MODULAR WATER TREATMENT PLANT USING FLOTATION

Description

Field of Invention

[0001] The field of the invention is that of water treatment with a view to purifying or making it potable.

[0002] More particularly, the invention relates to a flotation water treatment plant. Prior art

[0003] Contaminated liquids or water may contain suspended matter (particles, algae, bacteria, etc.) and dissolved matter (organic matter, micropollutants, etc.). There are several techniques available in the state of the art for treating suspended matter with the aim of reducing its levels.

[0004] These techniques include decantation and flotation.

[0005] Water treatment by flotation has many advantages over treatment by settling.

[0006] A first advantage is that the speed of treatment of water by flotation is higher than the speed of treatment by conventional decantation.

[0007] Another advantage is that flotation treatment achieves better removal of algae, as well as oils and greases compared to settling treatment for a higher flow rate of water to be treated.

[0008] Furthermore, another advantage of flotation treatment is that it reduces the volume of sludge produced.

[0009] Among the flotation processes, we distinguish: natural flotation, where the difference in density between the suspended matter and the water that contains it is naturally sufficient to allow their separation (the matter floats on the surface of the water); assisted flotation, which consists of blowing air bubbles into the mass of liquid to improve the separation of the particles and thus make them floatable; induced flotation, where the density of the suspended matter is initially greater than that of the water that contains it and is artificially reduced using gas bubbles. Indeed, certain solid or liquid particles can combine with gas bubbles to form “particle-bubble” bonds that are less dense than the water that contains them; Dissolved air flotation (DAF) is an induced flotation process that uses bubbles of very small diameter, in practice 40 to 70 micrometers in diameter.It generally involves a combination of different stages: coagulation to neutralize the surface charges of the colloids, and adsorption of dissolved materials; flocculation, using a flocculating polymer material allowing the agglomeration of the particles; injection of pressurized water allowing the microbubbles and the flocculated water to come into contact; separation allowing the separation of the floc and the clarified liquid; collection of the clarified liquid; collection of the floated "sludge".

[0010] The FAD technique is traditionally applied in the context of water purification, to good quality water, to cold water with little suspended matter, and especially to reservoir water rich in algae. FAD also finds its application in the treatment of municipal or industrial wastewater for purification.

[0011] Thus, document FR 2 916 196 A1 discloses a flotation installation typical of the prior art. Also disclosed by WO2008142026 is a flotation installation comprising a tank for contacting the water to be treated with air microbubbles, an area provided under this tank and separated from it by a perforated floor accommodating nozzles for injecting air microbubbles, and a flotation tank separated from the contact tank by a wall crossed in its upper part by the mixture of water and air microbubbles.

[0012] In this installation, the contact tank is provided at one end of the flotation tank, which has the disadvantage that within the contact tank the distribution of air microbubbles is not uniform but rather undergoes a gradient. In practice, there are more air bubbles in the area of ​​the flotation tank close to the contact tank than in the area of ​​the flotation tank far from it. This gradient leads to inhomogeneous treatment of the water arriving in the installation. Some of this water receives more air bubbles than the rest and is therefore better treated.

[0013] Another disadvantage is the design and dimensions of this installation, which makes it difficult to transport, particularly by container. However, there is a growing need on the market for water treatment installations, and in particular flotation units, which can be easily transported, particularly in containers that can be loaded onto container ships, so that they can be taken to sites far from their manufacturing site. This occurs, for example, when these installations are intended for use at natural disaster sites where water treatment facilities have been damaged or destroyed, or for rental for specific needs.

[0014] Another disadvantage is that such installations are not modular. However, there is a growing market demand for water treatment installations, particularly flotation units, which are modular in nature, allowing them to offer different treatment capacities and to avoid the use of oversized installations, which increase treatment costs.

[0015] In this regard, it should be noted that the Applicant has already proposed modular flotation installations, described in Italian patent applications ITTO20080399A1 ITTO20080401A1 and ITTO20080402A1. Such installations are made up of the combination of modules each having a U-shaped section with a side wall provided with a recess delimiting a contact zone with the water to be treated, a flocculant and white water. Thus, each module has on one of its walls, a recess in which the contact between the water to be treated and the white water is made. These installations are modular and make it possible to give the installation a more or less high capacity depending on the number of modules used to make it.

[0016] However, due to their dimensions (bulk), these installations are also not transportable in standard containers for maritime transport.

