WO2011161329A1

WO2011161329A1 - Bioreactor with separate oxygenation and trickling filter areas, and treatment method

Info

Publication number: WO2011161329A1
Application number: PCT/FR2011/000298
Authority: WO
Inventors: Jean-François GALLET; Georges Bonjour
Original assignee: Bio2E
Priority date: 2010-05-18
Filing date: 2011-05-17
Publication date: 2011-12-29
Also published as: FR2960159A1; EP2571820A1; FR2960159B1

Abstract

The invention relates to a system (1) for the biological treatment of liquid effluents, comprising a first "oxygenation" tank (2) and at least two other "trickling filter" tanks (3, 4) including a microorganism retaining packing (3a, 4a), in which tank 2 is connected to tanks 3 and 4 by means of a pipe (20) divided into a pipe (20a) for supplying tank 3 and a pipe (20b) for supplying tank 4. The system (1) also comprises: a pipe (25a) for discharging effluent from tank 3 and a pipe (25b) for discharging effluent from tank 4, which pipes (25a, 25b) are connected to a common discharge pipe (21) having an effluent circulation pump (17) disposed thereon; a pipe (22) for recirculating the treated effluent leaving tanks 3 and 4 in the direction of tank 2, said pipe (22) including a valve (15); and a pipe (23) for releasing the effluent from the system (1) to the exterior, said pipe (23) including a valve (16). The tanks (3, 4) each comprise a level sensor (3c, 4c) and are interconnected by means of a pipe (18) located in the lower part thereof. In addition, pipe 20a comprises a valve (5), pipe 20b comprises a valve (7), pipe 25a comprises a valve (9) and pipe 25b comprises a valve (10), and the opening of said valves (5, 7, 9, 10) is controlled by control means, such as to define an effluent circulation path in which the effluent first passes through tank 3, on through pipe 18 and into tank 4, or the effluent first passes through tank 4, on through pipe 18 and into tank 3.

Description

OXYGENATION BIOREACTOR AND SEPARATE BACTERIAL BEDS

PROCESSING METHOD AND METHOD

Field of the invention

The invention belongs to the field of bioreactors for the treatment of liquid effluents, and in particular the treatment of chemical effluents.

More particularly, the present invention relates to bioreactors for the treatment of chemical effluents, which comprise fixed beds.

State of the art

Biological treatment of water and effluents, in particular industrial effluents, has existed for many years. The bioreactors used for the biological treatment of chemical effluents include in particular fixed bed bioreactors also called biofilters or bacterial beds.

Among them, the patent EP 0 004 528 relates to a device and a method of purification of wastewater does not produce excess sludge. In the process described in this document, waste water containing biodegradable materials is processed in a fixed bed reactor, and the aqueous sludges from the reactor are aerobically digested after separation with water. The digested sludge is returned to the reactor or upstream of the reactor. In one embodiment, the water to be treated containing biodegradable substances is introduced into a bacterial bed, in which the biodegradable substances contained in the water to be treated are biologically oxidized. The purified water containing sludge is then transferred to a flotation vessel. In the flotation vessel, the sludge contained in the water is brought to the surface by the action of air. The aqueous slurry thus separated and concentrated is introduced into a digestion vessel, and is aerobically digested by aeration through the air introduced through an air intake device from a compressor. The digested liquid is returned to the wastewater supply circuit of the bacterial bed by means of a pump. It is therefore a process comprising the passage into two different reactors, one fixed bed, the second allowing aeration, and the method further comprises a recirculation from one reactor to the other.

The device described in US Pat. No. 5,518,620 allows treatment of water on a fixed bed, the material used for the fixed bed being an activated carbon fiber felt in a treatment tank. In one embodiment, a circulation vessel is provided on the water circuit. Part of the treated water leaving the tank through the pipe is introduced into the circulation tank for aeration through a means of aeration (eg an air pump). The aerated water is sent through the pipe to be mixed with the untreated water and introduced into the treatment tank. This configuration allows a good ventilation in cases where the tank is filled with large amounts of material, which makes aeration in this tank difficult. In another embodiment, the treated water can be stored in a tank and then sent to a membrane separator to filter microorganisms in the water, and obtain more purified water and "concentrated" water. The concentrated water 26 can be returned to the untreated water tank. This keeps the microorganisms in the treatment system. The wastewater treated by the device of this document is preferably industrial wastewater.

The device described in European patent EP 0 526 590 comprises three successive bioreactors operating sequentially. There is no recirculation of the liquid to be treated from the last tank to the first. Bioreactors are fixed bed reactors. An aeration panel is provided in each bioreactor. This device is used for the treatment of textile dyeing effluents.

The patent application US 2003/0226805 describes a wastewater treatment process comprising the steps of introducing the water to be treated into an oxygenation tank, wherein an aeration by air or an oxygen-enriched gas is realized to obtain a water enriched with oxygen; Introducing the oxygen enriched water into the bottom of a reactor containing a bed of biological activated carbon, so that the bed of activated carbon is foamed and treated water is formed in the upper part of the reactor; Filter and empty part of the treated water, and recycle another part of the water to the oxygenation tank to aerate with the water to be treated. The device described in this document comprises an oxygenation chamber and a recirculation of water.

US Pat. No. 6,926,830 describes a water treatment system comprising at least one reactor. The reactor comprises at least a first vessel connected to a second vessel. In the tanks, support materials for biomass growth are provided. Each tank has microorganisms suitable for a biodegradation step. In one embodiment, a system having three tanks in hydraulic connection with each other through openings in the walls is described. Air is introduced in the form of bubbles by diffusers to provide mixing and aeration to the tanks. A first tank contains a slurry suitable for a bioreaction stage, grown on supports. The supports are mobile, but can be fixed if ventilation is not activated. A second vessel contains a second slurry suitable for another bioreaction step, grown selectively on other carriers. The first tank can be considered as a fixed bed bioreactor and the second tank is a bioreactor with sludge aeration. In addition a recirculation can take place between the tanks.

Patent application WO 2009/101168 discloses a water treatment apparatus consisting of a fixed bed bioreactor, and an oxygenation tank. There is a recirculation from one tank to the other. The associated process is a batch process.

