EP4291322A1

EP4291322A1 - Method for operational control of a water treatment unit and water treatment unit for implementing such a method

Info

Publication number: EP4291322A1
Application number: EP22705770.0A
Authority: EP
Inventors: Khaled-Valentin AL MEZAYEN; Sylvain Masson
Original assignee: Inovaya SAS
Current assignee: Inovaya SAS
Priority date: 2021-02-10
Filing date: 2022-02-10
Publication date: 2023-12-20
Also published as: FR3119554A1; US20240082788A1; WO2022171717A1

Abstract

This method for operational control of a water treatment unit comprises at least the following steps of determining (1000) a value (D48) for the normalized flow rate, per unit area and per unit pressure, of an ultrafiltration membrane (48); treating (1004) the water if a difference (Δ1) between the normalized flow rate value and a first reference value (D481) is below or equal to a first threshold value (D1); regenerating (1010) the ultrafiltration membrane (48) if the difference (Δ1) between the normalized flow rate value and the first reference value (D481) is above the first threshold value (D1). The regeneration step (1010) comprises at least sub-steps consisting in backwashing (1011) the ultrafiltration membrane (48); interrupting (1012) the circulation of water through the treatment unit (2) and keeping it interrupted; heating (1014) the water in contact with the ultrafiltration membrane (48) in a filtration device (44, 48) having an ultrafiltration membrane during the interruption sub-step; and, after the heating step, backwashing (1016) the ultrafiltration membrane (48).

Description

TITLE: Control method in operation of a water treatment unit and water treatment unit for the implementation of such a method

The present invention relates to a method for controlling the operation of a water treatment unit which comprises at least one ultrafiltration membrane filtration device. The invention also relates to a water treatment unit allowing the implementation of such a method. Such a water treatment unit can be used for clarification, disinfection and reduction of pollutants in water, in particular micropollutants, such as endocrine disruptors, pesticide derivatives, herbicides. Such a water treatment unit can, in particular, be used for the purification of surface water, in accordance with the standards of a Regional Health Agency in France.

In the field of water treatment, it is known to have, on the path of a flow of water to be treated, various filters aimed at improving the quality of the water. These different filters can include filters operating on an essentially mechanical principle, which define orifices for the passage of water, in particular filters equipped with ultrafiltration membranes.

It is thus known from WO-A-2008/047393 to integrate an activated carbon filter into a first filtration unit, which is arranged upstream of a second filtration unit which is preferably of the ultrafiltration type. This approach makes it possible to combine the advantages of filtration by absorption and fine mechanical filtration, by ultrafiltration. In this known material, the ultrafiltration membrane or membranes tend to clog, under the effect of clogging agents or solid pollutants carried by the flowing water. This known equipment is equipped with several non-return valves which prevent circulation in the opposite direction, and therefore backwashing of the filters.

On the other hand, it is known from certain installations to backwash filters by circulating cleaning water therein, in the opposite direction to the direction of normal circulation of the water, corresponding to the treatment of the water. Even if such backwashing operations are carried out with care, they do not make it possible to completely eliminate the clogging agents and the pollutants, so that the permeability of an ultrafiltration membrane gradually decreases relatively quickly, except at using chemicals to thoroughly clean this membrane, which requires human handling by skilled labor and leads to a risk of pollution of the treated water.

JP-A-2008289959 discloses a filtration system which can be cleaned with a succession of steps during which the operation of the system is briefly interrupted. Water heated in a tank outside a filter is used when cleaning a filter. Cleaning efficiency is not optimal.

Similar problems arise with the material known from DE-U-29823757. It is these drawbacks that the invention can particularly remedy, by proposing a new method for controlling a water treatment unit in operation in which it is possible to extend the life of an ultrafiltration membrane. , minimizing the use of cleaning chemicals.

To this end, the invention relates to a method for controlling the operation of a water treatment unit comprising at least one ultrafiltration membrane filtration device, this method comprising at least the following steps: a) determination of a standardized flow rate value per unit area and per unit pressure of the ultrafiltration membrane b) treatment of the water with the treatment unit if a difference between the value of the standardized flow rate detected in step a) and a first reference value is less than or equal to a first threshold value; c) regeneration of the ultrafiltration membrane if the difference between the value of the normalized flow detected in step a) and the first reference value is greater than the first threshold value;

In addition, the regeneration step comprises at least one sub-step consisting of: c1) backwashing the ultrafiltration membrane.

In accordance with the invention, the regeneration step further comprises at least sub-steps consisting of: c2) interrupting and maintaining interrupted the circulation of water in the treatment unit; c3) heating the water in contact with the ultrafiltration membrane in the ultrafiltration membrane filtration device during substep c2); and c4) after step c3), backwash the ultrafiltration membrane.

Thanks to the invention, the regeneration step induces a surprising effect of a significant increase in the permeability of an ultrafiltration membrane, which makes it possible to extend its lifespan, without having recourse to chemical products during the retrofiltration. washing of steps c1) and c4). The water heated within the filtration device is in contact with the membrane and acts on the membrane for the duration of sub-step c2), which improves cleaning. This facilitates the operation of the processing unit which is simpler, and which can be managed remotely since it is not necessary for an operator to come on site to inject one or more cleaning products therein. According to advantageous but not obligatory aspects of the invention, such a method can incorporate one or more of the following characteristics, taken according to any technically permissible combination.

- The sub-step c2) is implemented for a duration of between 15 min and 6 hours, preferably between 30 and 90 min.

- Sub-step c3) is implemented until a temperature of the water in contact with the ultrafiltration membrane of between 10°C and 30°C, preferably between 15°C and 25°C, is reached, more preferably of the order of 20°C.

- The process is implemented automatically, without human intervention.

- The process comprises the following step, an alternative to step c): d) cold backwashing of the ultrafiltration membrane.

- Step c) of regeneration and step d) of cold backwashing are implemented alternately according to a difference between the value of the normalized flow detected in step a) and a second reference value , and/or the periodicity of a situation where the difference between the value of the normalized flow detected in step a) and the first reference value is greater than the first threshold value, and/or the percentage of water treated used for one or more successive backwashing steps, and/or

- at predetermined times, and/or depending on the quantity of water treated in the treatment unit.

