a lower elevation than the collection section (211). Figure for the abstract: Fig. 2

Description

Title of the invention: Wastewater filtration device for non-collective sanitation installation

[0001] The field of the invention relates to the design and manufacture of wastewater treatment equipment. More specifically, the invention relates to a wastewater filtration device, of the type incorporating a filtration tank intended to receive wastewater pre-treated by a septic tank.

[0002] In the case of non-collective sanitation, a distinction is made between homes connected to the collection network of their municipality and those that are not. Homes not connected to the collection network are generally equipped with a septic tank for the treatment of domestic wastewater (excluding rainwater) associated with a filtration system such as a filter sand tank.

[0003] There are also tanks, called filtration tanks, which are coupled to septic tanks in which the wastewater is pre-treated.

[0004] Such a filtration tank comprises an internal volume inside which waste water is brought to be filtered by at least one filtration stage, comprising a filter medium, located inside the filtration tank.

[0005] A lifting pump installed in the filtration tank, on the bottom of the latter, is intended to suck up the filtered water to evacuate it. It should be noted that, apart from the filter media, these tanks are thus most of the time partially empty of water.

[0006] A non-collective wastewater treatment installation may conventionally comprise prefabricated tanks intended to be buried in pits.

[0007] The tanks can be prefabricated in concrete, or in plastic.

[0008] Concrete tanks thus have a particularly high weight, and involve constraints for their transport and installation relating to this weight. Nevertheless, they have significant structural resistance and a natural capacity, due to their weight, to resist Archimedes' pressure if water invades the cavity in which they are buried.

[0009] Plastic tanks are therefore easier to transport and install.

[0010] However, they are subject to specific constraints resulting from the volume they occupy, and from the resistance as well as the lower density of the plastic material compared to a more resistant and dense material, such as concrete.

[0011] Indeed, being mostly partially empty of water, and because they are buried in pits and covered with a filling material, “light” tanks made of plastic material can have a tendency to come out of the ground under the effect submersion of the pit, or the presence of a water table, and constraints exerted by the water according to the principle of Archimedes' thrust. Palliative measures must therefore be implemented for these tanks, such as those described in particular in the patent documents published under numbers FR2999625 and FR3122101.

[0012] A more general problem relating to filtration devices comprising a prefabricated tank lies in the fouling of the tank, particles inexorably passing through the filter and accumulating at the bottom of the tank.

[0013] In this case, it is then necessary to carry out an in-depth overhaul of the tank requiring a heavy and costly intervention. Such an intervention often involves the entry into the tank of an operator who, in a context of dangerous gases such as sulfur hydroxide and methane, must be provided with personal protective equipment such as a diving suit.

[0014] The invention aims in particular to overcome the drawbacks of the prior art.

[0015] More specifically, the invention aims to propose a filtration device comprising a prefabricated filtration tank at least partially resolving the problem linked to the fouling of the tank.

[0016] The invention also aims to propose such a device which does not require such a recurrent in-depth overhaul as may be necessary with comparable tanks according to the prior art.

[0017] These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a filtration device for the filtration of waste water, the device comprising: - a prefabricated filtration tank comprising a bottom having an internal surface to the tank, the tank extending in height relative to the bottom; - at least one filtration stage located in the filtration tank; - a lifting pump installed in the filtration tank; characterized in that the internal surface of the bottom comprises: - a lifting section on which the lifting pump is installed; - a collection section comprising at least one gravity flow channel extending longitudinally towards the lifting section, the lifting section being located at a lower height than the collection section.

[0018] The filtration tank of the device according to the invention is less subject to fouling than other devices according to the prior art.

[0019] Indeed, thanks to the gravity flow channel oriented towards the lifting section, the flow water filtered by the filtration stage flows towards the lifting section, carrying potential particles having passed through the filtration stage. The filtered water concentrates in this flow channel to reach to the lifting section. The filtered water is thus likely to create a greater flow in this drainage channel to carry particles.

[0020] The shape of the internal surface of the bottom of the tank thus optimizes the evacuation of particles thanks to the filtered water which flows to the lifting pump.

