EP3077087A1

EP3077087A1 - Method for monitoring the integrity of filtering membranes during the operation thereof

Info

Publication number: EP3077087A1
Application number: EP14825410.5A
Authority: EP
Inventors: Nouhad Abidine
Original assignee: ABC Membranes
Current assignee: ABC Membranes
Priority date: 2013-12-05
Filing date: 2014-12-04
Publication date: 2016-10-12
Also published as: FR3014330B1; FR3014330A1; WO2015082855A1

Abstract

The invention relates to a method for monitoring the integrity of filtering membranes allowing the separation of a fluid into a first permeate (P) and a first concentrate (C). The first permeate (P) from the filtration acheived by the filtering membranes is concentrated by means of a separation module (M) including hollow fibres (Fc) provided inside the separation module (M) and capable of separating said first permeate (P) into a second permeate (P') and a second concentrate (C'). The concentrate (C') thus obtained is directed by means of a distributor (Vm) towards means for analysing the composition and/or the concentration of the second concentrate (C'). Next an analysis of the second concentrate (C') is carried out by means of at least one sensor (Cc), and the evolution over time of the result of the analysis conducted on the second concentrate (C') is examined in order to deduce therefrom information to quantify the integrity or lack of integrity of the membrane.

Description

METHOD OF CONTROLLING THE INTEGRITY OF FILTRATION MEMBRANES DURING THEIR OPERATION

Technical area

The present invention relates to membrane filtration and relates more particularly to a method for controlling the integrity of filtration membranes used, especially in water treatment plants. The invention also relates to a device for implementing this method.

Technological Background

Ultraviolet (UV) water disinfection, such as the chemical disinfection of water with chlorine-based derivatives or ozone, are commonly used solutions. But these techniques do not eliminate the skeletons and debris of these organisms, which remain in the treated water. The use of membranes for water filtration, unlike the aforementioned techniques, does not kill the bacteria but eliminates them by retention, and the quality of the water thus produced is significantly improved. Thus, during the chemical disinfection of water, a subsequent step that is mandatory to ensure sanitary stability in storage tanks and in the water distribution system, the risk of formation of disinfection by-products is limited.

The proper functioning of a filtration membrane is closely linked to the respect of its integrity. Thus, the disinfection capacity of a filtration membrane is reduced whenever a surface defect appears or, in the case of hollow fiber filtration, a fiber breaks. For example, the viral reduction of an ultrafiltration module which has a filtration area of about 55 m ² and containing between 15 and 20,000 new and intact hollow fibers is 6 to 7 log. This viral reduction is reduced to less than 3 log when the module has a single broken fiber. For this As a result, the public health monitoring agencies are obliging plant operators who use membrane filtration to disinfect water, to regularly monitor the integrity of installed membranes. These organizations now accept that these tests are not performed continuously but regularly. Nevertheless, they encourage operators, suppliers and researchers to develop integrity tests that can be carried out in operation and continuously, in order to guarantee the safety of the water produced at all times.

Previous Art

Ultrafiltration in drinking water treatment was used for the first time in 1988 at the Amoncourt plant in France (180 m ³ / day production). Since then, the use of hollow fibers of micro- or ultrafiltration has been growing and cumulative production across all applications exceeded several million m ³ / day. The number of water filtration facilities equipped with membranes has reached several thousand units worldwide and this number will grow at least annually by between 6 and 10% in the coming years.

Thanks to their cut-off threshold, often between 10 and 100 nanometers (0.01 - 0.1 μιτι), this type of membrane offers a capacity of reduction of microorganisms, bacteria and viruses which remains unequaled.

However, membranes used to disinfect water, whether they are flat membranes or hollow fibers, present two combined risks from their manufacturing protocol and the applied filtration process.

First, the membranes may have defects related to their manufacturing conditions (bubbles from a degassing defect of the collodion used to produce the membranes or generated by cavitation at the outlet of the die). In general, these defects are detected during the final tests performed by the membrane manufacturer or appear during the first months of use. Secondly, chemical, thermal or mechanical aging, or the combination of these different types of aging, can cause breaks between the constituent polymer chains of the membrane. These breaks are generally at the origin of the breakage of the fibers which can appear in the time. At the end of the life of the membranes, the number and the frequency of the breaks of fibers are accentuated which imposes the replacement of the modules.

Various techniques for verifying the integrity of the membranes have been described in the prior art. These can be classified into different categories.

