Water treatment unit and method for cleaning such a unit

Abstract

Water Treatment Unit and Method for Cleaning Such a Unit. The present invention relates to a water treatment unit (2) including a nanofiltration membrane filtration device (40). It includes a device for cleaning the filtration device (40), which comprises a sodium hydroxide reservoir (152), a hydrochloric acid reservoir (162), a neutralization tank (172), a first dosing element (154) for a molar quantity (Q1) of sodium hydroxide sent from the sodium hydroxide reservoir to the neutralization tank, a second dosing element (164) for a molar quantity (Q2) of hydrochloric acid sent from the hydrochloric acid reservoir to the neutralization tank, and a control unit (8). The control unit operates the dosing elements (154, 164) by dosing the same molar quantity (Q1, Q2) of sodium hydroxide and hydrochloric acid during each cleaning of the filtration device (40).This unit enables the implementation of a non-polluting cleaning method that uses minimal water and chemicals. Figure for the abbreviation: 1.

Description

Title of the invention: Water treatment unit and method of cleaning such a unit

[0001] The present invention relates to a water treatment unit comprising several filtration devices allowing in particular the clarification, disinfection and reduction of pollutants in the water, in particular micropollutants, such as endocrine disruptors, pesticide derivatives, herbicides, as well as the discoloration of the water. Such a unit can, in particular, be used for the purification of fresh surface water, in accordance with the standards of a Regional Health Agency in France.

[0002] In the field of water treatment, it is known to have, along the path of a flow of water to be treated, different filters aimed at improving the quality of the water. These different filters can include filters operating according to an essentially mechanical principle, which define orifices for the passage of water, and filters which operate by adsorption of certain pollutants.

[0003] WO-A-2022 / 171718 is known, which discloses a treatment unit of this type, effective and durable for treating water and which comprises several filtration devices mounted in series on the flow path of the water being treated, including an ultrafiltration membrane treatment device. This unit is generally satisfactory. However, in regions where the water to be treated is very colored and very loaded with organic carbon, the ultrafiltration technique is not always sufficient to lower the Total Organic Carbon or TOC level of the treated water. The addition of a nanofiltration unit downstream of this treatment unit would induce significant costs and complicate the installation, which is an obstacle to the improvement of this known unit. In addition, to maintain satisfactory efficiency, such a nanofiltration unit needs to be cleaned, particularly continuously.Continuous cleaning involves releasing part of the filtered water, loaded with impurities, into the environment, which consumes filtered water and significantly reduces the overall efficiency of the nanofiltration unit. In addition and at lower frequencies than cleaning with permeate, it is necessary to clean the nanofiltration unit with chemicals. However, these must be removed after cleaning, which poses a problem in treatment units located in remote areas, which are rarely accessed by a technician and which must operate automatically. Cleaning products are sometimes released into the environment, with a significant risk of pollution.

[0004] The aim of the invention is then to propose a water treatment unit allowing to effectively reduce TOC and whose performance is not significantly limited by the cleaning of its filtration device(s) and which does not cause chemical pollution of the ambient environment.

[0005] For this purpose, the invention relates to a water treatment unit including a nanofiltration membrane filtration device. The treatment unit comprises a device for cleaning the nanofiltration membrane filtration device which comprises:

[0006] - a soda tank;

[0007] - a hydrochloric acid tank;

[0008] - a neutralization tank;

[0009] - a first metering member for a molar quantity of soda sent from the tank of soda to the neutralization tank;

[0010] - a second member for dosing a molar quantity of hydrochloric acid sent from the hydrochloric acid tank to the neutralization tank; and

[0011] - a control unit for the dosing members.

[0012] According to the invention, the control unit is configured to control the first and second dosing members by dosing the same molar quantity of soda and hydrochloric acid sent to the neutralization tank, during each cleaning of the nanofiltration membrane filtration device.

[0013] Thanks to the invention, the two tanks of soda and hydrochloric acid allow these products to circulate in the nanofiltration membrane filtration device, which cleans it effectively, both for the treatment of organic materials with soda and for the treatment of non-organic agents, such as metals and limestone, with hydrochloric acid. The neutralization tank allows the soda and hydrochloric acid to react with each other, which gives water and salt according to the chemical neutralization reaction NaOH + HCl = NaCl + H2O. Since they are used with the same molar quantity, the soda and hydrochloric acid are completely consumed during their reaction in the neutralization tank.At the end of the neutralization reaction between the soda and the hydrochloric acid, the salt water present in the tank can be released into the surrounding environment without risk of basic pollution (with soda) or acid pollution (with hydrochloric acid).

[0014] According to other advantageous aspects of the invention, the water treatment unit comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0015] - The water treatment unit comprises a particle filtration device activated minerals, preferably arranged upstream of the nanofiltration membrane filtration device in a flow direction of the water being treated; a filtration device with filter media, preferably arranged downstream of the device nanofiltration membrane filtration device in a flow direction of the water being treated; and an ultrafiltration membrane filtration device, preferably arranged downstream of the nanofiltration membrane filtration device in the flow direction of the water being treated.

