FR2942791A1 - Device for cleaning wastewater, comprises a purification tank for receiving wastewater, a ventilation unit disposed in bottom of the tank and covered by a lower layer, and a plantation including aquatic plants such as reeds - Google Patents

Abstract

The device for cleaning wastewater, comprises a purification tank (2) for receiving wastewater (1), a ventilation unit (6) disposed in bottom of the tank and covered by a lower layer, and a plantation including aquatic plants such as reeds placed in an upper part of the tank. The tank comprises three layers superimposed of a filtering material in the form of grains or aggregates, the lower layer of grain size within a predetermined range located in the bottom of the tank, an intermediate layer of particle size less than the lower layer located above the lower layer, and a top layer. The device for cleaning wastewater, comprises a purification tank (2) for receiving wastewater (1), a ventilation unit (6) disposed in bottom of the tank and covered by a lower layer, and a plantation including aquatic plants such as reeds placed in an upper part of the tank. The tank comprises three layers superimposed of a filtering material in the form of grains or aggregates, the lower layer of grain size within a predetermined range located in the bottom of the tank, an intermediate layer of particle size less than the lower layer located above the lower layer, a top layer of grain size (2-4 mm) less than that of the intermediate layer located above the intermediate layer, an additional lower layer of particle size less than the intermediate layer located above the intermediate layer and below the upper layer, and an additional top layer between the lower layer and the upper layer and comprising an additional ventilation unit. The ventilation unit is used for recuperating the filtered and purified water. The top layer and additional lower layer are composed of porous type of material capable of promoting the development of micro-organisms. The porous material layer consists of shale expanded aggregate. The ventilation unit and additional ventilation unit are connected to a vertical pipe (5) forming a ventilation stack. A unit is arranged for distribution of wastewater between the purification tanks.

Description

B08 / 3640FR / GBO JV / JP - 08 Joint stock company called: J. VOISIN Compact sanitation device by planted filter, especially of the planted type of reeds Invention of: VOISIN Jean PAING Joëlle Compact sanitation device by planted filter, especially of the type planted with reeds

The present invention relates to a device for cleaning wastewater by filter, in particular of the planted type, for example planted with reeds. The sanitation device object of the invention is suitable for example for the treatment of wastewater discharged by a community or for the treatment of wastewater discharged by a dwelling of the type individual dwelling.

The wastewater treatment devices typically comprise two stages: the first stage filter, whose active filter bed consists of fine gravel, can be fed directly with raw sewage, whereas the second stage, whose basin is predominantly based on sand, completes the treatment of the carbon fraction of the essentially dissolved organic matter, as well as the oxidation of the nitrogenous compounds. The purifying processes are of course ensured by fixed microorganisms, present in the filtering mass. However, to be effective, such devices need a lot of space, especially because of their limited performance. These devices therefore imply installation constraints, in addition to maintenance costs. An object of the invention is to improve the efficiency of wastewater treatment.

In particular, an object of the invention is to increase the efficiency of treatment of a device by filter to allow in particular a reduction of the surface of the treatment device, for example in the case of a sanitation device autonomous. Another object of the invention is to obtain an equivalent or improved treatment with a device with a stage, for example in the case of a collective sanitation device. According to one aspect of the invention, there is provided a sanitation device comprising a purification tank provided for receiving the wastewater, the basin comprising at least three superimposed layers of filter materials in the form of grains or aggregates: a lower layer particle size within a predetermined range, located in the bottom of the basin, an intermediate layer of smaller particle size than the lower layer, located above the lower layer, and an upper layer of smaller particle size than the intermediate layer , located above the intermediate layer. The purification tank further comprises: a lower supplementary layer of smaller particle size than that of the intermediate layer, situated above the intermediate layer and below the upper layer, and an additional upper layer of particle size between that of the lower layer and that of the upper layer, located between the lower supplementary layer and the upper layer, and comprising additional ventilation means. The wastewater discharged into the pond is retained by the filter material and slowly passes through it. Through the filtering material, the wastewater is purified by physical mechanisms (filtration, adsorption), and by biological mechanisms (microbial degradation). Indeed, the environmental conditions are favorable for the development and activity of purifying bacteria fixed on the filter material (presence of oxygen, nutrient supply).

In order to obtain the filtering material, several superimposed layers in the form of grains or aggregates are available in the pond, enabling the mechanical filtration of the wastewater by gravity effect. Each layer comprises grains having a particle size in a determined range, and a particle size in a specific range corresponds to a percolation time of the wastewater through the layer. Depending on the granulometry, we obtain a more or less significant filtration of wastewater and a more or less slow flow of wastewater through the layer of aggregates.

