FR2924111A1 - Installation for biological treatment of water for drinking, comprises biological reactor housing a membrane, water routing unit, unit for adding powdery material inside reactor, unit for recuperation of treated water, and agitation unit - Google Patents

Abstract

The installation for biological treatment of water for drinking, comprises a biological reactor (7) housing a microfiltration-, an ultrafiltration- or a nanofiltration membrane (11), a unit (1) for routing the water inside the reactor, a unit (10) for adding a powdery material in suspension inside the reactor, a unit (12) for recuperating treated water, an agitation unit and/or mechanical and/or hydraulic sealing unit close to the membrane, a unit for injecting and mixing an oxidizing gas e.g. ozone in water, and a unit for counter-currently injecting treated water in the membrane. The installation for biological treatment of water for drinking, comprises a biological reactor (7) housing a microfiltration-, an ultrafiltration- or a nanofiltration membrane (11), a unit (1) for routing the water inside the reactor, a unit (10) for adding a powdery material in suspension inside the reactor, a unit (12) for recuperation of treated water, an agitation unit and/or mechanical and/or hydraulic sealing unit disposed near the membrane, a unit for injecting and mixing an oxidizing gas such as ozone in the water, a unit for counter-currently injecting treated water in the membrane, and a flocculation and/or coagulation unit and/or a clarification unit placed in upstream of the injecting and mixing unit. The powdery material is used as a support to a biomass. The injecting and mixing unit is placed in upstream of the biological reactor, and comprises a static mixer and a contact column. The agitation unit and/or mechanical and/or hydraulic sealing unit comprise an agitator with blades, and unit for recirculation of treated water. A unit is arranged for measuring the concentration of the pollutant contained in the water. The powdery material is activated carbon powder, zeolite, ion-exchanged resin and clay. An independent claim is included for a process for the treatment of drinking water.

Description

Biological treatment plant for a water with stirring means and / or mechanical and / or hydraulic declogging, and corresponding water treatment method. FIELD OF THE DISCLOSURE The field of the invention is that of the treatment of water. More specifically, the invention relates to a method of biological treatment of a water for the purpose of its potabilization. 2. Prior art Drinking water is most often produced from drilling water, spring water, karst water, surface water (river water) ... These waters may contain, in varying proportions, organic pollution, particularly nitrogen and carbon, pesticides, and heavy metals. Potabilization of these waters can be achieved by the implementation of treatment processes that generally include one or more biological-type treatment steps to reduce the biodegradable organic matter content. Water treatment plants have been proposed for the implementation of such treatment processes. Such installations conventionally comprise a biological filter in which the water to be treated is conveyed in such a way that the biologically degradable organic pollution it contains is degraded, at least in part. Such a biological filter accommodates a biomass attached to a material which can also have a role of adsorption of the organic material (for example granular activated carbon). New implementations are proposed with a biological reactor which accommodates a biomass, and where appropriate a material serving as a support for the biomass, such as, for example, powdered activated carbon. Biomass requires the alternation of aerobic and anoxic phases in order to degrade organic carbon and nitrogen pollution. In addition, in order to promote contact between the biomass and the water to be treated, it is generally necessary to create a stirring phenomenon inside the biological reactor.

Thus, it has been proposed to equip the biological reactors means for injecting a vent gas. The injection of an aeration gas makes it possible on the one hand to supply the biomass with the oxygen necessary for its development, and on the other hand to generate a phenomenon of agitation, called aeraulic agitation, because of the displacement of gas bubbles inside the biological reactor. In addition, membrane processes (ultrafiltration, micro filtration, and nanofiltration) have been developed. These consist in passing the water to be treated through membranes that physically retain the elements, initially present in the water, whose size is greater than the pore diameter formed in these membranes. It has thus been proposed to combine the implementation of membrane-type processes in biological reactors by providing that they house one or more membranes, for example microfiltration, ultrafiltration or nanofiltration, in such a way that part of the organic matter is retained by the membranes. This has led to improve the effectiveness of biological treatments. However, the problem of clogging membranes arises in membrane treatment processes. In fact, over time, the pores of the membranes become clogged, resulting in an increase in the pressure drop and a drop in the efficiency of the treatment plants. The clogging of the membranes requires regular cleaning of the membranes. For this purpose, it has been proposed to place the means for injecting an aeration gas in such a way that the gas bubbles rise up along the membranes and take off, during their displacement, the material agglomerated on the membranes. . This technique of using the injection of a gas into a biological reactor containing a membrane, has obtained satisfactory results both in terms of aeration and in terms of unclogging membranes. It has indeed been possible to determine sufficient injection levels to ensure good biomass development and good declogging of the membranes. 3. Disadvantages of the Prior Art Although this technique is particularly effective in terms of aeration and declogging, it nevertheless has some disadvantages. Among these disadvantages is the energetic character of this technique. Indeed, the injection of an aeration gas requires the implementation of booster whose operation generates a consumption of energy which is not negligible. Such consumption may thus represent a relatively high cost item in the operation of such water treatment installations. This cost is all the more important as the need for drinking water and thus for the treatment of potabilization continues to increase due to the population explosion, the industrial boom, and the increase in the standard of living of the populations. . In addition, the increasing quality requirements associated with the production of drinking water also lead to the multiplication of the implementation of such treatment processes, thus generating an increase in the energy consumption necessary for the production of drinking water. Beyond these financial considerations directly attributable to water purification structures, and the consumer, ecological considerations must also be taken into account.

