System and method for treating water

Abstract

The invention relates to a system (100) for treating water (101), the system comprising: - a selective nanofiltration device (115) connected to an inlet (105) for water to be treated; - an outlet (120) for a first permeate (116) from the nanofiltration device; - an outlet (125) for the first concentrate (117) from the nanofiltration device; - a reverse osmosis device (130) connected to the outlet for the first permeate from the nanofiltration device and configured to form: - an outlet (135) for a second permeate (131) from the reverse osmosis device; - an outlet (140) for a second concentrate (132) from the reverse osmosis device; and - a connection (145) between the outlet for the first concentrate and the outlet for the second permeate.

Description

[0001] WATER TREATMENT SYSTEM AND METHOD

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a system and a method for treating water. It applies, in particular, to the field of desalination of water, for example natural or waste water.

[0004] STATE OF THE ART

[0005] Natural or wastewater contains compounds such as mineral solutes, including dissolved salts, or organic solutes. In natural water, such compounds are naturally present, while in wastewater, these compounds come from inputs related to human, agricultural, and industrial activities.

[0006] Depending on the application and destination of the water, some dissolved compounds are undesirable while others can be beneficial. For example, in irrigation use, treated wastewater from treatment plants generally contains a high sodium load. Such a load gives the wastewater a salinity incompatible with agricultural needs. For example, irrigating vineyards with water with high salinity causes reduced crop yields, soil degradation, and groundwater pollution. The total salinity of water, including the mineral composition of the water and the proportion of different salts between them, significantly influences plant growth and soil fertility.

[0007] 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 a SAR reflects the quality of water in order to highlight whether such water is suitable for irrigating plantations, for example. The SAR is defined, for example, according to the following equation: equation in which:

[0008] - [N / A + ] is the concentration of monovalent species Na + , called sodium ion,

[0009] - [That 2+ ] is the concentration of divalent species Ca 2+ , called calcium ion, and

[0010] - [Mg 2+ ] is the concentration of divalent species Mg 2+ , called magnesium ion.

[0011] Preferably, a SAR, considered acceptable for a plant, has a value lower than 18.

[0012] A correction of the proportion of monovalent salts to divalent salts and a reduction in the overall salinity of the waters are necessary for the application of these salt-rich waters for irrigation of crops or green spaces. Such correction and reduction notably limit the problems of plant growth and soil salinization. Moreover, in the case of natural water resources, such waters present, for example, a problem of limited mineral concentration, but are polluted by nitrates, such as the NC anion, and / or ammonium, such as the NH4 cation. + Natural waters come, for example, from groundwater or surfaces polluted by human activity, such as agriculture and wastewater discharge. Such anthropogenic pollution makes the waters unsuitable for use as drinking water, for example.

[0013] Prior art solutions proposing a solution for reducing the total salinity of water disclose the use of a reverse osmosis device. However, such a device causes a rejection of all minerals without a significant degree of selectivity with respect to monovalent and divalent salts. More particularly, undesirable monovalent salts pass primarily in ionic leakage through the membrane of the reverse osmosis device. Such treatment by a reverse osmosis device of water with or without mixing of raw water upstream of the treatment:

[0014] - does not ensure a reduction in general salinity and

[0015] - does not show selectivity towards divalents or other molecules of interest, such as agronomic molecules, for example.

[0016] Thus, a reverse osmosis device does not allow a result to be obtained that meets the needs, constraints and / or standards imposed.

[0017] Furthermore, other prior art solutions proposing a solution for reducing the total salinity of water disclose the use of a nanofiltration device. Such filtration is selective with respect to divalent ions, that is to say that such ions are retained by the nanofiltration membrane and are concentrated in the solution called concentrate. Thus, the permeate resulting from such nanofiltration is rich in monovalent ions and partially demineralized. An inverse selectivity is therefore obtained, aggravating the original imbalance defined by the SAR of the water.

[0018] In addition, other prior art solutions disclose the use of an electrodialysis device. However, similar to the nanofiltration device, the permeate from the electrodialysis device is partially demineralized and mainly comprises monovalent ions.

[0019] Also, the prior art solutions describe uses of pH regulation to prevent the precipitation of minerals and sometimes to promote the rejection of certain substances by semi-permeable membranes, by acting on the dissociation of an acid or a base (pKa). However, these solutions for acidifying or alkalizing water do not, on their own, allow all the elements of agronomic interest to be preserved, a given pH being favorable to certain species and unfavorable to others. For example, optimization by pH regulation of the retention of ammoniacal nitrogen in irrigation water is opposed to optimization of the retention of ionized organic matter (for example, volatile fatty acids) or phosphorus, the pH conditions for one or other of the species being very different.There are also difficulties in the prior art in reconciling an optimal pH for the purpose of conserving nutrients with maintaining the solubility of salts present in water. Thus, for example, the alkaline pH required for the retention of volatile fatty acids is severely limited by the preservation of solubility conditions in the calco-carbonic equilibrium. These situations and limitations severely limit the scope of pH regulation alone for achieving the objectives of selecting elements of agronomic interest.