Thus, the different grain size layers are arranged so that the highest grain size layer is located at the bottom of the basin, and that the layer having a fine grain size is on the top. The fine-grained layer on the top allows for efficient filtration and purification of wastewater. The lower layers of higher granulometry allow drainage of wastewater. The lower supplementary layer, which also has a finer granulometry, makes it possible to refine the treatment of water, on a single basin or stage. In particular, the wastewater treatment devices according to the prior art use two stages or tanks successively mounted in the water conveying circuit, in order to obtain the desired level of purification. In this case, thanks to the use of the additional upper and lower layers, and the additional means of ventilation, it is possible to obtain with a single stage, the desired level of purification. It is thus possible to obtain at the outlet of the device treated water meeting the discharge standards and can be discharged directly into the natural environment. Furthermore, the increase in the processing performance of the device can also reduce the surface of the device. Thus, instead of using a device having a surface area of 2 m 2 / EH (equivalent-inhabitants), the present device may have a smaller surface area, for example 1.2 m 2 / EH, which brings not only a saving of space but also an economic gain through lower investment costs and lower operating costs. The sanitation device thus makes it possible to obtain improved treatment efficiency with only one pool. Preferably, the device comprises a ventilation means disposed in the bottom of the basin, the means being covered by at least the lower layer. The ventilation means may also be able to recover the filtered and purified water. In this case, the treated water is not dispersed in the soil located under the device, but is recovered by the means of ventilation to be conveyed either to an additional stage of treatment or to the natural environment (ditch, river, water course). water, etc.). The ventilation means may be for example a ventilation drain. To promote the fixation of bacteria on the filter material, it can be provided that the layers, and at least the fine particle size layers (the upper layer and the lower supplementary layer) consist of granules of porous material, with particular surface characteristics . It is thus possible to provide at least one layer made of porous type material capable of promoting the development of microorganisms, preferably the upper layer and the lower supplementary layer. The porous type material promotes the development of microorganisms because of its internal porosity and thus improves the purification performance compared to sand or gravel. For example, the porous type material may be aggregates of expanded shale or any other porous material, natural or artificial, with a defined particle size, non-friable, having chemical and physical characteristics compatible with bacterial purification and of interest. compared to conventional sand or gravel. Expanded shale aggregates may be for example those sold under the Mayennite brand. This material is in the form of grains or aggregates formed from a slate schist expanded by heat treatment at a temperature of between 1100 ° C. and 1200 ° C., and in particular at 1130 ° C., for a sufficient length of time, by example of the order of 60 to 240 minutes, in particular of the order of 190 minutes, and having an average density of 1.3. The expansion process decreases the natural density of the shale which is about 2.6. The firing creates a substantially constant structural porosity for all the grains and substantially increases their specific surface area, that is to say the total surface of the material, per unit mass, which is accessible, particularly to small molecules such as atoms or gas molecules, and microorganisms involved in water purification processes. Because of their high surface area, Mayennite aggregates have better cleaning performance than gravel. The shale aggregates obtained are calibrated and separated in order to subsequently form different grain size layers. The upper layer may have a particle size of between 2 and 4 mm, and the lower supplementary layer may have a particle size of between 0 and 4 mm. Preferably, the additional ventilation means is connected to at least one vertical pipe forming a ventilation chimney. The ventilation means can also be connected to the vertical pipe forming a ventilation chimney. The double network of ventilation means makes it possible in particular to improve the ventilation of the basin and thus to provide the necessary oxygen for the bacteria. To increase the capacity of a sanitation device, it can be provided that it comprises two purification tanks, and means for distributing wastewater between the purification tanks. To control the distribution, it will be possible to provide an alternate filling of the basins. Indeed, to improve a filtration, it is better to let the wastewater in a basin to ensure their slow and gradual transition through the layers of material. The alternative use of the two basins allows for periods of rest for each basin to allow the flow of wastewater with a satisfactory filtration and purification. The device may comprise a planting, in the upper part of the purification basin, of aquatic plants, for example reeds. Such plants allow water absorption by roots and evapotranspiration elimination, root secretions favoring flocculation of organic matter, mechanical movements of the rhizome, oxygen transport from the leaves to the roots, etc. Other advantages and features will appear on examining the detailed description of an embodiment given by way of non-limiting example and illustrated by the appended drawings in which: FIG. 1 is a schematic view from above of an autonomous or collective sanitation device according to the invention; - Figure 2 is a sectional view along the line II-II of Figure 1; - Figure 3 is a sectional view along the line III-III of Figure 1, and - Figure 4 is a schematic view illustrating in more detail the realization of a ventilation drain according to the teachings of the invention. In Figure 1, there is shown a set of wastewater treatment 1. The assembly 1 may comprise one or more purification tanks, connected in parallel in the direction of sewage circulation, and can be used alternately, so to have rest phases allowing the degradation of the accumulated compounds and the re-oxygenation of each pool. For purposes of simplification, only one basin 2 has been shown in FIG.

