EP2326595A1

EP2326595A1 - Optimized water treatment installation and process

Info

Publication number: EP2326595A1
Application number: EP09804537A
Authority: EP
Inventors: Gildas Manic; Nicolas David; Hervé BUISSON
Original assignee: Veolia Water Solutions and Technologies Support SAS
Current assignee: Veolia Water Solutions and Technologies Support SAS
Priority date: 2008-08-06
Filing date: 2009-07-27
Publication date: 2011-06-01
Also published as: AU2009278073A1; FR2934853B1; CA2732770A1; WO2010015543A1; FR2934853A1

Abstract

Optimized water treatment process. The invention relates to a process for treating water in an installation comprising a plurality of filtration units, said process comprising at least one step of filtration of said water in said filtration units under initial filtration conditions, and an optional step of modification of the value of at least one controlled parameter within a tolerance interval. According to the invention, such a process comprises: - a step of determining the value of at least one piece of information representative of the clogging capacity of the water to be filtered; - a first step of comparing said value of at least one piece of information representative of the clogging capacity with a predetermined threshold value; - a step of determining limits of said tolerance interval for said at least one controlled parameter as a function of said first comparison step, said step of determining the value of said at least one piece of information representative of the clogging capacity of the water to be filtered being obtained by making said water to be filtered pass, under conditions different from said initial filtration conditions, through at least one of said filtration units constituting a control filtration unit.

Description

INSTALLATION AND METHOD FOR OPTIMIZED WATER TREATMENT

1. Field of the invention

The field of the invention is that of the treatment of water. More specifically, the invention relates to the treatment of wastewater in view of their purification or treatment of water for the purpose of its potabilization, in filtration units.

The invention relates in particular, but not exclusively, to membrane bioreactors, biological filters (such as Biostyr® marketed by the Applicant), sand filters or membrane filters (such as those that can be used to reverse osmosis, ultrafiltration, nanofiltration or micro filtration).

2. Prior Art

Most of the filtration units used for water treatment include an open or closed vessel that forms a reactor. The water to be treated is introduced into this reactor in order to reduce the pollution. For example, it may undergo biological treatment.

These filtration units may be constituted by membranes or any other filtering material (sand, polystyrene beads, etc.).

When water is filtered, solids that are separated from the water are retained by these filtration units. Therefore, it is understood that the filtration of the water is accompanied by the progressive clogging of filtration units.

In order to limit the clogging of filtration units, different technologies can be implemented, such as backwashing or the use of aerators in the context of membrane biological reactors. These aerators, generally positioned below the membrane modules, make it possible to inject a gas (mainly air), preferably intermittently into the reactor. This gas rises in the form of bubbles along the membranes and creates on their surface a phenomenon of agitation which tends to limit their clogging. 3. Disadvantages of prior art However, the clogging of filtration units, which is not yet perfectly controlled, is at the origin of additional production costs which are large enough to constitute a major obstacle to the development of this type of processing technology. In particular, the clogging of the filtration units generates an increase in energy requirements. This is explained by the fact that the clogging of the filtration units is accompanied by an increase in the pressure drop across them which requires the creation of a larger depression so that the water to be treated passes through them. In addition, the filtration units have a lifetime that is even more limited as their progressive clogging requires increasing the depression required to pass the water through them.

This is why it is necessary to inject air to prevent and limit membrane clogging of a membrane bioreactor. The clogging of the membranes therefore requires the performance of maintenance operations to prevent wear of the membranes and restore their retention capacity.

For this purpose, the filtration phases can be alternated with: relaxation phases during which the flow through the membranes is stopped; backwashing phases during which water to be treated is injected countercurrently through the filtration material or membranes.

These phases are intended to remove the cake of particles that has deposited on the surface of the membranes. When the implementation of the phases mentioned above is not enough and the clogging of the filtration units becomes too great, it becomes necessary to proceed to curative treatment phases, for example maintenance cleaning or soaking phases with reagents. The maintenance of filtration units then imposes replacements of the filtration material, a relatively large workforce and consequently generates significant costs.

Techniques have been proposed to overcome this disadvantage. These techniques mainly concern the treatment of water in membrane bioreactors because they are the most complex and difficult to solve cases.

In particular, the international patent application bearing the number WO-Al -2007 / 006153 describes a water treatment technique with the objective of limiting energy expenditure while limiting the clogging of the membranes.