- The first reference value is adjusted after step c) of regeneration and, possibly after step d) of cold backwashing.

- The value of the standardized flow determined in step a) is related to a reference temperature.

According to another aspect, the invention relates to a water treatment unit configured for the implementation of a method as mentioned above, this unit comprising at least one ultrafiltration membrane filtration device. In accordance with the invention, this unit also comprises at least one device for heating the water present in the ultrafiltration membrane filtration device, as well as a system for measuring a pressure drop in a flow of water. water through this ultrafiltration membrane filtration device.

According to an advantageous aspect of the invention, the heating device comprises heating resistors in contact with a body of the membrane filtration device of ultrafiltration, annealed copper wires coupled with resistors or infrared heating systems.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of an embodiment of a water treatment unit and of a control method in operation of this unit, in accordance with its principle, given solely by way of example and made with reference to the appended drawings, in which:

[Fig 1] Figure 1 is a block diagram of a water treatment unit according to the invention, during operation for the treatment of a quantity of water;

[Fig 2] Figure 2 is the same diagram as Figure 1, during backwashing of a first filtration device of the water treatment unit;

[Fig 3] Figure 3 is the same diagram as Figure 1, during the backwashing of a second filtration device of the water treatment unit;

[Fig 4] Figure 4 is the same diagram as Figure 1, during backwashing of a third filtration device of the water treatment unit;

[Fig. 5] Figure 5 is a block diagram which illustrates a control method in operation of the water treatment unit of Figures 1 to 4; and

[Fig. 6] figure 6 is a representation of the evolution, as a function of time, of a normalized bit rate used in the process of figure 5.

Unit 2 shown in Figures 1 to 4 is used for the clarification, disinfection and reduction of pollutants of a quantity of water present in a tank 4 which belongs to unit 2 and which is supplied with water to be treated. by a pipe 6.

The processing unit 2 also comprises a control card 8 which includes at least one microprocessor 10 and a memory 12 in which is stored a program allowing the operation of the processing unit 2 to be controlled. The control card 8 is connected to various members, such as counters or solenoid valves of the processing unit 2 by connections not shown, which can be of the wired or wireless type. In the figures, dotted arrows having as their origin or destination the reference 8 surrounded in a circle show the transmission of information between certain components of the processing unit 2, other than solenoid valves, and the control card 8. The control card also controls the various solenoid valves of the processing unit, which are mentioned below, by means of wired or wireless links, not shown. The control board also receives the output signals from the pressure and temperature sensors mentioned below.

In Figures 1 to 4, the arrows E represent the direction of water flow in the pipes of the treatment unit 2. In the present description, the inlet and the outlet of a component of the treatment unit 2 are defined according to the normal direction of flow of the water in this unit, as the part through which the water enters or leaves this component, when a flow of water is being treated within this unit.

The processing unit 2 comprises a main pump 14 driven by an electric motor 16 controlled by the control card 8. An inlet pipe 18 connected to the inlet of the main pump 14 plunges into the tank 4 and is equipped, at its upstream end, a non-return valve 20.

The discharge outlet of the main pump 14 is connected by a pipe 22 to the inlet of a filtration device 24 with a mechanical effect, for example of the cyclone filter type. The outlet of the mechanical effect filter 24 is connected by a pipe 26 to the inlet 282 of a device 28 for activated mineral particle filtration.

On the other hand, a purge line 30 connects a purge outlet 242 of the mechanical effect filter 24 to a collector 32 of water loaded with clogging agents and pollutants, which flows into a tank 34 for collecting water loaded with .

A solenoid valve 36, controlled by the control card 8, is arranged on the purge line 30.

The filtration device 28 contains an activated mineral particle filter formed by glass grains whose size is between 0.4 and 1 mm and whose surface condition is modified, in the sense that these glass grains can be qualified as "activated". Such a filter is marketed, for example, by the Bayrol company under the AFM brand. The activation of the surface state of the glass grains induces an increase in their porosity.

The fact that the filtering medium of the filtration device 28 is formed of grains induces that the contact surface of this filtering medium with the water is relatively large, while conferring good compactness on this device. In addition, this type of filter media is compatible with backwashing, which would not necessarily be the case with filter media having particles of size less than 0.4 mm which could cause mineral particles to leak into the system. .

The outlet 284 of the filtration device 28 is connected to a pipe 38 whose diameter is greater than that of the pipe 26, for example 1.5 times greater. Thus the passage section of the water in the pipe 38 is enlarged compared to that of the pipes which are located upstream and downstream. The pipe 38 is generally U-shaped, with two vertical branches 382 and 384 and a horizontal branch 386. The foot of each horizontal branch 382 and 384 is connected to a dead arm 388 equipped with a removable plug 390. Given its relatively large diameter, the pipe 38 constitutes a zone for calming the flow of water at the outlet of the filtration device 28, which would allow solid particles which would be released into the water by the filter 28, to fall into the dead legs 190 where they can accumulate . This in particular prevents activated mineral particles from the filtration device 28 from abrading the membranes of the filters arranged downstream. This also makes it possible to recover by settling solid particles of clogging agents or pollutant present in the water downstream of the filtration device 28.

During an operating operation of the processing unit 2, and when all the pumps are stopped, it is possible to remove the removable plugs 390 to purge the dead arms 388 and recover the solid particles which are accumulated there.

When water circulates through the filtration device 28, a filtration cake is formed on the quantity of filter medium made up of the activated glass grains. This filtration cake participates in the filtration exerted by the filtration device 28.

A solenoid valve 40 is arranged at the downstream end of the pipe 38. A pipe 42 connects the solenoid valve 40 to the inlet 442 of an ultrafiltration device 44 which comprises four ultrafiltration modules 46, each of these modules ultrafiltration membrane comprising one or more ultrafiltration membranes 48, preferably hollow fiber ultrafiltration membranes.