The basin 2 is fed by a supply pipe 3. The supply pipe 3 may be a pipe disposed at a height greater than that of the basin, and capable of spreading on the upper surface of the basin the wastewater to be treated. Alternatively, the feed pipe 3 may comprise, as represented in FIG. 2, a main pipe 4 partly buried in the basin, and vertical pipes 5 stitched onto the main pipe 4 and opening at a height greater than that of the basin. so that the wastewater leaving the pipes 5 can spread over the surface of the basin 2. The pipes 5 may in particular be surrounded by anti-scouring plates. In particular, such a feed pipe 3 has the advantage of having a visual impact on the environment less important thanks to the buried parts, and also to allow a better distribution of wastewater on the surface of the basin 2.

As shown in Figures 2 and 3, on the bottom of the basin 2 is distributed a ventilation means 6, for example a ventilation drain, which may be in the form of a pipe with openings to allow the passage of air in both directions and / or water from the outside of the pipe to the inside of the pipe. The drain 6 is connected at one end to a vertical pipe 7 forming a ventilation chimney, and whose upper end 8 is at a height greater than the upper edge of the basin 2. The pipe 7 is provided with a cap ventilation 9.

The sanitation assembly 1 may also comprise a conduit for discharging the treated water 10. The evacuation pipe for the treated water 10 is connected to the drain 6, for example at the level of the connection between the drain 6 and the vertical pipe 7. The evacuation pipe 10 makes it possible to convey the wastewater recovered by the drain 6 to an outlet which can be a network of sewage spreading pipes, a ditch, a watercourse, or still a basin or a storage tank for subsequent reuse of the treated water, for example for watering. An additional ventilation means 11, for example an additional ventilation drain, is disposed in the basin 2, at a height greater than that of the drain 6. The additional ventilation drain 11 can also be connected at one end to the duct vertical 7 forming a ventilation chimney. The additional drain 11 is connected at its other end to a second vertical pipe 12 forming a ventilation chimney, whose upper end is located at a height greater than the upper edge of the basin 2 and is provided with a static aerator 13. additional drain ventilation 11 and the drain 6 allow better circulation of air, especially oxygen, in the basin 2, thanks in particular to their connection with the vertical pipe 7 forming a chimney. The drain 6 and the additional drain 11 can be made in the form of PVC cylindrical pipes provided with open slots. More particularly in the case of the additional drain 11 shown in Figure 4, there is provided two sets of slots 11a and 11b staggered on the upper half-periphery of the additional drain. The series IIa, llb of slots are effectively arranged on one side or the other with respect to a vertical plane of symmetry of the pipe, and they are interposed axially with respect to one another. The slots thus directed upward, promote the ventilation of the basin and limit the entrainment of water to be treated to the vertical pipe 7. In the case of the drain 6, it is possible to provide slots arranged in staggered rows on the lateral half-periphery of the drain, so that a series of slots is turned towards the top of the basin, to allow including a better ventilation thereof, and so that the other series of slots is turned towards the bottom of the basin to allow in particular the recovery of treated water and their routing towards the evacuation pipe 10.

Alternatively, it is also possible to use for the ventilation drains 6, 11, a honeycomb structure, a hollow box or any other system allowing the flow of air between the different layers of the basin 2. Layers of material superimposed 14 , 15, 16, 17, 18, here five in number, are arranged in the basin 2. A lower layer 14 covers the drain 6 disposed at the bottom of the basin 2. The lower layer 14 has a high particle size, between 10 and 20 mm. The thickness of the lower layer may be between 10 and 30 cm, for example about 20 cm. The lower layer 14 forms a coating of the drain 6. An intermediate layer 15 may consist of the same material, but having an intermediate particle size, greater than that of the lower layer 14, for example between 4 and 10 mm. The thickness of the intermediate layer 15 may be similar to that of the lower layer 14, that is to say between 10 and 30 cm, for example about 20 cm. The intermediate layer 15 is covered by a thin lower supplementary layer 16 consisting of expanded shale aggregates, for example Mayennite, with a particle size substantially between 0 and 4 mm, or even between 2 and 4 mm. The thickness of the upper supplementary layer 16 can be between 10 and 30 cm, for example 20 cm. The juxtaposition of the layers 16, 15 and 14 makes it possible to carry out the refining of the wastewater treatment.