US patent application 2009/0272689 discloses a water treatment device comprising an aeration means and a fixed bed bioreactor. The main vessel is divided into two sections by a wall comprising an orifice. The first section comprises a water aeration apparatus, the second section comprises a fixed bed bioreactor. The aeration section does not contain microorganisms

The devices described above have an oxygenation vessel and a separate fixed bed digestion vessel. However, these devices, and the processing methods associated with them, have the disadvantage that the fixed bed tank will show after a certain period of operation a decrease in its activity or efficiency, as well as a pressure drop. This decrease is related to the clogging of the microorganism support by sludge suspended in the effluent to be treated. Therefore, it is necessary to periodically clean the device. Another disadvantage of this type of device is the creation of preferential passages in the fixed bed, which reduces its efficiency.

The present invention proposes to overcome these disadvantages through a device, and its associated operating method, easy to use, avoiding the creation of preferential passages and allowing the "unclogging" of the fixed bed without prolonged stop of the device.

Object of the invention

A first subject of the invention is a system for the biological treatment of liquid effluents, preferably industrial effluents, comprising a first tank called an "oxygenation tank" equipped with an aeration system and supplied with effluent via a line comprising a valve, at least two other tanks called "bacterial bed" each comprising a support microorganism support, said first tank oxygenator being connected to each of said at least two bacterial bed tanks by a pipe, divided into a supply line of the first bacterial bed effluent tank and a supply line of the second bacterial bed tank in effluent, said system further comprising an outlet pipe of the effluent of the first bacterial bed, an outlet pipe of the effluent of the second bacterial bed, said pipes being connected to a common outlet pipe of the effluent, an effluent circulation pump being placed on said common pipe, a recirculation pipe of the treated effluent leaving the bacterial bed tanks to the oxygenation tank, an evacuation pipe of the effluent treated to the environment or a holding tank or other treatment system, a valve being placed on said effluent recirculation pipe and a valve being placed on said discharge pipe, said valves being able to control the amount of effluent to be returned to the oxygenation tank and / or to discharge to the natural environment or a holding tank,

said system further comprising the following features:

- The said bacterial bed tanks each comprise a level sensor, and said bacterial bed tanks are connected to each other by a pipe located in the lower part of said tanks and allowing the passage of the effluent of a tank with a bacterial bed in the other,

said supply line of the first bacterial bed comprises a valve allowing the passage of the effluent from said oxygenation vessel to said first bacterial bed, and said supply line of the second bacterial bed comprises a valve allowing the passage of the effluent from said oxygenation vessel to said second bacterial bed,

said outlet pipe of the effluent of the first bacterial bed comprises a valve for evacuation of the effluent of said first bacterial bed, and said effluent outlet of the effluent of the second bacterial bed. comprises a valve allowing evacuation of the effluent from said second bacterial bed,

the opening of the feed valves of the bacterial bed vats and the evacuation valves of the bacterial bed vats is controlled by control means, so as to define a circulation path of the effluent such that said effluent is goes first into the first bacterial tank and then through the connecting line between the bacterial bed tanks, and then into the second bacterial bed, or pass first into the second bacterial tank and then through the connecting line between the bacterial bed and then in the first bacterial bed.

Another subject of the invention is a method for treating liquid effluents using the system according to the invention.

The method comprises the steps of:

a) bringing the liquid effluent to be treated into the oxygenation tank,

b) extracting a portion of the effluent from the oxygenation vessel for delivery to the first bacterial bed, the valve on the feed line from the top of the first bacterial bed being opened and the valve placed on the supply line from the top of the first bacterial bed being closed,

c) passing the effluent from the first bacterial bed to the second bacterial bed by the conduit connecting the two bacterial bed tanks from below, d) discharging the effluent from the second bacterial bed tank by the discharge line at the top of the tank and the common discharge line, the valve on the discharge line at the top of the second bacterial bed being open and the valve at the top of the first bacterial bed being closed,

e) returning a portion X% of the effluent exiting the second bacterial bed to the oxygenation tank through the recirculation line, and simultaneously send the remaining portion (100-X)% of the effluent to a basin retention or to the natural environment or to another treatment system through the discharge pipe,

f) simultaneously with the preceding steps, measure the level of effluent in the first bacterial bed by means of the level probe with which it is equipped, g) automatically start the cycle of cleaning and declogging of the system, that is to say when a predetermined level measured by the level probes is achieved, either when a predetermined period of operation without interruption of the system is reached.

Description of figures FIGS. 1a to 1e show an embodiment of the invention in which the first and second bacterial bed cells are connected in series. Figure 1a is a schematic representation of the device according to the invention. FIGS. 1b to 1e are diagrammatic representations of the steps of the method according to the invention, in which the arrows represent the flow direction of the effluent to be treated in the device. FIGS. 1b and 1e show the effluent treatment process, FIGS. 1c and 1d show the cleaning stages of the bacterial bed tanks.

FIG. 2 represents another embodiment of the system according to the invention in which the first and the second bacterial bed vats can, as needed, operate in series or in parallel.

Figures 3a to 3f are schematic representations of the method according to the invention using the device shown in Figure 2, wherein the arrows represent the flow direction of the effluent to be treated in the device. FIGS. 3a and 3f show the effluent treatment method, in the case where the bacterial bed tanks operate in series, FIGS. 3b to 3e represent stages of the cleaning process of the bacterial bed vats corresponding to the series treatment. of the effluent to be treated.

Figures 4a to 4c are schematic representations of the method according to the invention using the device shown in Figure 2, wherein the arrows represent the flow direction of the effluent to be treated in the device. FIG. 4a represents the effluent treatment process in the case where the microburst tanks operate in parallel, FIGS. 4b to 4c show the cleaning stages of the bacterial bed cells corresponding to the parallel treatment of the effluent with treat.

FIG. 5 represents another embodiment of the system according to the invention in which the first and the second bacterial bed tanks operate in parallel, and in which one of the tanks can operate in effluent treatment, while the other tub works in counter-wash.