Within the meaning of the present invention, an ultrafiltration device is a filtration device designed to retain particles whose largest dimension is greater than or equal to 1 micrometer (pm). Here, the ultrafiltration membranes 48 define water passage pores, the largest average dimension of which is between 0.01 μm and 1 μm, preferably between 0.01 μm and 0.03 μm. The cut-off threshold of an ultrafiltration membrane is a particle size beyond which 90% of the particles are retained by the membrane. Experience shows that this cut-off threshold is generally around 10% of the largest average pore size. Thus, for pores with the largest average dimension equal to 1 μm, the cut-off threshold is around 0.1 μm.

The ultrafiltration modules 46, therefore their membranes 48, are preferably identical. The ultrafiltration modules 46 extend in parallel between the inlet 442 and the outlet 444 of the ultrafiltration device 44. Other arrangements of the ultrafiltration modules 46 are however possible.

The ultrafiltration membranes 48 are, for example, made of poly(sulfone) (PSu), poly(vinylidene fluoride) (PvDF) of the Kynar® type, of modified PVDF of the NEOPHIL® type or of a mixture of the first two materials mentioned. .

A heating device 54 is arranged at the level of the filtration device 44 and makes it possible to raise the temperature of the water in contact with the ultrafiltration membranes 48. This heating device 54 makes it possible, in particular, to prevent the water from freezing in the ultrafiltration device 44 during a stoppage of operation of the processing unit 2.

This heating device comprises electrical resistors which are in thermal contact with a body of each module 46, which contains one or more ultrafiltration membranes 48, and make it possible to heat the water which it contains.

A pipe 50 connects the outlet 444 of the filtration device 44 to the inlet 522 of an activated carbon filtration device 52. Activated carbon is an adsorbent filter medium of the filtration device 52, capable in particular of reducing the micropollutants present in the water, whether organic or inorganic, such as certain dissolved metals. In particular, an adsorbent media filter based on activated carbon makes it possible to retain micropollutants dissolved in the water to be treated, such as residues of pesticides, herbicides or drugs, or endocrine disruptors, and to make the water neutral in taste and smell.

On the other hand, a first pressure sensor 446 is arranged at the inlet of the filtration device 44 and makes it possible to know the pressure of the water entering this filtration device, while a second first pressure sensor 448 is arranged in outlet of the filtration device 44 and makes it possible to know the pressure of the water leaving this filtration device. The difference in the pressures respectively measured by the sensors 446 and 448 is representative of the pressure drop in the filtration device 44.

A temperature sensor 449 is installed on the pipe 42 and makes it possible to know the temperature of the water entering the filtration device 44.

A pipe 56 connects the outlet 524 of the activated carbon filtration device 52 to the inlet 582 of an ultrafiltration device 58 which comprises two ultrafiltration modules 60, which are preferably identical to each other and to the ultrafiltration modules 46, and which each comprise an ultrafiltration membrane 48.

A solenoid valve 62 is placed on the pipe 56, therefore between the outlet 524 of the activated carbon filtration device 52 and the inlet 582 of the ultrafiltration device.

The outlet 584 of the ultrafiltration device 58 is connected by a pipe 64 to a reservoir 66 for collecting the treated water. This tank 66 is itself connected to a user U by a pipe 68 equipped with a non-return valve 70 and which plunges into the tank 66.

The tubing 18, the pipes 22, 26, 38, 42, 50, 56 and 64, as well as the filtration devices 24, 28, 44, 52 and 58 together define a circuit C for the flow of water during treatment in unit 2.

A purge line 72 connects line 56, upstream of solenoid valve 62, to manifold 32. A solenoid valve 74 is arranged on line 72. A first meter 76 is arranged on line 22, between the main pump 14 and the mechanical effect filter 24.

A solenoid valve 77 is arranged on line 22, between meter 76 and mechanical effect filter 24.

A second meter 78 is arranged on line 64, between outlet 584 of ultrafiltration device 58 and reservoir 66. A solenoid valve 80 is arranged upstream of meter 78, on line 64. A manual valve 82 is arranged downstream meter 78, on pipe 94.

The comparison of the signals transmitted respectively by the computers 76 and 78 to the control board 8 allows the microprocessor 10 to detect a possible leak in the flow circuit C.

On the other hand, the processing unit 2 is equipped with a backwashing sub-assembly which comprises a backwashing pump 90 driven by an electric motor 92 controlled by the control card 8. An inlet pipe 94 of the backwash pump 90 is immersed in the reservoir 6 and is equipped, at its upstream end, with a non-return valve 96.

The discharge outlet of the backwash pump 90 is connected by a pipe 98 to two branches 100 and 110 which extend in parallel between the pipe 98 and the collector 32. The pump 90 is therefore a water booster pump clear ultrafiltered, in other words water treated by installation 2, pipe 98.

A counter 99 is installed on the pipe 98 and makes it possible to signal to the control board 8 what quantity of treated water is used to carry out each backwashing operation.

The branch 100 comprises a first section 102 which connects the pipe 98 to a point P1 of the pipe 42 located between the solenoid valve 40 and the upstream side 442 of the filtration device 44. The second section 104 of the branch 100 connects the point P1 to the manifold 32. Two solenoid valves 106 and 108 are respectively arranged on the sections 102 and 104.

The branch 110 comprises a first section 112 which connects the pipe 98 to a point P2 of the flow circuit C located on the pipe 50, between the outlet 444 of the ultrafiltration device 44 and the inlet 522 of the carbon filtration device active 52. The section 112 is divided into a first strand 112A which connects the pipe 98 to a point P3 and a second strand 112B which connects the point P3 and the point P2. Three solenoid valves 116, 117 and 118 are respectively arranged on the strands 112A and 112B and on the section 114.

Point P3 connects section 112 to a pipe 120 which connects pipe 26, upstream of inlet 282 of filtration device 28, to pipe 64, downstream of outlet 584 of ultrafiltration device 58. Point P3 splits pipe 120 in two sections 122 and 124, each equipped with a non-return valve 126, respectively 128, which passes away from point P3 and blocks in the opposite direction.

Section 122 connects pipe 26 to point P3. The section 124 connects the point P3 to a point P4 of the flow circuit C located, on the pipe 64, upstream of the solenoid valve 80.

Pipes 98, 100, 110 and 120 and the valves fitted to them also belong to the backwashing sub-assembly of processing unit 2.

