WATER TREATMENT SYSTEM AND METHOD

Abstract

TITLE OF THE INVENTION: WATER TREATMENT SYSTEM AND METHOD The water treatment system (100) (101) comprises: - a selective nanofiltration device (115), connected to an inlet (105) of water to be treated, - an outlet (120) of a first permeate (116) from the nanofiltration device, - an outlet (125) of the first concentrate (117) from the nanofiltration device, - a reverse osmosis device (130), connected to the outlet of the first permeate from the nanofiltration device and configured to form: - an outlet (135) of a second permeate (131) from the reverse osmosis device, - an outlet (140) of a second concentrate (132) from the reverse osmosis device, and - a connection (145) between the outlet of the first concentrate and the outlet of the Second permeate. Figure for the abbreviation: Figure 1

Description

Title of the invention: WATER TREATMENT SYSTEM AND METHOD Technical field of the invention

[0001] The present invention relates to a system and a method for water treatment. It applies, in particular, to the field of water desalination, for example natural or wastewater. State of the art

[0002] Natural or wastewater contains compounds such as mineral solutes, including dissolved salts, or organic solutes. In natural waters, such compounds are naturally present, whereas in wastewater, these compounds originate from inputs related to human, agricultural, and industrial activities.

[0003] Depending on the application and intended use of the water, some dissolved compounds are undesirable while others can be beneficial. For example, in irrigation applications, treated wastewater from sewage treatment plants generally contains a high sodium load. Such a load gives the wastewater a salinity incompatible with agronomic needs. For example, irrigating vineyards with water having a high salinity results in reduced crop yields, soil degradation, and groundwater pollution. The total salinity of the water, including its mineral composition and the proportions of the different salts, significantly influences plant growth and soil fertility.

[0004] The SAR, an acronym for "Sodium Adsorption Ratio," of water is an indicator of the balance between sodium salts, known as monovalent salts, and calcium and magnesium salts, known as divalent salts. In particular, such an SAR reflects the quality of the water in order to determine whether such water is suitable for irrigating crops, for example. The SAR is defined, for example, according to the following equation:

[0005] [Math.01] IAA?*1 54 / ? ™ Vl / 2([Ca2+] 4- [w2+])

[0006] in which: - [Na+] is the concentration of monovalent species Na+, called sodium ion, - [Ca2+] is the concentration of divalent species Ca2+, called calcium ion, and - [Mg2+] is the concentration of divalent species Mg2+, called magnesium ion.

[0007] Preferably, a SAR, considered acceptable for a plant, has a value less than 18.

[0008] A correction in the proportion of monovalent salts relative to divalent salts and a reduction in the overall salinity of the water are necessary for the application of this salt-rich water for irrigating crops or green spaces. Such correction and reduction notably limit problems with plant growth and soil salinization.

[0009] Furthermore, in the case of natural water resources, such waters may, for example, have a problem of limited mineral concentration but are polluted by nitrates, such as the NO3 anion, and / or ammonium, such as the NH4+ cation. Natural waters originate, for example, from groundwater or from surfaces polluted by human activity, such as agriculture and wastewater discharge. Such anthropogenic pollution renders the water unsuitable for use as drinking water, for example.

[0010] Prior art solutions proposing a way to reduce the total salinity of water disclose the use of a reverse osmosis device. However, such a device results in the rejection of all minerals without a significant degree of selectivity for monovalent and divalent salts. More specifically, undesirable monovalent salts preferentially pass through the membrane of the reverse osmosis device via ion leakage. Such treatment by a reverse osmosis device of water with or without mixing of raw water upstream of the treatment: - does not ensure a reduction in overall salinity and - does not exhibit selectivity towards divalents or other molecules of interest, such as agronomic molecules, for example.

[0011] Thus, a reverse osmosis device does not allow a result to be obtained in accordance with the needs, constraints and / or standards imposed.

[0012] Furthermore, other prior art solutions proposing a way to reduce the total salinity of water disclose the use of a nanofiltration device. Such filtration is selective for divalent ions, meaning that such ions are retained by the nanofiltration membrane and concentrate in the solution called the concentrate. Thus, the permeate resulting from such nanofiltration is rich in monovalent ions and partially demineralized. A reverse selectivity is therefore obtained, exacerbating the initial imbalance defined by the SAR of the water.

[0013] Furthermore, other prior art solutions disclose the use of an electrodialysis device. However, similarly to the nanofiltration device, the permeate from the electrodialysis device is partially demineralized and consists mainly of monovalent ions.

[0014] Furthermore, other prior art solutions disclose the use of a device incorporating an ion exchange mechanism. However, such a device does not prioritize the selection of divalent cations, such as Ca2+ and Mg2+, over monovalent ions. Specifically, only denitrification, corresponding to a reduction in nitrate ions (NO3), is achieved, for example, through ion exchange using a strong anionic resin and exchange with bicarbonate or chloride salts. Nevertheless, such a resin enriches the water with an exchanged anion, such as chloride, and therefore generates effluents with a high mineral concentration and very low chemical efficiency. Furthermore, such a solution has negative operating costs and environmental impacts.

