FR2644773A2 - Process and device for the purification of polluted water - Google Patents

Abstract

According to this process and by virtue of the corresponding device, the supply of the upper surface of the filter layer 2 with polluted water is ensured by means of a dispensing system 4-5 arranged above the latter, thus considerably reducing, or even completely eliminating, the periods of submersion of the filter layer 2. Furthermore, a draining base layer 3 is provided below the latter, made of a material of high permeability, such as granulate or geotextile. A network of drains 7 or of circulation passages is arranged inside this draining layer, these being connected both to a storage vessel 11 for recovery of the filtered water and to the device 10 for extracting or pulsing air intended to provide an air circulation inside the filter layer 2. Thus, this network is used not only for recovering the filtered water but also for the removal or the delivery of air travelling through the filter layer.

Description

 Process and device for the purification of polluted water '.

 The present invention relates to the method and the device which are the subject of the main patent. The purpose of this process and this device is to purify highly polluted water by treatment in a filter layer, and this by means of an aerobic microbial flora, the filter layer being kept unsaturated.

 In accordance with the essential characteristic of the method according to the main patent, the controlled atmosphere in the filter layer is guaranteed to be renewed, by organizing air circulation through it. To this end, the device described in the main patent comprises one or more networks of perforated tubes which are embedded inside the filter layer and which are intended to serve as means for supplying air under pressure or, on the contrary, for air suction means. The circulation of air thus organized, in one direction or the other, through the filtering layer has the effect of permanently maintaining in the latter an appropriate oxygen level, which allows an effective purification of the water to be treated.

 In the embodiment described in the main patent, it is planned that the clean-up water is eliminated within an underlying permeable ground, or else that it is recovered by means of a network of collection drains. arranged at the base of the device used.

 The object of the present invention is to provide a certain number of improvements to the method and to the device according to the main patent in order to increase its efficiency. To this end, these improvements are aimed in particular at considerably reducing the periods of submersion of the filter bed. However, these improvements also have the object of improving and simplifying the conditions for recovering clean water as well as the conditions for supplying or evacuating the air ensuring the circulation of air organized inside the filtering layer. .

To this end, the method according to the invention is essentially characterized in that
- firstly, the upper surface of the filtering layer is supplied with polluted water by means of a distributing system placed above it, thereby considerably reducing, or even completely eliminating, the periods submersion of the filter layer,
- on the other hand, a draining base layer made of a material of high permeability - such as aggregate or geotextile - is provided below this filtering layer of sand, by providing a network of drains or circulation passages which are connected both to a recovery tank for filtered water and to the extraction or air supply device designed to ensure air circulation inside the filtering layer .

 Thus this network is used not only for the recovery of filtered water, but also for the evacuation or the arrival of air circulating through the filtering layer. Furthermore, the significant reduction, or even the complete elimination of the submersion periods of the filtering layer, has the advantage of improving the conditions of infiltration of polluted water into the filtering layer, by allowing semi-permanent to permanent communication. of the internal atmosphere of the filter layer with the outside.

 The present invention also relates to a device specially designed for the implementation of this improved form of the present process.

The characteristics and advantages of this device, as well as of the method according to the invention, will appear during the following description. This is given with reference to the attached drawing for information only, and on which
Figure 1 is a schematic perspective view in section of the device according to the invention.

 Figure 2 is a partial sectional view of an alternative embodiment of this device.

 FIGS. 3 and 4 are partial sectional views, on different scales, of a drain provided in the case of FIG. 1 respectively and of an existing circulation passage in the case of FIG. 2.

 In the example shown in Figures 1 and 3, the device according to the invention comprises, inside a basin 1, the superposition of a filtering layer 2 and a draining base layer 3. The basin 1 can be arranged in the ground, its walls being waterproof. To this end, they can be made in masonry, or by compacting the corresponding soil or even by installing an impermeable membrane.

 The filter layer 2 is made of a porous and permeable material. The thickness, permeability and porosity of this material are chosen so as to obtain good infiltration of polluted water, strong bacterial development and free circulation of air.

This filtering layer can be constituted by a single layer of sand or by superposition of several layers of sand of different particle size. Thus, it may consist, for example, of a layer 1.50 m thick comprising the superposition of fine sand (particle size less than 1 mm) and coarser sand (particle size less than 4 mm).

 As for the draining layer 3, it is made up of gravel of greater particle size. Thus, it may consist, for example, of a layer approximately 20 cm thick of gravel having a particle size between 2 and 20 mm.

 Above the filter layer 2, there is a distributor system for supplying the device with polluted water to be treated. This distributor system comprises a network of tubes 4 starting from a pipe 5 for supplying polluted water. The tubes 4 are arranged above the filtering layer 2 and they comprise a series of orifices or outlet nozzles 4a to ensure a supply by simple gravity flow or by spraying under pressure. A valve 6 or any other suitable adjustment device, mounted on the supply line 5, makes it possible to adjust the supply flow so as to avoid, or at least considerably limit, the periods of submersion of the filtering layer 2 .

 Inside the draining base layer 3, there is provided a network of drains 7 placed against the bottom 8 of the basin 1. As shown in FIG. 3, these drains can be constituted by tubes whose walls have slits 7a allowing the penetration of water inside these drains. These are connected to a collecting pipe 9 which is connected both to an air suction device 10 and to a tank 11 for recovering clean water.

 In fact, in accordance with the method according to the invention, the drains 7 serve both to ensure the organization of an air circulation inside the filtering layer 2 and to recover the depolluted water circulating by gravity. in the draining layer 3. Consequently, a water circulation blade 12 is formed in the bottom of each drain 7, the rest of the available space serving for the circulation of air.

