Liquid filtration method and plant

Abstract

The invention relates to a method that comprises the following steps: - filtering an incoming liquid stream (30) by means of a filtration device (25) comprising a membrane module having a membrane filter (60), in order to form a permeate stream (40), at least one fraction of which constitutes the treated liquid stream, and a concentrate stream (50); - dividing one of the concentrate stream (50) and the permeate stream (40) into a first fraction (70), which is provided at an outlet (71) of the plant, and a second fraction (75); - measuring at least one parameter representative of the permeate stream (40) and comparing it to a range of target values; and - determining, by means of a control device (90), using the result of the comparison, a zero or non-zero flow rate of the second fraction; - recirculating the second fraction at the determined flow rate and mixing it with the stream to be treated.

Description

[0001] TITLE: Liquid filtration process and installation

[0002] The present invention relates to a method for filtering a liquid stream to be treated for the production of treated water, the method comprising the following steps:

[0003] - filtration, by a filtration device of a filtration installation, of an incoming liquid flow comprising at least a fraction of the flow to be treated, the filtration device comprising at least one membrane module having at least one filter membrane, to form:

[0004] (i) a permeate stream, comprising the liquid stream(s) from the incoming stream produced after passing through at least one of said filter membranes of the filtration device, at least a fraction of the permeate stream constituting the treated liquid stream from the process, and

[0005] (ii) a concentrate stream, comprising the liquid stream(s) from the incoming stream which have not passed through any filter membrane.

[0006] The present invention also relates to a corresponding filtration installation.

[0007] To treat liquid phases with a view to removing all or part of the solutes or undesirable compounds, and in particular in water treatment, for example for the production of drinking water, many processes include the implementation of one or more filtration stages.

[0008] The filtration step(s) are carried out using a filtration system comprising one or more filter membranes, in particular nanofiltration and / or reverse osmosis membranes. The filter membranes are arranged in membrane modules of various geometries. These include tubular modules, in which the membranes are placed inside a porous support tube or one pierced with drainage holes.

[0009] For a liquid composition to be treated at the inlet of the filtration installation, the composition of the liquid treated at the outlet of the installation depends in particular on the nature of the filter membranes, their number and the way in which they are associated with each other. The composition of the liquid treated also depends on the working temperature and pressure.

[0010] However, the composition of the liquid to be treated and / or its temperature are not necessarily constant over time, so that the composition of the treated liquid supplied by a given filtration installation may only be satisfactory part of the time, possibly making one or more additional treatment steps of the treated liquid necessary. For the production of drinking water, an additional treatment step is, for example, a post-mineralization step.

[0011] FR 3 096 279 describes a membrane filtration installation for liquids comprising a plurality of reverse osmosis and nanofiltration membranes.

[0012] The filtration system produces treated water with a target hardness regardless of the calcium ion composition of the water to be treated and / or the temperature of this water. To achieve this, a parameter of the water to be treated, chosen from the calcium ion concentration and the water temperature, is measured at the inlet of the system. A set of valves is used to define the membranes through which the water to be treated will actually pass, depending on this parameter, in order to obtain the target hardness at the outlet.

[0013] However, the adaptability of such an installation to the composition and temperature of the liquid to be treated is limited by the number of membrane combinations permitted by the different valves present in the installation.

[0014] Furthermore, adapting the number, type and order of the membrane modules comprising the filter membranes passed through according to a parameter at the inlet of the installation is not sufficient to guarantee the quality of the liquid at the outlet of the installation, insofar as the filtration properties of each of the filter membranes can change over time.

[0015] The installation is also complex to operate and maintain, particularly due to the large number of pieces of equipment required to modify the installation's configuration.

[0016] An aim of the invention is therefore to propose a liquid filtration method, simple to implement to obtain a treated liquid of controlled composition, in particular for a greater variety of compositions of liquids to be treated and / or a greater variety of operating temperatures.

[0017] To this end, the invention relates to a method for filtering a flow of liquid to be treated for the production of treated water, the method comprising the following steps:

[0018] - filtration, by a filtration device of a filtration installation, of an incoming liquid flow comprising at least a fraction of the flow to be treated, the filtration device comprising at least one membrane module having at least one filter membrane, to form:

[0019] (i) a permeate stream, comprising the liquid stream(s) from the incoming stream produced after passing through at least one of said filter membranes of the filtration device, at least a fraction of the permeate stream constituting the treated liquid stream from the process, and (ii) a concentrate stream, comprising the liquid stream(s) from the incoming stream and which have not passed through any filter membrane; the process being characterized by the following steps:

[0020] - dividing one of the concentrate stream and the permeate stream into a first fraction supplied to an outlet of the filtration plant, and a second fraction;

[0021] - in at least one nominal measurement configuration, measurement of at least one parameter representative of the permeate flow and comparison with a range of target values ​​defined by at least one predetermined threshold value; and

[0022] - determination by a control device of a zero or non-zero flow rate of the second fraction using the result of the comparison;

[0023] - recirculation of the second fraction at the flow rate determined by the control device and mixing with the flow to be treated to form the flow entering the filtration device.

[0024] The filtration method according to the invention comprises a control of the flows entering and leaving the filtration device of the installation by a parameter representative of the treated liquid obtained at the outlet of the installation.

[0025] The measurement of at least one parameter of the permeate flow and its comparison with a range of target values ​​makes it possible to evaluate the real effect of the filtration installation on the liquid to be treated, and to adapt, possibly in real time, the operation of this installation if this real effect is not the expected one.

[0026] The range of target values ​​is defined, for example, by a predetermined threshold value, the target values ​​then being the values ​​strictly greater than or greater than or equal to the threshold value, or alternatively the values ​​strictly less than or less than or equal to the threshold value. Alternatively, the range of target values ​​is defined by a predetermined lower threshold value and an upper threshold value, the target values ​​then being the values ​​between the lower and upper threshold values.