[0017] In addition, the fact that each module has its own dedicated contact area, in practice a recess, complicates the manufacturing of the modules and impacts the overall cost of such floats.

[0018] Finally, with this type of installation, it is necessary to regulate the production of white water before it is started, which in practice, leads to limiting the speed at which the water to be treated passes through it and limits its capacity. Objectives of the invention

[0019] The present invention aims to propose a modular flotation installation, which is simple to produce.

[0020] Another objective of the installation is to describe such an installation that is compact and transportable on a standardized container for maritime transport. Statement of the invention

[0021] All or part of these objectives are achieved by means of an installation according to claim 1.

[0022] The invention therefore proposes to arrange the contact tank no longer at the end of the flotation tank, as for example in the prior art according to WO2008056057, but along the latter. Concomitantly, the invention also provides that the contact tank delimits a contact zone common to all the modules, thus resolving the problem of complexity of production linked to the technique according to ITTO20080399A1, ITTO20080401A1 and ITTO20080402A1.

[0023] Modularity allows the installation to have a greater or lesser capacity depending on the number of modules used to create it.

[0024] According to the invention, the flow of water to be treated brought into the contact tank is perpendicular to the flow of water in the flotation tank. This goes against the practices of those skilled in the art who, conventionally, for a better distribution of mass and hydraulic flows within a flotation unit, plan to inject the water to be treated in a manner parallel to the distribution of the water in the flotation tank.

[0025] The dimensions of the modules will be chosen to allow the creation of installations according to the invention whose size will allow their transport in standardized containers for maritime transport.

[0026] Preferably, these modules will be designed in such a way that the installation obtained by associating them has a flotation tank whose height (H) is between 1 and 4 m, preferably between 1 and 2.5 m, and whose width (L) is between 0.5 and 4 m. It will be noted that height (H) means the distance between the water collection point present in the bottom of the flotation tank and the level at which the floated water is collected. Width (L) of the flotation tank is also understood to mean the distance between the vertical wall separating the contact tank and the flotation tank and the wall opposite it.

[0027] Advantageously, said means for supplying white water into the contact tank include a multiphase pump associated with nozzles capable of producing bubbles of very small diameter, in practice 40 to 70 micrometers in diameter.

[0028] The use of such nozzles allows the installation according to the present invention to be implemented at higher water mirror speeds in the flotation unit, in practice of the order of 20 to 25 m / h, than those which can be implemented with the flotation units of the prior art, generally limited to 10 m / h for similar water qualities.

[0029] Also advantageously, said means for supplying white water into the contact tank include a multiphase pump and a static mixer associated with nozzles capable of producing bubbles of very small diameter.

[0030] According to a preferred variant, said nozzles are provided at a height (h) from the bottom of said contact tank of between 0.2 and 2 meters.

[0031] Said nozzles are preferably provided with a nozzle density of between 3 and 30 nozzles, preferably between 5 and 12 nozzles, per square meter of bottom of the contact tank.

[0032] Also according to a variant, said assembly is produced by the association of 2 to 24, preferably 2 to 12 modules.

[0033] As already indicated above, the installations according to the invention have a size which allows their transport by standardized container for maritime transport.

[0034] Thus, preferably, the total length (TL) of the installation according to the invention is between 0.5 and 20 m, preferably between 1 and 12 m.

[0035] According to the invention, said means for supplying water to be treated into said contact tank comprise a perforated pipe provided longitudinally in the lower part of said contact tank.

[0036] Advantageously, said means for discharging treated water comprise at least one perforated pipe provided longitudinally in the lower part of said flotation tank.

[0037] Preferably, said means for discharging floating sludge comprise a scraper provided with means for moving along a longitudinal axis, transverse to the water distribution flow in the flotation tank.

[0038] Also preferably, the ratio between the height (H) of the flotation tank and its width (L) is greater than 1.1. List of figures

[0039] An embodiment, given merely as an example, of the flotation installation according to the present invention will now be described in detail, with reference to the drawings in which: [ Fig 1 ] there figure 1 represents a perspective view of an embodiment of the present invention; [ Fig 2 ] there figure 2 represents a partially transparent perspective view of this embodiment; [ Fig 3 ] there figure 3is a horizontal sectional view PP' of the installation intended to explain the water flows in the tanks thereof; [ Fig 4 ] there figure 4 is a perspective view of one of the modules constituting the set of contact and flotation tanks of this installation; [ Fig 5 ] there Figure 5 is a schematic top view of the contact and flotation tank assembly of this installation; [ Fig 6 ] there figure 6 is a side sectional view of the contact and flotation tank assembly of this installation; [ Fig 7 ] there figure 7 is a graph indicating the reduction of suspended matter in an effluent using a flotation installation of the prior art according to WO2008142026; [ Fig 8 ] there figure 8 is a graph indicating the contents of suspended matter at the inlet and outlet of a flotation installation according to the invention of the same effluent; [ Fig 9 ] there figure 9is a photograph taken from above the contact tank of the installation according to the invention described with reference to Figure 1 to 6 during the tests which allowed the development of the graph according to the figure 8 . Method of carrying out an installation according to the invention