The technique described in this document proposes to control various parameters of a water treatment process according to the value of the membrane resistance calculated during the treatment.

The value of the resistance is compared with two resistance threshold values: an upper limit value which corresponds to the maximum resistance value tenable by the membrane; a lower limit value below which it is possible to change the controlled parameters in order to achieve energy savings.

When the measured resistance value is higher than the upper limit value, which means that the clogging of the membrane is too important, the aeration rate is increased so as to limit clogging. When the resistance value is lower than the lower limit value, which means that the treatment of the water causes a weak clogging and therefore the need for aeration of the membranes is low, the aeration rate is reduced so as to allow to save energy. When the value of the resistor is between the upper limit and the lower limit, which means that the system is working properly, the controlled parameters are not modified

Parameters other than the aeration rate can also be controlled. These are organized hierarchically and are modified in a iterative, one after the other, until a satisfactory level of performance is achieved.

Such a technique would make it possible, as indicated in this patent application, to significantly reduce the energy consumption required for the aeration of the membranes. However, this technique has many disadvantages.

In particular, according to this technique, on the one hand the reference values at which the measured resistance value is compared, and on the other hand the reference values of the controlled parameters (for example aeration setpoint), are determined by experience in processing. a reference water in a typical installation. In other words, these values determined by experiment lead to optimally exploit the membranes used in this typical installation during the treatment of a water having the qualities of the treated water during the development of the system. . Thus, during the treatment of a water whose qualities are different from that of the water used in the development of the installation, the performance of the membranes are not exploited optimally.

In addition, the upper and lower limit values at which the measured resistance is compared are fixed. Thus, as long as the measured value of the membrane resistance is greater than the maximum value, the controlled parameter (s) are modified in such a way that the clogging of the membranes is limited, which implies that the production capacity of the system is limited. In other words, when the quality of the water to be treated is particularly bad, the prevention of clogging membranes will be favored at the expense of production capacity. This can lead to a situation in which the quantity of water produced is less than the needs and therefore insufficient.

In addition, this technique operates iteratively, that is to say that each controlled parameter is modified only if the previous modification of the higher parameter in the hierarchy did not lead to improve the efficiency of the system. This implies that after modifying a first parameter, the impact this change is evaluated. If the desired performance level is not achieved by this change of the first parameter, a second parameter must be changed, this being reiterated until the expected performance level is reached. Thus, when the quality of the water to be treated varies rapidly, the modifications made to improve the performance of the system do not exert any real positive impact due to the lack of responsiveness of the system.

4. Objectives of the invention

The invention particularly aims to overcome these disadvantages of the prior art. More specifically, an object of the invention is to provide a water treatment method that optimally utilizes the filtration units.

In particular, an objective of the invention is to provide such a technique that makes it possible to limit the clogging of the filtration units. An object of the invention is also to implement such a technique which is particularly effective including during the quality variations of the water to be treated.

The invention also aims to provide such a technique that allows under most operating conditions to produce a sufficient amount of treated water, that is to say corresponding to the wish.

5. Presentation of the invention

These objectives, as well as others which will appear later, are achieved by means of a water treatment process in an installation comprising a plurality of filtration units, said method comprising at least one filtration stage. of said water in said filtration units under initial filtration conditions, and a step of optionally changing the value of at least one controlled parameter within a tolerance range. According to the invention, such a method comprises: a step of determining the value of at least one information representative of the clogging power of the water to be filtered; a first step of comparing said value of at least one information representative of the clogging power with a predetermined threshold value; a step of determining the limits of said tolerance interval for said at least one controlled parameter according to said first comparison step, said step of determining the value of said at least one information representative of the clogging power of the water to be filtered being obtained by passing said water to be filtered, under conditions different from said initial filtration conditions, through at least one of said filtration units constituting a control filtration unit.

The characteristic that the water to be filtered passes through the control unit under conditions different from the initial filtration conditions in which it passes through the other filtration units means that the conditions of pressure, flow, duration. .. water transit within the control unit are different from those within the filtration units.

Thus, the invention is based on an original approach to the treatment of water within at least one reactor in which process parameters are controlled and the limits of the tolerance intervals of these parameters are modified as a function of the clogging power of the reactor. the water to be treated.