Some techniques are based on the diffusion of air through the membranes. Conventionally, after draining one side or both sides of the membranes, air (or gas) is introduced under pressure upstream side concentrate (raw water) or downstream permeate side (treated water) membranes. After stabilization of the air pressure, the pressure drop or the flow rate of the gas is measured over time. Depending on the speed of the pressure drop being measured, and based on data provided by the membrane manufacturer, it is then possible to qualify the integrity or lack of integrity of the membranes.

Alternatively, in the case of hollow fiber membranes immersed in a basin containing the raw water to be filtered, the test can be done by putting the permeate compartment of the membranes under vacuum. The measurement of the integrity of the membranes can then be done by measuring the rise of the pressure.

Patent FR 2894843 illustrates an example of implementation of such a technique.

These techniques have the disadvantage of being carried out only when the system is at a standstill, that is to say out of operation, and of requiring a long downtime (emptying, pressurization, test, re-watering). , ...). The total duration of an integrity test is generally close to or greater than the hour, when it is performed on a rack or block composed of several filtration modules. This time is significantly increased when tests are made on each module fitted to a water treatment plant or that the modules must be dismantled. Durations shutdown of the plant for 2 to 6 hours are then commonly observed, which is to the detriment of the production of the plant.

Other techniques are based on listening to the noise variation caused by the presence of air bubbles or gases. An air pressure is applied upstream of the hollow fibers (concentrate side) present inside a filtration module. In the presence of a fault or a broken fiber, the air passes through this fault and then generates a noise which is detected by a sensor installed on the filtration module, which makes it possible to identify the defective module. This protocol also requires stopping the filtration and therefore the system in order to carry out the test.

In patent FR 2775440, it is proposed to exploit the detection of a noise (or sound) emitted by the turbulence of a fluid passing through a broken fiber. However, this on-line measurement of noise (or sound) is not satisfactory because of spurious noise created by the other devices of the equipment that disturb the noise emitted by the flow of fluid through the leak.

Still other techniques propose using the clogging of a system equipped with two flat membranes placed in series to filter the permeate of an installation. This is the so-called "Mem-Shield" method, which is described in document WO 2007129994. The clogging of this system is subsequently used as an indicator related to the integrity of the membranes that equip the installation. The disadvantage of this test is its relatively high cost (about US $ 10,000 per unit) which led the inventors to propose to install the system for a set of modules and not for each module individually.

On a smaller scale, some techniques have been described based on the injection of fluorescent particles on the concentrate side and the detection of these particles on the permeate side. These tests have the disadvantage of adding fluorescent particles that are found in the treated water in case of fiber breakage, which is not acceptable for water intended for human consumption. Finally, patent FR 2809636 describes an integrity test protocol for nanofiltration and reverse osmosis membranes. For these applications, the phenomenon of concentration polarization causes a sharp rise in the concentration of salts and dissolved solids retained by the membrane on the concentrate side. The measurement of a target element, permeate side, is used as a tracer and can detect an integrity problem (breakage or leakage). Ideally, the target product is a product strongly retained by the membrane (retention> 98%) and is at a high concentration of origin in the liquid to be treated. The system continuously measures (or semi-continuous, ie at substantially regular time intervals) the concentration of the target element in the treated water, and compares this concentration with the reference value when the membrane is honest. When a variation is measured and detected, the formation of a defect is then determined, and remains to be located only.

This protocol is however not applicable with membranes of micro- or ultra-filtration. Indeed, during a fiber breakage or defect in the membrane (of the type of a hole), the variation of the concentration of colloid, particles or other products dissolved in the permeate is very low and hardly detectable. For example, for an industrial module developing a filter surface of 40 to 90 m ² , or 14,000 to 30,000 fibers, the variation in turbidity in the permeate is barely noticeable. Studies have shown that it is possible to measure a slight change in turbidity in the permeate only if the turbidity of the raw water is greater than 20 NTU. These same studies have shown that it is impossible to measure a turbidity variation, even with water at 20 NTU, since the measurement is carried out on a block composed of several modules.