Figures 6a to 6b are schematic representations of the method according to the invention using the device shown in Figure 5, in which the arrows represent the direction of flow of the effluent to be treated in the system. FIG. 6a shows the effluent treatment process, FIG. 6b shows the effluent treatment process in the case where a bacterial bed tank operates in effluent treatment and the second bacterial bed tank operates in against-washing. List of landmarks

System according to the invention

2 Oxygenation tank

2a Aeration device of the oxygenation tank 2

2b, Sludge evacuation valve of the oxygenation tank 2

2d Sludge pump

3.4 Bacteria tanks

3a, 4a Lids / supports for bacterial bed vats 3,4

3b, 4b de-clogging system, respectively 3.4 tanks

2c, 3c, 4c Level controls respectively 2,3,4

5,6 Supply valves for the bacterial bed 3

7,8 Supply valves for the bacterial bed 4

9, 13,33 Evacuation valves for the bacterial bed 3

10, 14,34 Bacteria Vessel Evacuation Valves 4

15.31 Recirculation valve for the effluent at the outlet of tanks 3,4, to tank 2

16.32 Evacuation valve for the effluent leaving the tanks 3,4,

17 Circulation pump

18 Conducting passage of the effluent between tanks 3 and 4 from the bottom of the tanks

0 Supply line effluent tanks 3,4 from the tank 2 1, 21 b Common pipes evacuation tanks 3,4

2,22b Tank recirculation lines 3,4 to tank 2

3 Effluent discharge pipe to a holding tank or the natural environment

0a, 20b Supply lines from the top of the bacterial bed vats 3,4

4a, 24b Bottom supply lines for bacterial bed vats 3,4

5a, 25b Top exhaust lines for bacterial bed vats 3,4

6a, 26b Bottom drain pipes of bacterial bed vats 3,4

7 Closing valve / opening of the effluent inlet pipe in the oxygenation tank 2

8 Valve closing / opening the pipe 18

9 Delivery line of the effluent to be treated in the system 1

0 Circulation pump

6a, 36b Bottom drain pipes of bacterial bed vats 3,4 Description of the invention

In the context of the invention, the terms "biological treatment" and biotreatment are used interchangeably. By biological treatment is meant the digestion of pollutants harmful to the environment and / or to the human being by appropriate microorganisms, generally bacteria, or yeasts or molds.

A first embodiment of a biological effluent treatment system according to the present invention is described with reference to FIG. 1. The system 1 according to the present invention comprises at least three separate treatment tanks connected to each other by pipes. .

A first tank 2, called "oxygenation tank", of relatively large volume, is used for at least partial oxygenation of the effluent to be treated. The main objective of the oxygenation of the effluent to be treated is to provide the necessary oxygen to the aerobic bacteria or microorganisms used for the biological treatment.

Typically, the volume of the oxygenation tank 2 is between 5 and 1000 m ³ , and preferably 50 to 150 m ³ . The volume of the oxygenation tank is adapted according to the volume of effluent to be treated.

In the present invention, the oxygenation is obtained by aeration of the effluent. Aeration is the process by which air flows through, is mixed with, or is dissolved in a liquid. The aeration of liquids is generally carried out either by passing the liquid through the air by means of fountains, cascades, impellers or cones, or by passing the air into the liquid by means of turbines. aeration or compressed air that can be combined as well as fine bubble diffusers, large bubble diffusers or linear air ducts.

In the system of the present invention, aeration is performed by passing air into the effluent to be treated. Aeration or oxygenation of the effluent to be treated can be done by any appropriate technique known to those skilled in the art. The equipment used for the aeration of the effluent to be treated can belong to three basic types: the air diffusion elements comprise, for example, a porous medium (such as a sintered tube) through which the air escapes into the mass of polluted liquid; surface aeration elements in which the oxygen transfer is carried out by high surface turbulence and liquid spraying and the submerged aeration systems in which air escapes beneath the rotating blades or vanes; a substantially submerged impeller member. In the system 1 according to the present invention, the aeration device 2a of the oxygenation tank 2 is preferably a micro-bubbling device. Micro-bubbling aeration devices (aerators) usually comprise either a micro-perforated tubular ramp, or a micro-perforated disc, the ramp or disc used to produce small diameter air bubbles. The objective is to guarantee a large air-water exchange surface.

At least two other tanks 3,4, called "bacterial bed tanks" or "bacterial beds", preferably of a volume smaller than that of the oxygenation tank 2, contain a fixed bacterial bed. The terms "bacterial bed", "biofilter", "fixed bed" and "fixed bacterial bed" are used interchangeably in the present description. The term "bacterial bed", "biofilter", "fixed bed" or "fixed bacterial bed" means a packing or substrate formed of inert porous supports having a void rate of the order of 50% (minerals, such as pozzolan, or organic polymers) on which the active mass of the micro-organisms is fixed, and through which the effluent to be treated is percolated.

The volume of each bacterial bed vat 3.4 is typically between 2 and 100 m ³ , and preferably between 2 and 50 m ³ . The volume of the tanks with bacterial beds 3,4 is adapted according to the volume of effluent to be treated.

The at least two bacterial bed vats 3,4 are in communication with the oxygenation tank 2 through a line 20 divided into a line 20a for supplying the bacterial bed 3 and a line 20b for feeding the bacterial bed tank 4. A valve 5 is placed on the pipe 20a. A valve 7 is placed on the pipe 20b. The supply valves 5.7 can supply simultaneously or alternatively the bacterial bed vats 3.4.

The at least two bacterial bed vats 3, 4 are also in communication with one another via a line 18 placed near the bottom of said bacterial bed vats 3, 4.

Each of said bacterial bed tanks 3,4 may be further provided with level 3c, 4c probes. Said level 3c, 4c probes have the main function of detecting or measuring the level of the effluent in each tank, in particular to control the flow direction of the effluent in the tanks 3,4 as a function of the level measured in each tank.

Valves 15, 16 also make it possible to direct the effluent exiting from the bacterial bed vats 3, 4 or back via line 22 to the oxygenation tank 2 so that it is treated again, either in downstream discharge via line 23 to a retention tank (not shown) or to the natural environment or to a treatment unit additional (not shown), or, preferably, for a portion X% back to the oxygenation tank 2 and for the remaining portion (100-X)% to the natural environment or a holding tank or other unit of treatment. Typically X is between 20 and 100. The recirculation of a part of the effluent is generally necessary because the oxygen content of the aqueous medium after passing through the oxygenation tank 2 is at most about 10 mg / l, this rate does not allow a sufficient depollution by the microorganisms for a single passage of the effluent in the tanks with bacterial bed 3,4. The recirculation rate at the outlet of the bacterial bed (X) tanks depends on the pollutant load rate present in the effluent to be treated, as well as on the destination (natural environment, basin or treatment unit) of the effluent from the effluent. system 1 according to the invention. On the other hand, the recycling of a portion of the effluent leaving the bacterial bed tanks allows the maintenance of the bacterial flora.

The system 1 according to the invention also comprises pumps 2d, 17. The pump 2d is placed at the outlet of the oxygenation tank 2 in order to eliminate the sludges which decant in the oxygenation tank 2. The pump 17 makes it possible to circulate the effluent in the system 1 according to the invention; it is preferably placed on the outlet pipe of the tanks 3,4.