An upper supplementary layer 17 covers the lower supplementary layer 16. The upper supplementary layer 17 has a particle size similar to that of the intermediate layer 15, for example between 4 and 10 mm. The thickness of the upper supplementary layer 17 may be chosen to be greater than that of the layers 14 to 16. In particular, the thickness may be between 20 and 40 cm, for example 30 cm. The upper supplementary layer 17 forms a coating for the additional ventilation drain 11. The upper supplementary layer 17 may also surround the main water supply pipe 4. The upper supplementary layer 17 is covered by a thin upper layer 18 consisting of expanded shale aggregates, for example Mayennite, with a particle size of substantially between 0 and 4 mm, preferably between 2 and 4 mm.

The thickness of the upper layer 18 may be between 20 and 40 cm, for example 30 cm. The juxtaposition of the layers 18 and 17 makes it possible to carry out a first stage of treatment of the wastewater. The supply pipe 3, and in particular the vertical pipes 5, opens into the basin 2 at a level higher than that of the upper layer 18. The supply pipe 3 can be fed, for example, from a distributor suitable for wastewater and capable of supplying the basin with tarpaulins and to distribute, where appropriate, the wastewater between the different basins. The feeding by sheeting makes it possible to have a good distribution of the effluent on all the surface of the basin, as well as a better oxygenation of the medium. In the upper layer 18, and optionally in the upper supplementary layer 17, plant implantation is provided that can take advantage of the substrates retained by the layers of filtration and purification material. For example, we can plan to plant reeds, especially reeds of the Phragmite type. Plants thus planted in the upper layers make it possible to prevent clogging of the surface of the filtering material by substances retained by said filter material. Such plants also allow the attachment and development of the purification bacteria on their rhizomes. It is thus possible to plant Phragmites Australis, at the rate of four plants per square meter, over the entire surface of the pond 2. The oxygen supply by the rhizomes makes it possible to promote the activity of the purification bacteria. Plants will also be able to recycle the substances retained by the upper layers, particularly nitrogen and phosphorus materials. An impermeable membrane 19 may be provided on the sides and the bottom of the basin 2, under the superposed layers 14 to 18. However, the treatment of the wastewater by the device 1 may allow a discharge directly into the ground. In this case, an impermeable membrane may be provided on the sides of the pool 2. The impermeable membrane may be for example a geomembrane, in particular high-density polyethylene (HDPE) placed on an anti-punching geotextile.

Edges 20 may be provided around the basin. The borders can be made of polypropylene, wood or concrete. In particular, they make it possible to protect pond 2 from runoff water. Furthermore, the sanitation device may also comprise a manhole 21 mounted at the end of the main pipe 4. The manhole 21 may in particular allow draining the main pipe 4, from its distal end, and possibly to cure it. In operation, wastewater is discharged into the basin 2. The water rest on the upper layer 18 and then progressively migrate through the upper layer 18, being firstly mechanically filtered, and secondly purified, because the material used to form the layer 18 has porosity characteristics favoring the fixation of the purification bacteria.

The wastewater thus passes through the upper layer 18 until it reaches the upper supplementary layer 17. The purification essentially occurs in the upper layer 18. The upper supplementary layer 17 makes it possible to continue the purification, to drain the treated water. It also promotes ventilation, including the additional ventilation drain 1l, and increase the performance of the device. The flow of water in this upper supplementary layer 17 is facilitated by the fact that it has a larger particle size than the upper layer 18. The upper supplementary layer 17 has more interstices between the aggregates, for easier circulation. The pre-treated wastewater arriving in the upper supplementary layer 17 gradually enters the lower supplementary layer 16. In particular, in order to limit the flow of pre-treated water into the additional ventilation drain 11, the latter may have a shape concave turned upward. The pre-treated water is then directed to the layer 16 rather than to the pipe 7. The ventilation chimneys 7, 12 allow an air supply or a gas extraction formed as a result of the purification and decomposition process. having occurred in layers 17, 18, and therefore better wastewater treatment. In particular, it may be noted that, during filtration, nitrification can occur, that is to say a transformation of the ammoniacal nitrogen present in the wastewater into nitrates. The arrangement of the slots, and in particular those of the additional ventilation duct 11 makes it possible to circulate the oxygen in the basin and to reject the gases formed during the treatment of the wastewater. The ventilation cap 9 is simply in the form of a protective cap covering the upper orifice of the first chimney 7, for example to prevent the fall of rainwater directly into the chimney 7. The static aerator 13 is in the form of a cap forming a shaped passage directly above the upper orifice of the second chimney 12 with a central portion of small thickness to promote an acceleration of air and aeration in the chimney 12. The waters pre-treated by the layers 17 and 18 then migrate progressively through the lower supplementary layer 16, being again mechanically filtered and purified. The wastewater thus passes through the upper supplementary layer 16 until it reaches the intermediate layer 15. The intermediate layer 15 and the lower layer 14 make it possible to continue the purification and to drain the treated water. The flow of water in these layers is facilitated because of their higher particle sizes.