[0040] In reference to the Figure 1 to 6 , the installation shown comprises a set 1 of tanks having a parallelepiped shape arranged on a chassis 1a. In addition to this set 1, this chassis 1a receives means for producing white water 10.

[0041] This set of tanks is made by combining two modules 2 as shown in the figure 4 It should be noted that in other embodiments it will obviously be possible to use more than two modules to produce said assembly.

[0042] These modules 2 are connected to each other and associated with end walls 2a and 2b to form the assembly 1 according to techniques known to those skilled in the art and thus produce a contact tank 3 and a flotation tank 6.

[0043] The contact tank 3 is provided with means for supplying water to be treated 4 and means for supplying white water 5.

[0044] The means for supplying water to be treated 4 include a perforated pipe provided in the lower part of the contact tank 3, longitudinally thereto.

[0045] The white water supply means 5 include a supply pipe equipped with nozzles 5a (see figure 6 ) allowing the generation of very small diameter air bubbles and connected to a multiphase pump (not shown).

[0046] This pipeline is planned to run parallel to the pipeline for the means of supplying water to be treated 4, above it. As can be seen on the figure 6, these nozzles are thus provided in the contact tank at a height (h) from the bottom 3a thereof, between 0.2 and 2 meters. The density of nozzles on the pipeline is studied in order to optimize the flotation process in the flotation tank and is, in practice, advantageously between 3 and 30 nozzles per square meter of bottom of the contact tank.

[0047] The flotation tank 6 is further provided with means for discharging treated water comprising two pipes 7, 7a provided in its lower part. The flotation tank 6 is separated from said contact tank by a vertical wall 8.

[0048] The flotation tank is also equipped with means for discharging floated sludge comprising a spillway 9 and a scraper 11 (visible on the Figure 5 ).

[0049] According to the invention, said contact tank 3 is provided along said flotation tank 6 and delimits a single contact zone of said water to be treated with said white water.

[0050] Also according to the invention, and with reference to the figure 3 , the means for supplying water to be treated 4 are designed to distribute the water to be treated in the contact tank 3 according to a longitudinal water supply flow, the distribution flow (A) of water in the flotation tank 3 being perpendicular to the water supply flow (B) in the contact tank 6.

[0051] In operation, the water to be treated is conveyed into the single flotation zone delimited by the flotation tank 3, via pipe 4, where it is brought into contact with the white water supplied by pipe 5 fitted with nozzles.

[0052] The very fine air bubbles dispensed by these nozzles immediately mix with the water to be treated and this mixture overflows through the wall 8 to enter the flotation tank 6. In this tank 8, the flotation of the materials to be separated from the water takes place thanks to the action of the air bubbles which, by mixing with these materials, reduce their density and therefore make them float.

[0053] Periodically, the scraper 11 is used to push the materials floating on the surface of the water present in the flotation tank but also in the contact tank towards the overflow 9, in order to be evacuated from the installation for possible treatment. For this purpose, this scraper has an axis 11a of movement perpendicular to the treatment flow A of the water in the flotation tank 6.

[0054] It will therefore be noted that the scraper 11 is designed to scrape both the surface of the water present in the flotation tank 6 and that present in the contact tank 3. Correspondingly, the spillway 9 extends transversely to these two tanks in order to be able to receive the floated materials.

[0055] The treated water is recovered in the lower part of the flotation tank via pipes 7 and 7a. Comparative tests

[0056] The flotation plant according to the invention described above and a flotation plant of the prior art according to WO2008142026 were implemented to treat an effluent consisting of water from a dairy industry.

[0057] In comparison, the installation according to the invention is much more compact than the tested prior art installation. In practice, this installation according to the invention is 30% smaller than the latter.

[0058] Furthermore, compared to this installation of the prior art, the installation according to the invention is modular and transportable in a container whereas that of the prior art is neither modular nor transportable.