The supports or packings of the bacterial beds 3a, 4a are preferably porous mineral materials such as diatoms, zeolites, expanded clay or not, calcined clay, shales, pozzolan. The supports may also be polymeric materials, such as polystyrene, or other known materials capable of supporting the growth of bacteria, such as anthracite and activated carbon. The preferred media are pozzolan and calcined clays, as it is the media that offers the lowest pressure drop. Zeolites can be used but have the disadvantage of being subject to attrition.

The microorganisms or bacteria used are those known to those skilled in the art, in particular for the treatment of industrial chemical effluents, and more particularly for the treatment of textile dyeing effluents.

Advantageously, said oxygenation vessel 2 also contains suspended microorganisms, so that a first biotreatment is performed in the oxygenation vessel 2. This allows a better overall efficiency of the biotreatment. These microorganisms may be identical to those of the bacterial beds of the tanks 3,4, and are in this case generally brought into the oxygenation tank 2 by the circulation of the effluent. The microorganisms present in the oxygenation tank 2 may be different from those of the bacterial bed tanks 3,4, and are in this case, they are brought from the outside of the system 1 with the effluent coming from the industrial plant emitting the effluent, and develop because the medium present in the oxygenation tank is favorable to them, or are introduced by seeding.

Advantageously, the control / command process of the system 1 according to the invention is conventionally carried out by control means (not shown) such as a programmable logic controller, and / or a suitable computer system. In particular, the valves 5, 7, 9, 10, 15, 16 are automatically controlled by the control means.

The treatment of the effluent is represented by FIGS. 1b and 1e. Particularly advantageously, during operation of the system 1 for the treatment of the effluent, the supply valve 5 of the tank 3 is open when the supply valve 7 of the tank 4 is closed, and vice versa, and the outlet valve 9 of the tank 3 is open when the outlet valve 10 of the tank 4 is closed and vice versa, and the outlet valve 9 of the tank 3 is closed when the supply valve 5 of the tank 3 is open and the outlet valve 10 is closed when the supply valve 7 of the tank 4 is open. In this way, the tanks with bacterial bed 3,4 are fed in series, with passage of the effluent either firstly by the tank 3, as represented by FIG. 1b, or firstly by the tank 4, such as as represented by Figure 1e.

In the embodiment of FIG. 1b, the effluent arrives through the valve 27 in the oxygenation tank 2, leaves the tank 2 via the line 20, passes into the bacterial bed 3, the valve 5 being open and the valve 7 being closed, passes through the conduit 18 of the bacterial bed 3 to the bacterial bed tank 4, out of the bacterial bed 4 tank by the pipe 25b, the valve 10 being open and the valve 9 being closed, passes through the pipe 21, then for a part X% returns to the oxygenation tank 2 by the pipe 22, and for a portion (100-X)% leaves the system 1 by the pipe 23.

In the embodiment of FIG. 1e, the effluent arrives through the valve 27 in the oxygenation tank 2, leaves the tank 2 via the pipe 20, passes into the bacterial bed 4, the valve 7 being open and the valve 5 being closed, passes through line 18 of the bacterial bed 4 to the bacterial bed 3, leaves the bacterial bed 3 by the pipe 25a, the valve 9 being open and the valve 10 being closed, passes through the pipe 21, then for a part X% returns to the oxygenation tank 2 by the pipe 22, and a part (100-X)% leaves the system 1 by the pipe 23. In other embodiments (not shown) in which the system 1 according to the invention comprises more than two tanks with a bacterial bed, the effluent to be treated passes first into the oxygenation tank 2, then successively in each bacterial bed tanks, then after passing through the last tank, X% of the effluent is recycled to the oxygenation tank 2 (X is between 20 and 100), the rest (0 to 80%) is rejected to a holding tank, to another effluent treatment system, or to the natural environment.

The level 3c, 4c probes check the level of the effluent in the respective bacterial bed tanks 3,4 and send information to the control means of the valves to trigger if necessary the cleaning cycle and the unclogging of the packings 3a, 4a vats with bacterial bed 3,4.

Periodic cleaning and declogging of the bacterial beds is essential for the proper functioning of the system. In this document, this cleaning and unclogging step is also referred to as "backwashing". Counter-washing is more precisely understood to mean the circulation of the effluent in countercurrent with respect to the direction in which it circulates during its biological treatment. Preferably, this cleaning and declogging is carried out in three phases. The first phase is aeration phase only, in the second phase there is simultaneous aeration and inversion of the direction of passage of the effluent, the third phase is a phase of circulation of the effluent in the same direction as that of the second phase, the aeration being cut off.

The cleaning and declogging steps detailed hereinafter concern the case where cleaning is triggered while the treatment of the effluent is done by first passing through the bacterial bed 3 then to the bacterial bed 4.

An optional "prewash" step may be considered. The valves 27, 16 are closed so that the circulation of the effluent is done in a closed circuit in the system 1. This step aims to reduce the COD (chemical oxygen demand) of the oxygenation vessel 2 This step is represented by Figure 1c.

In the first phase (not shown), which is a single aeration phase, the pump 17 is shut off, the valves 5.7 are closed, the aeration device 3b of the bacterial bed 3 is in operation. The valves 27, 16 are closed, the valve 15 is open. This first phase of aeration alone is oprionnelle.

The second phase is represented by Figure 1d. In the second phase, the aeration device 3b, of the bacterial bed 3 is in operation, the valve 16 is closed, the valve 15 is open, the inlet valve 27 of the effluent in the system 1 is closed, so that all the effluent circulates in closed circuit in the system 1. The supply valve 5 of the tank 3 is closed and the supply valve 7 of the tank 4 is open, and the outlet valve 9 of the tank 3 is open and the outlet valve 10 of the tank 4 is closed.

In the third phase, the valve 16 is closed, the valve 15 is open, the inlet valve 27 of the effluent in the system 1 is closed, so that all of the effluent circulates in closed circuit in the system 1. The supply valve 5 of the tank 3 is closed and the supply valve 7 of the tank 4 is open, and the outlet valve 9 of the tank 3 is open and the outlet valve 10 of the tank 4 is closed. This phase is identical to the previous phase, except that the aeration of the bacterial bed 3 is cut off. It is not the subject of a specific figure. We can refer to Figure 1d.