In FIG. 1, the pipes of the circuit C for the flow of the water being treated in the unit 2 are shown in thick lines, since this is the part of the treatment unit 2 in which the water circulates from reservoir 4 to reservoir 66.

During this circulation, the water is freed from the particles and pollutants it contains by passing successively through the filtration devices 24, 28, 44, 52 and 58.

The filtration device 24 makes it possible to carry out a relatively coarse filtration, which prevents clogging agents and large pollutants, typically greater than 150 μm, from flowing into the filtration device 28 which they could then quickly clog.

The filtration device 28 makes it possible, thanks to the mechanical effect of the activated mineral particles and of the cake present in this bed of particles, to rid the flow of clogging agents and relatively fine pollutants, typically with a maximum dimension of 4pm order.

The calming zone constituted by the pipe 38 makes it possible to protect the ultrafiltration membranes 48 from a possible release of mineral particles from the filter 28 which could cause abrasion and a reduction in the life of the ultrafiltration membranes 48 .

The water then reaches the level of the ultrafiltration device 44 where the ultrafiltration membranes 48 make it possible to retain the clogging agents and the pollutants of a size greater than the cut-off threshold of the membranes 48, i.e. between 0.01 pm and 0.1 pm .

The water that reaches the activated carbon filtration device 52 is thus freed from a large part of its clogging and polluting agents, which avoids rapid clogging of the activated carbon filter.

Thus, the filtration devices 24 and 28 protect the ultrafiltration device 44 against rapid fouling and the filtration devices 24, 28 and 44 protect the filtration device 52 against rapid fouling.

In the normal water treatment configuration in the flow circuit C, the second ultrafiltration device 58 has a safety function since it makes it possible to block, thanks to its membranes 48, particles which could have passed through the upstream filtration devices, namely the filtration devices 24, 28, 44 and 52. This safety function is particularly important in the event of rupture of one ultrafiltration membranes 48 of the first ultrafiltration device 44.

The number of ultrafiltration modules 46 is greater than the number of ultrafiltration modules 60. Indeed, under normal conditions of use of the processing unit 2, it is mainly the ultrafiltration device 44 which performs the function ultrafiltration. Thus, even if the ultrafiltration modules 60 are fewer in number than that of the ultrafiltration modules 46, the cumulative surface area of the ultrafiltration membranes 48 of the second ultrafiltration device 58 is sufficient to filter the water leaving the filtration 52, because this water has already undergone an ultrafiltration operation within the first ultrafiltration device 44. In other words, the water downstream of the filtration devices 44 and 52 has less tendency to clog the membranes of ultrafiltration 48 of the second filtration device 58, that the water leaving the filtration device 28 tends to clog the ultrafiltration membranes 48 of the first ultrafiltration device 44. This is why the cumulative surface area of the membranes ultrafiltration 48 of the second filtration device 58 may be less than the cumulative surface area of the ultrafiltration membranes 48 of the ultrafiltration device 44.

The various solenoid valves of the processing unit 2 are controlled by the control card 8. In the configuration of FIG. 1, the solenoid valves 77, 40, 62 and 80 are controlled in the open position by the control card 8, whereas the other solenoid valves are controlled in closed configuration. The non-return valves 126 and 128 prevent a short-circuit water circulation, in parallel to the circuit C, between the points P1 and P3, and a rise of water, from the flow circuit C towards the branch 110.

As the processing unit 2 operates, the various filtration devices tend to become clogged.

This is why processing unit 2 is configured to allow backwashing steps for some of its filtration devices.

The backwashing of a filtration device can take place at predetermined times, for example every 1 hour of use of the unit 2, or taking into account the effective clogging of one or more of the filtration devices, this fouling being able to be determined for each filtration device by measuring the pressure drop therein, for example by means of pressure sensors.

During a backwash step, the operation of the main pump 14 is stopped and the backwash pump 90 is activated. When it is appropriate to backwash the filtration devices 24 and 28, the solenoid valves 106, 40 and 36 are controlled in the open position by the control card 8, while the other solenoid valves are controlled in the closed position.

In this case, the water drawn from the tank 66 by the recirculation pump 90 circulates in the pipe 94, in the pipe 98, in the section 102 of the branch 100, up to the point P1, in the pipes 42 and 38 , through the filtration device 28, in the opposite direction to normal operation, that is to say from its outlet 284 to its inlet 282, in line 26, through the filtration device 24, to its outlet drain 242, and through pipe 30, until it reaches manifold 32.

This backwashing step is represented in figure 2 where the pipes in which the water actually circulates together constitute a first backwashing line L1 identified in thick lines.

As the backwashing is carried out with treated water, drawn from the tank 66, the risks of contamination of the filtration devices 24 and 28 are eliminated, to a large extent. This also applies to the other backwash configurations mentioned below.

The duration of the backwashing of the filtration devices 24 and 28 can be between 15 seconds (s) and 8 minutes (min), preferably between 30 s and 2 min. In practice, backwashing of the filtration devices 24 and 28 can be provided if the pressure drop between the inlet 282 and the outlet 284 of the filtration device 28 is greater than a first threshold value V1, for example equal at 2 bar. This pressure drop is measured by pressure sensors, not shown and known per se.

When it is appropriate to backwash the filtration device 44, the backwash pump 90 is activated and the solenoid valves 116, 117 and 108 are controlled in the open position by the control card 8, while the other solenoid valves are controlled in closed position.

This makes it possible to circulate water coming from the tank 66 in the pipe 94, in the pipe 98, in the branch 112 of the pipe 110 up to the point P2, in the pipe 50, through the filtration device 44 in opposite direction, from its output 444 to its input 442, in pipe 42 to point P1. As solenoid valve 40 is closed, the backwash water can then only flow in section 104 of pipe 100 as far as collector 32, then to tank 34.

This backwashing step is represented in figure 3 where the pipes in which the water actually circulates together constitute a second backwashing line L2 identified in thick lines.

The control card 8 automatically implements a control method in operation of the processing unit 2 which considers a normalized bit rate D48 assigned to the combined ultrafiltration membrane, consisting of all the ultrafiltration membranes 48 of the different ultrafiltration modules 46. In what follows, the different ultrafiltration membranes 48 are likened to the combined membrane, which is also called “combined ultrafiltration membrane 48” for simplicity.