[0027] The recirculation of a fraction of the concentrate or a fraction of the permeate determined according to the result observed at the outlet of the installation, and their mixing with the liquid to be treated modifies the composition of the liquid entering the filtration device, to obtain a satisfactory composition of treated liquid. This effect is obtained independently of fluctuations in the composition of the liquid to be treated and / or, among other things, the working temperature.

[0028] Recirculation of a concentrate fraction increases the concentration of a given chemical species that is too low in the treated liquid, in particular because filtration is excessive due to a particularly low operating temperature of the installation. On the contrary, recirculation of a permeate fraction dilutes the liquid to be treated if filtration is actually insufficient, for example due to a particularly high operating temperature of the installation or a particularly high concentration of a given compound, in particular of a given chemical or microbiological species in the liquid to be treated.

[0029] The filtration process also has the advantage of not requiring the multiplication of filtration means in a filtration installation on which it is implemented, only a recirculation loop for the permeate or concentrate flows being added to an existing filtration device.

[0030] According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0031] - the at least one parameter representative of the permeate flow is chosen from a temperature or a temporal variation of this temperature, a parameter representative of an electrical conductivity or a temporal variation of this electrical conductivity, a parameter representative of a concentration of an ionic or molecular species or of a group of ionic or molecular species or of a temporal variation of this concentration;

[0032] - in the division step, only the concentrate stream is divided into a first fraction and a second fraction, the first fraction of the concentrate stream being supplied to an outlet of the filtration plant, and the entire permeate stream constitutes the treated stream;

[0033] - in the division step, only the permeate stream is divided into a first fraction and a second fraction, the first fraction of the permeate stream constituting the treated stream and being supplied to an outlet of the filtration installation, and the entire concentrate stream is supplied to an outlet of the filtration installation;

[0034] - the division step comprises: a) at least a first phase of controlling a divider of the filtration installation to divide the permeate flow into a first fraction of the permeate flow which constitutes the treated flow, and a second fraction of the permeate flow which forms the second fraction intended to be recirculated, without dividing the concentrate flow, b) and at least a second phase of controlling a divider of the filtration installation to divide the concentrate flow into a first fraction of the concentrate flow, which is supplied to an outlet of the filtration installation, and a second fraction of the concentrate flow which forms the second fraction intended to be recirculated, without dividing the permeate flow; - several parameters representative of the permeate flow are measured and a weight is assigned to each of these parameters for determining the flow rate of the second fraction;

[0035] - the method further comprises the transmission of additional data representative of the composition of the flow to be treated, the additional data being used to determine the flow rate of the second fraction;

[0036] - the additional data are chosen from meteorological data, dates, data relating to a source of pollution upstream of the flow to be treated and measurement data from at least one additional measurement sensor of a parameter representative of the flow to be treated;

[0037] - the determination of the flow rate of the second fraction by the control device comprises the transition from the nominal measurement configuration to an alternative configuration, in which the value of the flow rate of the second fraction is determined as a function of at least one of the additional data transmitted, without using measurement of at least one parameter representative of the permeate flow;

[0038] - the filtration device comprises at least one membrane row comprising several filtration stages each comprising at least one membrane module comprising a filter membrane, in particular at least one pressure tube comprising a plurality of membrane modules, and the filtration step comprises, for at least one of said membrane rows, the production from at least part of the liquid flow entering the filtration device: i) of a permeate stream, bringing together liquid flows having passed through at least one filter membrane of at least one stage of the membrane row, the permeate stream being intended to form at least partially the permeate stream, and ii) of a concentrate stream, originating from the liquid flow entering the membrane row after introduction into all the stages of the membrane row successively without passing through any of the filter membranes of these stages,the concentrate stream being intended to at least partially form the concentrate flow;,

[0039] - the filtration device comprises a plurality of membrane rows, the filtration step comprising the grouping of the permeate streams from each of the membrane rows to form the permeate flow, and the grouping of the concentrate streams from each of the membrane rows to form the concentrate flow;

[0040] - the filtration method is configured for the production of a treated flow of which a respective concentration in at least one micropollutant of interest is included in a respective predetermined target value range; and - the filtration method is configured for the production of a treated flow of which a respective concentration in at least one ionic species, chosen from calcium ions, magnesium ions and their mixtures, is included in a respective predetermined target value range.

[0041] The invention also relates to an installation for filtering a liquid flow for the production of treated water, receiving a flow of liquid to be treated and providing a flow of treated liquid, the filtration installation comprising:

[0042] 1) a filtration device comprising at least one filter membrane, the filtration device being configured to provide, from an incoming flow of liquid comprising at least a fraction of the flow to be treated:

[0043] (i) a permeate stream, comprising all the liquid streams originating from the incoming stream after passing through at least one of said filter membranes, and of which at least a fraction constitutes the treated stream, and

[0044] (ii) a concentrate stream, originating from the incoming stream and which has not passed through any filter membrane,

[0045] 2) downstream of the filtration device, a divider of at least one of the concentrate flow and the permeate flow into a first fraction supplied to an outlet of the installation and into a second fraction,

[0046] 3) a system for recirculating the second fraction, configured to mix the second fraction with the flow to be treated so as to form the flow entering the filtration device, the installation further comprising:

[0047] 4) at least one device for measuring a parameter representative of the permeate flow,

[0048] 5) a divider control device, configured, in at least one nominal measurement configuration, to receive measurement data from the at least one measurement device, to compare the received measurement data to at least one range of target values ​​defined by at least one predetermined threshold value and to determine the value of a flow rate of the second fraction depending on the result of the comparison.

[0049] According to one embodiment, the filtration installation comprises one or more of the following characteristics:

[0050] - the at least one filter membrane is chosen from a reverse osmosis membrane and a nanofiltration membrane;

[0051] - the control device comprises a system for receiving additional data, chosen from meteorological data, dates, data relating to a source of pollution upstream of the flow to be treated and measurement data from at least one additional measurement sensor of a parameter of the flow to be treated, the control device being configured to switch from the nominal measurement configuration to an alternative configuration, in which the value of the flow rate of the second fraction is determined as a function of at least one of the additional data transmitted, without using measurement of at least one parameter representative of the permeate flow.