The reversal of the flow direction of the effluent during the backwash allows declogging and the elimination of possible preferential passages in the bacterial beds 3a, 4a.

The cleaning and declogging cycle is preferably followed by a phase of progressive reopening of the valves 15, 16 to allow the resumption of the normal operation of the system 1 (operation in treatment mode of the effluent).

When the treatment of the effluent is resumed after the backwashing, the effluent first passes through the bacterial bed 4 pus in the bacterial bed 3, as shown in Figure 1e. The flow direction of the effluent is thus reversed at each backwash.

In another embodiment of the system 1 according to the invention, represented with reference to FIG. 2, the system 1 further comprises a conduit 26a for evacuating the effluent from the bacterial bed 3 and a conduit 26b evacuation of the effluent from the bacterial bed 4, said conduits 26a, 26b being connected to the common discharge line 21. Said lines 26a, 26b are further placed in the lower part of each bacterial bed 3 4. A valve 13 is placed on the pipe 26a and a valve 14 is placed on the pipe 26b. In addition, a valve 28 is placed on the pipe 18 connecting the two bacterial bed tanks 3,4.

In this embodiment, the system 1 according to the invention also preferably comprises a line 24a for the arrival of the effluent from the bottom of the bacterial bed 3 and a line 24b for the arrival of the effluent by the bottom of the bacterial bed 4. A valve 6 is placed on the pipe 24a and a valve 8 is placed on the pipe 24b. In an embodiment represented by FIG. 3a, during the operation of the system in effluent treatment mode, the valves 6, 8, 13, 14 are closed, and the valve 28 is open. The operation of the system 1 for the treatment of the effluent is then identical to that of the system described above with reference to FIG.

The cleaning and declogging can also be performed as described above, the valves 6,8,13,14 being closed, and the valve 28 open. The optional pre-wash step is shown in Figure 3b. The backwash is represented in FIG. 3c.

An optional "pre-wash" step shown in Figure 3b may be considered. The valves 27, 16 are closed so that the circulation of the effluent is done in closed circuit in the system 1, the valves 6,8,13,14 are closed, and the valve 28 is open. This step aims to reduce the COD (chemical oxygen demand) oxygenation tank 2. This step is shown in Figure 3b.

In the first optional phase (not shown), which is a single aeration phase, the pump 17 is shut off, the valves 5, 7 are closed, the aeration device 3b of the bacterial bed 3 is in operation. The valves 27, 16 are closed, the valve 15 is open.

In the embodiment of FIG. 3c showing the second phase of the backwashing process, the aeration device 3b of the bacterial bed 3 is in operation, the valve 16 is closed, the valve 15 is open, the effluent inlet valve 27 in the system 1 is closed, so that all of the effluent circulates in closed circuit in the system 1, the valves 6,8,13,14 are closed, and the valve 28 is open. The supply valve 5 of the tank 3 is closed and the supply valve 7 of the tank 4 is open, and the outlet valve 9 of the tank 3 is open and the outlet valve 10 of the tank 4 is closed. .

In the third phase, the valve 16 is closed, the valve 15 is open, the inlet valve 27 of the effluent in the system 1 is closed, so that all of the effluent circulates in closed circuit in the system 1, the valves 6,8,13,14 are closed, and the valve 28 is open. The supply valve 5 of the tank 3 is closed and the supply valve 7 of the tank 4 is open, and the outlet valve 9 of the tank 3 is open and the outlet valve 10 of the tank 4 is closed. . Other embodiments of the declogging and cleaning of the bacterial bed tanks 3,4 are described with reference to Figures 3d and 3e.

In the embodiment of the backwash described with reference to Figure 3d, the valves 5,7,8,10,28,13,14 are closed, the valve 6 and the valve 9 are open. The effluent exits the oxygenation tank 2 through the pipe 20, and passes into the pipe 24a. It enters the bacterial bed 3 tank from the bottom and out of said tank by the pipe 25a. It then passes into the pipe 21, then returns to the oxygenation tank via line 22. In this embodiment, the cleaning and declogging only relate to the bacterial bed 3. This embodiment can be used by example when the sludge content of the effluent to be treated is low, which is relatively common in the case of the treatment of industrial effluents.

The resumption of treatment is done by progressively opening the valves 16 and 27, closing the valve 6 and opening the valve 7, so that the flow direction of the effluent is reversed compared to before cleaning and declogging .

In the embodiment of the backwash described with reference to Figure 3e, the valves 5,7,28,13,14 are closed, the valves 6,8,9,10 are open. The effluent exits the oxygenation tank 2 through the pipe 20, and passes into the pipe 24a and 24b. It enters simultaneously into the bacterial bed tanks 3 and 4 at the bottom and exits said tanks through lines 25a and 25b. It then passes into line 21 and then returns to the oxygenation tank via line 22.

The resumption of treatment is done by progressively opening the valves 16 and 27, closing the valves 6,8,10 and opening the valve 7, so that the flow direction of the effluent is reversed compared to before cleaning and unclogging.

Figures 4a to 4c show another embodiment of the treatment of the effluent in the system 1 according to the invention as shown in Figure 2, the treatment being "in parallel".

The operation of the system for the treatment of the effluent is described with reference to Figure 4a. The valves 13, 14 are open simultaneously. The valves 5.7 are also open simultaneously, and the valves 9, 10 are closed simultaneously. Part of the effluent to be treated from the oxygenation tank 2 arrives via the pipe 20a at the top of the bacterial bed 3, then leaves the bacterial bed 3 by the pipe 26a and the pipe 21. Simultaneously, the other part of the effluent to be treated from the oxygenation tank 2 arrives via the pipe 20b at the top of the bacterial bed 4, then out of the bacterial bed 4 by the pipe 26b and the pipe 21. Thus, the biotreatment is done in parallel in the two bacterial bed tanks 3,4, and not sequentially or " in series "as previously described.

The parallel mode of operation has a lower efficiency than the operating mode called "in series" and described with reference to Figures 3a to 3f. It may however be used, for example, in cases where the COD (chemical oxygen demand) objectives of the effluent leaving the system 1 are not very high, for example when said effluent is reprocessed after its exit from the system 1.

A cleaning and unclogging mode different from that described above can be used for the embodiment of the system 1 described with reference to Figure 2. The cleaning comprises the same three steps as previously described.

An optional "prewash" step shown in Figure 4b may be considered. The valves 27, 16 are closed and the valve 15 is opened so that the circulation of the effluent is done in a closed circuit in the system 1, the valves 6, 8, 9, 10 are closed, and the valves 13 , 14 are open. This step aims to reduce the COD (chemical oxygen demand) of the oxygenation vessel 2.

