AU2017383081B2

AU2017383081B2 - Facility and process for treating water

Info

Publication number: AU2017383081B2
Application number: AU2017383081A
Authority: AU
Inventors: Sébastien DELAGARDE
Original assignee: Suez International SAS
Current assignee: Suez International SAS
Priority date: 2016-12-22
Filing date: 2017-12-22
Publication date: 2023-06-01
Anticipated expiration: 2037-12-22
Also published as: EP3558874A1; EP3558874B1; CN110088044A; CL2019001738A1; MX2019007523A; FR3061169B1; AU2017383081A1; ES2928416T3; FR3061169A1; WO2018115500A1

Abstract

The invention is within the technical field of water treatment. A subject of the invention is a water treatment facility, comprising: means for conveying the water to be treated 1, optionally a coagulation zone 2 and/or a flocculation zone 3, into which said means for conveying the water to be treated open, a flotation reactor 4 comprising an inlet and a gravity filter 5, the water originating from said flotation reactor can flow by gravity into said gravity filter, the latter has a single-layer filtering media bed distributed over a height of less than 1 m. A facility according to the invention may also comprise a means for washing the gravity filter and/or a membrane filter for the filtration of the water originating from the gravity filter. Another subject of the invention is a water treatment process implemented using a facility according to the invention.

Description

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INSTALLATION AND PROCESS FOR TREATING WATER TECHNICAL FIELD OF THE INVENTION

[0001] The subject matter of the present invention is a water treatment facility for the purpose of potabilization or desalination, and a process implemented using such a facility.

[0002] The technical field of the invention is therefore that of water treatment, more specifically the field of treatment carried out upstream of a membrane filtration step.

DESCRIPTION OF THE PRIOR ART

[0003] In the field of water treatment, in particular for desalination or potabilization, the quality of the water upstream of the filtration membranes is of essential importance for the operation of a facility. This criterion is all the more important when the water to be treated is of particularly "difficult" quality or in the case of specific episodes of extensive growth of algae in the water to be treated.

[0004] Various documents of the prior art describe a water treatment process comprising a step of dissolved air flotation (DAF) combined with a gravity filtration step, optionally conducted prior to a membrane filtration step.

[0005] Conventionally, pre-treatment of water is carried out by means of independent structures such as a DAF facility followed by a filtration device, in particular a gravity filtration device. Such facilities have a considerable footprint.

[0006] A solution to this drawback is to combine structures with a DAFF (DAF filtration) or a DAF-UF (DAF-ultrafiltration) design.

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[0007] International application WO 2014/044619 describes a facility comprising a coagulation zone and a flocculation zone to which is connected a flotation reactor, said flotation reactor communicating with a gravity filter arranged such that the water originating from the flotation reactor flows into the gravity filter. Said gravity filter is distributed over a considerable height of between 1.5 m and 3 m. The filtering medium can be a single-layer medium composed of sand having a particle size of between 0.5 and 0.8 mm, or a multilayer medium, said multilayer medium always comprising at least one layer of sand having a particle size of between 0.5 and 0.8 mm. The rate of the filtration step through the gravity filter is between 10 and 30 m/h.

[0008] International application WO 93/15021 describes a facility comprising a filter through which water that has been pre-treated by flotation passes at a rate of 10 m/h. This filter has a height of 1 m and is composed of a layer of anthracite superposed on a layer of sand, or alternatively of a layer of sand.

[0009] Patent application US2009/0211974 describes a facility comprising a flotation zone and a membrane filtration zone. The filtration membranes are composed of horizontally or vertically juxtaposed modules.

[0010] The DAF-filter solutions of the prior art tend to allow water to be obtained having a quality such that no additional membrane filtration step is necessary. For this reason, these facilities must make use of filtration materials having a fine particle size in order to achieve efficient filtration and sufficient water quality. Indeed, these facilities comprise a layer having a particle size of 0.5 to 0.8 mm for the final filtration step.

[0011] These solutions are disadvantageous in that the filtration rate is limited to that of the filter, i.e. between 10 and 30 m/h, and there is a considerable pressure drop, with the pressure drop being proportional to the height of the medium and the flow rate. Indeed, while a "classical" DAF facility (one not having a filter) can be operated at a rate of up to 40 m/h, in a DAF-filter facility according to the prior art with conventional material heights, the rate is limited to 12 m/h. The solution proposed by a gravity filter as described in WO

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2014/044619, i.e. an increase in the height of the filtration material, increases the pressure drop, but also the total height of the structure, thus resulting in higher costs.