[0020] Still on the subject of pH regulation, the products traditionally used have no agronomic benefit and the salts and ions resulting from their dosage can negatively contribute to water quality and its SAR value. For example, the common use of hydrochloric acid and sodium hydroxide leads to an enrichment of the water with species harmful to crops (chloride and sodium).

[0021] Furthermore, other prior art solutions disclose the use of a device comprising an ion exchange means. However, a priority selection of divalent cations, such as Ca 2+ and Mg 2+ , against monovalent ions is not achieved by such a device. In particular, only denitration, corresponding to a reduction in nitrate ion NC, is, for example, achieved by ion exchange using a strong anionic resin and by exchange with bicarbonate or chloride salts. However, such a resin enriches the water with an exchanged anion, such as chloride and therefore generates effluents highly concentrated in mineral load with a very low chemical yield. Furthermore, such a solution has a negative operating cost and environmental impact.

[0022] Finally, other solutions of the prior art correspond to chemical precipitation techniques, but do not allow the reduction of the content of nitrate NC or sodium Na + waters.

[0023] STATEMENT OF THE INVENTION

[0024] The present invention aims to overcome all or part of these drawbacks. In particular, the system which is the subject of the invention is based on the combined use of a nanofiltration and reverse osmosis device.

[0025] The system that is the subject of the invention therefore offers a solution to meet the need for partial or total demineralization, and the need for selection of beneficial species. The system that is the subject of the invention allows:

[0026] - production of water enriched in divalent or trivalent ions to the detriment of monovalent ions, for example such as divalent Ca ions 2+ and Mg 2+ at the expense of the monovalent ion Na + , or the divalent ion SC>42 ' and PC>4 3 ' to the detriment of the monovalent ion CI-;

[0027] - a reduction of the mineral concentration in proportions adjustable by the system and

[0028] - conservation of a nutrient organic load present in wastewater, for applications of reuse of wastewater in irrigation, by means of a device for sorting compounds which combines pH regulation, with specific acids and bases, and a double membrane separation. 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:

[0029] - a first inlet of water to be treated,

[0030] - a selective nanofiltration device, connected to the inlet of the water to be treated and configured to form:

[0031] - a first permeate selectively comprising monovalent salts and

[0032] - a first concentrate selectively comprising divalent salts,

[0033] - an outlet of the first permeate from the nanofiltration device,

[0034] - an outlet of the first concentrate from the nanofiltration device,

[0035] - a reverse osmosis device, connected to the outlet of the first permeate from the nanofiltration device and configured to form:

[0036] - a second permeate comprising salt-free water and

[0037] - a second concentrate containing salts,

[0038] - an outlet for the second permeate from the reverse osmosis device,

[0039] - an outlet of the second concentrate from the reverse osmosis device and

[0040] - a connection between the outlet of the first concentrate and the outlet of the second permeate, the mixed water from the connection having:

[0041] - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and

[0042] - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated;

[0043] - system in which at least one pipe 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, configured so that the water leaving the adjustment means has an acidic, substantially neutral or basic pH;

[0044] - system which further comprises a means of adjusting the conversion rates of the nanofiltration device and / or the reverse osmosis device, the conversion rates corresponding to the ratios:

[0045] - between the flow rate of the first permeate and the flow rate of the water to be treated, and

[0046] - between the flow rate of the second permeate and the flow rate of the first permeate.

[0047] Thanks to these provisions, the system makes it possible to carry out a selection of so-called "target" species, such as divalent ions, by implementing two membrane filtration devices, in particular the nanofiltration device coupled with the reverse osmosis device. More precisely, the elements of the system make it possible to carry out:

[0048] - a selective concentration of so-called target elements, such as divalent mineral species also called divalent ions and nutrient organic charges in a concentrate from a membrane nanofiltration device; - a demineralization of the permeate from the nanofiltration device by the reverse osmosis device, generating a flow of demineralized water and a flow concentrated in undesirable species which constitutes, for example, a discharge. It is noted that the demineralized water is used to dilute the concentrate from the nanofiltration device;

[0049] - selective demineralization of water, in other words a reduction in mineral concentration, by reduction of monovalent ions such as Na + and NOs-

[0050] - selective conservation of NH4 concentration + , by a pH adjustment upstream of each membrane step;

[0051] - obtaining a SAR level compatible with, for example, a particular agronomic use;

[0052] - selective conservation of organic nutrients from, for example, recycled irrigation wastewater by adjusting the pH upstream of each membrane stage; and

[0053] - an improvement in hydraulic yields compared to yields 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.