This method is implemented by the microprocessor 10, by executing software stored in the memory 12.

The normalized flow rate D48 is expressed per unit area of the combined ultrafiltration membrane 48, in this case per m ² , and per unit of pressure of the ultrafiltration membrane, in this case in bars, denoted “b " in the following. This standardized flow rate is corrected by a temperature coefficient calculated from the temperature recorded at the inlet of the filtration device 44 by the sensor 449 and from a mathematical function given by the membrane manufacturer. A flow being expressed conventionally in litres/hour, the standardized flow D48 can thus be expressed in l/h/m ² /b.

This standardized flow rate D48 is representative of the permeability of the combined ultrafiltration membrane 48 insofar as the more the combined ultrafiltration membrane 48 is permeable, the higher this standardized flow rate. This flow rate D48 is therefore a data characterizing the fouling of the membranes, independently of the viscosity of the water, the membrane surface and the pressure difference at the terminals of the membranes.

Within the processing unit 2, the standardized flow D48 is measured, on the one hand, thanks to the counters 76 and/or 78 which make it possible to know the water flow, in l/h, in the circuit of flow C and, on the other hand, by the pressure sensors 446 and 448 which make it possible to know the pressure difference on either side of the combined ultrafiltration membrane 48.

The surface area of the combined ultrafiltration membrane 48 is known from the technical characteristics of the various ultrafiltration modules 46. This data is generally communicated by the manufacturer of the ultrafiltration modules and can be stored in the memory 12, as a parameter operation of the processing unit 2.

Thus, the control board 8 is capable of calculating, at each instant t and in a first step 994 of the method of the invention, the normalized flow rate D48 of the combined ultrafiltration membrane 48.

This first step 994 is implemented periodically, from an instant to of switching on the unit 2, with a periodicity comprised between 2 and 90 seconds, preferably equal to 15 seconds.

In a second step 996, it is checked whether the instant t of implementation of the step 994 is the instant to. If this is the case, an initialization step 998 is implemented, at the during which a first reference value D48i and a second reference value D48 ₂ are made equal to the value D48 of the normalized bit rate determined in step 994.

After step 998 if time t is equal to to, or directly after step 996 if time t is different from to, a step 1000 is implemented, in which two deviations are calculated, namely, a first difference value D1, equal to the difference between the first reference value D48i and the value calculated in step 994; and a second difference value D2, equal to the difference between the second reference value D48 ₂ and the value calculated in step 994.

We have the following relations: D1 = D48i -D48 and D2 = D48 ₂ -D48.

In a following step 1002 of the method, the first deviation or difference value D1 determined in step 1000 is compared with a threshold value D1 fixed in advance, for example equal to 1 l/h/m ² / b.

If, during step 1002, it is determined that the first difference value D1 is less than or equal to the threshold value D1, this is interpreted by the microprocessor 10 as the fact that the normalized bit rate D48 has dropped slightly compared to its reference value D48i. In this case, the combined ultrafiltration membrane 48 is considered to be unclogged and unfouled and the installation can operate normally, to treat the water, in the configuration represented in FIG. 1. This takes place during a step 1004 of the process of the invention.

The method then returns to step 994.

Otherwise, that is to say if the first difference value D1 is strictly greater than the threshold value D1, this is interpreted by the control card 8 as the fact that the fouling or clogging of the membranes ultrafiltration begins to be significant. In this case, a step 1007 of backwashing or a step 1010 of regeneration of the ultrafiltration membrane 48 is provided.

In the representation of FIG. 6, a start-up of the processing unit 2 at time to is considered. During operation of the processing unit 2, the combined ultrafiltration membrane 48 gradually clogs up, so that the value of the normalized flow rate D48 decreases gradually until the first difference value D1 reaches the value of threshold D1 at a time ti, which is detected during step 1002

In this case, a comparison step 1006 is implemented, during which the second difference value D2 determined in step 1000 is compared with a second threshold value D2 fixed in advance, for example equal to 3 .5 l/h/m ² /b. If, in step 1006, it is determined that the second difference value D2 is less than or equal to the threshold value D2, this is interpreted by the control card 8 as the fact that the normalized rate D48 has relatively little dropped relative to its reference value D48 ₂ at time t ₀ . In this case, the backwashing step 1007 is initiated, at time ti and up to a time t _å , step during which ultrafiltered water circulates in the backwashing line L2, as explained below above and shown in Figure 3.

This backwashing step takes place cold, in the sense that the heating device 54 is not activated at time ti, nor in the period following this time, at least until time t2.

This cold backwashing step is extended until the instant t2 when the booster pump 90 is stopped, and the main pump 14 is put into service again, which makes it possible to determine the value of the normalized flow rate again. D48 in a step 1008. This new value of the normalized bit rate D48 is normally higher than the value determined at time ti, and most often slightly lower than the reference value D48i, as visible in FIG. 6.

After step 1008, the reference value D48i is adjusted, in a step 1009, to the value of the standardized bit rate D48 determined during step 1008. In other words, the first reference value D48i is thus adjusted to the value determined at the end of step 1007 of cold backwashing.

After performing step 1009, the method returns to step 994.

From time t2, the installation operates again for water treatment, in the configuration represented in FIG. 1, and the normalized flow rate is again determined in step 994. Steps 1000 and implemented again, without implementation of step 998. Step 1004 is implemented until a time ¾ when the value of the normalized bit rate D48 is such that the first difference value D1 exceeds the value of threshold D1.

At this time t3, a new comparison step 1006 is implemented and, if the result of this comparison is that the second difference value D2 determined at step 1000 is lower than the threshold value D2, then a new step 1007 cold backwash is implemented.

Step 1007 continues until a time U when the installation returns to the water treatment configuration, with the main pump 14 in operation and the booster pump 90 stopped. Steps 1008 and 1009 are implemented again, before steps 994, 996, 1000 and 1002. This operation continues until a new time t ₅ where the value the first difference value D1 becomes strictly greater than the threshold value D1, time at which the steps 1006 and following are again implemented.