[0016] - The ultrafiltration membrane filtration device is arranged downstream of the filtration device with filter media in the direction of flow of the water being treated.

[0017] - The water treatment unit comprises a device for remineralizing the water in during treatment, arranged downstream of the nanofiltration membrane filtration device in a flow direction of the water being treated, preferably between the filter media filtration device and the ultrafiltration membrane filtration device.

[0018] - A cleaning water tank supplied, during water treatment, with water taken from the treatment unit, upstream of the remineralization device.

[0019] - The first and second metering members are metering pumps.

[0020] According to another aspect, the invention also relates to a method for cleaning a treatment unit as mentioned above, comprising steps of a) circulating a first molar quantity of sodium hydroxide through the nanofiltration membrane filtration device and into the neutralization tank; b) rinsing the nanofiltration membrane filtration device with water and directing the rinsing water to the neutralization tank; c) circulating a second molar quantity of hydrochloric acid through the nanofiltration membrane filtration device and into the neutralization tank, the second molar quantity of hydrochloric acid being equal to the first molar quantity of sodium hydroxide; and d) rinsing the nanofiltration membrane filtration device with water and directing the rinsing water to the neutralization tank.

[0021] This cleaning method is non-polluting, consuming little water and chemicals.

[0022] According to other advantageous aspects of the invention, this method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0023] - The method comprises steps e) and f) subsequent to steps a) to d) and consisting of e) allowing the molar quantities of soda and hydrochloric acid to react in the neutralization tank; and f) some time before the next cleaning, purging the neutralization tank.

[0024] - The processing unit is as described previously and steps b) and d) are carried out with water from the cleaning water tank.

[0025] - A part of a concentrate resulting from the circulation of water in the device of nanofiltration membrane filtration is discharged from the water treatment unit by means of a proportional valve controlled according to a physicochemical parameter of the water or a clogging rate of a nanofiltration membrane during treatment

[0026] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0027] [Fig-1] [Fig. 1] is a schematic diagram of a water treatment unit conforming to the invention, in operation for the treatment of a quantity of water;

[0028] [Fig.2] [Fig.2] is the same diagram as [Fig.l], during a backwash of a nanofiltration membrane filtration device of water treatment unit;

[0029] [Fig.3] [Fig.3] is the same diagram as [Fig.l], during cleaning with soda of the nanofiltration membrane filtration device of the water treatment unit;

[0030] [Fig.4] [Fig.4] is the same diagram as [Fig.l], during rinsing of the device nanofiltration membrane filtration;

[0031] [Fig.5] [Fig.5] is the same diagram as [Fig.l], when cleaning with chlorinated acid water of the nanofiltration membrane filtration device;

[0032] [Fig.6] [Fig.6] is the same diagram as [Fig.l], when the processing unit is in operation and fills a cleaning water tank; and

[0033] [Fig.7] [Fig.7] is the same diagram as [Fig.l], when the processing unit is in operation with a passage through the nanofiltration membrane filtration device in a direction opposite to that shown in [Fig.l].

[0034] In each figure, the thick lines identify the conduits through which a liquid flows in the configuration of the treatment unit corresponding to that figure. In each figure, the valves in the closed configuration are represented by two black triangles and the valves in the open configuration are represented by two white triangles.

[0035] Unit 2 shown in Figures 1 to 7 is used for the clarification, disinfection and reduction of pollutants in 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.

[0036] 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 operational control of the processing unit 2. The card 8 forms an electronic control unit for the processing unit 2. It is connected to various components, such as pumps, flow meters, sensors or solenoid valves, by connections not shown, which may be of the wired or wireless type. In the figures, dotted arrows having as their origin or destination the reference 8 surrounded by a circle show the transmission of information between certain organs of the processing unit 2, other than solenoid valves, and the control card 8. The control card 8 also controls the various solenoid valves of the processing unit, which are mentioned below, by means of wired or wireless connections not shown. The control card 8 also receives the output signals from pressure sensors belonging to the processing unit 2, most of which are not shown, for the sake of simplification.

[0037] In Figures 1 to 7, the arrows E represent a flow of water or a mixture of water and cleaning product in the pipes of the treatment unit 2.

[0038] In the present description, the inlet and outlet of a component of the treatment unit 2 are defined according to the normal direction of flow of water in this unit, as the part through which water enters or leaves this component, when a flow of water is being treated within this unit.

[0039] The treatment unit 2 comprises a main pump 14 driven by an electric motor 16 controlled by the control card 8. An intake pipe 18 connected to the inlet of the main pump 14 plunges into the tank 4 and is equipped, at its upstream end, with a non-return valve 20.

[0040] The discharge outlet of the main pump 14 is connected by a pipe 22 to the inlet 242 of a filtration device 24 with a mechanical effect, for example of the cyclone filter type.