[0054] Furthermore, in general, the system allows:

[0055] - produce water enriched in divalent ions to the detriment of monovalent ions, for example water enriched in: to the detriment of Na + , And to the detriment of Ch;

[0056] - reduce the mineral concentration in adjustable proportions; and

[0057] - in the case of wastewater, for example, retaining the organic nutrient load for wastewater reuse applications in irrigation, by adapting the degree of selectivity between desirable and undesirable species, depending, for example, on the objectives of the proportion of N / P / K elements and organic carbon in the water.

[0058] Thus, the system allows for the selective reduction of certain minerals or chemical compounds, while retaining the species useful for the mineral balance of the water.

[0059] Thanks to the pH adjustment method, the system allows pH adjustment according to needs. In particular, pH adjustment is carried out upstream of nanofiltration or upstream of reverse osmosis depending on the objectives and situations.

[0060] A first example of such pH adjustment is implemented in the case of regulation of ammonium concentration. Note that the target ammonium concentration in water is determined according to usage. For example:

[0061] - if ammonium is a desirable species, an adjustment to obtain an acidic pH is carried out. Such an adjustment promotes the formation of ammonium sulfate which is selectively present in the first concentrate of the nanofiltration device; - if ammonium is an undesirable species, an adjustment to obtain a substantially neutral or basic pH is carried out, such an adjustment promotes the selective presence of ammonium in the first permeate of the nanofiltration device. Additional demineralization of the water is therefore obtained in this case.

[0062] A second example of such pH adjustment is implemented in the case of regulation of the concentration of organic acids, determined according to uses. The use of specific chemical species for pH regulation such as phosphoric acid, potash, sodium hydroxide, sulfuric acid, nitric acid, ammonia, the combinations of which at the two dosage points allow the selection of the compound of interest and its retention in a precise form serving the interest of fertigation (word formed from fertilization and irrigation, concerning an agricultural technique consisting of applying soluble fertilizing elements in water via an irrigation system) of recycled water (example ammonium phosphate rather than ammonium chloride, potassium acetate rather than sodium acetate)

[0063] By means of the conversion rate adjustment means, the system allows for adjustment of the conversion rates of the nanofiltration device and / or the reverse osmosis device in order to optimize the separation performance, energy cost and durability of the membranes of the devices.

[0064] In embodiments, the pH adjustment means is configured to perform the pH adjustment according to a decision scheme of sorting the components of interest and / or the undesirable components according to the pH conditions favoring the permeation or the rejection of these components.

[0065] In embodiments, the pH adjusting means is configured to use, in combination, at least one acid and at least one specific base to contribute to sequencing with the benefit of balancing the N / P / K and organic carbon proportions.

[0066] In optional embodiments, the system further comprises a second inlet for water to be treated connected to the outlet of the first concentrate from the nanofiltration device.

[0067] 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 to the detriment 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.

[0068] Thus, the waters obtained downstream of the mixing with the first concentrate have a composition of ionic and organic species closer to the composition required for certain applications, such as the irrigation of plantations.

[0069] 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. Thanks to these provisions, the system allows an additional supply of water flow at the inlet of the reverse osmosis device by the introduction of water to be treated. An increase in the flow of water at the inlet of the reverse osmosis device is obtained, which increases the flow of demineralized water of the second permeate. It is noted that such a flow of salt-free water is then mixed with the first concentrate from the nanofiltration device. Thus, a greater dilution of the first concentrate is obtained by this additional supply of water to be treated upstream of the reverse osmosis device.

[0070] In optional embodiments, a unit for at least partial pretreatment of the water, connected to the inlet of the water to be treated, arranged upstream of the nanofiltration device and comprising at least one membrane filtration device.

[0071] Thanks to these provisions, all or part of the flow of water to be treated is pre-treated by a membrane device, thus making it possible to pre-adjust the mineral concentration of the water. Thus, the mineral concentration of the water treated downstream of the system is optimal.

[0072] In optional embodiments, the membrane filtration device of the pretreatment unit comprises a secondary reverse osmosis device, a secondary nanofiltration device, a microfiltration device and / or an ultrafiltration device.

[0073] Thanks to these provisions, the system allows different demineralizations and / or different treatments, for example upstream of the main nanofiltration device.

[0074] In optional embodiments, the pretreatment unit is connected to the outlet of the second concentrate from the reverse osmosis device, the second concentrate comprising salts being used as washing and unclogging water for the membrane filtration device of the pretreatment unit.

[0075] Thanks to these provisions, the salt-laden waters of the second concentrate are used for unclogging one or more membranes of the pretreatment unit. In particular, such salt-laden waters have significant unclogging properties applied, for example, to the unclogging of bacteria clogging membranes. The consumption of water initially used for unclogging is therefore reduced, or even zero, thus improving the overall efficiency of the system which includes a pretreatment unit.