[0052] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0053] [Fig. 1] Figure 1 represents a first filtration installation according to the invention;

[0054] [Fig. 2] Figure 2 represents a second filtration installation according to the invention;

[0055] [Fig. 3] Figure 3 represents a third filtration installation according to the invention.

[0056] Figure 1 illustrates a first filtration installation 10 configured to receive a flow to be treated 15 of liquid at an installation inlet 16 and to provide a treated flow 20 of liquid at an installation outlet 17.

[0057] The flow to be treated 15 is advantageously an aqueous phase, in particular water to be treated, such as waste water, industrial water, sea water, or drinking water or water in the process of being made potable.

[0058] The flow to be treated 15 in this case contains mainly water, as well as one or more solutes. The solutes can be ions. For example, these ions are calcium, magnesium, sodium, carbonate, bicarbonate, sulfate, chlorate ions. The solutes are for example organic molecules, such as organic matter, hydrocarbons or even micro-pollutants, in particular pesticides, drug residues or industrial residues.

[0059] The flow to be treated 15 also includes in certain cases suspended solid particles.

[0060] The installation 10 of FIG. 1 comprises a membrane line 25, configured to receive an incoming flow 30 of liquid at a membrane line inlet 32, and an inlet pipe 33 fluidly connecting the installation inlet 16 to the membrane line inlet 32. The incoming flow 30 comprises at least a portion of the flow to be treated 15.

[0061] The installation 10 also includes a pump 34 for pressurizing the incoming flow 30 positioned in the inlet pipe 33 upstream of the inlet 32.

[0062] The membrane line 25 is configured to provide a first membrane line outlet 35 with a permeate flow 40, and a second membrane line outlet 45 with a concentrate flow 50. The membrane line 25 comprises an upstream stage 55, a downstream stage 57 and possibly, as shown in FIG. 1, one or more intermediate stages 56.

[0063] Each stage 55, 56, 57 is configured to, from a received liquid stream, provide a permeate stream 55A, 56A, 57A and a concentrate stream 55B, 56B, 57B.

[0064] Each stage 55, 56, 57 comprises at least one membrane module comprising at least one filter membrane 60, preferably a plurality of filter membranes 60 in series.

[0065] The filter membrane 60 is advantageously chosen from a reverse osmosis membrane and a nanofiltration membrane.

[0066] Each stage 55, 56, 57 may typically comprise at least one pressure tube, each pressure tube typically comprising between one and eight membrane modules.

[0067] Each stage 55, 56, 57 may comprise several pressure tubes in parallel, each pressure tube receiving a fraction of the liquid stream received by the stage and providing a fraction of the permeate stream 55A, 56A, 57A and a fraction of the concentrate stream 55B, 56B, 57B.

[0068] Alternatively, the membrane line 25 comprises a plurality of different stages 55, 56, 57, the successive stages advantageously comprising numbers and types of filter membranes 60 different from each other. The number of filter membranes 60 of a given stage 55, 56, 57 is advantageously greater than that of the stages which are located downstream.

[0069] The stages 55, 56, 57 of FIG. 1 are, for example, connected in series from the point of view of the concentrate, so that the incoming flow 30 is the flow supplied to the upstream stage 55, the concentrate flow 50 consists of the concentrate flow 57C from the downstream stage 57 and the permeate flow 40 consists of the permeate flows 55A, 56A, 57A of the different stages 55, 56, 57 which have been grouped together.

[0070] Downstream of the second outlet 45 of the membrane line 25, the installation 10 comprises a divider 65, capable of dividing the concentrate flow 50 into a first fraction 70 which is brought to an outlet 71 of the installation 10 and into a second fraction 75.

[0071] The divider 65 of Figure 1 comprises a collection pipe 82 having one end connected to the outlet 45 of the membrane line 32, a recirculation branch 80, and a discharge branch 81, the branches 80, 81 being connected to another end of the collection pipe 82. The divider 65 further comprises a flow control valve 85 mounted on the recirculation branch 80. The valve 85 is for example a two-way valve, electrically controlled.

[0072] The installation 10 further comprises a control device 90 for the divider 65. The control device comprises, for example, a computer comprising at least one processor and at least one memory configured to store software modules capable of being executed by the processor to perform the functions described below. Alternatively, the computer comprises programmable logic components or dedicated integrated circuits, intended to perform the functions which will be described below.

[0073] The control device 90 is configured to receive measurement data of at least one parameter representative of the permeate flow 40, to generate a control signal for the valve 85 to control the flow rate of concentrate fluid 75 passing through the recirculation branch 80 as a function of the data received to adjust the or each representative parameter measured within the permeate flow 40, and to transmit this control signal to the valve 85.

[0074] The installation 10 comprises a system for recirculating the second fraction 75. In the embodiment of FIG. 1, the recirculation system comprises a tapping 95 connected to the valve 85 and to the inlet pipe 33 between the inlet 16 of the installation 10 and the inlet 32 ​​of the membrane line 25.

[0075] Downstream of the first outlet 35 of the membrane line 25, the installation 10 comprises a measurement sensor 100 configured to measure one or advantageously several parameters representative of the permeate flow 40 and transmit measurement data to the control device 90.

[0076] The measuring sensor 100 is advantageously positioned upstream of the outlet 17 as shown in FIG. 1.

[0077] Alternatively, the measuring sensor 100 or another measuring device is located in a laboratory located at a distance from the membrane line 25, a fraction of the permeate flow 40 being sampled continuously or periodically to be transmitted to the laboratory and analyzed in this laboratory by means of the measuring sensor 100 or the other measuring device.

[0078] The parameter representative of the permeate flow 40 to be measured is for example a physical parameter, in particular a temperature, an electrical conductivity, a pH or even a measurement of particles of the permeate flow 40, or a temporal variation of such a quantity.

[0079] For example, electrical conductivity can be measured according to ISO 7888:1985 of May 1985. For example, pH can be measured according to ISO 10523:2008 of December 2008.