[0041] The outlet 244 of the mechanical effect filtration device 24 is connected by a pipe 26 to the inlet 282 of a device 28 for filtration with activated mineral particles.

[0042] A pressure sensor 27 connected to the pipe 26 makes it possible to know the water pressure upstream of the activated mineral particle filtration device 28 and communicates with the control card 8. Other pressure or temperature sensors, not shown, are distributed along the water flow path within the treatment unit 2.

[0043] On the other hand, a purge pipe 30 connects a purge outlet 246 of the mechanical effect filtration device 24 to a collector 32 of water loaded with clogging agents and pollutants, which flows into a tank 34 for collecting loaded water. A solenoid valve 36, controlled by the control card 8, is arranged on the purge pipe 30.

[0044] 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 described as “activated”. Such a filter is marketed, for example, by the company Bayrol under the brand name AFM. Activating the surface condition of the glass grains leads to an increase in their porosity.

[0045] The fact that the filter medium of the filtration device 28 is formed of grains means that the contact surface of this filter medium with the water is relatively large, while giving good compactness to this device. In addition, this type of filter medium is compatible with backwashing, which would not necessarily be the case with a filter medium having particles smaller than 0.4 mm which could cause significant leaks of mineral particles into the system.

[0046] When water flows through the filtration device 28, a filter cake forms on the quantity of filter media consisting of the activated glass grains. This filter cake participates in the filtration carried out by the filtration device 28.

[0047] The outlet 284 of the filtration device 28 is connected through a pipe 38 to the inlet 401 of a filtration device 40 with a nanofiltration membrane.

[0048] For the purposes of the present invention, a filtration device 40 with a nanofiltration membrane comprises a membrane intended to retain compounds or ions whose largest dimension is of the order of the Angstrom (Â). The nanofiltration membrane of the filtration device 40 has pores of size between 0.5 and 7 nm.

[0049] The nanofiltration membrane filtration device 40 comprises a filter cartridge 402 in which one or more nanofiltration membranes 403 are housed and an arrangement of pipes 404 and valves 405, with a pump 406 and a flow meter 407, which make it possible to circulate the water in a first direction or in a second direction, opposite to the first direction, inside the filter cartridge 402, in contact with the membrane(s) 403.

[0050] In a variant of the invention not shown, the filtration device comprises several filter cartridges 402, preferably arranged in parallel on the flow path of the water being treated.

[0051] In the following, when the cartridge 402 is mentioned, this covers several cartridges in the case where the filtration device 40 comprises several cartridges 402. In the following, when the membrane 403 is mentioned, this covers several membranes, in the case where the cartridge 402 comprises several membranes and / or in the case where the filtration device 40 comprises several cartridges 402.

[0052] By way of non-limiting example, the nanofiltration membrane 403 may be made of poly(vinylidene fluoride) (PvDF) and the cartridge 402 may be of the type marketed by NX Filtration under the reference dNF40 or dNF80 or by Pentair under the reference X-Flow HFNano.

[0053] Advantageously, the water flows tangentially, in contact with the membrane 403, within the filter cartridge 402.

[0054] The nanofiltration membrane filtration device 40 makes it possible to significantly reduce, or even eliminate, the TOC of the water treated in the treatment unit 2. This prevents organic compounds present in the water from reacting with their surroundings. operation, in particular by generating tri-halo-methane or THM type components during the chlorination of the produced water, compounds which are carcinogenic, mutagenic and reprotoxic.

[0055] The outlet 408 of the nanofiltration membrane filtration device 40 is connected, through a pipe 42, to the inlet 442 of an activated carbon filtration device 44. The activated carbon is an adsorbent filter medium of the filtration device 44, capable in particular of removing 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 pesticide, herbicide or drug residues, or endocrine disruptors, and to make the water neutral in taste and odor.

[0056] The outlet 444 of the activated carbon filtration device 44 is connected by a pipe 46 to a device 48 for remineralizing the water being treated, which makes it possible to recharge the water filtered in the filtration devices 24, 40 and 44 with mineral particles, in order to make it suitable for consumption, according to the standards for water intended for consumption. Indeed, following the filtration carried out in the filtration devices 24, 40 and 44, the water being treated is very weakly mineralized, which should be corrected.

[0057] For example, the remineralization device 48 may comprise means for bringing the water arriving via the pipe 46 into contact with calcium carbonate, CaCO3, and magnesium carbonate, MgCO3.

[0058] The outlet 484 of the remineralization device 48 is connected, by a pipe 50, to the inlet 582 of an ultrafiltration device 58 which comprises two ultrafiltration cartridges 584, which are preferably identical to each other and which each comprise an ultrafiltration membrane 586.

[0059] The ultrafiltration device 58 is designed to retain particles whose largest dimension is greater than or equal to 1 micrometer (pm). Here, the ultrafiltration membranes 48 define pores for the passage of water, the largest average dimension of which is between 0.01 pm and 1 pm, preferably between 0.01 pm and 0.03 pm. 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 of the order of 10% of the largest average dimension of the pores. Thus, for pores with a largest average dimension equal to 1 pm, the cut-off threshold is approximately 0.1 pm.