[0076] In optional embodiments, the system further comprises a means for treatment with a sequestering additive specific to a predetermined chemical species disposed upstream of the nanofiltration device and / or the reverse osmosis device, as described above.

[0077] Thanks to these provisions, the system allows, by specific sequestration of certain chemical species, to prevent precipitation problems on the membranes of nanofiltration and / or reverse osmosis devices.

[0078] According to a second aspect, the present invention relates to a method for treating water having a predetermined mineral concentration and a predetermined concentration of monovalent salts, the method comprising:

[0079] - a first stage of entry of water to be treated; - a selective nanofiltration stage, downstream of the stage of entry of water to be treated, to form:

[0080] - a first permeate selectively comprising monovalent salts and

[0081] - a first concentrate selectively comprising divalent salts,

[0082] - a step for the output of the first permeate from the nanofiltration step,

[0083] - a step for the output of the first concentrate from the nanofiltration step,

[0084] - a reverse osmosis stage, downstream of the stage of the exit of the first permeate from the nanofiltration stage, to form:

[0085] - a second permeate comprising salt-free water and

[0086] - a second concentrate containing salts,

[0087] - a stage for the output of the second permeate from the reverse osmosis stage,

[0088] - a stage for the output of the second concentrate from the reverse osmosis stage and

[0089] - a connection step 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:

[0090] - a mineral concentration lower than the predetermined mineral concentration of the water to be treated and

[0091] - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated.

[0092] Preferably, the method which is the subject of the invention also comprises:

[0093] - a pH adjustment step, in at least the first inlet step of water to be treated and the outlet step of the first permeate from the nanofiltration step, so that the water leaving the adjustment means has an acidic, substantially neutral or basic pH, and / or

[0094] - a step of adjusting the conversion rates of the nanofiltration step and / or the reverse osmosis step, the conversion rates corresponding to the ratios:

[0095] - between the flow rate of the first permeate and the flow rate of the water to be treated, and

[0096] - between the flow rate of the second permeate and the flow rate of the first permeate.

[0097] The aims, advantages and particular characteristics of the method 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.

[0098] BRIEF DESCRIPTION OF THE FIGURES

[0099] Other advantages, aims and particular characteristics of the invention will emerge from the following non-limiting description of at least one particular embodiment of the system and method which are the subject of the present invention, with reference to the appended drawings, in which:

[0100] Figure 1 represents, schematically, a first particular embodiment of the system which is the subject of the present invention, Figure 2 represents, schematically, a second particular embodiment of the system which is the subject of the present invention,

[0101] Figure 3 schematically represents a third particular embodiment of the system which is the subject of the present invention,

[0102] Figure 4 schematically represents a fourth particular embodiment of the system which is the subject of the present invention,

[0103] Figure 5 schematically represents a fifth particular embodiment of the system which is the subject of the present invention,

[0104] Figure 6 schematically represents a sixth particular embodiment of the system which is the subject of the present invention,

[0105] Figure 7 schematically represents a seventh particular embodiment of the system which is the subject of the present invention, and

[0106] Figure 8 represents, schematically and in the form of a flowchart, a particular succession of steps of the method which is the subject of the present invention.

[0107] TERMINOLOGY

[0108] The expression "and / or", as used herein and in the claims, is to be understood to mean "either or both" of the elements so conjoined, i.e., elements which are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" are to be interpreted in the same way, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present, other than the elements specifically identified by the "and / or" clause, whether or not they are related to these 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.

[0109] 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, i.e., the inclusion of at least one, but also more than one, number or list of elements, and, optionally, additional elements not listed. 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.

[0110] As used in this specification and in the claims, the expression "at least one", with reference to a list of one or more elements, is to be understood to mean at least one element selected 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 every combination of elements in the list of elements. This definition also allows for the optional presence of elements other than the specifically identified elements in the list of elements to which the expression "at least one" refers, whether or not 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.

[0111] In the claims, as well as in the description below, all transitional expressions such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", "consisting of", and the like, are to be understood as open, i.e., as meaning including, but not limited to. Only the transitional expressions "consisting of" and "consisting essentially of" are to be understood as closed or semi-closed transitional expressions, respectively.

[0112] The following definitions are recalled here:

[0113] - The term “monovalent salt” refers to a salt consisting of two monovalent ions having respectively a positive charge noted “+” and a negative charge noted “-”;

[0114] - The term “monovalent ion” refers to an ion with a single negative or positive charge;

[0115] - The term “divalent salt” refers to a salt consisting of two divalent ions having respectively two positive charges “2+” and two negative charges “2-”;

[0116] - The terms "divalent ion" and "trivalent ion" refer to an ion having two negative or positive charges or, respectively, three positive or negative charges;

[0117] - The term "ion" is a generic term for monatomic ions, such as Ca ions 2+ , Mg 2+ and Na + , and polyatomic ions SC>4 2 ', NH4 + , NOs' ;

[0118] - The term “mineral concentration” refers to the total concentration, that is to say the sum of the concentrations, of the mineral species present in water;

[0119] - The term “mineral species” refers to, without limitation, a monovalent salt or a divalent salt;

[0120] - The term "water to be treated" refers to water with an ion concentration greater than a predetermined value, such value being a threshold defined according to, for example, the needs, standards and uses of such water. DESCRIPTION OF THE EMBODIMENTS

[0121] This description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment in an advantageous manner to form other embodiments of the invention.