The first optional step is a single aeration step in which the pump 17 is stopped and the devices 3b, 4b are in operation (this step is not shown).

In the second step represented by FIG. 4c, the aeration devices 3b, 4b are in operation, the valve 16 is closed, the valve 15 is open, the inlet valve 27 of the effluent in the system 1 is closed , so that all of the effluent circulates in closed circuit in the system 1. The valves 5, 7 are closed, the valves 6, 8 are open, the valves 9, 10 are open, the valves 13, 14 are closed. The flow direction of the effluent is therefore reversed relative to the direction of circulation in normal operation, so as to unclog and remove the preferential passages in the bacterial beds 3a, 4a.

In the third phase, the aeration devices 3b, 4b are stopped, the valve 16 is closed, the valve 15 is open, the inlet valve 27 of the effluent in the system 1 is closed, so that all of the effluent circulates in a closed circuit in the system 1. The valves 5, 7 are closed, the valves 6, 8 are open, the valves 9, 10 are open, the valves 13, 14 are closed. In another embodiment of the system 1 according to the invention, shown in FIG. 5, the pipe connecting said bacterial bed vats 3, 4 also makes it possible to evacuate the effluents from each of said vats 3, 4 via a common line. 21b. The segments 36a, 36b of said pipe allow the evacuation of effluents, they are located upstream of said common pipe 21b and are each provided with a valve 33,34 for the individual evacuation of each of said tanks 3,4 through said common pipe 21 b. Preferably, in this embodiment, the system 1 further comprises a pipe 22b provided with a valve 32 and connected to the pipe 22, and a pipe 23b provided with a valve 31.

The evacuation of the effluent leaving the bacterial bed vats 3.4 can be carried out in different ways. It can be done by gravity, and in this case, when it is desired to pass the effluent of a bacterial bed tank in the other, either the valves 31, 32 are closed or an additional valve can be provided on the common pipe 21b, this valve is then closed. The evacuation can also be done, as in the system 1 shown in FIG. 5, by actuating a pump 30, and in this case, when it is desired to pass the effluent from a bacterial bed. in the other, either the valves 31, 32 are closed or an additional valve can be provided on the common pipe 21b, this valve then being closed, or said pump 30 is stopped.

Thus, in the embodiment in which the effluent passes from one bacterial bed to the other, treatment of the effluent using the system 1 shown in FIG. 5 can be done in the same manner as in the case of the series operation described for the system 1 represented by FIGS. 1a and 1b, ie the effluent arrives through the valve 27 in the oxygenation tank 2, leaves the tank 2 via the pipe 20, passes into the bacterial bed 3 through the pipe 20a, the valve 5 being open and the valve 7 being closed, passes through the pipe formed by the segments 26a, 26b, 21b of the bacterial bed 3 to the bacterial bed tank 4, leaving the bacterial bed 4 through the pipe 25b, the valve 10 being open and the valve 9 being closed, passes through the pipe 21, then a part X% returns to the oxygenation tank 2 through the pipe 22, and for a part (100-X)% leaves the system 1 by the pipe 23.

In another embodiment in which the effluent does not pass from one bacterial bed to the other, treatment of the effluent using the system 1 shown in FIG. 5 can be done in the same manner as in the case of parallel operation described for the system 1 shown in Figure 2, ie: the valves 13,14 are open simultaneously. The valves 5.7 are also open simultaneously, and the valves 9, 10 are closed simultaneously. Part of the effluent to be treated from the oxygenation tank 2 arrives via the pipe 20a at the top of the bacterial bed 3, then leaves the bacterial bed 3 by the pipe 26a and the pipe 21. Simultaneously, the other part of the effluent to be treated from the oxygenation tank 2 arrives via the pipe 20b at the top of the bacterial bed 4, then leaves the bacterial bed 4 by the pipe 26b and the pipe 21. This embodiment is represented by Figure 6a.

Fig. 6b further shows an embodiment in which the bacterial bed 3 is used for treating the effluent, while the bacterial bed 4 undergoes a cleaning and declogging cycle. In this embodiment, the valves 6, 7, 9, 34, 16 are closed, the valves 5, 8, 10, 13, 15, 31, 32, are open. The effluent arriving from the oxygenation tank 2 passes into the pipe 20a and into the pipe 24b. Part of the effluent enters the bacterial bed 3 from the top through line 20a and exits at the bottom through line 26a and 21b. A portion is sent recirculating to the oxygenation tank 2 through the pipe 22b and the pipe 22, the other part is discharged outside the system 1 by the pipe 23b. Another part of the effluent passes into the pipe 24b, enters the bacterial bed 4 from the bottom, and leaves the bacterial bed 4 tank through the pipe 25b and the pipe 21. The entire outgoing effluent The bacterial bed 4 is returned to the oxygenation tank 2 for recirculation. Thus, the circulation in the bacterial bed 4 is countercurrent to the direction used for the treatment of the effluent.

In an embodiment not shown, and applicable to the systems 1 according to the invention as shown in Figures 1a, 2 or 5, during the backwash phase, an evacuation of sludge tanks 3,4 to a basin or a buffer tank placed downstream of the system 1 (beyond the valve 17) can be provided. This can be useful if the quantity of sludge produced is large (for example greater than 200 kg per 500 m ³ of treated effluent). The volume of this buffer tank will generally be between 10 and 100 m ³ .

On the other hand, in other embodiments (not shown), the system 1 according to the invention comprises more than two bacterial bed cells. In this case, and for series operation of the system according to the invention, the effluent to be treated passes first into the oxygenation tank 2, then successively into each of the bacterial bed tanks, then after passing through the the last tank, X% of the effluent is recycled to the oxygenation tank 2 (X is generally between 20 and 100), the rest (0 to 80%) is discharged to a holding tank, to another system of effluent treatment, or to the natural environment. For parallel operation of the system 1 according to the invention, the effluent to be treated passes first into the oxygenation tank 2, then at the same time in all the bacterial bed tanks, then X% of the effluent is recycled to the oxygenation tank 2 (X is generally between 20 and 100), the remainder (0 to 80%) is discharged to a tank of retention, to another effluent treatment system, or to the natural environment.

In cases where the effluent is very low in pollutants, or when it is discharged to another treatment system, it can be completely discharged out of system 1, ie there is no recirculation, and X is equal to 0.