The succession of steps 1007 to 1009 therefore allows a backwashing of the filtration device and the updating of the first reference value D48i which therefore corresponds, during normal operation of the unit 2 after a cold backwashing, to the value of the normalized flow D48 at the start of normal operation. Thus, as shown in FIG. 6, the variation of the normalized bit rate D48 over time is compared with the threshold value D1 for each normal operating period, taking into account the starting value of this bit rate over this period.

These steps 1007 to 1009 have no influence on the second reference value

D48 ₂ .

The operation described above continues as long as the comparison step 1006 does not detect that the value of the normalized bit rate D48 differs by more than the threshold value D2 from the second reference value D48 ₂ . If, during step 1006, it is determined that the second difference value D2 is strictly greater than the threshold value D2, this is interpreted by the control card 8 as the fact that the normalized bit rate D48 has dropped so significant relative to its reference value D48 ₂ at time t ₀ , to the point that a step 1010 for regenerating this membrane must be implemented.

This is represented in FIG. 6 at a time t, ₊₂ of resumption of the operation of the processing unit 2, after a cold backwashing which has occurred at the end of a period of normal operation between the times t, and ti _+i .

This regeneration step 1010, which then begins at time t ₊₂ , comprises a first sub-step 1011 of cold backwashing of the combined ultrafiltration membrane 48, which makes it possible to evacuate some of the clogging agents and pollutants, as explained above with reference to Figure 3 and as performed in step 1007.

The regeneration step 1010 comprises a second sub-step 1012 in which the circulation of water in the treatment unit 2 is stopped and kept stopped, in particular the two pumps 14 and 90 are stopped. . This interruption of the circulation of water in the treatment unit 2 has the effect that the water present in the ultrafiltration device 44 stagnates in this device, around the combined ultrafiltration membrane 48.

In a third sub-step 1014 of the regeneration step 1010, the water in contact with the ultrafiltration membrane 48 is heated by the heating device 54, which is activated by the control board 8. This sub-step heating takes place during the entire period when the water circulation is interrupted, that is to say throughout the sub-step 1012. In other words, the sub-steps 1012 and 1014 are concomitant.

During sub-step 1014, the temperature T of the stagnant water in contact with the ultrafiltration membrane 48 increases to a value which can be set between 10° C. and 30° C., preferably between 15°C and 25°C, more preferably around 20°C.

This temperature T can be detected by means of a temperature sensor integrated into at least one of the ultrafiltration modules 46, which can be of any known type and which is not shown in the figures, for the sake of simplification.

In practice, the sub-step 1012 is implemented for a period whose duration is between 15 minutes and six hours, preferably between 30 and 90 min.

This duration of interruption of the circulation of water, during the sub-step 1012, corresponds to the duration of the sub-step 1014 of heating the water and makes it possible to obtain a significant rise in temperature of the water at the contact of the ultrafiltration membrane 48. The value of 30 min is, in practice, a minimum to obtain a significant rise in the temperature T of the mass of water which stagnates in the filtration device 44. The value of 6 h is , in practice, a maximum because tests have shown that a longer duration of circulation and heating interruption does not significantly improve the performance of backwashing, or even reduces its performance for longer durations, whereas it decreases the performance of processing unit 2.

The regeneration step 1010 comprises a fourth sub-step 1016, subsequent to the sub-steps 1012 and 1014 and consisting in backwashing the filtration device, as explained above with reference to FIG. 3. This sub-step 1016 begins with the water that was heated in substep 1014.

Surprisingly, the backwash performed during sub-step 1016 is much more efficient than the cold backwash performed during step 1007 in the sense that the value of the normalized flow rate D48, determined during the restart of the processing unit 2 at a time t, corresponding to the end of step 1010, is significantly greater than the value of the normalized bit rate determined during the last step 994, at G time t _i+2 before the triggering of the regeneration step 1010 and greater than the first reference value D48i updated during the last step 1009. The permeability of the combined ultrafiltration membrane is therefore substantially increased during the regeneration step 1010.

Tests have shown, in an example where the threshold value D2 is close to 3.5 l/h/m ² /b, an increase in the normalized flow D48 of the order of 4.2 l/h/m ² /b at the end of a regeneration step 1010, relative to its value before this step. Thus, the value of the normalized flow D48 becomes greater by 0.7 l/h/m ² /b than the value D48 ₂ . Thus, the regeneration step 1010 can make it possible to increase the normalized flow rate D48 in steps up to a value of the order of +7 l/h/m ² /b in ten cycles of production/backwashing and regeneration , rather than seeing a loss of permeability typically seen in production/backwash cycles without regeneration.

During the lifetime of the processing unit 2, even if regeneration steps 1010 are successively used, the combined ultrafiltration membrane 48 can clog up progressively, even if it is less quickly than without regeneration.

This can be measured by determining, during a step 1018 subsequent to step 1010, the variation of the value of the normalized flow D48, determined during the last step 994 before the regeneration step, with respect to the second value reference D48 ₂ . This variation can be calculated in the form of the D48/D48 ₂ ratio. This ratio is compared with a threshold value D3, here chosen equal to 1.

If the ratio D48/D48 ₂ is strictly greater than the threshold value D3, then the microprocessor 10 considers that the normalized bit rate has increased and that the method can continue to be implemented with the same value of D48 ₂ as previously.

Otherwise, that is to say if the ratio D48/D48 ₂ is less than or equal to the threshold value D3, then it is considered that the normalized bit rate has dropped compared to the instant to, or to the last moment when the value of D48 ₂ has been set, and the value D48 ₂ is reset, in a step 1020, to the last value of the normalized bit rate determined in step 994. This amounts to shifting the point of origin of the comparison performed during the next steps 1006.

After step 1018, and possibly after step 1020, two steps 1022 and 1024 are implemented, which are respectively the same as steps 1008 and 1009 and which make it possible to adjust the first reference value D48i to the value determined after the regeneration step 1010.

The numerical values given above for the threshold values D1, D2 and D3 are not limiting. For example, the threshold value D1 can be between 0.1 and 5 l/h/m ² /b, preferably between 0.5 and 2 l/h/m ² /b, the threshold value D2 can be between 1 and 10 l/h/m ² /b, preferably between 2 and 4 l/h/m ² /b, and the threshold value D3 can be between 0.95 and 1, preferably equal to 1 . In all cases, the threshold value D1 is strictly lower than the threshold value D2.