SUMMARY OF THE INVENTION In order to overcome the disadvantages of the aforementioned prior art, it is proposed a method for controlling the integrity of filtration membranes that can be achieved during the operation of the installation (without interrupting the filtration cycle). without the addition of chemical compounds, which is easy to put into and reduces the discharges of treated fluid and thus lower the operating costs of an installation equipped with filtration membranes to control. More specifically, there is provided a method for controlling the integrity of at least one filtration membrane ensuring the separation of a fluid into a first permeate and a first concentrate, comprising the following steps: a / concentrating the first permeate from filtration by the filtration membrane by means of a separation module (M) comprising hollow fibers (Fc) present within the separation module (M) and adapted to separate the first permeate into a second permeate (Ρ ' ) and a second concentrate (C),

b / directing by means of a distributor (Vm) the second concentrate obtained at the outlet of the separation module to means for analyzing the composition and / or the concentration of the second concentrate,

and perform an analysis of the second concentrate by means of at least one sensor (Ce),

d / examining the evolution over time of the result of the analysis carried out on the second concentrate to deduce information integrity qualification or non-integrity of the membrane.

During step a /, the first permeate resulting from the filtration carried out by the controlled filtration membrane is thus concentrated via hollow fibers present within the separation module and whose function is to separate said first permeate. in another permeate and another concentrate depending on the state of the filtration membrane. Depending on the type of hollow fiber used and their cutoff threshold, a more or less significant concentration of the second concentrate can be obtained. The concentration of the first permeate may be obtained by various techniques known to those skilled in the art among which mention may be made of membrane evaporation, filtration, centrifugation, or filtration-centrifugation coupling. The interest of this first step of the process is to obtain a concentration of the suspended matter, particles and microorganisms which were not retained by the controlled filtration membrane and which were diluted by the first permeate produced by the honest parts. of membranes forming the major part of the whole module.

The splitter can be constructed as a multi-port valve which is connected to the separation module so as to collect the second concentrate and allow its analysis.

The analysis of the composition and / or concentration of the second concentrate may be carried out by one or more identical or complementary sensors whose function is to be able to determine the state of the quality of the concentrate. This step is performed with a level of precision unequaled compared to other known techniques for verifying the integrity of a filtration membrane. This result comes from the fact that, prior to the actual analysis step, and as previously explained, the second concentrate has been concentrated during step a /, which has the consequence of increasing the level of sensitivity. analyzes performed.

This makes it possible to obtain significant and usable results where normally, that is to say without the concentration step, the low content of the second concentrate does not make it possible to carry out analyzes with sufficient precision to detect variations. of concentrate parameters and the occurrence or not of a lack of integrity at the controlled membrane (s).

The sensors used to perform the analysis can be of different types and can accurately detect variations in the quality of the second concentrate. The action of several identical or different types of sensors can be combined so as to obtain complementarity and further refine the results of the analysis in progress. The last step of the method, of examining the evolution over time of the results of the analysis thus carried out by the one or more sensors on the second concentrate, can be carried out by various means which will be detailed below. This analysis makes it possible to inform the user on the integrity of the controlled filtration membranes according to the analyzes carried out by the one or more sensors. The defects are detected with all the more precision and reliability that they were amplified by the concentration step which made it possible to obtain the second concentrate. The variations in the quality of the concentrate analyzed can thus be monitored much more effectively than in the known techniques.

Depending on the nature of the separation module and the concentration technique that has been used, it is possible to interpret the changes in the quality of the second concentrate in time to determine whether or not the filtration membrane thus controlled has integrity.

Preferably, the cutoff threshold of the hollow fibers of the module is greater than, or close to, the cutoff threshold of the controlled filtration membrane. In this way, when the controlled filtration membrane is intact, the permeate is filtered at the hollow fibers of the separation module to directly give the second permeate without passing materials likely to be in the second concentrate. The change in the concentration of the first permeate at the level of the separation module during step a / is therefore zero and it is possible to track the absence of the second concentrate in time to confirm the good integrity of the controlled filtration membranes. .

In the event of a problem of integrity of the controlled filtration membrane, when the cutoff threshold of the hollow fibers of the separation module is greater than or close to the cutoff threshold of the controlled filtration membranes, the first permeate is filtered to give the second permeate and the second concentrate which reveals the possible presence of suspended matter, particles or microorganisms that should have been retained by the controlled filtration membrane. These suspended solids, particles or microorganisms are retained by the hollow fibers, hence the presence of a second concentrate with a certain concentration. Here again, the examination of the evolution of the quality of the second concentrate makes it possible to follow the state of integrity of the controlled filtration membrane. After identification and repair of the (or) filter membrane (s) controlled (s) as unintegrated (s), no suspended matter is no longer retained by the hollow fibers of the separation module and the concentration of the second concentrate falls to a zero level.