In the case where the filtration modules are membrane modules, this aspect of the invention is particularly interesting insofar as it optimizes the use of the membranes implemented according to operating constraints. Indeed, the fact of determining the clogging power of the water to be filtered and consequently modifying the tolerance interval of the controlled parameter (s) makes it possible to modify the controlled parameter (s) within ranges suitable for the treatment of this water. water through the membranes that are implemented.

This advantage is not only provided during the implementation of membrane modules. On the contrary, it can also be provided when other types of filtration units are used, such as sand filters, biological filters, and filters composed of a plurality of balls, for example made of polystyrene, immersed inside a column through which the filter passes. water to be treated ... whose clogging can be better controlled and the use can be optimized by the implementation of the invention.

In addition, this implementation makes it possible in particular to pass the water to be treated in an accelerated manner through a filtration unit similar to that used to filter the water so as to anticipate the behavior of the filtration modules during treatment water coming into the installation. This study then makes it possible to define the limits of the tolerance intervals of the various controlled parameters so that they are adjusted in ranges of values which make it possible to use in an optimal way the resources of the filtration modules taking into account the nature of the water to treat.

According to an advantageous characteristic of the invention, said step of determining the value of an information representative of the clogging power of the water to be filtered comprises the following sub-steps: performing successive filtering cycles of said water through said unit filter filtration; continuously measuring the evolution of the pressure or pressure drop across said control filter unit during each of said filter cycles; varying the value of the flow at which said water passes through said control filtration unit so that said water transits during each of said filtration cycles in a flow whose value is different from the value of the filtration flow of said water in at least one preceding filtration cycle; said information representative of the clogging power of the water to be filtered is the value of the circulation flow of said water recorded during one of said filtration cycles during which said pressure or said pressure drop increases beyond a predetermined threshold. The implementation of these steps makes it possible to define the critical flow, that is to say the flow of water passing through a filtration unit beyond which the clogging of this unit becomes irreversible. The critical flow is an indicator of the clogging power of the water to be filtered particularly representative and reliable. This technique of determination of the critical flow consequently makes it possible to obtain in a safe and precise manner an image of the clogging power of the water to be filtered.

Advantageously, a method according to the invention comprises for each of said units: a step of measuring the value of at least one piece of information representative of the resistance of said filtration units; a step of calculating the value of the resistance of said filtration units

a second step of comparing said value of the calculated resistance with a predetermined threshold resistance value; a step of possibly modifying said at least one controlled parameter as a function of said second comparison step.

It is recalled that the resistance of a filtration unit is equal to the inverse of its permeability. The permeability of a filtration unit is equal to the ratio of the flow of water passing through it to the pressure, the flow being itself equal to the ratio of the filtration rate to the filtration surface.

The invention is therefore based on the modification of controlled parameters as a function of the value of the resistance of the filtration units. Resistance is indeed an indicator that can effectively monitor the evolution over time clogging of filtration units. According to a preferred aspect of the invention, at least two of said parameters are modified simultaneously.

This feature ensures that a method according to the invention can effectively manage water quality variations.

According to another advantageous aspect, a treatment method according to the invention comprises a step of modifying said resistance value. threshold within a tolerance range.

It is therefore possible to correct the threshold value of the resistance of filtration units in order to allow to accept more clogging or on the contrary to limit it depending on the circumstances. In particular, according to yet another advantageous aspect, a method according to the invention comprises a step of choosing the value of the volume of water to be treated over a given period.

It is thus possible to correct the resistance threshold value so as to meet the needs for production of treated water. In this case, the process advantageously comprises: a step of measuring the volume of treated water; a third step of comparing the value of said volume of treated water with said selected water volume setpoint value to be processed over a given period; a step of possible correction of said threshold resistance value as a function of said third comparison step.

This makes it possible to modify the manner in which the controlled parameters are controlled in such a way as to enable the production of sufficient water. Thus, when the water is not produced in sufficient quantity, the resistance threshold value may be modified upwards so as to allow greater clogging of the membranes. It will then be possible to give priority to the production of water and to produce it so as to satisfy the needs to the detriment of the damage of the filtration units.

According to a preferred feature, said at least one controlled parameter is a parameter related to the clogging of said filtration units.

The implementation of the invention thus leads to control, at least to a better extent compared to the techniques of the prior art, the clogging of the filtration units.