[0080] Alternatively, the parameter representative of the permeate flow 40 is a chemical parameter such as a concentration of an ionic or molecular species dissolved in the permeate flow 40 or a temporal variation of this concentration. In the present application, the expression chemical parameter encompasses the microbiological parameters representative of the concentration of one or more microorganisms in the water, in particular a bacterium or a virus.

[0081] Alternatively, the parameter representative of the permeate flow 40 is a parameter representative of a concentration of a group of ionic or molecular species dissolved in the permeate flow 40 or of a temporal variation of this concentration. For example, the measurement sensor 100 is configured to measure a hydrotimetric titer (TH) or even the total organic carbon (TOC) or a fraction of the TOC, or a concentration of one or more micropollutants.

[0082] For example, the TOC can be measured according to the NF EN 1484 standard of July 1997.

[0083] For example, water hardness can be measured by titrimetric measurement, according to standard NF T90-003 of August 1984.

[0084] For example, the concentrations of calcium ions and magnesium ions can each be measured according to the NF EN ISO 14911 standard of October 1998.

[0085] For example, the concentration of nitrate ions can be measured according to the NF ISO 15923-1 standard of January 2014.

[0086] Thus, according to the invention, on the basis of the measurements of the or each parameter representative of the permeate flow 40 carried out by the measurement sensor 100, the control device 90 is configured to control the flow rate of the concentrate flow passing through the recirculation branch 80 and the tapping 92, in order to adjust in response the value of the or each parameter representative of the permeate flow 40.

[0087] A filtration method according to the invention, implemented in the installation 10 of figure 1, will now be described.

[0088] A flow to be treated 15 is supplied continuously or sequentially to the inlet 16 of the installation 10. As will be seen below, the flow to be treated 15 receives the second fraction 75 from the recirculation branch 80 to form the incoming flow 30 supplied to the inlet 32 ​​of the membrane line 25.

[0089] The incoming flow 30 enters, after pressurization by means of the pressurization pump 34, the upstream stage 55. A portion of the incoming flow 30 passes through the filtration membrane 60 of the upstream stage 55 to constitute an upstream permeate flow 55A. The remainder of the incoming flow 30 does not pass through the filtration membrane 60 of the upstream stage 55 and forms an upstream concentrate flow 55B.

[0090] The upstream concentrate stream 55B then enters the intermediate stage 56. A portion of the upstream concentrate stream 55B passes through the filter membrane 60 of the intermediate stage 56 to form an intermediate permeate stream 56A. The remainder of the upstream concentrate stream 55B does not pass through the filter membrane 60 of the intermediate stage 56 and forms the intermediate concentrate stream 56B.

[0091] The intermediate concentrate stream 56B then enters the downstream stage 57. A portion of the intermediate concentrate stream 56B passes through the filter membrane 60 of the downstream stage 57 to form the downstream permeate stream 57A. The remainder of the intermediate concentrate stream 56B does not pass through the filter membrane 60 of the downstream stage 57 and forms the downstream concentrate stream 57B.

[0092] The downstream concentrate flow 57B forms the concentrate flow 50 which is recovered at the second outlet 45 of the membrane line 25.

[0093] The permeate streams 55A, 56A, 57A are grouped together to constitute the permeate stream 40. The permeate stream 40 is produced at the first outlet 35 of the membrane line 25.

[0094] The measuring sensor 100 measures at given times the or each parameter to be measured in the permeate flow 40, then transmits the measurement results to the control device 90.

[0095] Advantageously, the measurement of one or more parameters is carried out periodically.

[0096] Advantageously, the measurement period depends on the parameter representative of the permeate flow to be measured. For example, if the treated flow 20 is a drinking water flow or one in the process of being made potable, the total organic carbon can be measured weekly and the hardness can be measured with a period of the order of a minute.

[0097] For the or each measured parameter, the control device 90 compares the value of the parameter to a range of predetermined target values ​​of the parameter.

[0098] The range of target values ​​is defined either by a predetermined threshold value, the target values ​​then being the values ​​strictly greater than or greater than or equal to the threshold value or strictly less than or less than or equal to the threshold value, or by a predetermined lower threshold value and an upper threshold value, the target values ​​then being the values ​​between the lower and upper threshold values.

[0099] Advantageously, the parameters representative of the permeate flow 40 include regulatory parameters, the threshold values ​​or target value ranges of which are imposed by a standard. In the example of drinking water, the regulatory parameters and the corresponding target value ranges are, for example, defined by the following standards: in France, by the decree of January 11, 2007 relating to the quality limits and references of raw water and water intended for human consumption mentioned in Articles R. 1321-2, R. 1321-3, R. 1321-7 and R. 1321-38 of the Public Health Code; in Europe, by European Union Directive No. 2020 / 2184 of December 16, 2020 relating to the quality of water intended for human consumption; internationally, by the “Guidelines for drinking-water quality, fourth edition, incorporating the 1st and 2nd addenda. Geneva: World Health Organization; 2022.” (ISBN 978-92-4-004506-4).

[0100] Advantageously, the parameters representative of the permeate flow 40 include comfort parameters, the target value ranges of which are not imposed by a standard. These parameters are possibly imposed by specifications freely defined by an operator or a user of the installation 10.

[0101] In the example of drinking water production, water hardness or conductivity can belong to the group of comfort parameters. The target value range for water hardness is, for example, [8°TH, 12°TH],

[0102] If the measurement result(s) are within the respective target value ranges, the control of the valve 85 advantageously remains identical.

[0103] If at least one measurement result is outside a target value range, the control device 90 determines a new value of the flow rate of the second fraction 75.

[0104] In one example, if a measurement result is too low compared to the respective target value range associated with that result, the flow rate of the second fraction 75 is increased. On the other hand, if the measurement result is too high compared to the respective target value range, the flow rate of the second fraction 75 is reduced or even stopped.

[0105] Advantageously, the measurement results of several different parameters representative of the permeate flow 40 are taken into account for determining the value of the flow rate of the second fraction 75.

[0106] Advantageously, priorities or weights are assigned to each of the parameters representative of the permeate flow 40 for determining the value of the flow rate of the second fraction 75.