[0122] Please note that the figures are not to scale.

[0123] Figure 1, which is not to scale, shows a schematic view of an embodiment of the system 100 which is the subject of the present invention. The system 100 is a system for treating water 101, called water to be treated 101, having a predetermined mineral concentration and a predetermined concentration of monovalent salts.

[0124] 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 these waters 101.

[0125] We observe, in figure 1, that the water treatment system 100 101 comprises:

[0126] - a first inlet 105 of water to be treated 101,

[0127] - a selective nanofiltration device 115,

[0128] - an outlet 120 of a first permeate 116 from the nanofiltration device 115,

[0129] - an outlet 125 of a first concentrate 117 from the nanofiltration device 115,

[0130] - a reverse osmosis device 130,

[0131] - an outlet 135 of a second permeate 131 from the reverse osmosis device 130,

[0132] - an outlet 140 of a second concentrate 132 from the reverse osmosis device 130,

[0133] - a connection 145 between the outlet 125 of the first concentrate 117 and the outlet 135 of the second permeate 131, and

[0134] - a production 146 from connection 145.

[0135] Selective nanofiltration device

[0136] We observe, in figure 1, that the selective nanofiltration device 115 is connected to the inlet 105 of water to be treated 101. Such a nanofiltration device 115 is configured to form:

[0137] - a first permeate 116 selectively comprising monovalent salts and

[0138] - a first concentrate 117 selectively comprising divalent salts.

[0139] It is noted that the monovalent salts present in the first permeate 116 correspond to the ions associated with such salts and capable of mainly passing through 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.

[0140] It is noted that the divalent salts present in the first concentrate 117 correspond to the ions associated with such salts and incapable of crossing 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 mainly retained by such a membrane.

[0141] In other words, the nanofiltration device is a membrane device having a so-called "cut-off" threshold corresponding to a rejection of divalent species significantly higher than the rejection of monovalent species. It is noted that the divalent species are, for example, respectively expressed by the following formulas: CaSO4 and NaCl. It is noted that such a cut-off threshold defines the selectivity of the so-called "selective" nanofiltration device.

[0142] Preferably, a nanofiltration device 115 is configured to form a first concentrate selectively comprising organic fillers, more particularly nutritive organic fillers. For example, such organic fillers are present in wastewater. Organic fillers 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 fillers correspond to compounds participating in plant growth.

[0143] It is noted that a nanofiltration device 115 comprises, for example, a membrane or a plurality of membranes in series or in parallel.

[0144] A nanofiltration device 115 preferably has a semi-permeable membrane whose cutting power makes it possible to reject molecules with a molecular weight greater than approximately 300 Da.

[0145] Reverse osmosis device

[0146] It is observed, in figure 1, that the reverse osmosis device 130 is connected to the outlet 120 of the first permeate 116 coming from the nanofiltration device 115. Such a reverse osmosis device 130 is configured to form:

[0147] - a second permeate 131 and

[0148] - a second concentrate 132.

[0149] It is noted that the waters of the second permeate 131 are generally free of salts, that is to say that such waters have a concentration close to 0. For example, the concentration of ions, associated with the salts, present in the second permeate 131 is defined by a percentage of the concentration of ions 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%.

[0150] In other words, the reverse osmosis device 130 is a membrane device allowing rejection of salts, such as sodium chloride. Preferably, such rejection is greater than 98%.

[0151] It is noted that a reverse osmosis device 130 comprises, for example, a membrane or a plurality of membranes in series or in parallel.

[0152] Mixing connection

[0153] It is observed, in figure 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. In particular, the connection 145 ensures the mixing of two flows, each flow corresponding to a flow of first concentrate 117 and a flow of second permeate 131. In other words, the connection 145 is a mixing point. For example, such a connection comprises a flow mixer, 117 and 131, known to those skilled in the art.

[0154] In particular, the connection 145 ensures the dilution of the flow of the first concentrate 117 comprising divalent salts. It is noted that downstream of the mixing of the two flows, a flow of first concentrate 117 and a flow of second permeate 131, a flow of mixed water 146 is generated.