Preferably, said at least one controlled parameter belongs to the group comprising: the filtration time in each of said filtration units; the filtration flux in each of said filtration units; the relaxation time of said filtration units; the aeration rate of said filtration units; the duration of aeration of said filtration units; the amount of filtration units implemented; activating a backwash cycle; the backwash flow rate, the backwash time, the backwash frequency, the volume of backwash water in each of said filtration units. ; the conversion rate; the opening or closing of a recirculation loop; activating a maintenance cleaning of said filtration units; activating a curative cleaning of said filtration units. Acting on at least one of these parameters makes it possible to control the impact of water treatment on the clogging of the filtration units.

The present application also relates to an installation for the implementation of such a method.

An installation of this type comprises: a battery of filtration units and aeration means of said filtration units; first means for withdrawing said water through said battery; means for measuring the resistance of said filtration units; means for measuring the value of information representative of the clogging power of said water to be filtered; means for controlling at least one processing parameter.

Also according to the invention, said means for measuring the value of an information representative of the clogging power comprise at least one filtration unit constituting a control filtration unit able to operate under different conditions of said battery and having the same characteristics. said filter units forming said battery, and second means for withdrawing said water through said control unit.

Advantageously, said filtration units belong to the group comprising: - sand filtration units; membrane filtration units; biological filtration units; filtration units on polystyrene beads.

The present technique can therefore be implemented for any type of filtration.

6. List of figures

Other features and advantages of the invention will emerge more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and nonlimiting example, and the appended drawings, among which: FIG. 1 presents a diagram of an installation according to the invention; Figure 2 shows a variant of an installation according to the invention; FIG. 3 illustrates a diagram of the control system of a method according to the invention. 7. Description of an embodiment of the invention

7.1. Reminder of the general principle of invention

The invention relates to a method for treating water within a reactor, such as for example a membrane-based biological reactor and in which at least one parameter such as, for example, the aeration rate of the membranes, the flow passing through the membranes ... is controlled in such a way that its value can evolve within a tolerance range. It is noted that this parameter can for example be modified according to the value of the membrane resistance measured in real time.

The invention is based on the implementation of a step of measuring an information representative of the clogging power and a comparison step of this value with a predetermined threshold value so as to change the limits of the tolerance interval of the controlled parameter (s).

This step of determining the value of information representative of the clogging power of the water to be filtered is obtained by passing the water to be treated under particular conditions through a control filtration unit.

This implementation makes it possible in particular to pass the water to be treated in an accelerated manner through a filtration unit similar to that used to filter the water so as to be able to anticipate the behavior of the filtration modules during the treatment of the water. water coming into the facility. This study then makes it possible to define the limits of the tolerance intervals of the various controlled parameters so that they are adjusted in ranges of values which make it possible to make optimum use of the resources of the filtration modules taking into account the nature of the water to treat.

The implementation of these steps is interesting in particular because it allows to change the operating ranges of the installation depending on the quality of the water to be treated.

Thus, when the clogging power is lower than a reference value, which means that the quality of the water to be treated is relatively good, the controlled parameters will be likely to evolve within a certain value range. If it is detected that the clogging power of the water to be filtered is greater than a reference value, which means that the quality of the water is deteriorating, the range in which the controlled parameters are likely to evolve will be modified. .

This aspect of the invention is particularly interesting insofar as it makes it possible to optimize the use of the membranes used as a function of the operating constraints. Indeed, the fact of determining the clogging power of the water to be filtered and consequently modifying the tolerance interval of the controlled parameter (s) makes it possible to modify the controlled parameter (s) within ranges suitable for the treatment of this water. water through the membranes that are implemented. According to another aspect of the invention, it is also provided that the resistance threshold value at which the real-time calculated resistance is compared may be varied. In particular, this value can be chosen, in a tolerance range whose limits will be predetermined, by comparing the flow to be treated over a given period with the flow already treated before the expiry of this period.

Thus, if we consider that 100 m ³ of water must be treated on a day but that at ³ A of the day only 50 m ³ have been treated, the threshold value of resistance will be raised so as to allow to produce water in the desired quantities, that is to say by exploiting more the capabilities of the membranes. In this case, we favor production over the membranes.

This is clearly opposed to the common practice of a person skilled in the art who, in the techniques of the prior art, favors the prevention of deterioration of the membranes, which may in certain cases lead to not reaching the level of production of treated water required.