[0015] Finally, other solutions of the prior art correspond to chemical precipitation techniques, but do not allow the reduction of the nitrate NO3 or sodium Na+ content of the waters. Summary of the invention

[0016] The present invention aims to remedy all or part of these drawbacks. In particular, the system of the invention is based on the combined use of a nanofiltration and reverse osmosis device.

[0017] The system that is the subject of the invention therefore offers a solution to meet the need for partial or total demineralization and the necessity of selecting beneficial species. The system that is the subject of the invention allows: - production of waters enriched in divalent or trivalent ions at the expense of monovalent ions, for example such as divalent ions Ca2+ and Mg2+ at the expense of the monovalent ion Na+, or divalent ions SO42 and PO43 at the expense of the monovalent ion Cl; - a reduction in mineral concentration in proportions adjustable by the system and - a conservation of a nutrient organic load present in wastewater, for wastewater reuse applications in irrigation.

[0018] The method of the present invention has advantages similar to those stated for the system of the present invention. Brief description of the figures

[0019] Other advantages, purposes and particular features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of the system and method that are the subject of the present invention, with reference to the accompanying drawings, in which:

[0020] [Fig. 1] schematically represents a first particular embodiment of the system that is the subject of the present invention,

[0021] [Fig.2] schematically represents a second particular embodiment of the system which is the subject of the present invention,

[0022] [Fig.3] schematically represents a third particular embodiment of the system which is the subject of the present invention,

[0023] [Fig.4] schematically represents a fourth particular embodiment of the system which is the subject of the present invention,

[0024] [Fig.5] schematically represents a fifth particular embodiment of the system which is the subject of the present invention,

[0025] [Fig.6] schematically represents a sixth particular embodiment of the system which is the subject of the present invention,

[0026] [Fig.7] schematically represents a seventh particular embodiment of the system which is the subject of the present invention, and

[0027] [Fig.8] represents, schematically and in the form of a flowchart, a succession of a particular step in the process which is the subject of the present invention.

[0028] Terminology

[0029] The expression "and / or", as used in this document and in the claims, shall be understood as meaning "either or both" of the elements thus joined, that is, elements that are present conjunctively in some cases and disjunctively in others. The multiple elements listed with "and / or" shall be interpreted in the same way, that is, "one or more" of the elements thus joined. Other elements may be present, other than the elements specifically identified by the "and / or" clause, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with open language such as "comprising" may refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0030] As used herein in the description and in the claims, "or" is to be understood as having the same meaning as "and / or" as defined above. For example, when separating elements in a list, "or" or "and / or" is to be interpreted as inclusive, that is, the inclusion of at least one, but also more than one, of a number or list of elements, and, optionally, of additional unlisted elements. Only terms clearly indicating the contrary, such as "only one of" or "exactly one of", or, when used in the claims, "consisting of", refer to the inclusion of only one element of a number or list of elements.

[0031] As used in this description and in the claims, The expression "at least one," when referring to a list of one or more elements, should be understood as meaning at least one element chosen from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements to which the expression "at least one" refers, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, optionally including more than one, A, without B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, without A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0032] In the claims, as well as in the description below, all transitive expressions such as "comprising", "including", "carrying", "having", "containing", "implying", "holding", "composed of", and others, shall be understood as open, that is to say, as meaning including, but not limited to. Only the transitive expressions "consisting of" and "consisting essentially of" shall be understood as closed or semi-closed transitive expressions, respectively.

[0033] The following definitions are recalled here: - The term "monovalent salt" refers to a salt consisting of two monovalent ions, one with a positive charge denoted "+" and the other with a negative charge denoted "-"; - The term "monovalent ion" refers to an ion with only one negative or positive charge; - The term "divalent salt" refers to a salt consisting of two divalent ions with two positive charges "2+" and two negative charges "2-" respectively; - The terms "divalent ion" and "trivalent ion" refer to an ion with two negative or positive charges, or, respectively, three positive or negative charges. - The term "ion" is a generic term designating monatomic ions, such as Ca2+, Mg2+ and Na+ ions, and polyatomic ions SO42, NH4+, NO3; - The term "mineral concentration" refers to the total concentration, that is, the sum of the concentrations, of the mineral species present in waters; - The term "mineral species" refers, in a non-restrictive manner, to a monovalent salt or a divalent salt; - The term "water to be treated" refers to water with an ion concentration greater than a predetermined value, such a value being a threshold defined according to, for example, the needs, standards and uses of such water.

[0034] Description of embodiments

[0035] The present description is given by way of non-limiting grammar, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0036] It should be noted from the outset that the figures are not to scale.