[0021] As can be understood, in the event of high demand on the filtration device, and a high flow rate of filtered water, the cleaning action by the filtered water is reinforced. The more water flows in large quantity and quickly over the internal surface of the bottom of the tank, and in particular in the flow channel, the more the water is capable of performing a scouring action on the particles accumulating on this internal surface of the bottom of the tank and of carrying these particles towards the lifting pump located on the lifting section.

[0022] Advantageously, the collection section comprises two gravity flow sections framing the gravity flow channel, each gravity flow section being inclined towards the gravity flow channel.

[0023] Each gravity flow pan thus directs the filtered water flowing along their surface towards the gravity flow channel. The gravity flow pans thus participate in forming a greater flow rate at the gravity flow channel.

[0024] According to a preferred design, the device comprises a base for the tank, the base delimiting a laying plane for the tank and providing a space above the laying plane in which the gravity flow channel extends.

[0025] The collection section of the internal surface of the bottom then corresponds to the part of this internal surface which is closest to the laying plane.

[0026] In this case, the gravity flow channel and the collection section do not interfere with the ability of the tank to rest on a flat surface, for example the surface of a slab.

[0027] Preferably, the device comprises a draining floor overhanging the gravity flow channel.

[0028] This draining floor, while forming a means of filtering the water flowing into the tank, also forms a means capable of retaining a filtering medium from the filtration stage, and preventing it from falling into the drainage channel.

[0029] Advantageously, the draining floor provides a free volume between it and the drainage channel.

[0030] A flow of filtered water flowing into the channel is thus not disturbed.

[0031] According to a preferred embodiment, the draining floor rests on the collection section on either side of the drainage channel, and the drainage channel has a cross-section curved towards the outside of the tank.

[0032] The drainage channel, by virtue of its shape and the presence of the overlying draining floor which rests on either side of the channel, then presents reinforced resistance against external pressures exerted against the tank at the level of the channel, for example that resulting from the invasion by water of the pit in which the tank is buried.

[0033] According to a preferred variant, the device comprises vertical reinforcements housed in the tank and resting on the bottom and on an upper wall of the tank which overhangs the bottom.

[0034] The resistance of the tank is thus reinforced.

[0035] Preferably, at least part of the vertical reinforcements rests on the bottom via the draining floor.

[0036] The resistance of the drainage channel is then particularly reinforced.

[0037] According to a preferred design, the bottom of the tank comprises: - a rigid shell made of a plastic and / or composite material; - at least one membrane linked at least partially to the rigid shell, and forming at least partially the internal surface of the bottom of the tank.

[0038] Thanks to this design, the internal surface of the bottom of the tank is not strictly dependent on the shape of the rigid shell of the tank. It is thus possible for this rigid shell to form reinforcements such as stiffeners, without these reinforcements forming spaces inside the tank that are likely to become clogged.

[0039] The invention also relates to a non-collective sanitation installation, comprising: - a pit dug in the ground and having a flat base; - a filtration device as described above, resting on the flat base; - a backfill material filling the pit around the filtration device.

[0040] This installation presents the advantages obtained thanks to the tank according to the invention as previously described.

[0041] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and non-limiting example, and the appended drawings among which: - [Fig.l] [Fig.l] is a side view of the device according to the invention; - [Fig.2] [Fig.2] is a side view along a median longitudinal section of the device according to the invention; - [Fig.3] [Fig.3] is a perspective view of the bottom of a tank according to a median longitudinal section of the device according to the invention; - [Fig.4] [Fig.4] is a perspective view of the bottom of a tank according to a horizontal section of the device according to the invention; - [Fig.5] [Fig.5] is a front view of the tank of the device according to the invention; - [Fig.6] [Fig.6] is a front view of the bottom of the tank according to a median cross-section of the device according to the invention.

[0042] Referring to Figures 1 to 6, a filtration device 1 for filtering wastewater is shown.

[0043] This device 1 comprises a prefabricated filtration tank 2.

[0044] By the expression "prefabricated", it is understood that the tank is not built at its installation site, and that it is designed to be manufactured at a dedicated manufacturing site, then transported to its installation site.