According to yet another aspect of the invention, the setpoints of several controlled parameters may vary simultaneously depending on the value of the resistance of the membranes. This is contrary to the prior art technique in which the controlled parameters are modified one by one in an order of priority and evaluating the impact of each of the modifications until a suitable level of performance is achieved. This characteristic of the invention makes it possible to significantly improve the reactivity of the process in the event of variation in the quality of the water to be treated.

7.2. Example of an embodiment of the invention 7.2.1. Architecture of a treatment facility

FIG. 1 illustrates a schematic representation of an installation intended for the implementation of a water treatment method according to the invention.

As it appears in this figure, such an installation comprises a biological reactor 10 containing water to be treated mixed with activated sludge. This biological reactor 10 houses a membrane filtration unit 11. This membrane filtration unit 11 can integrate a plurality of membrane modules, for example of the microfiltration, ultrafiltration, nanofiltration or reverse osmosis type. These membrane modules may for example comprise hollow fibers. , flat membranes, tubular membranes or membranes of any other type.

The biological reactor 10 also houses a control membrane module 12. This control membrane module 12 is identical and has the same characteristics as the modules that make up the membrane filtration unit 11.

Aeration means are provided in a lower portion of the biological reactor 10. These aeration means may take the form of gas injection nozzles 13, preferably air. These nozzles 13 are connected to a booster 14. The air injected into the biological reactor 10 provides a function of unclogging and / or preventing clogging of the filtration membranes. In fact, the air injected into the biological reactor 10 rises in the form of bubbles along the membranes so that it causes a stirring phenomenon on their surface. This agitation phenomenon makes it possible to limit the agglomeration of the activated sludge on the membranes and also makes it possible to remove a part of the accumulated deposit on the surface of the membranes, called cake.

Another aeration device (not shown) provides aeration of activated sludge for biological treatment.

The membrane filtration unit 11 is connected to a first variable rate filler pump 16. The indicator membrane module 12 is connected to a second variable rate filler pump 17.

This installation further comprises a battery of sensors (not shown) which make it possible to measure various information relating to the state of the system. It comprises in particular sensors which make it possible to measure, for each of the membrane modules of the filtration unit 11, the value of the information needed to calculate their resistance, including transmembrane pressure, flow, temperature. It also includes sensors for measuring all the information needed to calculate the flow through the control module 12, including flow, transmembrane pressure and temperature.

FIG. 2 illustrates a variant of an installation according to the invention in which a first 20 and a second 21 reactors are implemented. The first reactor 20 constitutes an activated sludge basin while the second reactor 21 houses the membrane modules. In this embodiment, the filtration modules are membrane modules. In variants, it may of course be other type of filtration unit such as sand filters ...

This installation also comprises means making it possible to control different parameters of the treatment method according to the different measurements made.

FIG. 3 represents a diagram which illustrates the control and control means of an installation according to the invention, as well as the way in which they interact.

In the present embodiment, the method according to the invention allows the control of four parameters: the filtration time; the filtration flow; the relaxation time; the aeration rate of the membranes. However, other parameters can be used like the time and the flow of retro washing ...

In variants of this embodiment, it may also be provided that more or less than four parameters are controlled. It may in particular be envisaged an embodiment according to which a single parameter is controlled. The control means here comprise six regulators (21 to 26). Four of these regulators make it possible to deliver a setpoint for controlling a controlled parameter by comparing the calculated value of the resistance of each of the modules with a predetermined threshold value: the regulator 22 makes it possible to deliver a filtration time setpoint; the regulator 23 makes it possible to deliver a flow setpoint or filtration flow (the flow being the flow rate relative to the filtration surface); the regulator 24 makes it possible to deliver a set of relaxation times; the regulator 25 makes it possible to deliver an aeration flow setpoint. The regulator 21 makes it possible to correct the tolerance interval in which the setpoint of each of the controlled parameters delivered by the regulators 22 to 25 must be situated, by comparing information representative of the clogging power of the water to be treated with a predetermined threshold value. .

The regulator 26 makes it possible to correct the resistance threshold value within an interval whose limits are predetermined, by comparing the volume of water treated over a given period with the volume of water that has actually been treated from the beginning. treatment.