[0037] Figure [1], which is not to scale, shows a schematic view of a mode of implementation of the system 100 which is the subject of the present invention. The system 100 is a water treatment system for water 101, referred to as water to be treated 101, having a predetermined mineral concentration and a predetermined concentration of monovalent salts.

[0038] It is noted that a predetermined mineral concentration corresponds to a total concentration of mineral species having a defined value, such a value being dependent, for example, on the nature of the water to be treated 101. Similarly, a predetermined concentration of monovalent salts is equal to a defined value, such a value being dependent, for example, on the nature of the water to be treated 101. It is also noted that the mineral concentration of the water 101 depends on the concentration of monovalent salts present in this water 101.

[0039] It can be seen in [Fig. 1] that the water treatment system 100 101 comprises: - a first inlet of 105 of water to be treated, 101 - a selective nanofiltration device 115, - an outlet 120 of a first permeate 116 from the nanofiltration device 115, - an outlet 125 of a first concentrate 117 from the nanofiltration device 115, - a reverse osmosis device 130, - an outlet 135 of a second permeate 131 from the reverse osmosis device 130, - an outlet 140 of a second concentrate 132 from the reverse osmosis device 130, - a connection 145 between the outlet 125 of the first concentrate 117 and the outlet 135 of the second permeate 131, and - a production 146 resulting from connection 145.

[0040] Selective nanofiltration device

[0041] As can be seen in [Fig. 1], the selective nanofiltration device 115 is connected to the inlet 105 of the water to be treated 101. Such a nanofiltration device 115 is configured to form: - a first permeate 116 selectively containing monovalent salts and - a first concentrate 117 selectively containing divalent salts.

[0042] It is noted that the monovalent salts present in the first permeate 116 correspond to the ions associated with such salts and capable of crossing predominantly the membrane of the nanofiltration device 115. In particular, such ions have a defined size in aqueous solution smaller than the size of the pores of the nanofiltration membrane.

[0043] It is noted that the divalent salts present in the first concentrate 117 correspond to the ions associated with such salts and unable to cross the membrane of the nanofiltration device 115. In particular, such ions have a defined size in aqueous solution greater than the size of the pores of the nanofiltration membrane and are mostly retained by such a membrane.

[0044] In other words, the nanofiltration device is a membrane device with a so-called "cutoff" threshold corresponding to a rejection of divalent species significantly greater than the rejection of monovalent species. It should be noted that divalent species are, for example, respectively expressed by the following formulas: CaSO4 and NaCl. It should be noted that such a cutoff threshold defines the selectivity of the so-called "selective" nanofiltration device.

[0045] Preferably, a nanofiltration device 115 is configured to form a first concentrate selectively containing organic loads, more particularly nutritive organic loads. For example, such organic loads are present in wastewater. Organic loads are all oxidizable carbon-based chemical compounds, which may also contain nitrogen and phosphorus, for example, vitamins, lipids, proteins, or carbohydrates. For example, nutritive organic loads correspond to compounds that participate in plant growth.

[0046] It is noted that a nanofiltration device 115 comprises, for example, a membrane or a plurality of membranes in series or in parallel.

[0047] A nanofiltration device 115 preferably has a semi-permeable membrane whose cutting power allows it to reject molecules with a molecular weight greater than approximately 300 Da.

[0048] Reverse osmosis device

[0049] As can be seen in [Fig. 1], the reverse osmosis device 130 is connected to the outlet 120 of the first permeate 116 from the nanofiltration device 115. Such a reverse osmosis device 130 is configured to form: - a second permeate 131 and - a second concentrate 132.

[0050] It is noted that the waters of the second permeate 131 are generally free of salts, That is to say, such waters have a concentration close to 0. For example, the concentration of ions, associated with salts, present in the second permeate 131 is defined as a percentage of the ion concentration present in the first permeate 116 from the nanofiltration device 115. Preferably, such a percentage is between 0% and 10%. More preferably, such a percentage is less than 2%.

[0051] In other words, the reverse osmosis device 130 is a membrane device that allows the rejection of salts, such as sodium chloride. Preferably, such rejection is greater than 98%.

[0052] It is noted that a reverse osmosis device 130 comprises, for example, a membrane or a plurality of membranes in series or in parallel.

[0053] Mixing connection

[0054] We observe, in [Fig.1], that a connection 145 between the outlet 125 of the first concentrate 117 and the outlet 135 of the second permeate 131 is present in the system 100.

[0055] In particular, the connection 145 ensures the mixing of two streams, each stream corresponding to a first concentrate stream 117 and a second permeate stream 131. In other words, the connection 145 is a mixing point. For example, such a connection includes a stream mixer, 117 and 131, known to those skilled in the art.