[0012] It is therefore desirable to be able to carry out filtration at rates greater than those described in the prior art, while at the same time limiting the height and cost of the structure.

PRESENTATION OF THE INVENTION

[0013] To this end, an embodiment of the invention relates to a water treatment facility comprising: - means for conveying the water to be treated, - optionally a coagulation zone and/or a flocculation zone, into which said means for conveying the water to be treated open, - a dissolved air flotation reactor comprising an inlet connected to said conveying means, and/or optionally an inlet connected to the outlet of said coagulation and/or flocculation zone, and - a gravity filter, said flotation reactor being at least partially superposed on said gravity filter and communicating with it such that the water originating from said flotation reactor can flow by gravity into said gravity filter, - optionally at least one washing means, in particular a backwashing means, of said gravity filter, and - optionally at least one membrane filter for filtering the water originating from the gravity filter, said gravity filter comprising a single-layer filtering medium bed comprised in a lower wall of said floatation reactor and distributed over a height of less than 1 m, wherein said filtering medium is composed of a layer of granular material having a particle size greater than or equal to 1.5 mm and less than or equal to 5 mm.

[0014] The term "gravity filter" is understood to refer to a porous medium by means of which a solid-liquid mixture is caused to percolate, with the solid

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particles ideally being retained in the intergranular spaces over most of the height of the layer.

[0015] The term "membrane filter" or filter with a membrane refers to a porous support at the surface of which a cake of solid particles is formed. In particular, such a membrane filter may be selected among any ultrafiltration means and any microfiltration means known to the person skilled in the art.

[0016] Said facility may comprise any suitable type of washing means; according to a particular embodiment, the washing means comprises a water and/or air counter-current injection means. The gravity filter may progressively become clogged during use. In order to maintain suitable filtration performance, and depending on the nature of the water treatment facility, washing cycles must be regularly implemented. The absence of washing may result in clogging of certain zones, allowing the water to pass only to a reduced extent, with the result that the pressure drop then increases more rapidly and filtration becomes more rapid and less efficient locally. These washings most often comprise the injection of water, and optionally air, in a counter-current through the gravity filter, and therefore constitute back-washing. The water, and optionally the air, are injected using injection means well known to the person skilled in the art, and make it possible to dislodge the material accumulated in the interstices of the filtering medium, after which said material is eliminated.

[0017] Surprisingly, such a facility allows the implementation of a flotation process followed by filtration in which the filtration rate is greater than 30 m/h.

[0018] The invention is therefore based, in a completely original manner, on the use of a single-layer gravity filter with a limited height after treatment of the water by a DAF step and optionally before a membrane filtration step.

[0019] Indeed, according to the teaching of the prior art, it is necessary to increase the height of filtering medium in order to sharply increase the filtration rate and thus the flow rate of the treated water. The above-mentioned international application WO 2014/044619 in fact specifies a preferred medium

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height of about 3 m, and the total medium height may reach a total of 8 m in the case of three-layer medium (page 10, lines 1-8).

[0020] Moreover, according to the prior art, the smaller the particle size of the filtering medium constituting the gravity filter, the better the quality of the filtered water, and it would therefore be indispensable for the filtering medium present in the gravity filter to comprise at least one layer of filtering medium of fine particle size, such as e.g. sand having a particle size of between 0.5 and 0.8 mm.

[0021] Astonishingly, the quality of the water obtained after treatment with a gravity filter in a facility according to the invention is sufficient to allow a step immediately following membrane filtration, in particular an ultrafiltration step.

[0022] A facility according to the invention does indeed make it possible to obtain a DAF-filter treatment rate that is greater than that of the facilities of the prior art, due in particular to the low height of the filtering medium, but also to the particle size, which is coarser than that ordinarily used for the filtering material. As the outlet water quality is superior to that obtained by means of DAF "alone", the size of the subsequent membrane filtration means can be reduced, thus reducing the cost of a facility.

[0023] An object of the present invention is therefore to provide a simple, reliable and economical method of water treatment and/or at least provide the public with a useful choice. The quality level of the water obtained using a DAF filter facility according to the invention is intermediate between that of DAF treated water and that of DAF filter-treated water according to the prior art, but is nonetheless entirely suitable for the final membrane filtration step. In a facility according to the invention, a single-layer filtering medium is advantageous in that it is less costly than a multilayer medium, and the low height thereof makes it possible to economize on the volume of washing water.