In another embodiment, the cutoff threshold of the hollow fibers of the separation module may also be less than the cutoff threshold of the controlled filtration membrane. In this case, when the membrane is intact, a low level of the second concentrate is retained by the hollow fibers corresponding to suspended matter, particles or microorganisms whose size was small enough to pass through the filtration membrane, but too large to pass through the hollow fibers and are therefore retained by them.

If a problem of integrity of the filtration membranes arises, when the cutting threshold of the hollow fibers of the separation module is lower than the cutoff threshold of the controlled filtration membranes, the hollow fibers retain a larger amount of second concentrate which reveals the presence of suspended solids, particles or microorganisms that should have been retained by the controlled filtration membranes and whose composition or concentration variation can be analyzed to determine the existence of a lack of integrity.

In a particular embodiment, said at least one sensor used to analyze the second concentrate makes it possible to measure one or more of the following parameters among the ultraviolet light absorption, the turbidity, the number or the size of the particles present. in the second concentrate. These parameters make it possible to characterize the concentration level of the concentrate with greater precision since it has been concentrated during step a /. As previously stated, only one sensor can be used or a combination of several sensors, to measure several of the aforementioned parameters, can be used in a complementary manner to further refine the results of the analyzes performed. Preferably, the method for controlling the integrity of filtration membranes comprises an additional step of measuring the variations of the pressure of the separation module by means of pressure sensors placed upstream and downstream of said separation module. This additional step makes it possible to check the operating state of the separation module and, if necessary, its integrity. Indeed, if the evolution over time of the measurements made by these two pressure sensors varies, this indicates that the separation module has a defect, such as clogging or breakage, and that its operation is no longer adapted. In this case, it is necessary to examine the origin of this defect and to find a solution.

In order to facilitate step d / of the method, the evolution over time of the composition and / or the concentration of the second concentrate can be processed by an analytical unit which makes it possible to analyze the results transmitted by the sensors and, the if necessary, by the pressure sensors. This information can be used to diagnose the state of integrity of the controlled filtration membranes and report and identify any occurrence of a lack of integrity. In some cases it may be necessary to clean the separation module. For this purpose, the first permeate may be directed by a secondary conduit to the separation module so as to allow backwashing of said separation module. This backwashing can thus maintain the good operating condition of the separation module and extend its life without having to change it as soon as a problem occurs.

In particular embodiments, the second permeate and the second concentrate may be directed independently of one another or in a common conduit to a storage tank (S) of the first permeate. This makes it possible to recover all or part of the fluids passing through the separation module and thus to reduce the losses that may be generated by the verification process of the integrity of the filtration membranes.

The present invention also relates to a device for controlling the integrity of filtration membranes, in particular by implementing the method described above, by offering a high accuracy and reliability in the results, a low cost and suitable for being used without interrupting the treatment cycle of filtered fluids.

More specifically, the invention relates to a device for monitoring the integrity of at least one filtration membrane adapted to ensure the separation of a fluid into a first permeate and a first concentrate comprising:

a separation module (M) comprising hollow fibers (Fc) present within the separation module (M) and capable of receiving the first permeate (P) and capable of separating it into a second permeate (Ρ ') and a second concentrate (C),

at least one sensor (Ce) able to perform an analysis of the composition and / or the concentration of the second concentrate,

a distributor (Vm) adapted to direct the second concentrate towards the sensor,

- Analysis means (A) of the evolution over time of the composition and / or the concentration of the second concentrate to derive information integrity qualification or non-integrity of the membrane.

The device thus comprises a separation module receiving the first permeate resulting from the separation carried out by the filtration membranes whose integrity it is desired to control. This separation module allows itself to be separated using hollow fibers capable of separating the first permeate by filtration into a second permeate and a second concentrate.

A splitter connected to the separation module makes it possible to direct the second concentrate towards means for analyzing the composition and / or the concentration of the second concentrate and to which it is also connected. This distributor makes it possible to direct the second concentrate of the modules not concerned by the analysis of the instant t towards the permeate storage tank of the installation or, failing that, towards the sewer. The means for analyzing the composition and / or the concentration of the second concentrate are constituted by at least one sensor capable of performing such an analysis. Analysis means themselves connected to said at least one sensor make it possible to follow the evolution over time of the composition and / or the concentration of the second concentrate.

Advantageously, the hollow fibers of the separation module have a cut-off threshold greater than or close to the cutoff threshold of the controlled filtration membrane. Depending on this cutoff threshold level, the user will be able to interpret the results of the membrane integrity check.