7.2.2. Calibration of the installation

AJ Determination of tolerance intervals for each controlled parameter

The calibration of an installation according to the invention comprises the determination of tolerance intervals for each controlled parameter according to the quality of the water to be treated. Thus, different water qualities will be assigned different tolerance intervals for each controlled parameter. These tolerance intervals are determined by experiment taking into account the clogging power of the water to be filtered, which is a parameter representative of the quality of the water to be treated.

The determination of the clogging power of the water to be filtered is obtained by determining, with the control module, the critical flow, that is to say the flow from which the clogging of the membrane becomes irreversible. The determination of the critical flux is obtained by subjecting the control module to a succession of filtration cycles, the value of the flux being increased between each cycle, for example by the implementation of a variable flow rate pump. The transmembrane pressure is measured continuously during each filtration cycle. This can for example be achieved by means of a manometer. When it is detected that the transmembrane pressure increases beyond a predetermined threshold, initially set empirically and adjusted case by case, during a filtration cycle, the value of the flow according to which the water to be processed is filtered during this cycle is the critical flow. This critical flow determination protocol is just one example.

Other methods could be implemented for this purpose.

In variants, it may be planned to carry out, between each filtration cycle, a relaxation phase, or backwashing so as to restore the membrane. It can also be expected that the flow is not systematically increased between two consecutive filter cycles.

During the development of the process, several experiments are carried out on the plant to treat water of different qualities and to determine for each of them optimal tolerance intervals for each of the controlled parameters. For each test with a water of particular quality, the instructions for each controlled parameter are modified and the impact of these modifications on the clogging of the membranes is evaluated so as to determine operating conditions allowing the optimal use of the membranes for the treatment of a water presenting these particular qualities. At the end of the development tests of the installation, at each tested critical flow value is assigned a tolerance interval for each of the controlled parameters allowing optimal exploitation of the membranes during the treatment of each type of water.

These tests also make it possible to determine for each installation, the average quality of the water which will be brought to be treated there. The quality of the water more frequently encountered during tests, represented by its clogging power, will be considered as the threshold value of clogging power. B / Determination of the resistance threshold value

As previously described, each controlled parameter can be modified by comparing the calculated resistance for each of the membranes to a threshold value.

According to one aspect of the invention, the threshold resistance value can vary within a tolerance range whose terminals are predefined.

More precisely, the regulator 26 makes it possible to correct the resistance threshold value by comparing the volume of water to be treated over a given period of time.

(eg a day) and the volume of water actually treated since the beginning of this period (eg since the morning). Thus, as the day progresses, if the quantity of water produced does not meet the needs, the regulator 26 makes it possible to modify the resistance threshold value so as to allow sufficient production of treated water.

Depending on the results of this comparison, the controller 26 may for example automatically switch between three treatment modes: cautious mode, optimal mode or maximum mode. Each treatment mode has a resistance value. If the quantity of water produced meets the requirements, the regulator 26 will choose to operate in optimal mode.

If the amount of water produced is greater than necessary, the regulator 26 switches to a cautious mode so as to favor the prevention of clogging to the production of the treated water. If, on the contrary, the water is not produced in sufficient quantity, the regulator

26 switches to maximum mode so as to favor the production of treated water taking full advantage of the capabilities of the membranes.

The regulators 22 to 25 then establish a relationship between the calculated resistance and the resistance setpoint delivered by the regulator 26, and issue instructions for each controlled parameter. 7.2.3. Implementation of the process

The implementation of a method according to the invention will now be described.

During the treatment of water, the critical flow that represents the clogging power of the water is determined as previously described by the implementation of a succession of filtration phases through the control module.

The regulator 21 then compares the value of the determined critical flux with one or more threshold values so as to modify the limits of the tolerance intervals of each controlled parameter.

In parallel, the measurements made by the different sensors make it possible to calculate the resistance of each membrane.

The regulators 22, 23, 24, 25 determine respectively as a function of the resistance of each membrane and the resistance reference which is related to the operating mode engaged by the regulator 26: a filtration time setpoint; a filtration flow set point; a set of relaxation time; an aeration flow instruction. The values of these setpoints are included in the tolerance intervals defined by the controller 21.

If the water quality deteriorates, that is to say that its clogging power increases, the controller 21 changes the limits of the tolerance intervals of each controlled parameter. If the setpoint of one of these parameters is outside its new range, it is modified accordingly. Otherwise, the deposit does not change.