[0060] The ultrafiltration cartridges 584, and therefore their membranes 586, are preferably identical. The ultrafiltration cartridges 584 extend in parallel between the inlet 582 and the outlet 584 of the ultrafiltration device 58. Other arrangements of the ultrafiltration cartridges 584 are however possible.

[0061] The ultrafiltration membranes 586 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.

[0062] Theoretically, the particles that should be retained in the ultrafiltration device 58 have already been retained in the nanofiltration membrane filtration device 40 because the membrane 403 has pores of a size much smaller than that of the pores of the membranes 586. The ultrafiltration device 58 therefore has little tendency to become clogged. It provides a safety function to retain particles in the event of a fault in the nanofiltration membrane filtration device 40, in particular in the event of a tear in the membrane 403. The ultrafiltration device 58 also has the function of preventing bacterial retro-contamination of the activated carbon and remineralization filtration device 44 and 48 which could occur in particular when the system is stopped. The ultrafiltration device 58 is optional and can be removed if these additional safety features are not required.

[0063] The outlet 584 of the ultrafiltration device 58 is connected by a pipe 60 to a tank 66 for collecting the treated water. This tank 66 is itself connected to a user network U by a pipe 68 equipped with a non-return valve 70 and which plunges into the tank 66.

[0064] The tubing 18, the pipes 22, 26, 38, 42, 46, 50 and 60, as well as the filtration devices 24, 28, 40, 44 and 58 together define a circuit C for the flow of the water being treated in the unit 2, from the tank 4 to the tank 66. This circuit C is represented by the thick lines in [Fig.l].

[0065] A first flow meter 76 is arranged on the pipe 22, between the main pump 14 and the mechanical effect filter 24.

[0066] A second flow meter 78 is arranged on the pipe 64, between the outlet 584 of the ultrafiltration device 58 and the reservoir 66.

[0067] These flow meters allow the control unit 8 to detect a malfunction of the treatment unit 2, in particular following clogging.

[0068] Between the filtration devices 44 and 48, the conduit 46 is connected through an injector 80 to a source of carbon dioxide CO2, such as a pressure tank 82. Thus, carbon dioxide CO2 can be introduced into the flow of water E being treated, just before this flow E encounters the calcium carbonate and the magnesium carbonate within the remineralization device 48. The presence of carbon dioxide in the flow of water E which enters the remineralization device 48 facilitates the dissolution of the calcium carbonate and the magnesium carbonate in the water. The carbon dioxide reduces the pH of the water flowing in the conduit 46, which increases the release of ions by the calcium carbonate and the magnesium carbonate. The remineralization of the filtered water is thereby facilitated. and increased.

[0069] Between the ultrafiltration device device 58 and the reservoir 66, the pipe 60 is connected through a metering pump 90 to a source of chlorine dioxide, C1O2. The injection of chlorine dioxide C102 into the water at the end of treatment makes it possible to secure the water by preventing the proliferation of bacteria, without risking creating THMs, which would potentially be the case if sodium hypochlorite (bleach) were injected at the end of treatment, because sodium hypochlorite reacts with certain organic compounds to generate THMs.

[0070] Thus, the joint use of the filtration device 40 with nanofiltration membrane and C1O2 makes it possible to avoid the production of THM thanks to the reduction of the COT and the non-use of sodium hypochlorite water.

[0071] Generally, the devices 80, 82, 90 and 92 are optional and their use can be decided according to the operating conditions planned for the processing unit 2.

[0072] During operation for the treatment of water drawn from the tank 4 and as represented by the thick lines in [Fig.l], the water flows in the flow circuit C, from the tank 4 to the tank 66. During this path, the water is successively filtered in the filtration devices 24, 28, 40, 44 and 58 and it receives carbon dioxide CO2 at the injector 80, calcium carbonate CaCO3 and magnesium carbonate, MgCO3, in the remineralization device 48 and chlorine dioxide C1O2 at the metering pump 90.

[0073] In the configuration of the treatment unit 2 shown in [Fig.l], the valves 405 of the nanofiltration membrane device 40 are positioned such that the water being treated flows in a so-called top-bottom direction, from top to bottom in [Fig.l], inside the cartridge 402, in contact with its membrane 403 and tangentially to this membrane.

[0074] Three water passage orifices are defined on the cartridge 402, namely a first orifice 402A, a second orifice 402B and a third orifice 402C. In the configuration of the valves shown in [Fig.l], the water enters the cartridge 402 through the first orifice 402A. The water which has not passed through the membrane 403 leaves the cartridge 402 through the second orifice 402B, while the water which has passed through the membrane 403 leaves through the third orifice 402C. The water leaving through the second orifice 402B follows a path defined by the valves 405 until it returns, passing through a non-return valve 409, to the inlet of the pump 406 where this quantity of water is added to that coming from the activated mineral particle filtration device 28.