Process

The present invention also relates to an effluent treatment method using the system 1.

In one embodiment, the method comprises the steps of:

a) bring the effluent to be treated into the oxygenation tank 2 by opening the valve 27, b) extract a portion of the effluent from the tank 2 to send it to the bacterial bed 3, opening the valve 5 and closing the valve 7, and the optional valves 6.8,

c) passing the effluent from the bacterial bed 3 to the bacterial bed 4 through the pipe 18, the optional valves 13,14 being closed, and the optional valve 28 being open,

d) evacuate the effluent from the tank 4 via the pipe 25b and the pipe 21, by opening the valve 10 and closing the valve 9,

e) returning a portion X% of the effluent exiting the tank 4 to the tank 2 by the recirculation pipe 22, and simultaneously send the remaining portion (100-X)% of the effluent to a retention basin or to the natural environment via the evacuation pipe 23, thanks to the pump 17

f) simultaneously with the preceding steps, measure the level of effluent in the tank 3 with the level 3c probe,

(g) Either when a predetermined period of uninterrupted operation of the system is reached, or when the predetermined level is reached in vessel 3, vessel 4 or both vessels, automatically initiate a backwash cycle of system 1, In one embodiment, the backwash cycle comprises the successive steps of:

h) optionally, closing the valve 27 and the valve 16, and completely opening the valve 15,

i) optionally, shut off the pump 17, and operate the aeration system 3b of the bacterial bed 3,

j) close the valve 5 and the valve 10 and open the valve 7 and the valve 9, so as to reverse the flow direction of the effluent in the tanks 3,4, if step h) was omitted, close the valve 27 and the valve 16 and completely open the valve 15, if the step i) was carried out, turn on the pump 17, or, if the step i) was omitted, put into operation the system of aeration 3b of the bacterial bed 3,

k) stopping the aeration system 3b of the bacterial bed 3 and continue the circulation of the effluent in the tank 3,

I) open the valve 16 and the valve 27 again, and resume the effluent treatment process, the bacterial bed 4 replacing the bacterial bed 3 and vice versa.

It is noted that at the end of step I), the treatment process is done with the valve 10 and the valve 5 closed, and the valve 7 and the valve 9 open, that is to say that the passage of the effluent is reversed with respect to step a) described above. The effluent passes first through the tank 4 and then through the tank 3.

In another embodiment, the backwash cycle comprises the successive steps of:

j) close the valve 5, the valve 10, the optional valve 28 and open the valve 6 and the valve 9, so as to reverse the direction of passage of the effluent in the tank 3, and cut off the circulation of the effluent in the tank 4, if step h) was omitted, close the valve 27 and the valve 16 and completely open the valve 15, if step i) was carried out, turn on the pump 17, or, if step i) has been omitted, put into operation the aeration system 3b of the bacterial bed 3, k) stopping the aeration system 3b of the bacterial bed 3 and continue the circulation of the effluent,

I) re-open the valve 16 and the valve 27, close the valve 6, open the valve 7 and the valve 28, and resume the effluent treatment process, the bacterial bed 4 replacing the bacterial bed 3 and vice versa.

In yet another embodiment, the backwash cycle comprises the successive steps of:

i) optionally, cut the pump 17, and operate the aeration system 3b of the bacterial bed 3, and the aeration system 4b of the bacterial bed 4,

j) close the valve 5 and open the valve 9 and the optional valves 6 and 8, so as to simultaneously feed the tanks 3.4 from the effluent, if step h) was omitted, close the valve 27 and the valve 16 and completely open the valve 15, if step i) was performed, turn on the pump 17, or, if step i) was omitted, put into operation the aeration system 3b of the bacterial bed 3,

k) stopping the aeration system 3b of the bacterial bed 3 and the aeration system 4b of the bacterial bed 4, and continue the circulation of the effluent,

I) re-open the valve 16 and the valve 27, close the valve 6 and the valve 8, open the valve 7, the valve 9 and the valve 28, and resume the effluent treatment process, the bed pan bacterial 4 replacing the bacterial bed 3 and vice versa.

The operating time between two cycles of cleaning and declogging system 1 is typically between 24 and 48 hours.

In another embodiment corresponding to the embodiment of the system 1 according to the invention represented by FIG. 2, the effluent treatment process comprises the steps of:

a) bringing the effluent to be treated into the oxygenation vessel 2, b) extracting part of the effluent from the tank 2 to send it to the first bacterial bed 3 and the second bacterial bed 4, the valve 5 and the valve 7 being open,

c) evacuate the effluent of the bacterial bed tanks 3,4 through the lines 26a, 26b, the valves 13, 14 being open,

d) returning a portion X% of the effluent leaving the bacterial bed vats 3.4 to the oxygenation tank 2 through the recirculation line 22, and simultaneously send the remaining portion (100-X)% of the effluent by the evacuation pipe 23 to a retention pond or to the natural environment,

e) triggering a cleaning and declogging cycle of the system 1, either when a predetermined level measured by the level 3c and / or 4c probes is reached, or when a predetermined period of operation without interruption of the system is reached.

In one embodiment, the backwash cycle comprises the successive steps of:

f) optionally, closing the valve 27 and the valve 16, and completely opening the valve 15,

g) optionally, cut the pump 17, and operate the aeration system 3b of the bacterial bed 3, and the aeration system 4b of the bacterial bed 4,

h) close the valve 5 and the valve 7, open the valve 9, the valve 10 and the optional valves 6 and 8, close the valves 13, 14, so as to simultaneously feed the tanks 3.4 from the effluent, if step f) has been omitted, close the valve 27 and the valve 16 and open the valve 15 completely, if step g) has been carried out, turn on the pump 17, or, if the step g) has been omitted, put into operation the aeration system 3b of the bacterial bed 3, i) stop the aeration system 3b of the bacterial bed 3 and the aeration system 4b of the bacterial bed 4, and continue the circulation of the effluent,

j) open the valve 16 and the valve 27 again, close the valves 6,8,9,10 open the valves 5,7,13,14 and resume the effluent treatment process.