[0056] In particular, connection 145 ensures the dilution of the first concentrate flow 117 containing divalent salts. It is noted that downstream of the mixing of the two streams, a stream of first concentrate 117 and a stream of second permeate 131, a stream of mixed waters 146 is generated.

[0057] In particular, the mixed waters 146 from connection 145 exhibit: - a concentration of divalent salts lower than the concentration of divalent salts of the first concentrate 117 from the nanofiltration device 115, - a mineral concentration lower than the predetermined mineral concentration of the water to be treated, - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated, - a SAR value lower than water 101, and - a concentration of nutritious organic matter.

[0058] It is noted that the mixed waters 146 are, for example, compliant with the constraints imposed by envisaged applications, such as the irrigation of plantations.

[0059] Optional inlets for water to be treated

[0060] Figure 2, which is not to scale, shows a schematic view of one embodiment of the system 200 which is the subject of the present invention.

[0061] In embodiments such as that shown in [Fig. 2], the system 200 includes a second inlet 201 of water to be treated 101. We observe that the second inlet 201 is connected to the outlet 125 of the first concentrate 117 from the nanofiltration device 115.

[0062] In other embodiments (not shown), the waters circulating in the second inlet 201 and the waters to be treated 101 introduced into the nanofiltration device 115 are of a different nature.

[0063] In other words, the water flow circulating in the second inlet 201 and the flow of the first concentrate 117 are mixed.

[0064] In embodiments such as that shown in [Fig.2], the system 200 includes a third inlet 202 of water to be treated 101. It is observed that the third inlet 202 is connected to the outlet 120 of the first permeate 116 from the nanofiltration device 115.

[0065] In other embodiments (not shown), the waters circulating in the third inlet 202 and the waters to be treated 101 introduced into the nanofiltration device 115 are of a different nature.

[0066] In other words, the water flow circulating in the third inlet 202 and the flow of the first permeate 116 are mixed upstream of the reverse osmosis device 130.

[0067] It should be noted that the inlets, 105, 201 and 202, and the outlets, 125, 140 and 135, designate, for example, pipes configured to carry a flow of water. Such pipes are known to a person skilled in the art.

[0068] Means for adjusting the pH

[0069] Figure 3, which is not to scale, shows a schematic view of one embodiment of the system 300 that is the subject of the present invention. The water treatment system 300 101 comprises: - a first inlet 105 of water to be treated 101 comprising a means 301 for adjusting the pH and - an outlet 120 of the first permeate 116, from the nanofiltration device 115, comprising a pH adjustment means 302.

[0070] It is noted that the water exiting the adjustment means, 301 and 302, has an acidic, substantially neutral, or basic pH. The base or acid is injected by the adjustment means 301 and 302 using a servo-controlled metering pump: - either to a set pH level for the packaged water, - or simply to a dosage proportional to the flow rate of water to be treated.

[0071] In embodiments, a means for adjusting waters to acidic pH, 301 and / or 302, includes a means for adding an acid in a predetermined quantity.

[0072] In other embodiments, an adjustment means, 301 and / or 302, of waters in basic pH includes a means for adding a base in a predetermined quantity.

[0073] In variants, an adjustment means, 301 and / or 302, of waters in neutral pH includes a means for adding a base and / or an acid in a predetermined quantity.

[0074] It is noted that the amount of base or acid to be added depends on the target pH and the initial pH of the waters upstream of the adjustment means, 301 and 302.

[0075] Thus, the device of the invention has the ability to retain ammonium as a fertilizer, or not, depending on a pH strategy. This same strategy applies to a portion of the organic matter, in particular organic acids (for example, volatile fatty acids) whose concentrations can be increased or decreased by adjusting the pH.

[0076] Pretreatment unit

[0077] Figure 4, not to scale, shows a schematic view of an embodiment of the system 400 of the present invention. The water treatment system 400 101 comprises a water pretreatment unit 401. This pretreatment unit 401 is connected to an inlet 105 of the water to be treated 101. Figure 4 shows that the pretreatment unit 401 is located upstream of the nanofiltration device 115. In particular, the pretreatment unit 401 comprises a membrane filtration device 402 or a plurality of membrane filtration devices 402.

[0078] It is noted that the pretreatment unit 401 is configured to generate the water to be treated 101 introduced into the nanofiltration device 115.

[0079] In embodiments, the membrane filtration device 402 of the pretreatment unit 401 comprises a secondary reverse osmosis device, a secondary nanofiltration device, a microfiltration device and / or an ultrafiltration device.

[0080] For example, a microfiltration device has a porous membrane with a pore size between 0.1 pm and 10 pm. A microfiltration device ensures, for example, the retention of particles, bacteria and / or microalgae suspended in water.

[0081] For example, an ultrafiltration device has a porous membrane with a pore size between 1 and 100 nm.

[0082] It is noted that the secondary nanofiltration device is of the same nature as the nanofiltration device 115 or of a different nature.