[0075] Thus the pipes 404, the valves 405 and the pump 406 make it possible to ensure recirculation of the water which has not been filtered in the cartridge 402. The flow meter 407 allows verification that the recirculation loop provided by pump 406 is indeed operating, by comparing the flow rate it detects with that in pipe 38, upstream of inlet 401, which is detected by flow meter 76.

[0076] In the configuration shown in [Fig. 7], which is a configuration for producing filtered water like the configuration in [Fig. 1], the water enters the cartridge 402 through its second orifice 402B. The filtered water exits through the third orifice 402C and the unfiltered water exits through the first orifice 402A. From this first orifice 402A it is redirected by the circuit defined by the pipes 404 and the valves 405 to the inlet of the pump 406 where it joins the water coming from the activated mineral particle filtration device 28. In this configuration, where the water flows into the cartridge 402 from bottom to top in [Fig. 7], it is considered that the flow takes place in the bottom-top direction within the nanofiltration membrane device 40.

[0077] The configurations of figures 1 and 7 can be used alternatively, at the user's choice, to treat the water in the treatment unit 2 by circulating it in the circuit C. This alternative operation in the two configurations is supposed to provide better performance and reduce the probability of clogging of a fiber of one of the nanofiltration or ultrafiltration membranes, in the case of tangential filtration.

[0078] A discharge line 180 connects the nanofiltration membrane device 40 to the manifold 32 through a solenoid valve 182 and a flow meter 184. The control card 8 controls the solenoid valve 182. In the water production configuration shown in [Fig.l], the valve 182 is open, so that a portion of the water flow recirculating within the nanofiltration membrane device 40 is directed toward the tank 34, which makes it possible to evacuate a portion of the concentrate from the recirculation loop formed by the lines 404 and the valves 405 toward the tank 34. In this case, the valve 405 located above the discharge line 180 in the representation of FIGS. 1 to 7 is closed.

[0079] Between the nanofiltration membrane device 40 and the activated carbon filtration device, the pipe 46 is connected, by an auxiliary pipe 110, to a cleaning water storage tank 112.

[0080] On the other hand, a solenoid valve 43 is interposed on the pipe 42, between the connection point of the auxiliary pipe 110 on the pipe 42 and the activated carbon filtration device 44.

[0081] When it is necessary to fill the cleaning water tank 112, the solenoid valve 43 is closed and the solenoid valve 114 is open, which corresponds to the configuration of the treatment unit 2 shown in [Fig.6].

[0082] A level controller 116 is used to detect when a required level of water is reached inside the cleaning water tank 112 and report it to the control board 8.

[0083] In practice, the solenoid valve 182 may be a proportional leakage valve which allows a fraction of the flow of water recirculating within the nanofiltration membrane device 40 to pass, during treatment of the water within the unit 2.

[0084] Advantageously, the degree of opening of the solenoid valve 182 is controlled by the control card 8 as a function of a physicochemical parameter of the water flow E within the treatment unit 2, for example a parameter detected by a sensor 120 connected to the pipe 46 upstream of the connection point of the discharge pipe 180 and which detects the presence of organic compounds by ultraviolet spectrophotometry.

[0085] Ultraviolet spectrophotometry is based on the absorbance of light by organic compounds at a given wavelength, for example 254 nm. The value of the spectrophotometry parameter detected by the sensor 120 can be communicated to the control card 8 which then controls the proportional solenoid valve 182 as a function of this parameter to allow more water to pass when the proportion of organic compounds is higher and less water in the opposite case. This makes it possible to evacuate from the circuit C a quantity of water loaded with organic compounds, while optimizing the overall production efficiency of the unit.

[0086] Alternatively, other physical or chemical parameters of the water being treated may be used to adjust the opening of the solenoid valve 182 by the control card 8, for example the conductivity of the water circulating in the pipe 408.

[0087] According to another variant, the opening of the solenoid valve 182 by the control card 8 is controlled as a function of the proportion of clogging agent in the water circulating in the pipe 408, this proportion being detected by the measurement of emission-excitation spectra at different wavelengths.

[0088] Alternatively, the clogging rate of the nanofiltration membrane 403 during treatment can be used to adjust the opening of the solenoid valve 182 by the control card 8. This clogging can be determined by pressure difference across the nanofiltration membrane or by permeability of the nanofiltration membrane as stated in the invention WO-A-2022 / 171718.

[0089] This possibility of modifying the degree of opening of the solenoid valve 182 makes it possible to adapt the output of the unit 2, that is to say the raw water / produced water ratio, the quality of the raw water being variable over time, in particular for surface water, depending on the weather and the season.

[0090] The cleaning water tank 112 is connected, by a pipe 130 and through a solenoid valve 132, to a cleaning pump 134 whose motor 136 is controlled by the control card 8. A flow meter 138 is installed at the outlet of the pump 134, on a pipe 140 which connects this pump to the pipe 38, between the filtration devices 28 and 40.