[0045] This filtration tank 2 is advantageously formed from a rigid shell 20 made of plastic and / or composite material.

[0046] For example, tank 2 is manufactured by rotational molding.

[0047] With reference to figures 1, 2, and 5, the filtration tank 2 comprises: - a background 21; - an upper wall 23; - a peripheral wall 22 extending from the bottom 21 to the upper wall 23.

[0048] As detailed below, the tank 2 is intended to rest on a part of its shell 20 which forms a part of the bottom 21 of the tank 2. The tank 2 thus extends in height from its bottom 21.

[0049] For the sake of clarity, spatial references are shown in Figures 1 and 2, these references include a horizontal axis H, and a vertical axis V.

[0050] The position of the tank 2, relative to these spatial references, corresponds to the position of the tank 2 once its installation is complete.

[0051] The tank 2 also comprises a main inspection chamber 24 and a secondary inspection chamber 25.

[0052] As illustrated by [Fig. 1], the tank 2 has a main filtration part 201, and a secondary part 202 dedicated to lifting filtered water.

[0053] With reference to [Fig.2], the filtration device 1 comprises at least one filtration stage 4 (illustrated schematically) which is located in the filtration tank 2. More precisely, the filtration device 1 comprises a single filtration stage 4 which is located in the main filtration part 201. It is conceivable, according to other embodiments, that the filtration device 1 comprises several filtration stages, such as two or three filtration stages.

[0054] This filtration stage 4 can for example be formed from clay balls, plant fibers such as coconut fibers, and has a height which can be between 30 centimeters and 1.5 meters depending on the material and the level of treatment requirement, and being for example of the order of 60 centimeters.

[0055] Although this is not shown, the filtration device 1 also comprises means for supplying water to be filtered designed to supply the filtration step with water to be filtered.

[0056] The filtration device 1 is in particular designed to be arranged next to a wastewater treatment tank, the treated water emerging from said tank being intended to feed the filtration device 1.

[0057] As illustrated by Figures 2 to 4, the filtration device 1 also comprises a lifting pump 6 installed in the filtration tank 2.

[0058] With reference to figures 2 to 4, and 6, the bottom 21 has an internal surface 210 to the tank 2.

[0059] This internal surface 210 corresponds to the surface which delimits in the lower part the internal volume in which the water to be filtered is treated, and the filtered water is collected.

[0060] This internal surface 210 comprises: - a lifting section 212 on which the lifting pump 6 is installed; - a 211 collection section.

[0061] The lifting section 212 is located at a lower height than the collection section 211. In this way, the filtered water collected by the collection section 211 is directed towards the lifting section 212 to be pumped there by the lifting pump 6.

[0062] The collection section 211 essentially corresponds to the internal surface 210 directly above the main filtration part 201 of the tank, while the collection section 212 essentially corresponds to the internal surface 210 directly above the secondary part 202 of the tank 2.

[0063] The collection section 211 comprises at least one gravity flow channel 5 extending longitudinally towards the lifting section.

[0064] By gravity flow, it is understood that the channel 5 has at least one slope relative to the horizontal when the device is installed, this slope allowing the flow of a liquid in a predetermined direction under the effect of gravity.

[0065] According to one possible embodiment, the collection section 211 may comprise a plurality of flow channels 5, for example extending parallel to each other.

[0066] According to the present embodiment, the collection section 211 comprises a single gravity flow channel 5.

[0067] The gravity flow channel 5 concentrates the filtered water and allows the creation of a flow of filtered water directed towards the lifting section 212.

[0068] With reference to [Fig.2], the flow channel 5 has a slope 51 greater than or equal to 1%, and less than or equal to 20%, preferably less than or equal to 10%, and even more preferably less than or equal to 5%.

[0069] Below 1%, the efficiency of the gravity flow channel 5 is too reduced, and above 20%, the longitudinal dimension of the tank 2 must be too reduced. From 10%, the longitudinal dimension of the tank 2 can be advantageous, and the range of 1% to 5% offers a good ratio between the capacity to create a flow in the channel 5 to evacuate particles and the longitudinal dimension of the tank 2.