[0107] For example, the comfort parameters have different weights from each other, the regulatory parameters have different weights from each other, and the regulatory parameters have higher weights than the comfort parameters. The flow rate of the second fraction 75 determined then results from a compromise between the degradation of certain parameters representative of the permeate flow 40 and the improvement of other parameters representative of the permeate flow 40.

[0108] For example, the flow rate of the second fraction 75 is chosen so that the regulatory parameters of higher priority are within the respective target value range after adjustment of this flow rate, some of the other parameters, in particular the comfort parameters, may approach their respective target value range, without however reaching it.

[0109] In an example of drinking water production, the installation 10 may have been sized so that the hardness of the water supplied to the outlet 17 is in the range [8°TH, 12°TH] with the flow of water to be treated 15 received by this installation 10 throughout the year, considering that this flow is always received at temperatures above 15°C.

[0110] If the temperature of the flow to be treated 15 drops below 15°C in winter, the pores of the filters contract, the filtration is sometimes excessive, leading to a hardness too low for the comfort of a drinking water consumer. In this example, the recirculation of the second fraction 75 with a non-zero flow rate adjusts the water hardness. Such a measure is taken without degrading certain regulatory parameters.

[0111] Optionally, the control device 90 receives additional data from one or more measuring sensors (not shown) of a parameter of the flow to be treated 15 placed upstream of the membrane line 25. The parameter of the flow to be treated 15 is advantageously of the same type as the parameters of the permeate flow 40.

[0112] Optionally, the control device 90 receives additional data representative of the composition of the flow to be treated 15 transmitted by a remote operator or not and possibly extracted from a database. In the example of the production of drinking water, this may in particular be spreading data or meteorological data. The spreading data makes it possible, for example, to alert on point pollution, in particular due to a micropollutant. The meteorological data makes it possible, for example, to anticipate a possible variation in the temperature or composition of water, for example under the effect of a flood upstream of the installation 10.

[0113] To this end, the filtration installation 10 may comprise one or more additional measurement sensors (not shown) upstream of the inlet 16, each additional sensor being configured to measure at least one additional data representative of the composition of the flow to be treated 15. The value of the flow rate of the second fraction 75 is then optionally determined by the control device 90 also as a function of this additional data.

[0114] In particular, the control device 90 is configured to interrogate a database correlating at least one parameter representative of the flow to be treated 15 to at least one parameter representative of the permeate flow 40.

[0115] Advantageously, weights are assigned to the additional data for determining the value of the flow rate of the second fraction 75, for example as a function of an expected impact of this additional data on the composition of the treated flow 20.

[0116] In a particular embodiment, the control device 90 is capable of switching from a nominal configuration in which at least one of the weights assigned to the measured parameters is non-zero, the weights assigned to the additional data being negative or not negative, to an alternative configuration in which at least one of the weights assigned to the additional data is non-zero, and all the weights assigned to the measured parameters are negative. This arrangement makes it possible to keep the installation 10 in operation in the event of failure of the measurement sensor 100. This arrangement also makes it possible to adjust, if necessary, the operation of the installation 10 between two measurements by the measurement sensor 100.

[0117] The value of the flow rate of the second fraction 75 is then transmitted by the control device 90 to the valve 85 of the divider 65, the opening of which is adjusted accordingly.

[0118] The second fraction 75 of the concentrate flow 50 then circulates through the pipe 95 from the valve 85 to be mixed with the flow to be treated 15 upstream of the inlet 32 ​​of the membrane line 25 and thus constitute the incoming flow 30.

[0119] The modification of the composition of the incoming flow 30 imposed by the modification of the flow rate of the second fraction 75 results in a modification of the composition of the treated flow 20.

[0120] Optionally, the value of the flow rate of the second fraction 75 is determined by the control device 90 and adjusted accordingly in an incremental manner, until an optimal composition of the flow to be treated 20 with respect to the flow to be treated 15 and the adaptation capacities of the installation 10 is reached.

[0121] Optionally, the value of the flow rate of the second fraction 75 is determined by the control device 90 and adjusted accordingly periodically, the corresponding period being for example of the order of a time characteristic of the variations of one or more parameters representative of the permeate flow 40.

[0122] A second installation 10 according to the invention is shown in Figure 2. This installation differs from that shown in Figure 1 in that the divider 65 is configured to divide the permeate flow 40 into a first fraction 110 which constitutes the treated flow 20 produced by the outlet 17 of the installation 10 and into a second recirculation fraction 115. The concentrate flow 50 is fully recovered at the outlet 71 of the installation 10.

[0123] The recirculation system in this case comprises a pipe 120 for recirculating the second fraction 115 connected to the valve 85 and to the inlet pipe 33 between the inlet 16 of the installation 10 and the inlet 32 ​​of the membrane line 25.

[0124] Advantageously, the recirculation system also comprises a pump 125. The pump 125 makes it possible to compensate for a pressure drop between the incoming flow 30 and the second fraction 115 of the permeate flow 40.

[0125] The operation of this installation 10 is similar to that of the first installation. It differs from the operation of the first installation in that the control device 90 determines and controls a value of the flow rate of the second fraction 115 of the permeate flow 40.

[0126] For example, if a measurement result obtained using the measuring sensor 100 is too low compared to the respective target value range, the flow rate of the second fraction 115 is reduced or even cancelled. On the other hand, if the measurement result obtained using the measuring sensor 100 is too high compared to the respective target value range, the flow rate of the second fraction 115 is increased.

[0127] The second fraction 115 of the permeate flow 40 then circulates through the pipe 120 from the valve 85 to be mixed with the flow to be treated 15 upstream of the inlet 32 ​​of the membrane line 25 and thus constitute the incoming flow 30.

[0128] Several installations 10 according to the embodiment of figure 2 can be placed in parallel, each installation 10 receiving a fraction of the flow to be treated 15. In this case, each installation 10 can be equipped with a dedicated pump 125 or a pump 125 can be shared between several installations 10.