[0024] Particularly advantageously, the single-layer filtering medium bed is distributed over a height greater than or equal to 0.5 m and less than 1 m.

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[0025] Particularly advantageously, the filtering medium bed is composed of a layer of a granular material having a particle size greater than 0.8 mm, preferably greater than 0.8 mm and less than or equal to 5 mm, and preferably greater than 0.8 mm and less than or equal to 4 mm.

[0026] Particularly advantageously, the filtering medium is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm, preferably greater than or equal to 1.5 mm and less than or equal to 5 mm, preferably greater than or equal to 1.5 mm and less than or equal to 4 mm, and more preferably greater than or equal to 2.5 mm and less than or equal to 4 mm.

[0027] A granular material is characterized by various parameters, in particular particle size, which is defined by the two parameters: effective size (ES) and coefficient of uniformity (CU), the shape of the grains: angular (crushed material), round (river or sea sand), or more or less flat (characterized by a flattening coefficient), and brittleness, which allows the selection of materials capable of being used in filtration without the risk of production of fines resulting from washing operations.

[0028] The choice of the most suitable medium for the facility is made by a person skilled in the art according to the known characteristics of each of the materials. This choice depends on the nature of the water to be filtered (direct filtration of untreated water, filtration of decanted water, biological filtration of secondary or tertiary waste water) and on the quality of the water one wishes to obtain. It also depends on the type of filter used and the available pressure drop.

[0029] Particularly advantageously, the granular material is selected among anthracite, pumice stone, Filtralite, activated carbon or zeolite.

[0030] According to an even more particular aspect, in a facility according to the invention, the granular material of the filtering medium of the gravity filter is anthracite.

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[0031] According to an even more particular aspect, in a facility according to the invention, the gravity filter comprises a single-layer anthracite bed, the anthracite being characterized by a particle size greater than or equal to 1.5 mm and less than or equal to 5 mm, and preferably greater than or equal to 1.5 mm and less than or equal to 4 mm.

[0032] Particularly advantageously, the flotation reactor comprises a lower wall that at least partially comprises the filtering medium. More particularly, the lower wall of said flotation reactor comprises the filtering medium.

[0033] Particularly advantageously, at least one part of the lower wall of the flotation reactor comprises a floor supporting said filtering medium. Preferably, in a facility according to the invention, the lower wall of said flotation reactor comprises a floor, in particular of metal, supporting said filtering medium.

[0034] The role of said floor is to ensure: - uniform distribution of the washing fluids, most particularly the washing air, - air- and water-tightness, particularly during the washing phase, - mechanical resistance to ascending forces (washing) and descending forces (filtration, rapid emptying), and - durable operation without intervention.

[0035] Among the floors usable in a facility according to the invention, one can mention floors of the type "Leopold@" or the type "Tetra@ LP Block" from Severn Trent.

[0036] The invention also relates to a water treatment process for the purpose of potabilization or desalination, said process comprising at least one treatment cycle of said water in a facility according to one of the embodiments described above, comprising: - optionally a coagulation and/or flocculation step of the water to be treated,

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- a flotation step in an air dissolved flotation reactor of the water optionally coming from said coagulation and/or flocculation step, - a gravity filtration step in a gravity filter of the water originating from said flotation step, said flotation reactor being at least partially superposed on said gravity filter, - optionally at least one washing cycle of said gravity filter comprising a backwashing step of said gravity filter, and - optionally a membrane filtration step of the water coming from the gravity filtration step, said gravity filter comprising a single-layer filtering medium bed comprised in a lower wall of said flotation reactor and distributed over a height of less than 1 m, wherein said filtering medium is composed of a layer of granular material having a particle size greater than or equal to 1.5 mm and less than or equal to 5 mm.

[0037] The water treated by the process can be used as feed water for a desalting unit or a desalination unit, in particular by reverse osmosis. The treated water can also be conveyed to a potabilization means.

[0038] This process has the essential advantage of making it possible to achieve a water treatment rate of greater than 30 m/h.

[0039] Particularly advantageously, the single-layer filtering medium bed is distributed over a height of less than 1 m and is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm, preferably greater than or equal to 1.5 mm and less than or equal to 5 mm, preferably greater than or equal to 1.5 mm and less than or equal to 4 mm, and more preferably greater than 2.5 mm and less than or equal to 4 mm.