In a particular embodiment, pressure sensors placed upstream and downstream of the separation module make it possible to measure the pressure variations of said separation module. These sensors make it possible to control the level of clogging or the integrity of the membranes present inside the separation module and according to the results indicate to the user whether to proceed to a cleaning of these (by backwashing or by chemical washing) or replace them by changing the entire separation module. Preferably, an analytical unit makes it possible to process the evolution over time of the composition and / or the concentration of the second concentrate. This plant makes it possible to process the results of several separation modules possibly present on the different filtration modules of the same fluid treatment station.

Advantageously, the separation module has a helical configuration that optimizes the ergonomics of the separation module. Indeed, in this way the first permeate can pass inside the separation module in a significant length without the separation module occupies a space too large, which reduces the size of said separation module and represents an advantage in the installation of the device. In a particular embodiment, a secondary duct makes it possible to direct the first permeate towards the separation module so as to allow backwashing of said separation module. This secondary duct is therefore a bypass route of the first permeate which is used to bring it into contact with the separation module in the opposite direction to the normal operation of the device according to the invention when the separation module concentrates the first permeate.

In another embodiment, a storage tank of the first permeate is adapted to receive the second permeate and / or the second concentrate. Thus, the second permeate and the second concentrate can reach this reservoir either directly from the separation module or via the distributor. . In this way, the losses likely to result from the implementation of the method of controlling the integrity of the filtration membranes are almost zero since the second permeate and the second concentrate can be recovered.

A particularly advantageous use of the device for checking the integrity of at least one filtration membrane according to the invention can be carried out in a water treatment station comprising a plurality of filtration modules implementing filtration membranes, each filtration module being respectively associated with one of a plurality of filtration membrane integrity control devices according to the invention, the distributor of which is common to all the devices, all of said devices being connected to the single common distributor arranged to direct the second concentrates respectively from the devices to common means of analysis of the composition and / or concentration of the second concentrates and to common means of analysis of the evolution over time of the composition and / or concentration of the second concentrates. Brief Description of Drawings

Other features and advantages of the invention will become apparent on reading the description which follows. This is purely illustrative and should be read with reference to Figures 1 and 2 attached, which are schematic representations of devices for monitoring the integrity of filtration membranes according to embodiments of the invention.

Detailed description of an embodiment

The description of an embodiment of the method and of a device making it possible to implement this method is given below with reference to an example.

Principle of the method for controlling the integrity of filtration membranes according to the invention

To understand the operation of the method according to the invention, we will describe in the following a device for implementing the method for controlling the integrity of filtration membranes according to the invention, said device being used in the present example at a water treatment plant E based on membrane filtration.

The device according to the invention is thus connected to the network of said water treatment station E so as to recover a portion of the filtered water in the form of a first permeate P. The device according to the invention is composed of a separation module M consisting of a hollow tube which preferably has a twisted helical shape and inside which is present a set of hollow fibers Fc comprising about ten fibers. According to the characteristics of the treated liquid, in this case the water filtered by the treatment station in the present example, these hollow fibers Fc have a cut-off point greater than, equal to or less than that of the membranes. present on the station. By way of non-limiting example, hollow fibers Fc that can be used in the separation module M can be produced according to a manufacturing protocol that makes it possible to ensure an inner diameter of the fibers of 0.90 +/- 0.02 mm. Likewise, the manufacturing conditions make it possible to obtain a water permeability equal to 220 +/- 20 l / hm ² .bar measured at a temperature of 20 ° C. and this with a cut-off point vis-à-vis Dextran equals, for example, about 80,000 daltons. The two characteristics mentioned above were determined according to AFNOR specifications in force in France.

By its configuration, the separation module M is for example in the form of a micromodule equipped with a sufficient filtration area (from 200 to 800 cm ² depending on the capacity of the separation module) and which favors the length of item. This construction makes it possible to maximize the concentration of the products retained by the internal surface of the hollow fibers Fc throughout the separation module M. The recovery of a second permeate P 'at the outlet of the separation module M takes place in a rather bulky channel to minimize the pressure drop due to the flow downstream of the separation module M. This ensures the separation module M a better operation during filtration / concentration and during its eventual backwash which will be detailed below.

FIG. 1 schematically illustrates the operating principle of a separation module M used for the concentration of the first permeate P recovered after the membrane filtration carried out at the water treatment station E.