[0129] A third installation 10 according to the invention is shown in Figure 3. This installation 10 comprises several membrane lines 25A, 25B, 25C, 25D in parallel from the point of view of the incoming flow 30 received at the inlet 32 ​​of the installation comprising the plurality of membrane lines 25A, 25B, 25C, 25D.

[0130] Only the detail of membrane line 25D has been shown. Membrane lines 25A, 25B, 25C, 25D are identical or not.

[0131] Each of the membrane rows 25A, 25B, 25C, 25D is configured to receive a respective fraction 30A, 30B, 30C, 30D of the incoming stream 30 and to provide a respective permeate stream 40A, 40B, 40C, 40D and a respective concentrate stream 50A, 50B, 50C, 50D.

[0132] The permeate streams 40A, 40B, 40C, 40D from each of the membrane lines 25A, 25B, 25C, 25D are grouped to form the permeate stream 40 supplied to the outlet 35 of the installation 10.

[0133] The concentrate streams 50A, 50B, 50C, 50D from each of the membrane lines 25A, 25B, 25C, 25D are grouped to form the concentrate stream 50 supplied to the outlet 45 of the assembly 130.

[0134] As for the installation 10 of figure 1, the concentrate flow 50 grouping the different concentrate streams 50A, 50B, 50C, 50D is divided into a first fraction 70 which is brought to the outlet 71 of the installation 10 by the evacuation branch 81 and a second fraction 75 which is recirculated by the recirculation branch 80.

[0135] The measuring sensor 100 is mounted on a pipe 135 grouping the different permeate streams 40A, 40B, 40C, 40D downstream of each of the membrane lines 25A, 25B, 25C, 25D.

[0136] The control device 90 is configured to control the second fraction 75 reinjected into the incoming flow 30 upstream of all the membrane lines 25A, 25B, 25C, 25D according to the result of the comparison of each parameter measured in the permeate flow 40 by the sensor 100 with the respective target value range.

[0137] The configuration for controlling the quality of the output flow of the installation 10 is thus managed in a simple manner by distributing the incoming flow 30 between the different parallel membrane lines 25A, 25B, 25C, 25D and by pooling the control of the second fraction 75 of recirculated concentrate flow 50.

[0138] In a variant, not shown, the installation 10 of figure 3 is modified to add a recirculation of the permeate flow 40 grouping the different permeate streams 40A, 40B, 40C, 40D downstream of each of the membrane rows 25A, 25B, 25C, 25D

[0139] As previously, the control device 100 is configured to control the second fraction 115 of the permeate flow 40 reinjected into the incoming flow 30 upstream of all the membrane lines 25A, 25B, 25C, 25D according to the result of the comparison of each parameter measured in the permeate flow 40 by the sensor 100 with the respective target value range.

[0140] Optionally, one or more of the membrane lines 25A, 25B, 25C, 25D are not used permanently.

[0141] In a fourth installation 10 according to the invention, not shown, the divider 65 is configured to divide the permeate flow 40 into a first fraction 110 which constitutes the treated flow 20 supplied at the outlet 17 of the installation 10 and a second fraction 115, and also to divide the concentrate flow 50 into a first fraction 70 which is supplied at an outlet 71 of the installation 10 and a second fraction 75.

[0142] The recirculation system is configured for selective recirculation of the second fraction 115 of the permeate stream 40 and the second fraction 75 of the concentrate stream 50.

[0143] Advantageously, the divider 65 is configured so that in a first selective recirculation mode, the second fraction 115 of the permeate flow 40 is recycled, and so that the second fraction 75 of the concentrate flow 50 is not, or in other words, so that the flow rate of the second fraction 75 of the concentrate flow 50 is zero, and so that, in a second selective recirculation mode, the second fraction 75 of the concentrate flow 50 is recycled, and so that the second fraction 115 of the permeate flow 40 is not, or in other words, the flow rate of the second fraction 115 of the permeate flow 40 is zero.

[0144] In this case, the filtration method comprises a step of controlling the selective recirculation mode of the fraction to be recirculated from among the second fraction 115 of the permeate flow 40 and the second fraction 75 of the concentrate flow 50.

[0145] This control of the selective recirculation mode can be carried out based on the measurement result and / or one or more additional data.

[0146] The operation of this installation 10 is therefore a combination of that of the installations shown in Figures 1 and 2, in that the control device 90 determines, depending on the flow to be selectively recirculated at the time considered, either a value of the flow rate of the second fraction 115 of the permeate flow 40, or a value of the flow rate of the first fraction 70 of the concentrate flow 50.

[0147] The second fraction 115 of the permeate flow 40 and the second fraction of the concentrate flow 50 pass through the recirculation system to be mixed with the flow to be treated 15 upstream of the inlet 32 ​​of the membrane line 25 and thus constitute the incoming flow 30.

[0148] Optionally, the fourth installation 10 comprises a plurality of membrane lines 25A, 25B, 25C, 25D on the principle of the installation 10 shown in FIG. 3.

[0149] In all cases, the installation 10 according to the invention has the advantage of not requiring a multiplication of the filtering elements to increase the range of compositions of liquids which can be treated by the installation 10 and of environmental operating conditions of the installation 10. The first installation 10 shown in FIG. 1 is particularly suitable when the deviations from nominal operation are most often due to excessive filtration and require an increase in the concentration of certain chemical species to compensate for this excess filtration.

[0150] The second installation 10 shown in Figure 2 is particularly advantageous when the deviations from nominal operation are mainly due to insufficient filtration and require a reduction in the concentration of certain chemical species to compensate for this excess filtration.

[0151] The fourth installation 10 according to the invention combines the advantages of the first installation 10 shown in Figure 1 and of the second installation shown in Figure 2, by adapting to all directions of variation of the parameters, in particular physical or chemical at the input of the installation 10.

[0152] The third installation 10 according to the invention is modular in terms of the number and type of membrane rows 25A, 25B, 25C, 25D used, determining the filtration capacity of the installation 10 at a given time. This capacity is further modulated by the recirculation of the second fraction 115 of the permeate flow 40 and / or the second fraction 75 of the concentrate flow 50.