Indeed, the importance attached to the issue of preservation and respect for the environment is becoming more pronounced and the requirements to limit the degradation of natural environments in this area are becoming more and more important. This desire to preserve the environment nowadays goes particularly through the control of energy consumption. Thus, the control of energy has become a major technological challenge that contemporary societies must take up. In addition to the financial and ecological disadvantages of this technique of the prior art, it also has a disadvantage relating to the clogging of the membranes, in particular during the treatment of hard water. This disadvantage results in the fact that the injection of air causes a degassing of the water to be treated, which gives it incrusting properties generating a risk of deposition of calcium carbonate on the membranes. 4. OBJECTIVES OF THE INVENTION The object of the invention is notably to overcome these disadvantages of the prior art. More specifically, an objective of the invention is to provide, in at least one embodiment, a potabilization technique the implementation of which leads to participation in respect and preservation of the environment.

In particular, the present invention has the objective, in at least one embodiment, of reducing the energy consumption necessary for its implementation, at least compared to the techniques of the prior art. Another objective of the invention is, in at least one embodiment, to produce drinking water whose qualities meet the requirements in the field. Another object of the invention is to implement, in at least one embodiment, such a technique that is simple, reliable and effective. 5. OBJECT OF THE INVENTION These objectives, as well as others which will appear thereafter, are achieved by means of a biological water treatment plant, for the purpose of its potabilization, comprising: biological reactor housing at least one microfiltration or ultrafiltration or nanofiltration membrane; means for conveying said water inside said biological reactor; means for adding, inside said biological reactor, at least one pulverulent material in suspension serving as a support for a biomass; means for recovering treated water. According to the invention, such an installation comprises means for stirring and / or mechanical and / or hydraulic unclogging arranged essentially in the vicinity of said membrane, said installation not comprising aeraulic stirring means. Also according to the invention, such an installation comprises means for injecting and mixing an oxidizing gas such as ozone in said water, said injection and mixing means being placed upstream of said biological reactor. Thus, the invention is based on an original approach that consists of replacing the aeration means conventionally associated with a biological reactor so as to inject a particular aeration gas to feed and stir the biomass it contains and to unclog the membranes it houses, by means of stirring and / or mechanical and / or hydraulic declogging. The implementation of such means of agitation and / or mechanical and / or hydraulic declogging leads to reduce the energy consumption necessary for the creation of a stirring phenomenon in the biological reactor and the declogging of the membrane . Such a reduction in energy consumption leads to satisfying both financial and ecological requirements. Moreover, as has been explained, the injection of air causes a degassing of the water to be treated, which gives it incrusting properties generating a risk of deposition of calcium carbonate on the membranes. Thus, the fact of not providing aerator agitation also makes it possible to limit the mineral clogging of the membranes in the case of treatment of hard water. The injection of oxidizing gas by the injection and mixing means into the water to be treated with an oxidizing gas, which are placed upstream of the biological reactor, leads to oxidation of the organic pollution and therefore on the one hand to reduce the amount of organic pollution and secondly reduce the size of organic pollution particles before they are injected into the reactor. The term particles includes indifferently soluble particles and insoluble particles that make up organic pollution.