[0155] In particular, the mixed waters 146 from connection 145 present:

[0156] - a concentration of divalent salts lower than the concentration of divalent salts of the first concentrate 117 from the nanofiltration device 115,

[0157] - a mineral concentration lower than the predetermined mineral concentration of the water to be treated,

[0158] - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated,

[0159] - a SAR value lower than water 101, and

[0160] - a concentration of nutritious organic matter.

[0161] 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.

[0162] Optional inlets for water to be treated

[0163] Figure 2, which is not to scale, shows a schematic view of an embodiment of the system 200 which is the subject of the present invention.

[0164] In embodiments, such as that shown in FIG. 2, the system 200 comprises a second inlet 201 for water to be treated 101. It can be seen that the second inlet 201 is connected to the outlet 125 of the first concentrate 117 from the nanofiltration device 115.

[0165] In other embodiments (not shown), the water circulating in the second inlet 201 and the water to be treated 101 introduced into the nanofiltration device 115 are of a different nature.

[0166] In other words, the flow of water circulating in the second inlet 201 and the flow of first concentrate 117 are mixed.

[0167] In embodiments, such as that shown in FIG. 2, the system 200 comprises a third inlet 202 for water to be treated 101. It can be seen that the third inlet 202 is connected to the outlet 120 of the first permeate 116 from the nanofiltration device 115.

[0168] In other embodiments (not shown), the water circulating in the third inlet 202 and the water to be treated 101 introduced into the nanofiltration device 115 are of a different nature.

[0169] In other words, the flow of water circulating in the third inlet 202 and the flow of the first permeate 116 are mixed upstream of the reverse osmosis device 130. It is noted that the inlets, 105, 201 and 202, and the outlets, 125, 140 and 135 designate, for example, pipes configured to transport a flow of water. Such pipes are known to those skilled in the art.

[0170] pH adjustment method

[0171] Figure 3, which is not to scale, shows a schematic view of an embodiment of the system 300 which is the subject of the present invention. The water treatment system 300 101 comprises:

[0172] - a first inlet 105 of water to be treated 101 comprising a means 301 for adjusting the pH and

[0173] - an outlet 120 of the first permeate 116, coming from the nanofiltration device 115, comprising a pH adjustment means 302.

[0174] It is noted that the water leaving 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 by means of a controlled dosing pump:

[0175] - either to a pH setting of the packaged water,

[0176] - or simply at a dosage proportional to the flow rate of water to be treated.

[0177] In embodiments, a means 301 and / or 302 for adjusting water to an acidic pH comprises a means for adding an acid in a predetermined amount.

[0178] In other embodiments, a means 301 and / or 302 for adjusting the water to a basic pH comprises a means for adding a base in a predetermined amount.

[0179] In variants, a means 301 and / or 302 for adjusting water to neutral pH comprises a means for adding a base and / or an acid in a predetermined quantity.

[0180] It is noted that the quantity of base or acid to be added depends on the target pH and the initial pH of the water upstream of the adjustment means, 301 and 302.

[0181] Thus, the device has the ability to achieve a real sorting of the substances of interest by separating the two pH regulations, on either side, of a nanofiltration membrane and upstream of a reverse osmosis, 301 and 302, thus making possible the staged selection of substances of interest, not only by rejection of the membrane in the concentrate, but also by selective permeation through the nanofiltration membranes, then reverse osmosis to bring together substances in the produced water. The process makes possible, for example, new combinations of selection and rejection of substances. The following table illustrates the solutions offered by the process in the case of the presence of ammonium and VFA (volatile fatty acids), with different situations where the process offers the possibility of adapting the proportions N, P, K and organic carbon.

[0182] Preferably, as illustrated in figure 3, the system 300 further comprises a 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:

[0183] - 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.

[0184] The adjustment means 701 is described with reference to FIG. 7.

[0185] Preferably, the pH adjustment means 301, 302 is configured to carry out the pH adjustment according to a decision scheme for sorting the components of interest and / or the undesirable components according to the pH conditions favoring the permeation or rejection of these components.

[0186] Preferably, the pH adjustment means 301, 302 is configured to use, in a combined manner, at least one acid and at least one specific base to contribute to the sequential sorting with the benefit of balancing the N / P / K and organic carbon proportions.

[0187] Pretreatment unit

[0188] Figure 4, which is not to scale, shows a schematic view of an embodiment of the system 400 which is the subject of the present invention. The water treatment system 400 101 comprises a water pretreatment unit 401. Such a 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 arranged 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.

[0189] It is noted that the pretreatment unit 401 is configured to generate the water to be treated 101 introduced into the nanofiltration device 115.

[0190] 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.

[0191] 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.

[0192] For example, an ultrafiltration device has a porous membrane with a pore size between 1 and 100 nm.

[0193] It is noted that the secondary nanofiltration device is of the same nature as the nanofiltration device 115 or of a different nature.

[0194] 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.