[0070] Typically, the flow channel 5 has a slope of 2% which optimizes the two aforementioned characteristics.

[0071] More specifically with reference to [Fig.6], the gravity flow channel 5 has a cross-section comprising a central portion framed by two lateral portions.

[0072] The lateral portions have, from the outside of the section of the channel towards the central portion, an external part rounded towards the inside of the tank (i.e. defining a concavity open towards the outside of the tank), followed by a transition part having a rounding towards the outside of the tank (i.e. defining a concavity open towards the inside of the tank) forming a transition between the external part and the central portion of the channel 5.

[0073] At the interface between the external part and the transition part, the cross-section of the channel 5 has a tangent tending to approach the vertical. This tends to cause a flow of water to “fall” towards the central portion of the channel 5.

[0074] The central portion of the flow channel 5, as can be seen, has a shape tending to flatten, that is to say having a radius of curvature greater than that presented for example by the rounding of the transition part.

[0075] It is conceivable that a part of the central portion is strictly planar, in particular a part which would be centered on the central portion.

[0076] As can be seen in Figures 1 to 6, and more specifically in [Fig.4], the bottom 21 and in particular the collection section 211 have a rectangular shape with a large length and a small width.

[0077] In [Fig.4], a spatial reference formed by a trihedron is represented, and presents: - a horizontal axis H; - a vertical axis V extending perpendicular to the horizontal axis H; - a depth axis P (also extending horizontally), perpendicular to the horizontal axis H and the vertical axis V.

[0078] According to this reference, the bottom 21 extends in length along the horizontal axis H, presenting the collection section 211 then the lifting section 212.

[0079] The drainage channel 5 extends along the horizontal axis H.

[0080] The drainage channel 5 thus has a significant length with respect to the surface of the bottom 21 projected into a horizontal plane.

[0081] As can be seen in the figures, the flow channel 5 is centered in the collection section 211.

[0082] As illustrated by [Fig.6], the flow channel 5 has a cross-section curved towards the outside of the tank 2. This shape allows the channel 5 to better resist external stresses and to accelerate the flow rate, which prevents the accumulation of residues in the bottom of the device.

[0083] With reference to Figures 2 to 4, the tank 2 has an overflow 213 at the interface between the collection section 211 and the lifting section 212, and more precisely at the lowest end of the flow channel 5, towards the lifting section 212.

[0084] The spillway 213 has a longitudinal section in an arc of a circle accelerating the speed of a flow of water leaving the gravity flow channel 5.

[0085] With reference to figures 1 to 5, the secondary part 202 of the tank 2 has a substantially cylindrical shape and has at its lower part a truncated cone-shaped housing 60, with a section decreasing towards the lifting section 212, to accommodate the pump 6.

[0086] In other words, the lifting section 212 corresponds to the disc-shaped surface at the base of the frustoconical housing 60.

[0087] This truncated housing 60 is adapted to the lifting pump 6. The lifting section 212 has in particular a diameter corresponding to the space taken up on the ground by the lifting pump 6, with a margin allowing the insertion of the pump 6.

[0088] The truncated cone shape makes it possible to maximize the grouping of the filtered water to be raised at the level of the pump, above the lifting section 212, and the resistance of this part of the tank 2, while presenting a secondary part 202 facilitating the maintenance of the lifting pump 6 (for example for its insertion / extraction) thanks to the larger diameter above the truncated cone part.

[0089] With reference to Figures 3, 4, and 6, the collection section 211 comprises two gravity flow panels 52 which frame the gravity flow channel 5. As can be seen in [Fig.6], each gravity flow panel 52 is inclined towards the gravity flow channel 5.

[0090] According to an embodiment envisaged, not shown, these gravity flow panels 52 directly border the flow channel 5 by extending along the channel 5.

[0091] The collection section 211 also comprises a front face 53 of gravity flow also inclined towards the channel 5, and located opposite the lifting section 212 relative to the flow channel 5.

[0092] According to the present embodiment, and as detailed below, the collection section 211 comprises edges interposed between the channel 5 and the gravity flow sides 52.

[0093] With reference to figures 4, 5, and 6, the device 1 comprises a base 7 for the tank 2.