The reduction in the size of organic pollution particles has two advantages: - in terms of clogging, small particles tend to clog membranes to a lesser extent, and are more easily peelable from the membranes; - In terms of the degradation of organic pollution, the production of small particles, easily biodegradable, leads to facilitate their abatement within the biological reactor. In other words, it increases the biodegradable share of organic pollution. In practice, the size of these particles can be reduced by a factor of approximately 10. Such a reduction in the size of the particles of organic pollution generated by the injection of oxidizing gas makes it possible, by virtue of the advantages it provides to substitute the use of aerator agitation and declogging means by means of stirring and / or mechanical and / or hydraulic declogging that consume less energy. According to an advantageous characteristic of the invention, said mechanical and / or hydraulic agitation and / or unclogging means comprise at least one paddle stirrer. According to another advantageous characteristic, said mechanical and / or hydraulic stirring and / or unclogging means comprise means for recirculating a portion of treated water in line with said membrane. The use, preferably permanently, of such paddle stirrer (s) or such oxidant gas injection means makes it possible to simply but effectively generate a stirring phenomenon inside the chamber. biological reactor in order to optimize the contacting of the water to be treated with the biomass and the pulverulent material. It also makes it possible to obtain a satisfactory stirring of the membranes in such a way as to obtain their unclogging. According to a preferred feature of the invention, such an installation comprises means for injecting a part of water treated against the current of said membrane. The implementation, preferably in a cyclic manner, of such injection means makes it possible to circulate treated water against the current of the membranes. It is thus possible to generate a fairly simple stirring of the membranes so as to unclog effectively and restore their initial performance. According to a preferred embodiment of the invention, said means for injecting and mixing an oxidizing gas comprise a static mixer. The implementation of a static mixer makes it possible to inject the oxidizing gas into the water to be treated optimally.

Preferably, said means for injecting and mixing an oxidizing gas comprise a contact column. Such a contact column has the advantage of promoting the contacting of the water to be treated with the oxidizing gas and therefore of promoting and optimizing the oxidation reaction of pollutants, especially of organic nature.

According to a preferred characteristic, the plant according to the invention further comprises at least one coagulation and / or flocculation unit and / or a clarification unit placed upstream of said injection and mixing means for an oxidizing gas. The use of such coagulation / flocculation / settling units upstream of the injection zone of the oxidizing gas, preferably in the case where the water to be treated is relatively heavily loaded with pollutants that can be coagulated and flocculated. , allows him to undergo a pretreatment leading to reduce the concentration of suspended solids and colloidal materials.

Advantageously, an installation according to the invention comprises means for measuring the concentration of at least one pollutant contained in said water. It is thus possible to know precisely the pollutant levels of the water to be treated. The nature and the quantity of pulverulent materials injected can then be determined in particular according to these measurements of concentration of pollutants. This leads to optimize the treatment of water and the consumption of powdery materials. Preferably, said powdery material belongs to at least the group comprising activated carbon powder, zeolites, ion exchange resins, clays.

The zeolites and clays will preferably be injected so as to reduce the concentrations of heavy metals. Powdered activated carbon and ion exchange resins will be advantageously injected so as to reduce organic pollution and pesticides. The invention also relates to a method of treating water, for the purpose of its potabilisation, in a biological treatment plant which comprises the steps of: injecting and mixing said oxidizing gas with said water; conveying said mixed water to said oxidizing gas in said biological reactor; Bringing said water into contact with at least one powdery material by activating said adding means; - Agitate said water and / or decolourate said membrane by activation of said stirring means and / or mechanical and / or hydraulic declogging. Preferably, said activation of said stirring means and / or mechanical and / or hydraulic declogging is carried out continuously or discontinuously. It is thus possible, by continuous operation, to obtain stirring within the reactor necessary to ensure that the water is brought into sufficient contact with the biomass and the powdery material, and in such a way that prevent clogging and unclog membranes.

According to an advantageous feature of the invention, such a method further comprises a step of injecting a portion of the treated water countercurrently to said membrane by activation of said injection means of said treated water.