[0195] Figure 5, which is not to scale, shows a schematic view of an embodiment of the system 500 which 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 from the reverse osmosis device 130.

[0196] It is noted that the second concentrate 132 comprises predominantly monovalent salts at high concentration. The second concentrate 132 is used as washing and unclogging water for the membrane filtration device 402 of the pretreatment unit 401.

[0197] 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.

[0198] Means of treatment by a sequestering additive Figure 6, which is not to scale, shows a schematic view of an embodiment of the system 600 which is the subject of the present invention. The system 600 comprises a means of treatment 601 by a sequestering additive. In particular, such a sequestering additive is specific to a predetermined chemical species.

[0199] It should be noted that the term "sequestrant" is used even if it does not necessarily designate a complexation. It is, for the majority of cases, an anti-scale product by threshold effect. The doses used are very clearly lower than the doses of the reaction stoichiometry with the potentially sequestered element, but act on the crystallization mechanism by hindering or delaying its formation. The anti-scale character by threshold effect or dispersant depends on the type of molecule and its molecular weight. The main element targeted by the "sequestrant" is calcium carbonate, the crystallization of which responds to the calco-carbonic equilibrium.

[0200] In this case, it can act in conjunction with pH adjustment by acidification and CO2 formation. Other species are maintained in over-stabilization (i.e. in a concentration higher than their theoretical solubility), such as barium sulfate, strontium sulfate, calcium sulfate, silica, magnesium silicate, calcium fluoride, calcium phosphate, etc.

[0201] 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 the anti-scale character rather by threshold or dispersant effect.

[0202] EDTA is a powerful complexing agent, but is not used as a preventative "sequestrant". However, it can be used for curative maintenance operations (complexing cleaning to break up the deposits formed).

[0203] In embodiments, such as that shown in FIG. 6, the treatment means 601 with a sequestering additive is arranged upstream of the nanofiltration device 115.

[0204] In embodiments (not shown), the treatment means 601 with a sequestering additive is arranged upstream of the reverse osmosis device 130.

[0205] It is noted that, in these embodiments, the predetermined chemical species is undesirable and has a limited or even zero concentration in the flow of water to be treated 101 downstream of the treatment means 601 by a sequestering additive.

[0206] In embodiments, the sequestering agent is one of those described above and specific for one or more predetermined chemical species such as those described above.

[0207] Means of adjusting conversion rates

[0208] Figure 7, which is not to scale, shows a schematic view of an embodiment of the system 700 which is the subject of the present invention. The system 700 comprises 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 adjusting a flow rate using a manual or automatic adjustment valve. The concentrate flow rate is adjusted to correspond to a target percentage of the total flow rate admitted into the device.

[0209] In particular, such conversion rates correspond to the ratios:

[0210] - between the flow rate of the first permeate 116 and the flow rate of the water to be treated 101, and

[0211] - between the flow rate of the second permeate 131 and the flow rate of the first permeate 116.

[0212] In embodiments, the adjustment means 701 comprises a means (not shown) for regulating the flow rate of the water to be treated 101. Such a regulation means is controlled as a function of the conversion rate to be achieved for the nanofiltration device 115. For example, the conversion rate to be achieved is defined by a targeted performance inherent to the nanofiltration device 115.

[0213] In embodiments, the adjustment means 701 comprises a means for regulating (not shown) the flow rate of the first permeate 116. 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 targeted performance inherent to the reverse osmosis device 130.

[0214] Water treatment process

[0215] Figure 8 shows a schematic view of an embodiment of the method 800 which is the subject of the present invention. The method 800 is a method for treating water having a predetermined mineral concentration and a predetermined concentration of monovalent salts.

[0216] The 800 water treatment process includes:

[0217] - a first stage 805 of water inlet to be treated;

[0218] - a selective nanofiltration step 810, downstream of the water inlet step to be treated,

[0219] - an output step 815 of the first permeate from the nanofiltration step,

[0220] - an output step 820 of the first concentrate from the nanofiltration step,

[0221] - a reverse osmosis stage 825, downstream of the stage of the output of the first permeate from the nanofiltration stage,

[0222] - an output stage 835 of the second permeate from the reverse osmosis stage,

[0223] - an output stage 830 of the second concentrate from the reverse osmosis stage and

[0224] - a connection step 840 for mixing the first concentrate from one output step and the second permeate from another output step.

[0225] During the selective nanofiltration step 810, a first permeate selectively comprising monovalent salts is formed and a first concentrate selectively comprising divalent salts is also formed.

[0226] During the reverse osmosis step 825 a second permeate comprising salt-free water is formed and a second concentrate comprising salts is also formed.

[0227] During the connection step 840, a dilution of the first concentrate is carried out. 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,

[0228] - a concentration of monovalent salts lower than the predetermined concentration of monovalent salts in the water to be treated,

[0229] - a SAR value lower than water 101, and

[0230] - a concentration of nutrients, for example nutrients and nitrogenous materials.