A valve V directs, in turn, the first permeate P of a membrane filtration module tested to the separation module M to ensure the concentration of the first permeate P. A second valve V ₂ in communication with the valve V and a secondary duct D is then closed while a third valve V ₃ in communication with the valve V and the separation module M is open. To ensure backwashing of the separation module M, the valve V ₂ is open and the valve V ₃ is closed, allowing the first permeate P to arrive at the level of the separation module M against the direction via the secondary conduit D. A fourth valve V ₄ in communication with the secondary conduit D is arranged to direct, in turn, the first permeate P to the separation module M or a storage tank S. A fifth valve V ₅ in communication with the valve V ₄ provides the backwashing while a sixth valve V ₆ is arranged to send the first permeate P to the tank of storage S.

When the valve V ₃ is open and the valve V ₂ is closed, the first permeate P is treated by the separation module M. It is then filtered through the hollow fibers Fc and can be separated into a second permeate P ' and a second concentrate C. When the valves V ₅ and V ₆ are open and the valve V ₄ is closed, the second permeate P 'is directed to the storage tank S or to the sewer. A valve V ₇ makes it possible to direct the second concentrate C of the separation module M towards a sensor Ce via a splitter Vm. In this case, a valve V ₈ in communication with the valve V ₇ and a storage tank S is closed while a valve V ₉ in communication with the valve (V ₇ ) and the distributor Vm is open. An assembly I can be defined, this set I representing a device according to the invention constituted by a separation module M receiving the first permeate P, a secondary duct D and the valves Vi to V ₉ .

For a membrane filtration module F developing a filtering surface of 50 to 70 m ² in a water treatment plant, we use a device for controlling the integrity of filtration membranes according to the set I comprising a module M separation, which develops only 400 cm ² of filtration area. The separation module M contains only 10 hollow fibers Fc placed in a cartridge of useful length of 1.5 m. In this way, the total filtration of the volume of the filtration module M (here of 9.5 ml) is done in about 15 seconds. This can be done under an effective pressure of 0.25 bar pressure at 20 ° C. As a result, by continuously filtering water for 5 minutes with this separation module M, a concentration factor of 20 is obtained for the suspended solids, particles, viruses, bacteria or any other product retained by the membrane placed at first rank.

FIG. 2 schematically illustrates the filtration carried out by several devices I (li, l ₂ , l _n , etc.) connected to several modules F (Fi, F ₂ , F _n , etc.). Each separation module M of a device I receives a first permeate P (Pi, P ₂ , P _n , etc.) that it can filter continuously and the second concentrate C thus obtained (C'i, C ₂ , C ' _n , etc. ..) is sent to a common distributor Vm in the form of a multichannel valve. The filtration duration of each separation module M of a device I can be modulated according to the desired concentration and the sensitivity of the sensors used downstream of each separation module M. Thus, for example, the filtration time of a separation module M may be equivalent to a complete filtration cycle. This multichannel valve can select a separation module M from several separation modules M of several devices I, each being associated with a filtration module F used within the same water treatment station E. The various separation modules M are then used in turn. The multichannel valve then sends the second concentrate C from a separation module M to the measuring cell of the analyzer or analyzers such as concentration sensors Ce associated with an analytical unit A installed downstream of the separation modules M .

Initially, the analyzes are performed on the separation modules M associated with the filtration modules F of the water treatment station E, each filtration module F having intact filtration membranes. A result, reference, is generated and corresponds to each filtration module F installed so each separation module M. On an installation equipped with 12, 24 or even 30 filtration modules F which filter water during a cycle of 30 minutes, it is possible to carry out a measurement series of 10 to 20 seconds for each of the modules F and thus avoid the first 3 to 5 minutes of start of concentration cycle that can lead to a disruptive result. The advantage of this method is that it makes it possible to use robust equipment that has an approved efficiency (conventional multichannel distributor and for example a Hach turbidimeter for performing measurements online). The only element that may require maintenance is the separation module M. Indeed, once clogged, it may require either a backwash or a chemical wash, or a standard exchange. Backwashing of the separation modules M can be done at any time and after each filtration cycle if necessary. Indeed, during the filtration cycle of the installation, it is sufficient to open the valves V _; V ₂ , V ₄ , V ₅ , V ₇ , V ₈ and close the valves V ₃ , V ₆ and V ₉ to retrolve the module (s) M that is desired to unclog. Likewise, pressure sensors Cp placed upstream and downstream of a separation module M make it possible to signal a loss of charge threshold which indicates that it is necessary to wash it chemically. Finally, the standard exchange would not be a major obstacle because the modules are produced as reliable but low cost consumables.