[0083] It is noted that the secondary reverse osmosis device is of the same nature as the reverse osmosis device 130 or of a different nature.

[0084] Figure 5, which is not to scale, shows a schematic view of one embodiment of the system 500 that is the subject of the present invention. The system 500 comprises a pretreatment unit 401 connected to an outlet 540 of the second concentrate 132 derived from the reverse osmosis device 130.

[0085] It is noted that the second concentrate 132 contains predominantly monovalent salts at high concentrations. The second concentrate 132 is used as washing and unclogging water for the membrane filtration device 402 of the pretreatment unit 401.

[0086] In particular, the second concentrate 132 loaded with monovalent salts is circulated through the membrane of the membrane device 402 of the pretreatment unit 401, thus ensuring the unclogging of such a membrane.

[0087] Means of treatment by means of a sequestering additive

[0088] Figure 6, which is not to scale, shows a schematic view of an embodiment of the system 600 of the present invention. The system 600 comprises a treatment means 601 for a sequestering additive. In particular, such a sequestering additive is specific to a predetermined chemical species.

[0089] It should be noted that the term "sequestering agent" is commonly used even though it does not necessarily imply complexation. In most cases, it is a threshold-effect anti-scaling agent. The doses used are significantly lower than the doses required for stoichiometric reaction with the potentially sequestered element, but they act on the crystallization mechanism by inhibiting or delaying its formation. The threshold-effect or dispersing action depends on the type of molecule and its molecular weight. The main element targeted by the "sequestering agent" is calcium carbonate, whose crystallization follows the calcium-carbonate equilibrium.

[0090] In this case, it can act in conjunction with pH adjustment through acidification and CO2 formation. Other species are maintained in over-stabilization (i.e., at a concentration higher than their theoretical solubility), such as barium sulfate, strontium sulfate, calcium sulfate, silica, magnesium silicate, calcium fluoride, calcium phosphate...

[0091] The products used are generally phosphonates or acrylates. In the case of the former, they can effectively sequester metals such as iron. In the case of the latter, the molecular weight determines whether they act as a threshold anti-scalant or a dispersant.

[0092] EDTA is a powerful complexing agent but is not used as a preventive "sequestering agent". However, it can be used for corrective maintenance operations (complexing cleaning to break down formed deposits).

[0093] In embodiments such as that shown in [Fig.6], the sequestering additive treatment means 601 is disposed upstream of the nanofiltration device 115.

[0094] In embodiments (not shown), the sequestering additive treatment means 601 is disposed upstream of the reverse osmosis device 130.

[0095] It is noted that, in these embodiments, the predetermined chemical species is undesirable and has a limited or even zero concentration in the water flow to be treated 101 downstream of the treatment means 601 by a sequestering additive.

[0096] In embodiments, the sequestering agent is a compound among those described above and specific to one or more predetermined chemical species such as those described above.

[0097] Means of adjusting conversion rates

[0098] Figure 7, not to scale, shows a schematic view of an embodiment of the system 700 of the present invention. The system 700 includes a means 701 for adjusting the conversion rates of the nanofiltration device and / or the reverse osmosis device. In practice, the conversion rate is adjusted by setting a flow rate using a manual or automatic control valve. The concentrate flow rate is set to correspond to a target percentage of the total flow rate admitted into the device.

[0099] In particular, such conversion rates correspond to the following ratios: - between the flow rate of the first permeate 116 and the flow rate of the water to be treated 101, and - between the flow rate of the second permeate 131 and the flow rate of the first permeate 116.

[0100] In embodiments, the adjustment means 701 includes a means for regulating the flow rate of the water to be treated 101 (not shown). Such a regulating means is controlled according to the conversion rate to be achieved for the nanofiltration device 115. For example, the conversion rate to be achieved is defined by a target performance inherent in the nanofiltration device 115.

[0101] In embodiments, the adjustment means 701 includes a means for regulating the flow rate of the first permeate 116 (not shown). Such a regulating means is controlled according to the conversion rate to be achieved for the reverse osmosis device 130. For example, the conversion rate to be achieved is defined by a target performance inherent in the reverse osmosis device 130.

[0102] Water treatment process

[0103] Figure 8 shows a schematic view of an embodiment of process 800, which is the subject of the present invention. Process 800 is a water treatment process for water having a predetermined mineral concentration and a predetermined concentration of monovalent salts.

[0104] The water treatment process 800 comprises: - a first step 805 of water inlet to be treated; - a selective nanofiltration stage 810, downstream of the water inlet stage to be treated, - an outlet step 815 of the first permeate from the nanofiltration step, - an outlet step 820 of the first concentrate from the nanofiltration step, - a reverse osmosis step 825, downstream of the first permeate outlet step from the nanofiltration step, - an outlet step 835 of the second permeate from the reverse osmosis step, - an outlet step 830 of the second concentrate from the reverse osmosis step and - a connection step 840 to mix the first concentrate from one outlet step and the second permeate from another outlet step.