[0091] An auxiliary pipe 142 connects the pipe 140 to the pipe 46, in the vicinity of the outlet 408 of the nanofiltration membrane device 40. A solenoid valve 144 controlled by the control card 8 controls the flow of water in the pipe 142. The auxiliary pipe 142 is connected, through the pipe 46, the outlet 408 and one of the pipes 404, to the third orifice 402C of the cartridge 402.

[0092] A first tap PI made on the pipe 140 allows the connection of an auxiliary pipe 150 supplied with soda from a soda tank 152. A metering pump 154 ​​controlled by the control card 8 draws the soda from the tank 152 and injects it, into the pipe 140 and at the level of the tap PI, in a molar quantity Qi determined by the control card 8 and precisely metered by the metering pump 154.

[0093] A second tapping P2 made on the pipe 140 allows the connection of an auxiliary pipe 160 supplied with hydrochloric acid from a hydrochloric acid reservoir 162. A metering pump 164 controlled by the control card 8 draws the acid from the reservoir 162 and injects it, into the pipe 140 and at the tapping P2, in a molar quantity Q2 determined by the control card 8 and precisely metered by the metering pump 164.

[0094] A non-return valve 156, respectively 166, is mounted on each auxiliary pipe 150 and 160 and prevents the circulation of water from the pipe 140 to the tanks 152 and 162.

[0095] Another auxiliary pipe 170 is connected to one of the pipes 404 and supplies a neutralization tank 172, that is to say a reservoir intended to receive liquids and within which a neutralization reaction between an acid and a base can take place.

[0096] A solenoid valve 174 controls the flow of liquid in the auxiliary line 170, between the line 404 and the neutralization tank 172.

[0097] On the other hand, a discharge pipe 176 connects the neutralization tank 172 to the collector 32 and is equipped with a solenoid valve 178.

[0098] The solenoid valves 174 and 176 are controlled by the control card 8.

[0099] When it is appropriate to backwash the nano membrane device 40 filtration, the circulation of water in the circuit C is interrupted, by stopping the operation of the main pump 14 and by switching to the closed position different valves distributed along the circuit C, as shown in [Fig.2]. Then, the cleaning pump 134 is activated and injects water into the pipe 140 and into the auxiliary pipe 142 whose solenoid valve 144 is open. In this configuration, the solenoid valve 144 allows water to flow from the pipe 140 to the third port 402C of the cartridge 402, so that the water enters the cartridge 406 through the port 402C, which is its outlet port in the normal operating configuration of the treatment unit 2, shown in Figures 1 and 7.

[0100] The water leaves the cartridge 402 through the second orifice 402B and flows, from there, into one of the pipes 404, through the valves 405 which are open and into the auxiliary pipe 180, through the solenoid valve 182 which is completely open and the flow meter 184, until it reaches the collector 32 and from there into the recovery tank 34.

[0101] This backwashing operation makes it possible to avoid clogging of the pores of the membrane 403. It does not require the use of chemical products and the backwashing water can be discharged into the ambient environment without any major risk of pollution.

[0102] When it is appropriate to carry out chemical cleaning of the membrane 403, the following steps are implemented.

[0103] In a first step, the pumps 134 and 154 are actuated by the control card 8 to inject the determined molar quantity Qi of soda, coming from the tank 152 and metered by the metering pump 154, into a flow E of cleaning water coming from the cleaning water tank 112. In this step shown in [Fig. 3], the solenoid valve 144 is closed and the valves 405 are opened or closed so that the mixture E + Qi of cleaning water and soda circulates in the pipes 404 and inside the cartridge 402, preferably tangentially to the membrane 403, between the orifices 402A and 402B. As in the treatment configuration shown in [Fig.l], a partial recycling of the mixture E + Qi of water and soda can be carried out, using the pump 406. This improves the effect of the cleaning of the membrane 403 by the soda.In this configuration, the solenoid valve 174 is open to allow the mixture of water and soda to flow from the tanks 112 and 152 into the neutralization tank 172.

[0104] In the first step, the circulation of soda within the nanofiltration membrane device 40 makes it possible to remove the organic matter which tends to be deposited on the membrane 403, thanks to the tangential flow produced between the orifices 402A and 402B.

[0105] This first stage lasts approximately thirty minutes.

[0106] In a second step, the nanofiltration membrane device 40 is rinsed by injecting into it a quantity of water from the cleaning water tank 112 and pumped by the pump 134 controlled by the control card 8, as shown in [Fig.4].

[0107] In this configuration, the valves 405 of the nanofiltration membrane device 40 and the solenoid valve 174 are in the same positions as in the configuration of [Fig.3]. The rinsing water is therefore also directed towards the neutralization tank 172.

[0108] The second stage lasts between 1 and 5 minutes and allows the residual soda to be evacuated to the neutralization tank 172.