[0040] Particularly advantageously, said gravity filtration step is implemented at a rate greater than 30 m/h.

[0041] Particularly advantageously, said gravity filtration step is implemented at a rate of between 30 m/h and 50 m/h.

[0042] Particularly advantageously, the process according to the invention also comprises a membrane filtration step of the water after the gravity filtration step, in particular an ultrafiltration step.

BRIEF DESCRIPTION OF THE FIGURES

[0043] Other characteristics and advantages of the invention will be found in the following description with reference to Fig. 1, which shows a water treatment facility according to an embodiment of the invention.

DETAILED DESCRIPTIONOFAN EMBODIMENT

[0044] Fig. 1 shows a water treatment facility, said facility comprising: * means for conveying the water to be treated 1, Sa coagulation zone 2 into which said conveying means 1 of the water to be treated open, Sa flotation reactor 4 comprising an inlet connected to the outlet of a flocculation zone 3, and Sa gravity filter 5, said flotation reactor 4 being at least partially superposed on said gravity filter 5 and communicating with it such that the water originating from said flotation reactor can flow by gravity into said gravity filter, said gravity filter comprising a single-layer filtering medium bed distributed over a height of less than 1 m.

[0045] In the coagulation zone 2 of the facility of Fig. 1, a coagulant 7 can be added to and then mixed with the water to be treated using suitable means. The addition of a coagulant, such as in particular ferric chloride or aluminium sulphate, causes coagulation of the colloidal particles and the particles in suspension in the water to be treated, in particular algae, phytoplankton and a portion of the organic matter. Once their charges have been neutralized, the colloids agglomerate with one another by piston-type agitation to form "floc" in the hydraulic flocculation zone 3. In the flocculation zone 3 of the facility of Fig. 1, a flocculating agent 8 (or coagulation adjuvant) can be added to and then mixed with the water to be treated using suitable means. The addition of a

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flocculating agent allows agglomeration of the particles into larger-sized clusters. The water, which has first been coagulated and also flocculated, is then conveyed to the zone for injection of water supersaturated with oxygen 9, atmospheric nitrogen, or any other suitable gas. Due to the effect of expansion of the gas inside the flotation reactor 4, gas bubbles form while rising to the surface of the flotation reactor 4, conveying with them any floc present in the water. The mixture of air bubbles and floc can then be evacuated by overflowing from the separation zone 10 of the flotation reactor, in particular via a chute 11 into which it can be pushed by means of a scraping device provided for this purpose.

[0046] The facility of Fig. 1 also comprises a gravity filter 5, with the flotation reactor 4 being at least partially superposed on this gravity filter 5 and communicating with it such that the water originating from said flotation reactor can flow by gravity into said gravity filter. This gravity filter accommodates a single-layer filtering medium, i.e. composed of a single layer of a given filtering material, said medium being distributed over a height of less than 1 m. The treated water originating from the gravity filter is then conveyed via a conveying means 6 and can then optionally be filtered by means of a membrane filter.

[0047] The water treatment process implemented by the facility of Fig. 1 comprises one or several successive treatment cycles consisting of introduction of the water to be treated using conveying means 1 into the coagulation tank 2 and then into the flocculation tank 3. At least one coagulating reagent 7 and at least one flocculating reagent 8 are injected and mixed with the water to be treated. Under the effect of the coagulating reagent, the colloidal particles and particles in suspension present in the water to be treated agglomerate and form floc. The water is then filtered through the gravity filter 5, and the water originating from said filtration is conveyed by a conveying means 6 and can then be treated by any membrane filtration process, in particular ultrafiltration or microfiltration.

[0048] Comparative water treatment tests were conducted in a facility according to the invention in the presence of various single-layer gravity filters

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having a height of 0.8 m, consisting of a filtering medium with a particle size of 1.5 mm; 4 mm or 5 mm.

[0049] In these tests, a filtering medium having respective particle sizes of 1.5; 4 or 5 mm is obtained using anthracite specified by the manufacturer for a particle size of between 1 and 3 mm, between 3 and 5 mm or between 5 and 8 mm, respectively.

[0050] Various parameters are measured and compared, in particular the quality of the water treated after filtration with each of the gravity filters and its suitability for a subsequent membrane filtration step. The rate of passage through each of the gravity filters is also determined.