[0153] Generally speaking, in the present application, the expression “filtration installation 10” means an installation dedicated to the production of the treated flow 20, and in particular an installation on an industrial scale.

[0154] For example, the filtration installation 10 is capable of producing between ten thousand and several million cubic meters of treated liquid per day, the treated liquid being in a particular embodiment produced continuously.

[0155] The installation 10 can in particular be configured to receive the flow to be treated 15 of liquid continuously and to produce the treated flow 20 of liquid continuously.

[0156] In the case where the flow to be treated 15 is drinking water or water in the process of being made potable, the treated flow 20 is for example configured to be:

[0157] - supplied to a subsequent user for use on a site remote from a site where the installation 10 is located, for its implementation for domestic or industrial use if the composition of the treated water flow 20 allows it, in particular for its consumption if the treated flow 20 is a drinking water flow; and / or

[0158] - supplied at the input of another water treatment installation, configured to apply a subsequent treatment to the treated flow 20 before its use on the remote site mentioned in the previous paragraph, for example a treatment other than filtration, the installation 10 being in this case for example a treatment module of a fluid purification station, in particular water.

[0159] In the case where the flow to be treated 15 is wastewater, for example industrial water, the treated flow 20 is for example configured to be:

[0160] - supplied to a subsequent user for reuse on a site remote from a site where the installation 10 is located, for implementation for domestic or industrial use if the composition of the treated water flow 20 allows it, in particular for consumption if the treated flow 20 is a drinking water flow; and / or

[0161] - supplied at the input of another water treatment installation, configured to apply a subsequent treatment to the treated flow 20, for example a treatment other than filtration, the installation 10 being in this case for example a treatment module of a fluid purification station, in particular water; and / or

[0162] - released into the environment if the composition of the treated water flow 20 allows it.

[0163] The installation 10 is in particular configured to allow the production of the treated flow 20 with a quality conforming to a specification provided a priori, in a manner largely independent of variations in the composition and / or the temperature of the flow to be treated 15 and / or of variations in the temperature of the membrane module and / or of possible scaling and / or partial clogging of the filter membranes of the membrane module, and this without significant interruption of this production, thanks to the real-time adaptation of the nature of the second recirculated fraction and the recirculation flow rate of this second fraction.

[0164] The second fraction can, depending on the embodiments, either come from the permeate flow only, or from the permeate only, or a mixture of permeate and concentrate. Thanks to the invention, it is possible:

[0165] - not only to compensate in real time for insufficient filtration by recirculation of permeate, in particular to maintain a concentration of at least one first given solute below an upper threshold value imposed by the specifications

[0166] - but also, in the case where the second fraction is at least partially formed of permeate, to compensate for a temporary excess filtration of the membrane module, which would for example be caused by a variation in temperature and / or a variation in the composition of the flow to be treated 15, in particular to maintain a concentration of at least one second solute above a lower threshold value imposed by the specifications.

[0167] In a particular embodiment, the first solute is chosen from micropollutants, in particular from micropollutants mentioned in European Union directive no. 2020 / 2184 of 16 / 12 / 20 relating to the quality of water intended for human consumption.

[0168] In a particular embodiment, the second solute comprises a solute chosen from magnesium ions, calcium ions and mixtures thereof.

[0169] By compliance with a specification, it is understood that the method according to the invention makes it possible to obtain a permeate flow whose concentration of each solute targeted in the specification respects a respective target, which does not necessarily mean that each of these concentrations is lower than the corresponding concentration of the flow to be treated.

[0170] In some cases, it may be appropriate to increase the concentration of one or more solutes, for example magnesium and calcium ions, in order to obtain sufficient water hardness for the consumption of the treated flow, while maintaining or reducing the concentration of one or more other solutes, such as micropollutants.

Claims

CLAIMS 1. Method for filtering a flow of liquid to be treated (15) for the production of treated water, the method comprising the following steps: - filtration, by a filtration device (25, 130) of a filtration installation (10), of an incoming liquid flow (30) comprising at least a fraction of the flow to be treated (15), the filtration device (25, 130) comprising at least one membrane module having at least one filter membrane (60), to form: (i) a permeate flow (40), comprising the liquid flow(s) (40A, 40B, 40C, 40D) from the incoming flow (30) produced after passing through at least one of said filter membranes (60) of the filtration device (25, 130), at least a fraction of the permeate flow (40) constituting the treated liquid flow (20) from the process, and (ii) a concentrate stream (50), comprising the liquid stream(s) (50A, 50B, 50C, 50D) from the incoming stream (30) and which have not passed through any filter membrane (60); the method being characterized by the following steps: - dividing one of the concentrate stream (50) and the permeate stream (40) into a first fraction (70, 110) supplied to an outlet (71, 17) of the filtration installation (10), and a second fraction (75, 115); - in at least one nominal measurement configuration, measurement of at least one parameter representative of the permeate flow (40) and comparison with a range of target values ​​defined by at least one predetermined threshold value; - determination by a control device (90) of a zero or non-zero flow rate of the second fraction (75, 115) using the result of the comparison; and - recirculation of the second fraction (75, 115) at the flow rate determined by the control device (90) and mixing with the flow to be treated (15) to form the incoming flow (30) in the filtration device (25, 130).

2. Filtration method according to claim 1, in which the at least one parameter representative of the permeate flow (40) is chosen from a temperature or a temporal variation of this temperature, a parameter representative of an electrical conductivity or a temporal variation of this electrical conductivity, a parameter representative of a concentration of an ionic or molecular species or of a group of ionic or molecular species or of a temporal variation of this concentration.

3. A filtration method according to any one of the preceding claims, wherein, in the dividing step, only the concentrate stream (50) is divided into a first fraction (70) and a second fraction (75), the first fraction (70) of the concentrate stream being supplied to an outlet (71) of the filtration installation (10), and the entire permeate stream (40) constituting the treated stream (20).