[0109] In a third step shown in [Fig. 5], the determined molar quantity Q2 of hydrochloric acid, coming from the reservoir 162 and metered by the metering pump 164, is mixed with a flow E of cleaning water coming from the reservoir 112, by simultaneously activating the pumps 134 and 164, which has the effect of circulating a mixture E + Q2 of water and hydrochloric acid through the nanofiltration membrane device 40, following the same path as in the steps of FIGS. 3 and 4.

[0110] The third step makes it possible to remove non-organic agents, in particular metals and limestone, preferably by proceeding by tangential cleaning of the membrane 403.

[0111] This third stage lasts approximately thirty minutes.

[0112] In a fourth step, the nanofiltration membrane device 40 is rinsed, by operating the treatment unit 2 in the configuration of [Fig.4], i.e. as in the second step.

[0113] The fourth step has the same duration as the second step and allows the traces of hydrochloric acid to be evacuated to the neutralization tank 172.

[0114] Since the water cleaning tank 112 is filled from the pipe 46, upstream of the remineralization device 48, the cleaning water is little or not at all loaded with limestone, so that it does not risk inducing untimely deposits of limestone within the nanofiltration membrane device 40 during the first and second stages, mentioned above. The elimination of limestone using hydrochloric acid is therefore particularly effective.

[0115] The control card 8 is programmed, in particular by a series of instructions stored in the memory 12, to control the metering pumps 154 and 164 in such a way that, during each chemical cleaning, that is to say during each succession of the first to fourth stages mentioned above, the molar quantity Qi of soda poured into the neutralization tank 172 at the end of the first and second stages is equal to the molar quantity Q2 of hydrochloric acid poured into the neutralization tank at the end of the third and fourth stages.

[0116] Thus, the neutralization reaction NaOH + HCl = NaCl + H2O can take place, during a fifth step of the chemical cleaning process, in a stoichiometric manner, by completely consuming the soda and hydrochloric acid poured into the neutralization tank 172 during the first to fourth steps, which has the consequence that, at the end of this neutralization reaction, the liquid present in the Neutralization tank 172 no longer contains soda or hydrochloric acid, but consists solely of salt water.

[0117] According to an advantageous aspect of the invention and to ensure additional safety, a pH sensor 179 is installed in the neutralization tank 172 and connected to the control card 8 which prevents the release of the solution contained in this tank if this solution is not neutralized.

[0118] This liquid can then be safely discharged, during a sixth step of the chemical cleaning process, to the recovery tank 34, through the discharge pipe 176, by opening the solenoid valve 178.

[0119] Advantageously, this sixth step of evacuating the contents of the neutralization tank 172 is carried out shortly before the first step of the next cleaning of the nanofiltration membrane filtration device 40. Here, a short time corresponds to a duration representing less than 15% of the time interval between two successive chemical cleanings. This duration is advantageously 24 hours. In other words, there is a significant time interval between two chemical cleaning operations of the filtration device 40 so that the fifth step of neutralizing the hydrochloric acid and the sodium hydroxide can consume all of the hydrochloric acid and the sodium hydroxide, before purging the neutralization tank 172.

[0120] This time interval, which depends on the fouling rate of the nanofiltration membrane filtration device 40, is generally of the order of several days, preferably one week, which leaves enough time for the neutralization reaction of the fifth stage to continue to completion, consuming all the soda and all the hydrochloric acid discharged during the first to fourth stages.

[0121] The fact that the molar masses Qi and Q2 are equal for each chemical cleaning makes it possible to empty the neutralization tank after each chemical cleaning.

[0122] It is clear from the above that the reservoirs 112, 152, 162 and 172, the pumps 134, 154 and 164, the pipes 140, 142, 150, 160 and 176, as well as the associated valves 114, 144, 174, 178 and 182 together constitute an effective cleaning device for the ultrafiltration membrane filtration device 40.

[0123] The approach of using sodium hydroxide and hydrochloric acid in identical molar quantities Qi and Q2 runs counter to the practice of cleaning water treatment unit components which generally uses more base than acid, in particular more sodium hydroxide than hydrochloric acid, because the main concern is the removal of organic matter by sodium hydroxide and less hydrochloric acid is needed.

[0124] When restarting the treatment unit 2, at the end of the chemical cleaning operation, a possible residue of hydrochloric acid in the membrane device 40 nanofiltration is carried to the remineralization device 48, where this residual hydrochloric acid is neutralized by calcium carbonate and magnesium carbonate. Thus, the risks of traces of hydrochloric acid ending up in the water discharged into the tank 66 are minimized.

[0125] In summary, the treatment unit and the method of the invention guarantee effective cleaning of the nanofiltration membrane filtration device 40, and therefore an effective reduction of the TOC. The products used during the chemical cleaning of the nanofiltration membrane filtration device 40 are not discharged into nature since they neutralize in the neutralization tank 72. In addition, the water treatment unit 2 does not induce the creation of THMs, which is favorable in terms of health.