If the modification of the quality of the water has an impact on the calculated resistance of each of the membranes, then the regulators 22, 23, 24, 25 will deliver new setpoints located in the new intervals defined by the regulator 21. The operator fixes for the day a set of water volume to be treated. The volume of water treated since the morning is calculated during the implementation of the process. If, as the day goes by, a comparison by the regulator 26 of the volume to be treated on the day and the volume actually passed since the beginning of the day makes it possible to detect that the system does not make it possible to produce water in sufficient quantities, the regulator 26 will change the resistance setpoint. As a result, membrane capacities can be further exploited to increase productivity at the expense of their service life. According to a variant, it can be provided the implementation of two control horizons. A control horizon, called "short horizon", can be implemented to monitor the evolution of clogging. A control horizon, called "long horizon" can be implemented to monitor the evolution of the volume of water produced. It is noted that the short and long horizons can be linked for example by a multiplier factor relationship.

For example, if we consider that a filtration cycle has a duration of

15 minutes, and that the calculation of the evolution of the resistance is done on 5 to 10 cycles, this calculation will be realized in less than three hours. If we consider that the short and long horizons are linked by a multiplying factor of 8, the monitoring of the volume of treated water will be done over 24 hours.

The general principle of implementing a method according to the invention being set, examples of the behavior of the regulation are now described.

A / Cautious mode

Table 1 gathers the data relating to a starting situation called initial situation.

As indicated in this table 1, the standard set of water to be filtered, which corresponds to the reference value of the critical flow through the control module, is set at 40 L / h / m ² . The daily volume of water to be treated is set at 100 m ³ / d. Finally, the long-term sealing setpoint, that is to say the resistance for each of the membranes is set at 4 m ^' Vj.

A calculation of the long-term clogging of the membranes on consecutive cycles to determine that it is equal to 3 m ^'Vj. It is therefore below the set point (4 m ^' Vj).

The measurement of the daily volume of treated water makes it possible to determine that it is equal to 110 m Zj, that is to say that it is greater than the set point.

The starting situation is therefore a situation in which the treatment plant produces more water than necessary without clogging the membranes. The cautious mode is then engaged by the regulator 26 and the regulator 21 does not modify the thresholds of the different controlled parameters.

B / Maximum mode Assuming that, starting from this situation, a polluting substance arrives in the water to be treated. The values corresponding to this situation are grouped together in Table 2.

Table 2: Values after pollution spike

The critical flux representing the clogging power of the water is now 30 L / h / m ² . It is therefore lower than the set point which means that the water is more clogging.

It is then necessary to change the configuration of the installation so as to preserve the membranes. The regulator 21 consequently modifies the tolerance ranges of the various parameters controlled so that their ranges of evolution are restricted to a treatment area more in adequacy with the water to be treated.

It is noted that the regulators operate in a conventional manner. It can for example be PID controllers.

The regulators 22 and 23 do not modify the value of the setpoint they deliver, insofar as it is in the modified range. On the other hand, the regulators 24 and 25 respectively modify the value of the setpoint they deliver so that it is in the new interval defined by the regulator 21.

In parallel, the regulator 26 compares the volume of treated water with the volume of water to be treated daily. The daily volume, whose value is now 90 m ³ / d, is below the set point, ie the quantity of water produced is less than necessary. The regulator 26 switches on the maximum mode so as to allow sufficient water to be produced by making greater use of the capacity of the installation. The regulator 26 then delivers a so-called maximum long-term sealing setpoint within the tolerance range so as to allow greater clogging of the membranes, that is to say to further exploit the capabilities of the membranes in order to produce enough water.

The regulators 22 to 25 respectively deliver, by comparing the measured value of the long-term clogging with the long-term sealing setpoint delivered by the regulator 26, setpoints included in the intervals defined by the regulator 21 so as to increase the production of treated water.

In this example, the filtration time and the aeration of the membranes are increased by the regulators 22 and 25 within their intervals so as to increase the volume of treated water.

C / Optimal Mode

Since the measurement of the critical flow makes it possible to detect that the pollution has passed, that is to say that the water is filtered better, which occurs when its clogging power (critical flow) becomes equal to the setpoint of type of water to be filtered, the controller 21 changes again the limits of the tolerance intervals of the various controlled parameters.

The values corresponding to this situation are summarized in Table 3. Table 3: values after pollution peak treatment

The treated water is now produced in sufficient quantities. The regulator 26 then actuates the optimal mode.