4. A filtration method according to any one of claims 1 and 2, wherein, in the dividing step, only the permeate stream (40) is divided into a first fraction (110) and a second fraction (115), the first fraction (110) of the permeate stream (40) constituting the treated stream (20) and being supplied to an outlet (17) of the filtration plant (10), and the entire concentrate stream (50) is supplied to an outlet (71) of the filtration plant (10).

5. A filtration method according to any one of claims 1 and 2, wherein the dividing step comprises: - at least a first phase of controlling a divider (65) of the filtration installation to divide the permeate flow (40) into a first fraction (110) of the permeate flow (40) which constitutes the treated flow (20), and a second fraction (115) of the permeate flow (40) which forms the second fraction intended to be recirculated, without dividing the concentrate flow (50), - and at least a second phase of controlling a divider (65) of the filtration installation to divide the concentrate flow (50) into a first fraction (70) of the concentrate flow (50), which is supplied to an outlet of the filtration installation (10), and a second fraction (75) of the concentrate flow (50) which forms the second fraction intended to be recirculated, without dividing the permeate flow (40).

6. Filtration method according to any one of the preceding claims, in which several parameters representative of the permeate flow (40) are measured and a weight is assigned to each of these parameters for the determination of the flow rate of the second fraction (75, 115).

7. A filtration method according to any one of the preceding claims, further comprising: - the transmission of additional data representative of the composition of the flow to be processed, the additional data being used to determine the flow rate of the second fraction (75, 115).

8. Filtration method according to claim 7, in which the additional data are chosen from meteorological data, dates, data relating to a source of pollution upstream of the flow to be treated (15) and measurement data from at least one additional measurement sensor of a parameter representative of the flow to be treated (15).

9. Filtration method according to claim 7 or 8, in which the determination of the flow rate of the second fraction (75, 115) by the control device (90) comprises the transition from the nominal measurement configuration to an alternative configuration, in which the value of the flow rate of the second fraction (75, 115) is determined as a function of at least one of the complementary data transmitted, without using measurement of at least one parameter representative of the permeate flow (40).

10. Filtration method according to any one of the preceding claims, wherein the filtration device (130) comprises at least one membrane row (25A, 25B, 25C, 25D) comprising several filtration stages (55, 56, 57) each comprising at least one membrane module comprising a filter membrane (60), in particular at least one pressure tube comprising a plurality of membrane modules, and the filtration step comprises, for at least one of said membrane rows (25A, 25B, 25C, 25D), the production from at least a portion of the liquid flow entering the filtration device: - a permeate stream (40A, 40B, 40C, 40D), bringing together liquid flows having passed through at least one filter membrane (60) of at least one stage (55, 56, 57) of the membrane row (25A, 25B, 25C, 25D), the permeate stream being intended to at least partially form the permeate flow (40), and - a concentrate stream (50A, 50B, 50C, 50D), originating from the incoming liquid flow (30A, 30B, 30C, 30D) in the membrane line (25A, 25B, 25C, 25D) after introduction into all the stages of the membrane line successively without passing through any of the filter membranes (60) of these stages, the concentrate stream being intended to at least partially form the concentrate flow (50).

11. A filtration method according to claim 10, wherein the filtration device comprises a plurality of membrane rows (25A, 25B, 25C, 25D), the filtration step comprising grouping the permeate streams (40A, 40B, 40C, 40D) from each of the membrane rows to form the permeate stream (40), and grouping the concentrate streams (50A, 50B, 50C, 50D) from each of the membrane rows to form the concentrate stream (50).

12. Filtration method according to any one of the preceding claims, configured for the production of a treated flow (20) of which a respective concentration of at least one micropollutant of interest is included in a respective predetermined target value range.

13. Filtration method according to any one of the preceding claims, configured for the production of a treated flow (20) of which a respective concentration of at least one ionic species, chosen from calcium ions, magnesium ions and their mixtures, is included in a respective predetermined target value range.

14. Installation (10) for filtering a liquid flow for the production of treated water, receiving a flow of liquid to be treated (15) and providing a flow of treated liquid (20), the filtration installation (10) comprising: - a filtration device (25, 130) comprising at least one filter membrane (60), the filtration device (25, 130) being configured to provide, from an incoming flow (30) of liquid comprising at least a fraction of the flow to be treated (15): (i) a permeate flow (40), comprising all the liquid flows (40A, 40B, 40C, 40D) originating from the incoming flow (30) after passing through at least one of said filter membranes (60), and of which at least a fraction constitutes the treated flow (20), and (ii) a concentrate stream (50), originating from the incoming stream (30) and which has not passed through any filter membrane (60), - downstream of the filtration device (25, 130), a divider (65) of at least one of the concentrate flow (50) and the permeate flow (40) into a first fraction (70, 110) supplied to an outlet (17, 71) of the installation (10) and into a second fraction (75, 115), - a recirculation system (80, 120) for the second fraction (75, 115), configured to mix the second fraction (75, 115) with the flow to be treated (15) so as to form the incoming flow (30) in the filtration device (25, 130), the installation (10) being characterized in that it further comprises: - at least one device for measuring a parameter representative of the permeate flow (40), - a control device (90) of the divider (65), configured, in at least one nominal measurement configuration, to receive measurement data from the at least one measurement device, to compare the received measurement data to at least one range of target values ​​defined by at least one predetermined threshold value and to determine the value of a flow rate of the second fraction (75, 115) as a function of the result of the comparison.

15. Filtration installation (10) according to claim 14, in which the at least one filter membrane (60) is chosen from a reverse osmosis membrane and a nanofiltration membrane.

16. Filtration installation (10) according to claim 14 or claim 15, in which the control device (90) comprises a system for receiving additional data, chosen from meteorological data, dates, data relating to a source of pollution upstream of the flow to be treated (15) and measurement data from at least one additional sensor for measuring a parameter of the flow to be treated (15), the control device (90) being configured to switch from the nominal measurement configuration to an alternative configuration, in which the value of the flow rate of the second fraction (75, 115) is determined as a function of at least one of the additional data transmitted, without using measurement of at least one parameter representative of the permeate flow (40).

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