As a variant, the step 1006, which makes it possible to choose between the implementation of the cold backwashing step 1007 or the implementation of the regeneration step 1010, can be based on a criterion other than the comparison of the second difference value D2 with the threshold value D2. In particular, using the output signals from counters 76, 78 and 99, it can be considered that the regeneration step 1010 is implemented if the water consumed during one or more successive backwashing steps 1007 cold represents a percentage greater than or equal to a threshold value, for example 30%, of the water treated by the unit 2 over a given period of time. Otherwise, step 1007 of cold backwashing is implemented.

According to another approach, the cold backwashing 1007 and regeneration 1010 steps can be distributed over time at fixed intervals. For example, a backwash step 1008 may be provided every 15 min and a regeneration step 1010 every 4 hours. In this case, it is not necessary to implement a step comparable to step 1006 and the internal clock of the control card 8 makes it possible to manage this aspect.

According to another approach, the distribution between the cold backwashing 1007 and regeneration 1010 stages can be carried out according to the quantity of water treated in the installation. For example, a cold backwash step 1007 can be implemented after the treatment of 200 liters of water and a regeneration step 1010 can be implemented after the treatment of 2000 liters of water. In this case also, it is not necessary to implement a step comparable to step 1006.

According to yet another approach, the distribution between the cold backwashing 1007 and regeneration 1010 steps can be carried out taking into account the frequency of implementation of the cold backwashing steps 1007. For example, it can be considered that if the normal operating time, in the configuration of Figure 1, between two interruptions for backwashing, is less than 10 minutes, then a regeneration step must be implemented.

The regeneration step 1010 can also be implemented as a priority when the filtration system does not deliver drinking water, at night for example, especially if the system is powered using photovoltaic panels.

The approaches mentioned above for determining how steps 1007 and 1010 are implemented can be combined with each other.

According to an optional aspect of the invention, applicable to all the modes of distribution between steps 1007 and 1010, the standardized flow rate D48 can be related to a reference temperature, for example to a temperature of 20°C. In other words, the normalized flow D48 is then corrected according to the difference between the temperature detected by the sensor 449 and the reference value. This correction, which takes into account the properties of the combined ultrafiltration membrane 48, is carried out according to the indications of the manufacturer of this membrane. Step 1010 makes it possible to extend the lifetime of the combined ultrafiltration membrane 48, by increasing its permeability, at the end of the regeneration steps 1010, without injection into the processing unit 2 of chemicals for cleaning this membrane ultrafiltration.

One hypothesis would be that the heating of the water in contact with the ultrafiltration membrane 48, during sub-step 1014, would have the effect of bringing the combined ultrafiltration membrane 48 and the clogging agents and pollutants present in its pores and on its surface at an optimum temperature, where the latter would form bonds between them, which would facilitate the separation of these clogging agents and these pollutants vis-à-vis the combined ultrafiltration membrane 48, during the backwash sub-step 116.

This is potentially the reason why the backwashing carried out during step 1016 is more effective than a backwashing without temperature variation carried out at step 1007, to the point that the value of the normalized flow rate D48 would be higher , at the end of the regeneration step 1010, compared to the same value at the end of the cold backwashing step 1007.

The method of the invention has the advantage of being implemented automatically by the control board 8, without human intervention. In particular, this method does not require the injection of cleaning products into the pipes of the processing unit 2, which dispenses with an operator having to go, at regular intervals, to the place of installation of the processing unit. treatment 2.

The combination of the cold backwashing 1007 and regeneration 1010 steps is quite advantageous, since it allows the cold backwashing steps 1007 to quickly clean the ultrafiltration membrane 48 as long as this remains effective, then that the regeneration step 1010 allows thorough cleaning, even if it takes longer.

According to a variant of the method of the invention, sub-step 1014 can only extend over part of the period of the interruption of sub-step 1012.

The cold backwashing step 1007 is however optional and a method can be envisaged in which the regeneration step 1010 is systematically implemented as soon as the value of the normalized flow rate D48 becomes strictly lower than the first value of threshold deviates from the first reference value D48i by a difference strictly greater than the threshold value D1.

When it is appropriate to backwash the filtration device 58, the backwash pump 90 is activated and the solenoid valves 116, 62 and 74 are switched to the open position by the control board 8, while the other solenoid valves are held in the closed position.

This makes it possible to circulate the water taken from the tank 66 in the pipe 94, in the pipe 98, in the strand 112A up to the point P3, in the branch 124, from the point P3 to the point P4, in the pipe 64, in the filtration device 58, in the opposite direction, from its outlet 584 to its inlet 582, in the pipes 62 and 72, as far as the collector 32. Downstream of the solenoid valve 62 with respect to the direction of flow of water in this configuration, the backwashing water does not go up the pipe 56 towards the outlet 524 of the filtration device 52, because the closing of the valves 40, 106, 108, 117 and 118 prevents a flow towards this outlet 524.

This backwashing step is represented in figure 4 where the pipes in which the water actually circulates together constitute a third backwashing line L3 identified in thick lines.

The backwashing cycles of the filtration devices 44 and 58 can be carried out in a coordinated manner or not, depending on the detected degree of fouling of the ultrafiltration membranes 48, this detection possibly taking place by measuring a pressure drop. or a normalized flow rate of water per unit time, per unit area, per unit pressure and at a given temperature. As a variant, the backwashing of the filtration devices 44 and 58 is carried out periodically independently of the pressure drop or the normalized flow rate.

The number of solenoid valves necessary to operate the processing unit 2 in the normal configuration where the water circulates in the circuit C or during the backwashing stages is relatively low. In the example, processing unit 2 comprises eleven solenoid valves.

The mechanical effect filtration device 24 serves as a pre-filter for the series of four filtration devices 28, 44, 52 and 58. Depending on the quality of the water taken from the tank 4, this filtration device 24 can be omitted. . It is therefore optional.