[0094] This base 7 delimits a laying plane 70 of the tank 2.

[0095] As can be seen, the base of the housing 60 is at the level of this plane of pose 70, thus allowing the lifting section 212 to be at the lowest height of the internal surface of the bottom, while not exceeding the height of the pose plane 70.

[0096] According to the present embodiment, this base 7 is formed by the rigid shell 20 of the tank 2.

[0097] The base 7 comprises, still according to the present embodiment: - two beams 71; - stiffeners 72.

[0098] As mentioned previously, and with reference to Figures 5 and 6, each beam 71 is formed by the rigid shell 20 which has a U-shaped section at the level of the beam 71.

[0099] These beams 71 extend longitudinally along the collection section 211, and in particular along the channel 5.

[0100] The beams 71 have, along their length, and from the laying plane 70 which they help to form, notches 711 reinforcing their structural resistance and allowing the passage of the forks of a lifting trolley.

[0101] The stiffeners 72 extend transversely to the beams 71. They also have an external lower surface participating in forming the laying plane 70.

[0102] These stiffeners 72 are formed by the rigid shell 20 and contribute to the structural resistance of the tank 2.

[0103] These beams 71 and these stiffeners 72 form outwardly facing recesses relative to the internal volume of the tank 2. Nevertheless, they do not form spaces susceptible to fouling.

[0104] Indeed, as illustrated by [Fig.6], the device 1 comprises, according to the present embodiment, membranes 9 partially linked to the rigid shell 20.

[0105] These membranes 9 are watertight, and are for example glued to the rigid shell 20 at the level of the edges and the gravity flow panels 52.

[0106] The crevices formed by the beams 71 and the stiffeners 72 can be filled, for example with sand or water.

[0107] The membranes 9 partially form the internal surface of the bottom 21 of the tank 2. In fact, the membranes 9 are coupled to the rigid shell 20 by being stretched above the crevices formed in particular by the beams 71 and the stiffeners 72.

[0108] As shown in [Fig.6] by arrow E, water filtered by the filtration stage 4 can flow along the membrane 9 to the gravity flow channel 5.

[0109] According to one possible embodiment, the device 1 could comprise only a single membrane, which would for example also be glued in the channel 5 gravity flow.

[0110] The membrane(s) 9 are for example formed from EPDM rubber (acronym for ethylene-propylene-diene monomer).

[0111] The base 7 provides a space above the installation plane 70 in which the gravity flow channel 5 extends.

[0112] This space is notably formed between the two beams 71.

[0113] The height of the base 7, and thus of the beams 71, allows the channel 5 to flow gravity to present an optimized slope to form a water flow towards the lifting section.

[0114] According to the present embodiment and with reference to figures 2, 3, 4, and 6, the device 1 comprises a draining floor 8.

[0115] The draining floor 8 may for example be formed by a honeycomb grid with vertical cells to which is coupled a geotextile felt allowing the filtered water to flow. This draining floor 8 is made for example of polyethylene.

[0116] This draining floor 8 overhangs the gravity flow channel 5. For this purpose, the draining floor 8 rests on either side of the gravity flow channel 5, on the edges inserted between the channel 5 and the gravity flow panels 52.

[0117] Although this is not shown, the presence of the draining floor 8 does not limit the flow of filtered water from the gravity flow sections 52 into the channel 5. Indeed, the device comprises ad hoc means allowing the filtered water flowing along the gravity flow sections 52 to pass the draining floor. These means may for example take the form of wedges raising the draining floor 8 from the edges, or of a filter foam having a reinforcement allowing it to support the filtering floor 8, or of a combination of the wedges and a surplus of the geotextile felt of the draining floor 8.

[0118] As can be seen more precisely in [Fig.6], the draining floor 8 provides a free volume between it and the gravity flow channel 5.

[0119] The device 1 also comprises vertical reinforcements 31 housed in the tank 2 and resting on the bottom 21 and on the upper wall 23 of the tank 2 which overhangs the bottom 21.