[0105] During the selective nanofiltration step 810, a first permeate selectively containing monovalent salts is formed and a first concentrate selectively containing divalent salts is also formed.

[0106] During the reverse osmosis step 825 a second permeate comprising salt-free waters is formed and a second concentrate comprising salts is also formed.

[0107] During the connection step 840, the first concentrate is diluted. In particular, the mixed waters resulting from such a connection step 840 have: - a mineral concentration lower than the predetermined mineral concentration of the waters to be treated, - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated, - a SAR value lower than water 101, and - a concentration of nutrients, for example nutrients and nitrogenous matter.

[0108] Preferably, the means of systems 100, 200, 300, 400, 500, 600 and / or 700 are configured to implement the steps of process 800 and their embodiments as set out above and process 800 and its various embodiments can be implemented by means of systems 100, 200, 300, 400, 500, 600 and / or 700.

[0109] In addition, in some embodiments, the process of the invention is a process for selecting species dissolved in water by mixing a nanofiltration concentrate obtained from raw water, also called water to be treated, optionally pre-treated, a mixture made with - demineralized water obtained from the permeate of a reverse osmosis filtering

[0110] the permeate of nanofiltration, or - to a mixture of nanofiltration permeate and possibly pre-treated raw water.

[0111] Furthermore, in some embodiments, the device of the invention produces salinity-balanced water by correcting the SAR or, more generally, ensures the selective reduction of the concentration of undesirable species while maintaining concentrations of species beneficial to the intended application. The application the intended use being, for example, irrigation from wastewater or the purification of water contaminated by nitrate and / or ammonium.

[0112] In embodiments, the device of the invention ensures pH adjustment upstream of nanofiltration or reverse osmosis.

[0113] Such an adjustment aims to promote the isolation of a species (in particular ammonium, ammonia and certain organic acids, for example volatile fatty acids) on either side of the membrane, so as to promote or avoid the presence of the species in the water produced by the device. Description of the invention

[0114] According to a first aspect, the present invention relates to a water treatment system having a predetermined mineral concentration and a predetermined concentration of monovalent salts, the system comprising: - an initial inlet of wastewater to be treated, - a selective nanofiltration device, connected to the inlet of the water to be treated and configured to form: - a first permeate selectively containing monovalent salts and - a first concentrate selectively containing divalent salts, - an outlet of the first permeate from the nanofiltration device, - an outlet of the first concentrate from the nanofiltration device, - a reverse osmosis device, connected to the outlet of the first permeate from the nanofiltration device and configured to form: - a second permeate containing salt-free waters and - a second concentrate containing salts, - an outlet of the second permeate from the reverse osmosis unit, - an outlet of the second concentrate from the reverse osmosis unit, and - a connection between the outlet of the first concentrate and the outlet of the second permeate, the mixed waters from the connection exhibiting: - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts of the waters to be treated.

[0115] Thanks to these arrangements, the system allows for the selection of so-called "target" species, such as divalent ions, through the implementation of two membrane filtration devices, namely the nanofiltration device coupled to the reverse osmosis device. More specifically, the system elements allow for: - a selective concentration of so-called target elements, such as divalent mineral species, also called divalent ions, and nutrient organic loads in a concentrate from a membrane nanofiltration device; - Demineralization of the permeate from the nanofiltration device by the reverse osmosis device, generating a stream of demineralized water and a stream concentrated in undesirable species, which constitutes, for example, a discharge. Note that the demineralized water is used to dilute the concentrate from the nanofiltration device; - Selective demineralization of the water, in other words, a reduction in mineral concentration, by reducing monovalent ions such as Na+ and NO3; - Selective preservation of the NH4+ concentration, by adjusting the pH; - obtaining a level of SAR compatible with, for example, a particular agronomic use; - the preservation of organic nutrients originating, for example, from wastewater recycled for irrigation; and - an improvement in hydraulic efficiency compared to efficiency obtained by so-called "conventional" membrane demineralization, i.e. via a single nanofiltration or single reverse osmosis device. Such an improvement is also obtained for hard and highly mineralized waters.

[0116] Furthermore, in general, the system allows: - to produce water enriched in divalent ions at the expense of monovalent ions, for example water enriched in: - Ca2+ and Mg2+ at the expense of Na+, and - SO42 and PO43 at the expense of Cl; - reduce the mineral concentration within adjustable proportions; and - in the case of wastewater for example, to retain the nutrient organic load for wastewater reuse applications in irrigation.

[0117] Thus, the system makes it possible to selectively reduce certain minerals or chemical compounds, while preserving the species useful for the mineral balance of the water.

[0118] In optional embodiments, the system further comprises a second inlet of water to be treated connected to the outlet of the first concentrate from the nanofiltration device.