Alternatively, the ultrafiltration device 44 or the ultrafiltration device 58 comprises only one ultrafiltration membrane. In this case, the cumulative surface area of either of these devices is equal to the surface area of its ultrafiltration membrane.

As a variant, the numbers of ultrafiltration modules of the ultrafiltration devices 44 and 58 are respectively different from 4 and 2. They can be 2 and 1, 3 and 1, 5 and 3, 6 and 4, etc. ... depending on the unit area of each ultrafiltration membrane 48 and the flow rate of water to be treated in unit 2.

According to another variant, a heating device of the type of the heating device 54 can be associated with the fourth filtration device 58. In this case, the method of the invention can also or alternatively be implemented with regard to the combined ultrafiltration membrane 48 of the second ultrafiltration device 58.

The heater(s) 54 and/or the like need not be of the electrical resistance type and may alternatively be made of annealed (oxygen-free) copper wire coupled to resistors or fiberglass infrared heaters. electrified carbon (heating fabric strips).

According to yet another variant, the activated carbon filter device 52 can be replaced by another filtration device with an adsorbent filter medium, for example granular zeolite which adsorbs compounds such as uranium.

According to another variant, the filter medium can consist of metal granules covered with a layer of metal oxide. These may be iron granules covered with a layer of manganese oxide. A filter media filter based on granules treated with manganese dioxide, for example, makes it possible to retain pollutants dissolved in the water to be treated, such as iron, manganese, arsenic, cadmium, hydrogen sulphide and make the water neutral in taste and smell.

According to yet another variant, the processing unit 2 can include one or more additional filtration device(s), arranged downstream of the filtration device 52 with filter media, such as a iron oxide filter or an ion exchange resin filter. Preferably, this or these additional filtration devices are arranged, along the flow circuit C, between the filtration device with filter media 52, that is to say with activated carbon in the example, and the second ultrafiltration device 58.

An ion exchange resin allows, for example, the reduction of ammoniacal nitrogen in the water. The ion exchange resin can be of the anionic or cationic type, in gel form or in macroporous form.

According to a particular application, if the water to be treated is brackish, or if it is sea water, the treatment unit 2 can be associated with a reverse osmosis or electrodialysis unit or else with nano-filtration which is installed downstream of unit 2. A nano-filtration unit is provided to retain compounds or ions whose largest dimension is of the order of Angstrom (Å). A nano-filtration unit comprises one or more membranes with pore sizes generally between 1 and 7 nm.

Treatment unit 2 can be used for clarification, disinfection and reduction of micropollutants from surface water. The clarification is carried out by means of filtration devices 28 and 44, the disinfection is carried out by means of filtration devices 44 and 58 and the reduction of micropollutants is carried out by means of the filter media device 52. The treatment unit 2 allows the potabilisation of water, its preparation with a view to its use in an industrial process or its pre-desalination.

The embodiment and the variants contemplated above can be combined to generate new embodiments of the invention.

Claims

1. Method for controlling in operation a water treatment unit (2) comprising at least one filtration device (44, 58) with an ultrafiltration membrane (48), this method comprising at least the following steps: a ) determination (1000) of a normalized flow rate value (D48) per unit area and per unit pressure of the ultrafiltration membrane (48); b) treatment of the water (1004) with the treatment unit if a difference (D1) between the value of the standardized flow detected in step a) and a first reference value (D48i) is less than or equal to a first threshold value (D1); c) regeneration (1010) of the ultrafiltration membrane (48) if the difference (D1) between the value of the standardized flow detected in step a) and the first reference value (D48i) is greater than the first value of threshold (D1); and the regeneration step (1010) comprising at least one substep consisting of: c1) backwashing (1011) the ultrafiltration membrane (48); characterized in that the regeneration step (1010) further comprises at least sub-steps consisting of: c2) interrupting (1012) and maintaining the circulation of water in the treatment unit (2) interrupted; c3) heating (1014) the water in contact with the ultrafiltration membrane (48) in the ultrafiltration membrane filtration device (44, 58) during sub-step c2); and c4) after step c3), backwashing (1016) the ultrafiltration membrane (48).

2. Method according to claim 1, characterized in that sub-step c2) is implemented for a duration of between 15 min and 6 hours, preferably between 30 and 90 min.

3. Method according to one of the preceding claims, characterized in that sub-step c3) is implemented until a temperature of the water in contact with the ultrafiltration membrane (48) of between 10° C and 30°C, preferably between 15°C and 25°C, more preferably of the order of 20°C.

4. Method according to one of the preceding claims, characterized in that it is implemented automatically, without human intervention.

5. Method according to one of the preceding claims, characterized in that it comprises the following step, an alternative to step c): d) cold backwashing (1007) of the ultrafiltration membrane.

6. Method according to claim 5, characterized in that step c) of regeneration (1010) and step d) of cold backwashing (1007) are implemented alternately according to a difference (D2 ) between the value of the normalized flow (D48) detected in step a) and a second reference value (D482), and/or the periodicity of a situation where the difference (D1) between the value of the normalized flow ( D48) detected in step a) and the first reference value (D48i) is greater than the first threshold value (D1), and/or the percentage of treated water used for one or more backwashing steps ( 1008) successive, and/or

- at predetermined times, and/or depending on the quantity of water treated in the treatment unit (2).

7. Method according to one of the preceding claims, characterized in that the first reference value (D48i) is adjusted (1009, 1024) after step c) of regeneration (1010) and, optionally after step d) cold backwash (1007).

8. Method according to one of the preceding claims, characterized in that the value of the normalized flow (D48) determined in step a) is related to a reference temperature.

9. Water treatment unit (2) configured for the implementation of a method according to one of the preceding claims, comprising at least one filtration device

(44, 58) with an ultrafiltration membrane (48), characterized in that it comprises at least one device (54) for heating the water present in the filtration device (44, 58) with an ultrafiltration membrane (48) and a system (8, 446, 448) for measuring a pressure drop of a flow of water through the ultrafiltration membrane filtration device.

10. Unit according to claim 9, characterized in that the heating device comprises heating resistors in contact with a body of the filtration device (44, 58) with an ultrafiltration membrane (48), annealed copper wires coupled to resistors or infrared heating systems.