As in the example illustrated, a gradual variation of particle size between the layers is preferable because if a thin particle size layer was disposed directly on a much larger particle size layer, a mixture of the grains of the different layers at the interface between the layers, which would not maintain the layout and homogeneity of the different layers, and more particularly the layers 16 and 18. The treated wastewater entering the lower layer 14 enter the drain 6 and flow gradually to In particular, a drain 6 with a minimum slope of 0.5% can be provided in order to direct the treated water collected by the drain 6 towards the evacuation pipe 10. The ventilation chimney 7 allows a gas extraction formed as a result of the process of purification and decontamination in the layers 16 to 14. The capacity of such a device Filtration and purification can be increased in a simple way by providing a basin 2 of upper surface, or by adding an additional basin. For this, it is sufficient to connect the different basins with each other through distribution lines comprising a distributor. In particular, it will be possible to provide a number of basins proportional to two or three. These basins are mounted in parallel in the direction of circulation of wastewater, each pool operating alternately with a feeding period followed by a rest period. The rest period makes it possible, in particular, to drain the sludge retained on the surface, the bacterial degradation of the compounds retained in the pond and the oxygenation of the latter. The use of material obtained from aggregates of expanded shale then calibrated has been described. It has been found that this material thus prepared has satisfactory characteristics for filtration. Such granules have in particular a substantially constant porosity and a high specific surface. These aggregates are available with specific particle sizes for layer formation. Of course, it will be possible to use any material that can be obtained with different particle sizes, and having significant filtration capabilities, including materials with a high porosity and high specific surfaces. It may be possible to provide for the use of layers consisting of different materials. Thanks to the invention, a sewage treatment device is obtained that is more compact, more efficient and capable of treating wastewater in a single stage. The wastewater can be discharged into a river, a ditch, infiltrated into the ground, or stored for later use in a tank or basin, for example for watering plants.15

Claims (10)

REVENDICATIONS1. Sanitation device (1) for wastewater comprising a purification tank (2) designed to receive the wastewater, the basin comprising at least three superposed layers of filtering materials in the form of grains or aggregates: a lower layer (14) particle size within a predetermined range, located in the bottom of the basin, an intermediate layer (15) of smaller particle size than that of the lower layer, located above the lower layer, and an upper layer (18) of smaller particle size to that of the intermediate layer, located above the intermediate layer, characterized in that the purification tank comprises - an additional lower layer (16) of smaller particle size than that of the intermediate layer, located above the layer intermediate and below the upper layer, and - an additional upper layer (17) of particle size between that of the lower layer and that of the upper layer, located between the lower supplementary layer and the upper layer, and comprising additional ventilation means (11). 2. Device according to claim 1 comprising a ventilation means (6) disposed in the bottom of the basin, the means being covered by at least the lower layer (14). 3. Device according to claim 2 wherein the ventilation means (6) is also capable of recovering the filtered and purified water. 4. Device according to one of the preceding claims wherein at least one layer is made of porous type material capable of promoting the development of microorganisms, preferably the upper layer (18) and the lower supplementary layer (16). 5. Device according to claim 4, wherein the porous-type material layer is a layer consisting of expanded shale aggregates. 6. Device according to one of the preceding claims wherein the upper layer (18) has a particle size of between 2 and 4mm, and the lower supplementary layer has a particle size of between 0 and 4mm. 7. Device according to one of the preceding claims wherein the additional ventilation means (11) is connected to at least one vertical pipe (7) forming a ventilation chimney. 8. Device according to claims 2 and 7 wherein the ventilation means (6) is also connected to the vertical pipe (7) forming a ventilation chimney. 9. Device according to any one of the preceding claims, comprising at least two purification tanks, and means for distributing wastewater between the purification tanks. 10. Device according to any one of the preceding claims, comprising a planting, in the upper part of the purification pool, of aquatic plants, for example reeds.