If, despite the peak pollution, the long-term clogging of the membranes has not changed, the instructions issued by the regulators 22, 23, 24, 25 will not change (values in parentheses). In the opposite situation, these regulators will deliver instructions whose values will be included in the intervals defined by the regulator 21.

Claims

A method of treating water in an installation comprising a plurality of filtration units (11), said method comprising at least one step of filtration of said water into said filtration units (11) under initial filtration conditions, and a step of possibly modifying the value of at least one controlled parameter within a tolerance interval, characterized in that said method comprises: a step of determining the value of at least one representative information of the clogging ability of the water to be filtered; a first step of comparing said value of at least one piece of information representative of the clogging power with a predetermined threshold value; a step of determining the limits of said tolerance interval for said at least one controlled parameter according to said first comparison step, said step of determining the value of said at least one information representative of the clogging power of the water to be filtered being obtained by passing said water to be filtered, under conditions different from said initial filtration conditions, through at least one of said filtration units constituting a control filtration unit (12).

2. Water treatment method according to claim 1, characterized in that said step of determining the value of an information representative of the clogging power of the water to be filtered comprises the following substeps: perform filtration cycles successive said water through said control filtration unit (12); continuously measuring the change in pressure or pressure drop across said control filtration unit (12) during each of said filtration cycles; varying the value of the flow at which said water passes through said control filtration unit (12) such that said water transits through each of said filtering cycles in a flow whose value is different to the value of the flow of filtration of said water in at least one preceding filtration cycle; said information representative of the clogging power of the water to be filtered is the value of the circulation flow of said water recorded during one of said filtration cycles in which said pressure or said pressure drop increases beyond a predetermined threshold.

3. Water treatment method according to any one of claims 1 or 2, characterized in that it comprises for each of said units (11): - a step of measuring the value of at least one piece of information representative of the resistance of said filtration units (11); a step of calculating the value of the resistance of said filtering units (11); a second step of comparing said value of the calculated resistance with a predetermined threshold resistance value; a step of possibly modifying said at least one controlled parameter as a function of said second comparison step.

4. A method of treating water according to any one of claims 1 to

3, characterized in that at least two controlled parameters are modified simultaneously.

A method of treating water according to any one of claims 1 to

4, characterized in that it comprises a step of modifying said threshold resistance value in a tolerance interval.

6. Water treatment method according to claim 5, characterized in that it comprises a step of choosing the value of the volume of water to be treated over a given period.

7. A method of treating water according to claims 5 and 6, characterized in that it comprises: a step of measuring the volume of treated water; a third step of comparing the value of said volume of treated water with said chosen value of volume of water to be treated over a given period; a step of possibly correcting said threshold resistance value as a function of said third comparison step.

8. water treatment method according to any one of claims 1 to 7, characterized in that said at least one controlled parameter is a parameter related to the clogging of said filtration units.

9. Water treatment method according to claim 8, characterized in that said at least one controlled parameter belongs to the group comprising: the filtration time in each of said filtration units; the filtration flow in each of said filtration units; the relaxation time of said filtration units; the aeration rate of said filtration units; the duration of aeration of said filtration units; the quantity of filtration units used; activating a backwash cycle; the backwash flow rate, the backwash time, the backwash frequency, the volume of backwash water in each of said filtration units. ; - the conversion rate; the opening or closing of a recirculation loop; activating a maintenance cleaning of said filtration units; activating a curative cleaning of said filtration units.

10. Treatment plant for the implementation of a water treatment process according to any one of claims 1 to 9, characterized in that it comprises: a battery of filtration units (11, 12) and aeration means (13, 14) of said filtration units (11, 12); first withdrawing means (16) for said water through said battery (11); means for measuring the resistance of said filtering units (11); means for measuring the value of information representative of the clogging power of said water to be filtered; means for controlling at least one processing parameter, and in that said means for measuring the value of information representative of the clogging power comprise at least one filtration unit constituting a control filtration unit (12) suitable for operating under different conditions of said battery and having the same characteristics as said filtration units (ll) forming said battery, and second means for withdrawing said water through said control unit (12).

11. Processing plant according to any one of claims 9 or 10, characterized in that said filtration units (11, 12) belong to the group comprising: sand filtration units; membrane filtration units; biological filtration units; filtration units on polystyrene beads.