This injection makes it possible to provide additional declogging of the membranes so as to restore their level of performance. Advantageously, said activation of said means for injecting said treated water is carried out intermittently. This makes it possible to use these means only when the level of clogging requires it, and consequently to further limit energy consumption. According to a preferred feature, said activation of said adding means is carried out as a function of at least one information representative of the concentration of at least one pollutant contained in said water, and / or as a function of at least one information representative of the temperature of said water. This optimizes the treatment of water and the consumption of powdery materials. 6. List of Figures Other features and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and nonlimiting example, and the accompanying drawings. of which: - Figure 1 schematically illustrates a biological treatment plant according to the invention; FIG. 2 illustrates a graph on which the values of the turbidity of the water and of the permeability of the membranes noted during the tests carried out on a plant according to the prior art and those found during tests carried out on an installation according to the invention. 7. Description of an embodiment of the invention 7.1. Recall of the Principle of the Invention The general principle of the invention is based on the use of injection and mixing means in the water to be treated with an oxidizing gas upstream of the biological reactor in such a way that the particles organic pollution are oxidized and therefore reduced in size before being injected into the reactor. This approach makes it possible to replace the aeration means conventionally associated with a biological reactor in order to aerate the biomass it contains and to unclog the membranes that it houses, by means of stirring and / or mechanical and / or hydraulic declogging of which the implementation generates a lower energy consumption. The combination of these means, which act in synergy, leads to reduce energy consumption and meet both financial and ecological requirements. 7.2. EXAMPLE OF AN EMBODIMENT OF A PROCESSING PLANT According to the invention In connection with FIG. 1, an embodiment of a water treatment installation according to the invention is presented. As shown in this FIG. 1, water to be treated (still called raw water) is conveyed via a feed pipe 1 into a coagulation / flocculation tank 3. Means of injection 5 of coagulating reagents and flocculating reagents are arranged in such a way that these reagents can be injected into the water to be treated contained in the tank 3. The water contained in this tank can then undergo a coagulation / flocculation step so that the Suspended and colloidal materials agglomerate and form flocs. The water thus coagulated and flocculated is conveyed to clarification means via a pipe 2. These clarification means are here represented in the form of a decanter 4. It is noted that any suitable type of decanter 30 can be used. whether it is lamellar or not.

The previously coagulated and flocculated water then undergoes a settling step at the end of which the flocs it contains separate from the liquid phase by gravity and are deposited at the bottom of the settling tank 4. The sludge thus formed can be evacuated at by means of a first purge 6 so as to be directed for example to a sludge treatment zone (not shown). The means of coagulation / flocculation and clarification are means for pretreatment of the raw water. It is however noted that in an alternative embodiment of this embodiment, these pretreatment means may not be implemented, in particular when the quality of the water to be treated so allows, that is to say when the raw water is not or little loaded with pollutants likely to be coagulated and / or flocculated. Overflows of the decanter 4 are conveyed via a pipe 8 and a pump 8a to an oxidation zone so that they undergo a preoxidation.

This oxidation zone comprises a static reactor 14 inside which an oxidizing gas, which is in this case ozonized air, is injected into the previously clarified water. The water thus mixed with ozonated air is conveyed inside a contact column 15. The use of this contact column 15 makes it possible to optimize the oxidation reaction which occurs in the atmosphere. water to treat. Under the effect of contacting the water to be treated with ozonated air, the organic pollution is oxidized, at least in part, so that the particle size of organic pollution is reduced. Small organic pollution particles are more easily biodegradable. In other words, this oxidation with ozone, also called ozonation, leads to increase the biodegradable part of the organic pollution contained in the water before its biological treatment. The ozonated water is then poured inside a biological reactor 7 by means of a pipe 17.

As shown, this biological reactor 7 houses a membrane module 11 comprising at least one filtration membrane such as micro filtration, ultrafiltration or nanofiltration. Injection means 10 of at least one pulverulent material are arranged in such a way that these materials can be injected into the interior of the biological reactor 7. These pulverulent materials serve to support a biomass that develops inside the biological reactor 7 so as to biologically treat the water. The pulverulent materials that can be injected inside the biological reactor 7 may advantageously comprise reactive or non-reactive powders. These reactive powders may preferentially comprise CAP (activated charcoal powder) and / or ion exchange resins so as to reduce the levels of pesticides and organic matter in the water.

These reactive powders may also comprise zeolites and clays in order to reduce the concentration of heavy metals initially present in the water to be treated. Measuring means 10a are provided so that the pollutant concentrations of the water present in the biological reactor 7 can be measured. The injection means 10 of at least one powdery material are slaved to these measuring means 10a. In this way, the nature and amounts of the reactive powders injected into the biological reactor 7 will be determined according to the pollutant load to be treated. The biological reactor 7 also houses, in a lower part, mechanical and / or hydraulic stirring and / or unclogging means 9. These mechanical and / or hydraulic stirring and / or unclogging means 9 may for example include a paddle stirrer.