[0126] In a variant of the invention not shown, the metering pumps 154 and 164 can be replaced by other metering members, such as hydraulic metering pumps coupled to solenoid valves.

[0127] According to a variant of the invention not shown, the control card 8 can be replaced by another type of control unit, in particular electronic, such as a programmable controller.

[0128] According to a variant of the invention not shown, the order of the filtration devices 24, 28, 40, 44 and 58 within the processing unit can be modified. In addition, some of these filtration devices are optional. This is particularly the case for the filtration devices 24, 28, 44 and 58.

[0129] According to a non-represented variant of the invention, the activated carbon filtration device 44, which is arranged within the treatment unit 2, can be modified by granules making it possible to reduce other specific problems of dissolved pollutants that have not been satisfactorily reduced by nanofiltration. For example, dissolved metals can be reduced by a mixture of copper and zinc-based particles, such as the product marketed under the brand name KDF by the company KDF Fluid Treatment, Inc.. According to another example, specific organic micropollutants can be reduced by a granular activated carbon of mineral origin. According to yet another example, other specific problems, such as the presence of fluorine, can be treated by the use of activated alumina such as the product marketed under the brand name Actiguard AA400G by the company Axens).

[0130] Any feature described for one embodiment or variation in the foregoing may be implemented for the other embodiments and variations described above, as long as technically feasible.

Claims

Claims

1. Water treatment unit (2) including a nanofiltration membrane filtration device (40), characterized in that it comprises a device (112, 114, 134, 140-144, 150-156, 160-166, 170-178, 182) for cleaning the nanofiltration membrane filtration device which comprises: - a soda tank (152); - a hydrochloric acid tank (162); - a neutralization tank (172); - a first metering member (154) for a molar quantity (Qi) of soda sent from the soda tank to the neutralization tank; - a second metering member (164) for a molar quantity (Q2) of hydrochloric acid sent from the hydrochloric acid tank to the neutralization tank; and - a control unit (8) for the dosing devices, and in that the control unit is configured to control the first and second dosing members (154, 164) by dosing the same molar quantity (Q1Q2) of soda and hydrochloric acid sent to the neutralization tank (172), during each cleaning of the nanofiltration membrane filtration device (40).

2. Water treatment unit according to claim 1, characterized in that it comprises - a filtration device (28) with activated mineral particles, preferably arranged upstream of the filtration device (40) with nanofiltration membrane in a flow direction (E) of the water being treated; - a filtration device (44) with filter media, preferably arranged downstream of the nanofiltration membrane filtration device in a flow direction of the water being treated; and - a filtration device (58) with an ultrafiltration membrane, preferably arranged downstream of the filtration device with a nanofiltration membrane in the direction of flow of the water being treated.

3. Water treatment unit according to claim 2, characterized in that the ultrafiltration membrane filtration device (58) is arranged downstream of the filter medium filtration device (44) in the flow direction (E) of the water being treated.

4. Water treatment unit according to one of claims 2 and 3, characterized in that it comprises a device (48) for remineralizing the water during treatment, arranged downstream of the nanofiltration membrane filtration device (40) in a direction of flow of the water during treatment, preferably between the filtration device (44) with filter media and the filtration device (58) with ultrafiltration membrane.

5. Water treatment unit according to claim 4, characterized in that it comprises a cleaning water tank (112) supplied, during water treatment, with water taken from the treatment unit (2), upstream of the remineralization device (48).

6. Water treatment unit according to one of the preceding claims, characterized in that the first and second dosing members are dosing pumps (154, 164).

7. A method for cleaning a water treatment unit (2) according to one of the preceding claims, characterized in that it comprises at least the following steps: a. circulating a first molar quantity (Qi) of sodium hydroxide through the nanofiltration membrane filtration device (40) and into the neutralization tank (172); b. rinsing the nanofiltration membrane filtration device (40) with water and directing the rinsing water to the neutralization tank (172); c. circulating a second molar quantity (Q2) of hydrochloric acid through the nanofiltration membrane filtration device and into the neutralization tank, the second molar quantity (Q2) of hydrochloric acid being equal to the first molar quantity (Qi) of sodium hydroxide; and d. rinse the nanofiltration membrane filtration device (40) with water and direct the rinsing water to the neutralization tank (172).

8. Method according to claim 7, characterized in that it comprises steps subsequent to steps a) to d) and consisting of: e) allowing the molar quantities (Q1Q2) of soda and the hydrochloric acid to react in the neutralization tank (172); and f) some time before the next cleaning, purging the neutralization tank (172).

9. Method according to one of claims 7 and 8, characterized in that the treatment unit (2) is according to claim 5 and in that steps b) and d) are carried out with water from the cleaning water tank (112).

10. Method characterized in that a portion of a concentrate resulting from the circulation of water in the nanofiltration membrane filtration device (40) is evacuated from the water treatment unit (2) by means of a proportional valve (182) controlled as a function of a physicochemical parameter of the water or a clogging rate of a nanofiltration membrane (403) during treatment.

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