By way of illustration, the clogging of the separation modules M can occur in the following two cases:

1 - Presence in filtered water of solutes that partially pass through the filtration membranes that equip the installation in question. These are usually organic materials that may be present in the raw water and are very poorly retained by the membranes that equip the facility. In this case, one will choose hollow fibers Fc which have a threshold of cuts slightly higher than that of the filtration membranes of the filtration modules F equipping the installation in order to minimize the impact of the adsorption phenomenon that may occur.

2- Various pollutants, large sizes, which are in the raw water have passed through the leak and are found on its filtering surface of the filtration membranes that equip the separation module M. In this case, the backwashing of the module separation M would restore the essence of its initial performance. In addition, in both cases, the separation modules M can be periodically disassembled and washed using one (or more) single washing agent (s). However, simultaneous backflushing is effective in a large number of cases if the material constituting the membranes of the separation modules M is well adapted to the quality of the water filtered by the filtration modules F of the installation.

In the case of an installation equipped with modules F each having a filtration area equal to 55 m ² , it is possible to monitor the turbidity as a means of analysis to identify a module F which contains a faulty fiber. In this case, the turbidity of the raw water is equal to 2 NTU and that of the permeate P of an integrated module F is less than or equal to 0.1 NTU (generally 0.06 to 0.08 NTU). To visualize a reliable change in the measurement to be made, ie to carry out a sensitive and robust analysis from an analytical point of view, it is necessary to concentrate the first permeate P by a factor of between 7 and 10. In this way , the variation in turbidity read by a conventional turbidimeter becomes quite reliable and representative of a significant variation. Indeed, instead of following a turbidity close to 0.1 NTU, the turbidity measured will be close to 0.2 to 0.5 NTU depending on the size of the leak observed (50 micron hole or fracture of a fiber over 15,000 constituent fibers of a module). The attribution of this increase in turbidity can thus be linked to a significant variation in the quality of the water because it is no longer linked to a potential error in the measurement made by the device.

Note finally that the measurement was made during the tenth minute of the first filter cycle that followed the installation of the F modules with the defect. In this respect, the proposed system gives very reliable results that can be related to the presence of a hole in a fiber and this result is even more clear in case of broken fiber. Other characteristics of the separation module M of a device for controlling the integrity of filtration membranes I according to the invention

To improve the visibility of the change in the characteristics of concentrated water by a separation module M, the following basic precautions must be taken:

The feed pipe from the first permeate P to the separation module M is a flexible plastic tube made of polyamide, polyethylene or teflon with an internal diameter of 8 mm.

The discharge pipe of the first permeate P of the separation module M is also a plastic tube of 8 mm internal diameter.

The second permeate P 'of the separation module M is evacuated through a large orifice so as to minimize the pressure drop created by the flow of the water thus filtered.

4 The outlet pipe of the second concentrate C of the separation module M is a plastic tube of internal diameter of only 2 mm.

At least three pneumatic valves (3-way valves) or electrical valves will be used to isolate the separation module M or to impose specific conditions on it:

at. Condition 1 - total filtration with V _; V ₃ , V ₅ , V ₆ open and

V ₂ , V ₄ and V ₇ closed,

b. Condition 2 - filtration + permanent purge with V _; V ₃ , V ₅ , V ₆ , V ₇ and V ₉ open and V ₂ , V ₄ , and V ₈ closed,

vs. Condition 3 - purge only mode with Vi, V ₃ , V ₇ and V ₉ open and V ₂ , V ₄ , V ₅ and V ₈ closed. This mode can be used to flush the separation module M to reduce the risk of clogging it incurs. This mode makes it possible, if it is of controlled duration, to feed the sensors Ce by the second concentrate C accumulated in the separation module M during the concentration period (ie total filtration period) that one just realized. The dimensions of the pipes chosen make it possible to impose a ratio of section equal to 1/16 between the discharge of the valve V ₉ and the supply and discharge of the other valves. The water is concentrated with a separation module M equipped with only 10 hollow fibers of 0.9 mm in diameter, ie a section ratio between the outlet of the valve V ₉ and the entry of the fibers equal to approximately 0.5. The valve V ₉ can be fully open as we have previously described. However, it is possible to maximize the filtration within each separation module M by concentrating the first permeate P of the filtration modules F tested with the valve V ₉ closed. In this case, the second concentrate C of the separation module M is periodically discharged to the means for analyzing the composition and / or the concentration of the second concentrate C. Note that in this case, the use of a multi-channel valve is no longer needed to manage the distribution of the second concentrate C of each of the separation modules M, this function being provided by the analytical central A of the overall management of the installation.