[0051] These results show the favourable efficacy of a filtration means according to the invention compared to the means known in the prior art.

[0052] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of "including, but not limited to". Conditional language used herein, such as, among others, "can,""could,""might,""may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

[0053] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art

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forms part of the common general knowledge in the field of endeavour in any country in the world.

[0054] The disclosure may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

[0055] Where, in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

Claims

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1. A water treatment facility comprising: - means for conveying the water to be treated, - a dissolved air flotation reactor comprising an inlet connected to said conveying means, and - a gravity filter, said flotation reactor being at least partially superposed on said gravity filter and communicating with it such that the water originating from said flotation reactor can flow by gravity into said gravity filter, said gravity filter having a single-layer filtering medium bed comprised in a lower wall of said flotation reactor and distributed over a height of less than 1 m, wherein said filtering medium is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm and less than or equal to 5 mm.

2. The facility as claimed in claim 1, wherein the facility comprises a coagulation zone and/or a flocculation zone, into which said means for conveying the water to be treated open.

3. The facility as claimed in claim 2, wherein the said inlet of the dissolved air flotation reactor is further connected to the outlet of said coagulation and/or flocculation zone.

4. The facility as claimed in claim 2, wherein the said dissolved air flotation reactor additionally comprises an inlet connected to the outlet of said coagulation and/or flocculation zone.

5. The facility as claimed in any of claims 1 to 4, wherein the facility comprises at least one washing means of said gravity filter.

6. The facility as claimed in claim 5, wherein said at least one washing means is a backwashing means of said gravity filter.

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7. The facility as claimed in any of claims 1 to 6, wherein the facility comprises at least one membrane filter for filtering the water originating from the gravity filter.

8. The facility as claimed in any of claims 1 to 7, wherein said single-layer filtering medium bed is distributed over a height greater than or equal to 0.5 m and less than 1 m.

9. The facility as claimed in any of claims 1 to 8, wherein said filtering medium is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm and less than or equal to 4 mm, and more preferably greater than or equal to 2.5 mm and less than or equal to 4 mm.

10. The facility as claimed in any of claims 1 to 9, wherein said granular material is selected among anthracite, pumice stone, Filtralite, activated carbon or zeolite.

11. The facility as claimed in claim 1, wherein said lower wall of said flotation reactor comprises a floor supporting said filtering medium.

12. A water treatment process for the purpose of potabilization or desalination, said process comprising at least one treatment cycle of said water in a facility as claimed in one of claims 1 to 11 comprising: - a flotation step in an air dissolved flotation reactor of the water, - a gravity filtration step in a gravity filter of the water originating from said flotation step, said flotation reactor being at least partially superposed on said gravity filter, - optionally a membrane filtration step of the water coming from the gravity filtration step, said gravity filter having a single-layer filtering medium bed comprised in a lower wall of said flotation reactor and distributed over a height of less than 1 m, wherein said filtering medium is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm and less than or

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equal to 5 mm.

13. The water treatment process as claimed in claim 12, wherein the process comprises a coagulation and/or flocculation step of the water to be treated prior to the said flotation step.

14. The water treatment process as claimed in claim 13, wherein the said flotation step in an air dissolved flotation reactor is of the water coming from said coagulation and/or flocculation step.

15. The water treatment process as claimed in any of claims 12 to 14, wherein following said gravity filtration step, the process comprises at least one washing cycle of said gravity filter comprising a backwashing step of said gravity filter.

16. The water treatment process as claimed in any of claims 12 to 15, wherein the process comprises a membrane filtration step of the water coming from the gravity filtration step following the said gravity filtration step.

17. The water treatment process as claimed in any of claims 12 to 16, wherein said single-layer filtering medium bed is distributed over a height of less than 1 m and is composed of a layer of a granular material having a particle size greater than or equal to 1.5 mm and less than or equal to 4 mm, and more preferably greater than 2.5 mm and less than or equal to 4 mm.

18. The water treatment process as claimed in any of claims 12 to 17, wherein said gravity filtration step is implemented at a rate greater than 30 m/h.

19. The water treatment process as claimed in any of claims 12 to 18, wherein said gravity filtration step is implemented at a rate of between 30 m/h and 50 m/h.

20. The water treatment process as claimed in any of claims 12 to 19, also comprising a membrane filtration step of the water after the gravity filtration step, in particular an ultrafiltration step.