[0059] Different batches of said effluent were treated by the installation according to WO2008142026 and, for each batch, the suspended solids (SS) contents at the inlet on the raw water and at the outlet of the installation on the clarified water were measured to deduce, for each batch, the reduction rate, expressed in %, in these materials.

[0060] During these tests, a coagulant and a flocculant were injected into the installation.

[0061] The tests were carried out by passing the effluent through the installation at a mirror speed of 26 m / h.

[0062] In reference to the figure 7 , variable rates of reduction of suspended matter depending on the batches were observed from 85% to 98%.

[0063] Different batches of the same effluent were then treated using the embodiment of the invention described with reference to Figure 1 to 6 .

[0064] In reference to the figure 8 , for each batch, the suspended solids contents (TSS) at the inlet and outlet of the installation were measured. Based on these measurements, the suspended solids reduction rates were calculated and proved to be entirely comparable to those obtained with the installation according to WO2008142026.

[0065] The tests were carried out by passing the effluent through the installation at mirror speeds also similar to those implemented with the prior art installation, varying from 20 to 25 m / h depending on the batches.

[0066] These comparative tests demonstrate that the installation according to the invention allows treatment performances equivalent to those of the installation of the prior art while being 30% smaller than the latter.

[0067] This results from the better distribution of white water in the contact tank made possible by the invention. With reference to the photograph according to the figure 9 , which shows a uniformly white tint of the mixture of effluent and white water present in the contact tank of the installation according to the Figure 1 to 6 , the invention in fact makes it possible to distribute the white water uniformly in the contact tank and therefore to ensure that the entire treated effluent is brought into contact with the same quantity of white water.

Claims

1. Installation for treating water by flotation, comprising a substantially parallelepipedal assembly (1) produced by connecting modules (2, 2a), said assembly comprising a contact tank (3) which is provided with supply means for water to be treated (4) including a perforated pipe provided longitudinally in its lower part and supply means for white water (5) including a supply pipe for white water provided with nozzles, said supply pipe for white water being provided parallel and above said perforated pipe, a flotation tank (6) which is provided with means for discharging treated water (7, 7a), said flotation tank (6) being separated from said contact tank by a vertical wall (8), and means for discharging floated sludge, characterised in that said contact tank (3) is provided along said flotation tank (6) and delimits a single contact zone for said water to be treated with said white water, and in that said supply means for water to be treated (4) are configured to distribute the water to be treated in said contact tank according to a longitudinal water supply flow through said perforated pipe, the water distribution flow in the flotation tank (A), which correspond to the flow of water which cross by overflow said vertical wall (8) to go from the contact tank (3) to the flotation tank (6), being perpendicular to said water supply flow (B) in said contact tank.

2. Installation according to claim 1, characterised in that the height (H) of the flotation tank is comprised between 1 and 4 m, preferably between 1 and 2.5 m, and that the width (L) of the flotation tank is comprised between 0.5 and 4 m.

3. Installation according to claim 1 or 2, characterised in that said means for supplying white water in the contact tank include a multiphase pump associated with nozzles capable of producing bubbles of a very small diameter.

4. Installation according to claim 3, characterised in that said means for supplying white water in the contact tank include a multiphase pump and a static mixer associated with nozzles capable of producing bubbles of a very small diameter.

5. Installation according to claim 3 or 4, characterised in that said nozzles are provided at a height (h) from the bottom of said contact tank comprised between 0.2 and 2 metres.

6. Installation according to claim 5, characterised in that said nozzles are provided with a nozzle density comprised between 3 and 30 nozzles, preferably between 5 and 12 nozzles, per square metre of said contact tank bottom.

7. Installation according to any one of the preceding claims, characterised in that said assembly is produced by connecting 2 to 24, preferably 2 to 12, modules.

8. Installation according to any one of the preceding claims, characterised in that its total length (LT) is comprised between 0.5 and 20 m, preferably between 1 and 12 m.

9. Installation according to any one of the preceding claims, characterised in that said means for discharging treated water comprise at least one perforated pipe provided longitudinally in the lower part of said flotation tank.

10. Installation according to any one of the preceding claims, characterised in that said means for discharging floating sludge comprise a scraper provided with means for moving along a longitudinal axis, transverse to the water distribution flow (A) in the flotation tank.

11. Installation according to any of the preceding claims, characterised in that the ratio between the height (H) and the width (L) of the flotation tank is greater than 1.1.