In most cases, it is possible to manage the concentration by the separation modules M and send the water thus concentrated for analysis by the system (s) of analysis A. To do this, it Just make sure that the first permeate P of the filter block is at least under a pressure of 0.25 bar. Similarly, the increase in the pressure in the compartment of the first permeate P allows a more advantageous operation of the device according to the invention. In fact, the concentration factor increases with the pressure as a driving force, which reduces the number of acquisition units A needed on a large plant. However, the backpressure applied permanently in the permeate compartment P of the installation must be less than 0.5 bar. This precaution of use makes it possible to minimize the irreversible clogging of the separation modules M. Finally, it would suffice to regulate this pressure by means of a control valve adapted to the conditions applied (flow rate and pressure) in the case where the The main filtration plant operates with a permanent counterpressure greater than 0.5 bar.

Claims

1. A method for controlling the integrity of at least one filtration membrane ensuring the separation of a fluid into a first permeate (P) and a first concentrate (C), characterized in that it comprises the following steps:

a / concentrating the first permeate resulting from the filtration by the filtration membrane by means of a separation module (M) comprising hollow fibers (Fc) present within the separation module (M) and adapted to separate the first permeate in a second permeate (Ρ ') and a second concentrate (C),

2. A method for controlling the integrity of filtration membranes according to claim 1, wherein the cutoff threshold of the hollow fibers of the separation module is greater than or close to the cutoff threshold of the controlled filtration membranes.

3. A method of controlling the integrity of filtration membranes according to claim 1 or 2, wherein the sensor makes it possible to measure at least one of the parameters comprising the absorption of the ultraviolet light, the turbidity, the number or the size of the particles present in the second concentrate.

The method for controlling the integrity of filtration membranes according to any one of claims 1 to 3, further comprising a step of measuring the pressure variations at the separation module by means of pressure sensors ( Cp) placed upstream and downstream of said separation module.

5. A method for controlling the integrity of filtration membranes according to any one of claims 1 to 4, wherein the first permeate is directed by a secondary duct (D) to the separation module so as to allow a backwash of said separation module.

6. A method of controlling the integrity of filtration membranes according to any one of claims 1 to 5, wherein the second permeate is directed to a storage tank (S) of the first permeate.

7. A method of controlling the integrity of filtration membranes according to any one of claims 1 to 6, wherein the second concentrate is directed to a storage tank (S) of the first permeate.

8. Device for checking the integrity of at least one filtration membrane adapted to ensure the separation of a fluid into a first permeate (P) and a first concentrate (C), characterized in that it comprises:

a distributor (Vm) adapted to direct the second concentrate towards the sensor,

9. Device for controlling the integrity of filtration membranes according to claim 8 wherein the hollow fibers of the separation module have a cut-off threshold greater than or close to the cutoff threshold of the controlled filtration membrane.

10. A filter membrane integrity control device according to any one of claims 8 to 9 further comprising sensors of pressure (Cp) placed upstream and downstream of the separation module for measuring the pressure variations at said separation module.

1 1. A device for monitoring the integrity of filtration membranes according to any one of claims 8 to 10 further comprising an analytical unit (A) adapted to treat the evolution over time of the composition and / or the concentration of the second concentrate.

12. Device for monitoring the integrity of filtration membranes according to any one of claims 8 to 1 1 wherein the separation module has a helical configuration.

13. Device for monitoring the integrity of filtration membranes according to any one of claims 8 to 12 further comprising a secondary conduit (D) adapted to direct the first permeate to the separation module so as to allow backwashing said separation module.

14. Device for monitoring the integrity of filtration membranes according to any one of claims 8 to 13 further comprising a storage tank (S) of the first permeate adapted to receive the second permeate and / or the second concentrate.

15. Water treatment station (E) comprising a plurality of filtration modules (F) implementing filtration membranes, each filter module (F) being respectively associated with one of a plurality of control devices the integrity of filtration membranes (I) according to any one of claims 8 to 14 whose distributor (Vm) is common to all devices, all of said devices being connected to the single common distributor (Vm) arranged to direct the second concentrates (C) respectively from the devices to common means of analysis of the composition and / or concentration of the second concentrates and to common means of analysis (A) of the evolution over time the composition and / or the concentration of the second concentrates.