[0231] Preferably, the method which is the subject of the invention also comprises (not shown):

[0232] - a pH adjustment step, in at least the first inlet step of water to be treated and the outlet step of the first permeate from the nanofiltration step, so that the water leaving the adjustment means has an acidic, substantially neutral or basic pH;

[0233] - a step of adjusting the conversion rates of the nanofiltration step and / or the reverse osmosis step, the conversion rates corresponding to the ratios:

[0234] - between the flow rate of the first permeate and the flow rate of the water to be treated, and

[0235] - between the flow rate of the second permeate and the flow rate of the first permeate.

[0236] Preferably, the means of the systems 100, 200, 300, 400, 500, 600 and / or 700 are configured to implement the steps of the method 800 and their embodiments as set out above and the method 800 as well as its different embodiments can be implemented by the means of the systems 100, 200, 300, 400, 500, 600 and / or 700.

[0237] Additionally, in embodiments, the method which is the subject of the invention is a method for selecting species dissolved in water by mixing a nanofiltration concentrate obtained from raw water, also called water to be treated, optionally pretreated, mixing carried out with

[0238] - demineralized water obtained from the permeate of reverse osmosis filtering the permeate of nanofiltration, where

[0239] - to a mixture of nanofiltration permeate and possibly pre-treated raw water.

[0240] Furthermore, in embodiments, the device which is the subject 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 beneficial species for the intended application. The intended application being, for example, irrigation from wastewater or the purification of water contaminated by nitrate and / or ammonium.

[0241] In embodiments, the device of the invention provides pH adjustment upstream of nanofiltration or reverse osmosis.

[0242] 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. The different embodiments of the system which is the subject of the invention are intended to be combined to form other embodiments of the invention. In particular, the systems 300 and 700 are intended to be combined to form a system comprising both at least one pH adjustment means described with reference to Figure 3 and a means of adjusting the conversion rates described with reference to Figure 7.

[0243] The means of acidifying or alkalizing the water and the means of adjusting the conversion rates make it possible to preserve all the elements of agronomic interest, a given pH being favorable to certain species and unfavorable to others. With this system and the corresponding process, optimization by pH regulation of the retention of ammoniacal nitrogen in the irrigation water and optimization of the retention of ionized organic matter (for example, volatile fatty acids) or phosphorus are jointly obtained. This system makes it possible to reconcile an optimal pH for the objective of conserving nutrients and maintaining the solubility of the salts present in the water. Thus, for example, the alkaline pH required for the retention of volatile fatty acids does not oppose the conservation of solubility conditions in the calco-carbonic balance. This system thus makes it possible to achieve objectives of selection of elements of agronomic interest.

[0244] In addition, for pH regulation, the products used are preferably of agronomic interest and the salts and ions resulting from their dosage contribute positively to the quality of the water and its SAR value. For example, the use of hydrochloric acid and sodium hydroxide is preferably avoided to prevent enrichment of the water with species harmful to crops (chloride and sodium).

Claims

CLAIMS 1. System (300) 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) of water to be treated, - a selective nanofiltration device (115), connected to the inlet of 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) of the first permeate from the nanofiltration device, - an outlet (125) of 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) of the second permeate from the reverse osmosis device, - an outlet (140, 540) of 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 in the water to be treated; - system 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, configured so that the water leaving the adjustment means has an acidic, substantially neutral or basic pH; - system which further comprises a 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.

2. System (300) according to claim 1, wherein the pH adjustment means (301, 302) is configured to carry out the pH adjustment according to a decision scheme for sorting the components of interest and / or the undesirable components according to the pH conditions favoring the permeation or the rejection of these components.

3. System (300) according to one of claims 1 or 2, in which the pH adjustment means (301, 302) is configured to use, in combination, at least one acid and at least one specific base to contribute to the sequential sorting with the benefit of balancing the N / P / K and organic carbon proportions.

4. System (300) according to one of claims 1 to 3, which further comprises a second inlet (201) for water to be treated (101) connected to the outlet (125) of the first concentrate (117) from the nanofiltration device (115).

5. System (300) according to one of claims 1 to 4, 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).

6. System (400, 500) according to one of claims 1 to 5, 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).

7. System (400) according to claim 6, 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.

8. System (500) according to one of claims 6 or 7, 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.

9. System (600) according to one of claims 1 to 8, 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).

10. Method (800) for treating water having a predetermined mineral concentration and a predetermined monovalent salt concentration, the method 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 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; - a pH adjustment step, in at least the first inlet step of water to be treated and the outlet step of the first permeate from the nanofiltration step, so that the water leaving the adjustment means has an acidic, substantially neutral or basic pH; - a step of adjusting the conversion rates of the nanofiltration step and / or the reverse osmosis step, 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.

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