In another embodiment, these stirring means and / or mechanical and / or hydraulic unclogging 9 may for example comprise water injection means to be treated. The implementation, permanently, of such means of agitation and / or mechanical and / or hydraulic declogging makes it possible to produce a double effect: it makes it possible to generate a stirring phenomenon inside the biological reactor 7 of such that the contacting of the water to be treated with the biomass and the pulverulent materials is optimized; it also makes it possible to ensure the agitation of the membranes in order to unclog them. It is recalled that the technique according to the invention makes it possible to replace the means of agitation and / or aeration declogging conventionally used in the techniques of the prior art by these stirring and / or mechanical unclogging means and / or hydraulic whose operation requires less energy. However, the unclogging of the membranes by the implementation of these stirring means and / or mechanical and / or hydraulic unclogging is only possible to the extent that the water to be treated is previously oxidized so as to reduce the size particles of organic pollution which facilitates its treatment by biological means. The sludge produced in the biological reactor 7 is discharged by means of a low purge 18 and can be mixed with sludge 6 evacuated under the decanter 4 to be conveyed to a treatment zone (not shown). The water contained in the biological reactor 7 is filtered from the outside towards the inside of the membranes of the membrane module 11 by the implementation of a suction pump 12a. The drinking water thus produced flows partly into a storage tank 13 by means of a pipe 12. The other part of the drinking water produced is collected by means of a pipe 12 '.

Part of the produced drinking water, contained in the tank 13 or not, can be used to ensure a periodic hydraulic unclogging membranes of the membrane module 11. For this purpose, valves 16a and 16b can be cyclically open and 5 closed so as to inject treated water against the current of the membranes (from the inside to the outside). In another embodiment (not illustrated) of the technique according to the invention, it may be provided that the unclogging of the membranes is obtained, at least in part, by the implementation of a recirculation of the water. to treat 10 to the right of the membranes. 7.3. Tests Tests were conducted to demonstrate the effectiveness of a water treatment process according to the invention (stirring and / or mechanical and / or hydraulic declogging), both in terms of the quality of the water. water produced only in terms of energy savings to which it can lead compared to the techniques according to the prior art (agitation and air cleaning unclogging). 7.3.1. Operating conditions The installations implemented during the tests included 94.5 m of Zenon ZW500D hollow fiber submerged membranes. The biological reactor was supplied with water to be treated previously decanted and ozonated at a flow rate of 1.8 m3 / h, ie a flow of 25 L / h.m2 at 20 ° C. The filtration time was 10 minutes between two backwashes which lasted 30 seconds at a flow rate of 3.2 m3 / h. The treated raw water had a turbidity of 1.82, a MES concentration (Suspended Materials) of 1.6 mg / l and a temperature of 9 ° C. 7.3.2. Aeration agitation and declogging (prior art) A first series of tests consisted in injecting aeration gas at a flow rate of the order of 0.5 Nm 3 / h / m 2 in the membranes so as to prevent their clogging. 7.3.3. Hydraulic stirring and unclogging (technique according to the invention) A second series of tests consisted in substituting the aeration by a recirculation of fluid at the membranes' right at a flow rate of the order of 13.5 m3 / h (ie 7 , 5 times the filtration rate). 7.3.4. Comparative Results A / Clogging Level and Water Quality Figure 2 shows a graph showing the values of water turbidity and membrane permeability recorded during the first series of tests (Zone A). ) and those found during the second series of tests (zone B). It can be observed that during the reference period (zone A), the average permeability is stable at 230 L / h.m2.bar at 20 ° C, with a fall of about 10 L / h.m2.bar at 20 ° C between two backwashes, each backwash 15 to restore the initial performance of the membrane. The replacement of the aeration by a recirculation of the fluid to the right of the membranes leads to raise an average permeability of 204 L / h.m2.bar at 20 ° C with a fall between 20 and 25 L / h.m2.bar at 20 ° C between two backwashes, each backwash to restore the initial performance 20 of the membrane. The results of these tests have therefore shown that the recirculation of water in the right of the membranes makes it possible to limit the clogging of the membranes in the same proportions as the aeration. In addition, the turbidity of the water was the same during both sets of tests.

In other words, the technique according to the invention makes it possible to produce water of equivalent quality to a water produced by the implementation of a method according to the prior art with a level of clogging of the same order. B / Energy Gains Table I below includes in particular the energy consumption of a pump necessary for the recirculation of liquid to the right of the membranes (technique according to the invention) and the aeration (prior art). For information, the abbreviation HMT stands for Total Manometric Height. This is a quantity generally used to describe the pressure of a pump. It represents a pressure difference expressed, most often, in meters of water column. The value of the energy consumed for supplying a liquid recirculation pump to the membranes for the treatment of one cubic meter of drinking water was 0.120 KWh. The value of the energy consumed to aerate the biological reactor for the treatment of one m3 of drinking water was 0.525 KWh. In conclusion, the use of the technique according to the invention has made it possible to reduce, by a factor of the order of 5, the energy consumption required for the treatment of water purification. In other words, the implementation of a water treatment technique according to the invention makes it possible, because it leads to reducing the energy consumptions necessary for the treatment, to satisfy both the order requirements only ecological requirements, without neglecting the quality of the water produced.