[0119] Thanks to these provisions, the mineralization of the water to be treated, which has been mixed with the first concentrate, is modified by favoring divalent species at the expense of monovalent species. Furthermore, when the water to be treated circulating in the second inlet is wastewater, the concentration of organic loads initially present in this wastewater is increased downstream of the mixing with the first concentrate.

[0120] Thus, the waters obtained downstream of the mixture with the first concentrate have a composition in ionic and organic species closer to the composition required for certain applications, such as the irrigation of plantations.

[0121] In optional embodiments, the system further comprises a third inlet of water to be treated connected to the outlet of the first permeate from the nanofiltration device.

[0122] Thanks to these arrangements, the system allows for an additional water flow at the inlet of the reverse osmosis unit by introducing wastewater. An increase in the water flow at the inlet of the reverse osmosis unit is obtained, which increases the flow of demineralized water in the second permeate. It should be noted that this flow of salt-free water is then mixed with the first concentrate from the nanofiltration unit. Thus, a greater dilution of the first concentrate is achieved by this additional supply of wastewater upstream of the reverse osmosis unit.

[0123] In optional embodiments, at least one conduit among the first inlet of water to be treated and the outlet of the first permeate from the nanofiltration device further comprises a pH adjustment means, the water at the outlet of the adjustment means being at acidic, substantially neutral or basic pH.

[0124] Thanks to these provisions, the system allows pH adjustment according to requirements. In particular, pH adjustment is carried out upstream of nanofiltration or upstream of reverse osmosis depending on the objectives and situations.

[0125] A first example of such a pH adjustment is implemented in the case of regulating ammonium concentration. It should be noted that the target ammonium concentration in the water is determined according to its intended use. For example:

[0126] - if ammonium is a desirable species, an adjustment to obtain an acidic pH is achieved. Such an adjustment promotes the formation of ammonium sulfate, which is selectively present in the first concentrate of the nanofiltration device;

[0127] - if ammonium is an undesirable species, an adjustment to obtain a pH sen If a neutral or basic solution is used, such an adjustment promotes the selective presence of ammonium in the first permeate of the nanofiltration device. Additional demineralization of the water is therefore achieved in this case.

[0128] A second example of such pH adjustment is implemented in the case of regulation of the concentration of organic acids, determined according to uses.

[0129] In optional embodiments, a pretreatment unit at least partially connected to the inlet of the water to be treated, arranged upstream of the nanofiltration device and comprising at least one membrane filtration device.

[0130] Thanks to these arrangements, all or part of the water flow to be treated is pre-treated by a membrane device, thus allowing the mineral concentration of the water to be pre-adjusted. As a result, the mineral concentration of the treated water downstream of the system is optimal.

[0131] In optional embodiments, the membrane filtration device of The pretreatment unit includes a secondary reverse osmosis device, a secondary nanofiltration device, a microfiltration device and / or an ultrafiltration device.

[0132] Thanks to these provisions, the system allows different demineralizations and / or different treatments, for example upstream of the main nanofiltration device.

[0133] In optional embodiments, the pretreatment unit is connected to the outlet of the second concentrate from the reverse osmosis device, the second concentrate containing salts being used as wash and unclogging water for the membrane filtration device of the pretreatment unit.

[0134] Thanks to these arrangements, the salt-laden water from the second concentrate is used for unclogging one or more membranes in the pretreatment unit. In particular, such salt-laden water exhibits significant unclogging properties, which can be applied, for example, to the removal of bacteria that clog membranes. The consumption of water initially used for unclogging is therefore reduced, or even eliminated, thus improving the overall efficiency of the system, which includes a pretreatment unit.

[0135] In optional embodiments, the system further comprises a means of treatment by a specific sequestering additive of a predetermined chemical species disposed upstream of the nanofiltration device and / or the reverse osmosis device, as described above.

[0136] Thanks to these provisions, the system makes it possible, by specific sequestration of certain chemical species, to prevent precipitation problems on the membranes of nanofiltration and / or reverse osmosis devices.

[0137] In optional embodiments, the system further comprises a means for adjusting the conversion rates of the nanofiltration device and / or the reverse osmosis device, the conversion rates corresponding to the ratios: - between the flow rate of the first permeate and the flow rate of the water to be treated, and - between the flow rate of the second permeate and the flow rate of the first permeate.

[0138] Thanks to these provisions, the system makes it possible to adjust the conversion rates of the nanofiltration device and / or the reverse osmosis device in order to optimize the separation performance, energy cost and the durability of the membranes of the devices.