 In the example mentioned above, this circulation is carried out continuously by suction at the base of the treatment basin. However, it could just as easily be carried out continuously by air discharge at the base of this basin. In this case, the suction device 10 would be replaced by a pressurized air delivery device. Furthermore, instead of carrying out a continuous circulation inside the filtering layer 2, it would be possible to carry out predetermined sequences of pressurization and / or depressurization, as provided for in the main patent.

 In accordance with the method according to the present invention, the treatment tank is supplied with polluted water by adjusting the distributor system 4-5 so as to limit as much as possible, or even completely eliminate, the periods of submersion of the upper surface of the filter layer 2.

 It is possible to carry out continuous infiltration, in which case the hydraulic load provided must be less than that which would be likely to create a permanent layer of water on the surface of the filtering layer. However, it is also possible to carry out intermittent infiltration by sequential supply of polluted water. In this case, the periods of submersion of the surface of the filtering layer 2 must be very short compared to the periods of emersion of the latter.

In both cases, a permanent or semi-permanent communication is thus obtained between the atmosphere of the filtering layer 2 and the outside, which improves the conditions of infiltration of polluted water into the filtering layer. .

 Polluted water thus infiltrated into layer 2 crosses it by gravity to reach the draining base layer 3. However, during the crossing of the filtering layer, polluted water undergoes purification due to its treatment by the microbial flora contained in this layer. The effectiveness of this treatment is due to the fact that there is a controlled renewal of the atmosphere in this filtering layer due to the circulation of air provided inside it. After this treatment, the depolluted water is collected in the drains 7 and evacuated to the reservoir 11.

 As already indicated, the organized air circulation inside the filter layer can be ensured by a continuous vacuum at the base of this layer. This depression can be obtained by means of a fan applying a relatively low depression, the value of which can correspond, for example, to a column of water of 20 cm. But again, instead of a continuous vacuum aeration, it is possible to perform aeration by air discharge from the bottom, and this with similar results. Moreover, it is also possible to carry out predetermined spraying and / or delivery sequences.

 The device according to the invention is not limited to the single embodiment described above. Thus, FIGS. 3 and 4 represent a variant in which the draining base layer 3 of gravel is replaced by a draining lower layer 3a made of a geotextile material. This draining layer is disposed against the bottom 8a of the corresponding basin. However, this bottom comprises a series of channels 13 which make it possible to obtain, at the base of the drained layer 3a, a series of circulation passages 14 capable of replacing the drains 7 provided in the previous embodiment.

 Indeed, these passages 14 which communicate freely with the draining layer 3a in geotextile, can both collect the treated water and serve as circulation passages for the organization of air circulation through the filtering layer 2. A for this purpose, these passages 14 are connected to a collecting pipe such as the pipe 9 provided in the previous example, the latter being itself connected both to a fan unit and to a tank for recovering treated water.

 Thus, this device is capable of allowing the implementation of the method according to the invention, under the same conditions as the device described above.

 However, many variants and other embodiments can be envisaged.

 The method and the device according to the invention can be used for the purification of highly polluted water, for example waste water from industrial installations or waste water from a community or urban agglomeration. The tests carried out in a pilot installation corresponding to the device according to the invention have shown that the capacity for eliminating organic pollution from such a device can be of the order of 1.5 Kg of COD (Chemical Demand in Oxygen) through my filter layer. As for the consumption of electric current required to achieve continuous aeration thereof, it is less than 17W per m2 of the infiltration surface.

Claims (6)

 1. Process for the purification of polluted water according to claim 1 of the main patent in which the controlled renewal of the atmosphere in the filtering layer is ensured by the organization of an air circulation inside it, while maintaining this filter layer unsaturated, characterized in that  - on the one hand, the supply of polluted water to the upper surface of the filter layer (2) is ensured by means of a distributor system (4-5) placed above it, thereby reducing considerably, or even completely eliminating, the periods of submersion of the filtering layer (2),  - on the other hand, a draining base layer (3, 3a) made of a material with high permeability such as aggregate or geotextile is provided below this filtering layer (2) made of sand. draining layer, a network of drains (7) or circulation passages (14) which are connected both to a tank (ll) for recovering filtered water and to the disposal (10) for extraction or air intended to ensure air circulation inside the filter layer (2), so that this network is used not only for the recovery of filtered water, but also for the evacuation or arrival of the air flowing through the filter layer.  2. Method according to claim 1, characterized in that the supply of polluted water being carried out continuously, the distributor system (4-5) is adjusted so that the hydraulic load supplied is less than that which would be likely to create a permanent layer of water on the surface of the filter layer (2).  3. Method according to claim 1, characterized in that the supply of polluted water being carried out intermittently, the distributor system (4-5) is adjusted so that the periods of submersion of the filter layer (2) are longer shorter than the periods of emergence thereof.  4. Method according to one of claims 1 to 3, characterized in that the air circulation inside the filtering layer (2) is ensured by a continuous suction of air in the bottom draining layer (3- 3a).  5. Method according to one of claims 1 to 3, characterized in that the air circulation inside the filtering layer (2) is ensured by a continuous discharge of air in the draining lower layer (3- 3a).  6. Device for implementing the method according to claim 1, by controlled renewal of the atmosphere in the filter layer by organizing an air circulation inside thereof, while maintaining this saturated filter layer, characterized in that  - on the one hand, above the filtering layer (2), it includes a distributor system (4-5) for supplying polluted water, which is capable of considerably reducing, or even completely eliminating, the periods of submersion the filter layer (2),  - on the other hand, below it, there is provided a draining base layer (3-3a) of a material of high permeability - such as aggregate or geotextile - inside which is disposed a network of drains (7) or circulation passages (14), connected both to a tank (ll) for recovering filtered water and to the device (10) for extracting or supplying air intended to ensure circulation of air inside the filter layer.