17 Membrane area 94.5 m2 Theoretical calculation for the pump of 24.8 1 / h.m2 recirculation Permeate flow at 20 ° C Flow of treated water 1.8 m3 / h Recirculation 7.5 Ratio Recirculation / filtration Flow rate 13,5 m3 / h Density 1 Kg / dm3 HMT 3,5 m Pump efficiency 70% Pump power 0,18 kW Energy consumption per pump 0,18 kWh Ration Energy / m3 / h 0,014 kWh / (m3 / h) 0,102 kWh / (m3Eau Aeration 0,5 treated) Aeration flow m3 / h / m2 Aeration flow 47,25 m3 / h Ratio Energy / m3 / h 0,02 kWh / (m3 / h) Energy consumed for air 0.945 kWh 0.525 kWh / (m3Eau Ratio Aeration / Recirculation 5.14 treated) Table 1

Claims (14)

1. Installation for biological treatment of water, for the purpose of its potabilisation, comprising: - a biological reactor (7) housing at least one membrane (11) for microfiltration or ultrafiltration or nanofiltration; means for conveying (1) said water inside said biological reactor (7); means for adding (10) inside said biological reactor (7) at least one pulverulent suspension material serving as support for a biomass; - Recovery means (12, 12 ') of a treated water, characterized in that it comprises means (9) for stirring and / or mechanical and / or hydraulic unclogging arranged substantially in proximity to said membrane ( 11), said installation not including aeraulic stirring means, and in that it comprises means for injecting and mixing (14) an oxidizing gas such as ozone in said water, said means injection and mixing devices (14) being placed upstream of said biological reactor (7). 2. Water treatment plant according to claim 1, characterized in that said means (9) for stirring and / or mechanical and / or hydraulic declogging comprise at least one paddle stirrer. 3. Water treatment plant according to any one of claims 1 and 2, characterized in that said means (9) for agitation and / or mechanical and / or hydraulic unclogging comprise recirculation means of a part treated water at the right of said membrane (11). 25 4. Water treatment plant according to any one of claims 1 to 3, characterized in that it comprises means for injecting a portion of water treated against the current of said membrane (11). 5. Water treatment plant according to any one of claims 1 to 4, characterized in that said means (14) for injecting and mixing an oxidizing gas comprise a static mixer (14). 6. water treatment plant according to any one of claims 1 to 5, characterized in that said means for injecting and mixing an oxidizing gas comprise a contact column (15). 7. Installation for treating a water according to any one of claims 1 to 6, characterized in that it further comprises at least one unit (3, 5, 4) of flocculation and / or coagulation and / or a clarification unit placed upstream of said means (14) for injecting and mixing an oxidizing gas. 8. water treatment plant according to any one of claims 1 to 7, characterized in that it comprises means for measuring (10a) the concentration of at least one pollutant contained in said water. 9. water treatment plant according to any one of claims 1 to 8, characterized in that said powder material belongs to at least the group comprising activated carbon powder, zeolites, ion exchange resins, clays . 10. A method of treating water, for the purpose of its potabilization, in a biological treatment plant according to any one of claims 1 to 9, characterized in that it comprises the steps of: - injecting and mixing said gas oxidizing with said water; supplying said mixed water to said oxidizing gas in said biological reactor (7); bringing said water into contact with at least one powdery material by activating said adding means (10); - Agitate said water and / or decolourate said membrane (11) by activation of said means (9) for agitation and / or mechanical and / or hydraulic declogging. 11. A method of water treatment according to claim 10, characterized in that said activation of said means (9) for agitation and / or mechanical and / or hydraulic declogging is carried out continuously or discontinuously. 12. A method of treating water according to any one of claims 10 and 11, characterized in that it further comprises a step of injecting a portion of the treated water against the current of said membrane (11) by activation of said injection means of said treated water. 13. A method of treating water according to claim 12, characterized in that said activation of said means for injecting said treated water is carried out intermittently. 14. Water treatment method according to any one of claims 10 to 13, characterized in that said activation of said adding means (10) is implemented according to at least one information representative of the concentration of water. at least one pollutant contained in said water, and / or as a function of at least one information representative of the temperature of said water.