[0120] Two of the vertical reinforcements 31 bear on the bottom 21 via the draining floor 8. More precisely, each vertical reinforcement 31 is coupled to a crosspiece 310 extending transversely on the draining floor 8, parallel to the depth axis P, as illustrated by [Fig.4].

[0121] The device 1 previously described is used to form non-collective sanitation installations which is also an object of the invention.

[0122] Such an installation comprises: - a pit dug in the ground; - device 1 inserted into the pit; - a backfill material.

[0123] The pit made in the ground must have sufficient height to allow the insertion of the tank 2, while allowing the inspection holes and a ventilation chimney to emerge from the surface of the surrounding ground.

[0124] This pit must have a flat base on which the filtration device, and more specifically the tank 2, rests by means of the base 7.

[0125] This flat base can in particular be formed by a raft.

[0126] Finally, the backfill material is used to fill the pit, around the filtration device 1. This backfill material may, for example, correspond to part of the earth from the excavation of the pit.

[0127] The filtration device 1 and the installation previously described have a significant capacity to resist fouling thanks to the bottom of the tank 2 which makes it possible to easily flush, in the direction of the lifting pump for evacuation, unfiltered particles likely to create fouling, under the effect of a flow of filtered water.

[0128] This solution produces its effects as soon as water flows into the filtration tank, and does not require one-off intervention by a human operator in the tank to initiate it.

[0129] During the annual maintenance of the installation, any deposit of material on the bottom is easily evacuated by the injunction of water via a rigid pipe which crosses the filter medium, thanks to the gravity flow channel 5 and its slope. For information, flat-bottomed tanks according to the prior art do not allow this possibility, which leads to fouling of the bottom of the tank and a downgrading of the quality of the discharge.

Claims

Claims

1. Filtration device (1) for filtering wastewater, the device (1) comprising: - a prefabricated filtration tank (2) comprising a bottom (21) having an internal surface (210) to the tank (2), the tank extending in height relative to the bottom; - at least one filtration stage (4) located in the filtration tank (2); - a lifting pump (6) installed in the filtration tank (2); characterized in that the internal surface of the bottom (21) comprises: - a lifting section (212) on which the lifting pump (6) is installed; - a collection section (211) comprising at least one gravity flow channel (5) extending longitudinally towards the lifting section (212), the lifting section (212) being located in height lower than the collection section (211).

2. Device (1) according to the preceding claim, characterized in that the collection section (211) comprises two gravity flow sections (52) framing the gravity flow channel (5), each gravity flow section (52) being inclined in the direction of the gravity flow channel (5).

3. Device (1) according to any one of the preceding claims, characterized in that it comprises a base (7) for the tank (2), the base (7) delimiting a laying plane (70) of the tank (2) and providing a space above the laying plane (70) in which the gravity flow channel (5) extends.

4. Device (1) according to any one of the preceding claims, characterized in that it comprises a draining floor (8) overhanging the gravity flow channel (5).

5. Device (1) according to the preceding claim, characterized in that the draining floor (8) provides a free volume between it and the gravity flow channel (5).

6. Device (1) according to any one of claims 4 and 5, characterized in that the draining floor (8) rests on the collection section (211) on either side of the gravity flow channel (5), and in that the gravity flow channel (5) has a cross-section curved towards the outside of the tank (2).

7. Device (1) according to any one of the preceding claims, characterized in that it comprises vertical reinforcements (31) housed in the tank (2) and bearing on the bottom (21) and on an upper wall (23) of the tank (2) which overhangs the bottom (21).

8. Device (1) according to claims 6 and 7, characterized in that at least part of the vertical reinforcements (31) rests on the bottom (21) via the draining floor (8).

9. Device (1) according to any one of the preceding claims, characterized in that the bottom (21) of the tank (2) comprises: - a rigid shell (20) made of a plastic and / or composite material; - at least one membrane (9) linked at least partially to the rigid shell (20), and at least partially forming the internal surface of the bottom (21) of the tank (2).

10. Non-collective sanitation installation, comprising: - a pit formed in a ground and having a flat base; - a filtration device (1) according to any one of the preceding claims, resting on the flat base; - a backfill material filling the pit around the filtration device (1).

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