[0139] According to a second aspect, the present invention relates to a process for treating water having a predetermined mineral concentration and a predetermined concentration of monovalent salts, the process comprising: - a first step of input of water to be treated; - a selective nanofiltration step, downstream of the water inlet step to be treated, to form: - a first permeate selectively containing monovalent salts and - a first concentrate selectively containing divalent salts, - an outlet step for the first permeate resulting from the nanofiltration step, - an output stage for the first concentrate obtained from the nanofiltration stage, - a reverse osmosis step, downstream of the first permeate exit step from the nanofiltration step, to form: - a second permeate containing salt-free waters and - a second concentrate containing salts, - an outlet stage for the second permeate resulting from the reverse osmosis stage, - an output stage for the second concentrate from the reverse osmosis stage and - a connection step to mix the first concentrate from one outlet step and the second permeate from another outlet step, the mixed waters from the connection step exhibiting: - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts of the waters to be treated.

[0140] The aims, advantages and special features of the process which is the subject of the present invention being similar to those of the system which is the subject of the present invention, they are not recalled here.

Claims

Claims

1. System (100, 200, 300, 400, 500) for treating water (101) having a predetermined mineral concentration and a predetermined concentration of monovalent salts, the system being characterized in that it comprises: - a first inlet (105) for water to be treated, - a selective nanofiltration device (115), connected to the inlet for water to be treated and configured to form: - a first permeate (116) selectively comprising monovalent salts and - a first concentrate (117) selectively comprising divalent salts, - an outlet (120) for the first permeate from the nanofiltration device, - an outlet (125) for the first concentrate from the nanofiltration device, - a reverse osmosis device (130), connected to the outlet of the first permeate from the nanofiltration device and configured to form: - a second permeate (131) comprising salt-free water and - a second concentrate (132) comprising salts,- an outlet (135) for the second permeate from the reverse osmosis device, - an outlet (140, 540) for the second concentrate from the reverse osmosis device and - a connection (145) between the outlet of the first concentrate and the outlet of the second permeate, the mixed water (146) from the connection having: - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts of the water to be treated.,

2. System (200, 300, 400, 500) according to claim 1, which further comprises a second inlet (201) of water to be treated (101) connected to the outlet (125) of the first concentrate (117) from the nanofiltration device (115).

3. System (200, 300, 400, 500) according to one of claims 1 or 2, which further comprises a third inlet (202) for water to be treated (101). connected to the outlet (120) of the first permeate (116) from the nanofiltration device (115).

4. System (300) according to one of claims 1 to 3, in which at least one pipe among the first inlet (105) of water to be treated (101) and the outlet (120) of the first permeate (116) from the nanofiltration device (115) further comprises a means (301, 302) for adjusting the pH, the water leaving the adjustment means being at acidic, substantially neutral or basic pH.

5. System (400, 500) according to one of claims 1 to 4, which further comprises a unit (401) for at least partial pretreatment of the water, connected to the inlet (105) of the water to be treated (101), arranged upstream of the nanofiltration device (115) and comprising at least one membrane filtration device (402).

6. System (400) according to claim 5, wherein the membrane filtration device (402) of the pretreatment unit (401) comprises a secondary reverse osmosis device, a secondary nanofiltration device, a microfiltration device and / or an ultrafiltration device.

7. System (500) according to one of claims 5 or 6, in which the pretreatment unit (401) is connected to the outlet (540) of the second concentrate (132) from the reverse osmosis device (130), the second concentrate (132) comprising salts being used as washing and unclogging water for the membrane filtration device (402) of the pretreatment unit.

8. System (600) according to one of claims 1 to 7, which further comprises a treatment means (601) with a sequestering additive specific to a predetermined chemical species arranged upstream of the nanofiltration device (115) and / or the reverse osmosis device (130).

9. System (700) according to one of claims 1 to 8, which further comprises means (701) for adjusting the conversion rates of the nanofiltration device (115) and / or the reverse osmosis device (130), the conversion rates corresponding to the ratios: - between the flow rate of the first permeate (116) and the flow rate of the water to be treated (101), and - between the flow rate of the second permeate (131) and the flow rate of the first permeate.

10. Method (800) for treating water having a predetermined mineral concentration and a predetermined concentration of monovalent salts completed, the process being characterized in that it comprises: - a first stage (805) of entry of water to be treated; - a selective nanofiltration step (810), downstream of the water inlet step to be treated, to form: - a first permeate selectively comprising monovalent salts and - a first concentrate selectively comprising divalent salts, - an outlet step (815) of the first permeate resulting from the nanofiltration step, - an output step (820) of the first concentrate from the nanofiltration step, - a reverse osmosis stage (825), downstream of the stage of the outlet of the first permeate from the nanofiltration stage, to form: - a second permeate comprising salt-free water and - a second concentrate containing salts, - an outlet stage (835) of the second permeate from the reverse osmosis stage, - an output stage (830) of the second concentrate from the reverse osmosis stage and - a connection step (840) for mixing the first concentrate from an output step and the second permeate from another output step, the mixed water from the connection step having: - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated.

Images