The operating time between two cycles of cleaning and declogging of the system 1 is typically between 24 and 48 hours. In another embodiment corresponding to the embodiment of the system 1 according to the invention represented by FIG. 5, the method comprises the steps of:

a) bringing the effluent to be treated into the oxygenation tank 2 by opening the valve 27, b) extracting a portion of the effluent from the tank 2 to send it to the bacterial bed 3, by opening the valve 5 and by closing the valve 7, and the optional valves 6.8,

c) passing the effluent from the bacterial bed 3 to the bacterial bed 4 through the line segments 29a, 29b, 21b, the valves 33, 34 being open, the optional valve 35 being closed, or the pump 30 being stopped, or the valves 31, 32 being closed, the optional valves 13, 14 being closed,

d) discharging the effluent from the bacterial bed 4 through line 25b and line 21, by opening the valve 10 and closing the valve 9,

(g) Either when a predetermined period of uninterrupted operation of the system is reached, or when the predetermined level is reached in vessel 3, vessel 4 or both vessels, automatically initiate a backwash cycle of system 1,

In another embodiment corresponding to the embodiment of the system 1 according to the invention represented by FIG. 5, the method comprises the steps of:

a) bring the effluent to be treated into the oxygenation tank 2 by opening the valve 27, b) extract a portion of the effluent from the tank 2 to send it to the bacterial bed 3 by opening the valve 5 and closing the valve 6, and towards the bacterial bed 4 by closing the valve 7, and opening the valve 8, discharging the effluent from the bacterial bed 3 through line 29a and line 21b, by opening valve 33 and closing valve 9,

returning a portion X% of the effluent exiting the tank 3 to the tank 2 through the recirculation line 22b and the recirculation line 22, and simultaneously send the remaining portion (100-X)% of the effluent to a basin retention or to the natural environment via the evacuation pipe 23b, by means of the pump 30 or by gravity,

simultaneously with steps c) and d), evacuate the effluent from the bacterial bed 4 by the pipe 25b and the pipe 21, by opening the valve 10 and closing the valve 9 and the valve 34,

returning all the effluent exiting the tank 4 to the tank 2 through the recirculation line 22, thanks to the pump 17, the valve 15 being open and the valve 16 being closed,

when a predetermined period of uninterrupted operation of the system is reached, close the valves 5, 10, 33, and open the valves 7, 9, 34.

Advantages

The main advantages provided by this invention over existing devices, in which the two stages (oxygenation and biotreatment) are carried out in the same tank, are:

- Optimization of oxygenation by intensive micro-bubbling in the oxygenation tank;

- The optimization of the surface of the bacterial bed with respect to the volume thereof, with supports preferably mineral:

o volcanic (eg pozzolan),

o oceanic (plankton) (eg diatoms),

o clay and expanded clay,

o Zeolites.

Plastic substrates can be used for specific effluent applications resulting from chemical processes and treatments aimed at reducing the content of dangerous substances in water (micropollutants).

Carbon supports (graphite, activated carbon) can also be used. The backwashing time is reduced, or the backwashing can take place in masked time.

Reducing the risk of clogging through periodic and automatic cleaning and declogging;

The deletion of preferential passages because:

o The sending of a non-turbulent aqueous fluid on the bacterial bed, o Counter-washing to clean the bacterial bed (if necessary stimulated by compressed air, used only for this operation)

The limitation of the impact MES (suspended solids) possible through the successive stages of treatment.

The reduction of the COD during the use of the system according to the invention is greater than that of the existing systems.

Biomass is protected from accidental destruction by the different tanks. Accidental destruction may be due to a significant increase in the temperature of the effluent entering the oxygenation tank, a change in pH, which becomes too low or too high, the presence of strong oxidizing products or other bactericidal products.

Claims

System (1) for biological treatment of liquid effluents, preferably industrial effluents, comprising a first tank (2) called "oxygenation tank" equipped with an aeration system (2a) and supplied with liquid effluent to be treated by a pipe (29) comprising a valve (27), at least two other tanks (3,4) called "bacterial bed" each comprising a lining (3a, 4a) microorganism support, said first oxygenation tank (2) being connected to each of said at least two bacterial bed vats (3,4) by a line (20), divided into a line (20a) for supplying the first bacterial bed (3) with effluent and a line (20b) supplying the second bacterial bed tank (4) with effluent, said system (1) further comprising an outlet pipe (25a) of the effluent of the first bacterial bed tank (3), an outlet pipe (25b) of the effluent of the second bacterial bed tank (4), said pipes (25a, 25b) being connected to a common outlet pipe (21) of the effluent, an effluent circulation pump (17) being placed on said common outlet pipe (21), a pipe (22) for recirculating the effluent treated outgoing from the bacterial bed tanks (3, 4) to the oxygenation tank (2), a pipe (23) for discharging treated effluent into the natural environment or a holding tank or another treatment system , a valve (15) being placed on said recirculation pipe (22) and a valve (16) being placed on said discharge pipe (23), said valves (15, 16) being able to control the quantity of effluent to return to the oxygenation tank (2) and / or to discharge to the natural environment or a holding tank,

said system (1) being characterized in that:

said bacterial bed vats (3,4) each comprise a level probe (3c, 4c), and said bacterial bed vats (3,4) are connected to each other by a line (18) located in the lower part of said tanks and allowing the passage of the effluent from one bacterial bed to the other,

said pipe (20a) comprises a valve (5) allowing the effluent of said oxygenation tank (2) to pass to said first bacterial bed.

(3), and said pipe (20b) comprises a valve (7) allowing the passage of the effluent from said oxygenation vessel (2) to said second bacterial bed.

(4), said outlet pipe (25a) comprises a valve (9) allowing the discharge of the effluent from said first bacterial bed (3), and said outlet pipe (25b) comprises a valve (10) allowing the discharging the effluent from said second bacterial bed (4),

the opening of the supply valves (5, 7) and the discharge valves (9, 10) is controlled by control means, so as to define a flow path for the effluent such that said effluent is goes first into the first bacterial tank (3) and then through the pipe (18) and then into the second bacterial bed (4), either passes first into the second bacterial tank (4) and then through the pipe (18) then in the first bacterial bed (3).

2. System (1) according to claim 1 characterized in that it further comprises additional supply lines (24a, 24b) of each bacterial bed tank (3,4) said pipe (24a) having a valve ( 6) supplying the bacterial bed (3) and said duct (24b) comprising a valve (8) for supplying the bacterial bed (4) and said ducts being connected to the tanks (3,4) at the bottom of each tank (3, 4), so as to feed the tanks (3, 4) through the bottom, the opening of the valves (6, 8) being controlled by said control means.

3. System (1) according to claim 1 or 2 characterized in that it further comprises:

- an evacuation pipe (26a) of the bacterial bed (3) having a valve (13) for evacuation of the bacterial bed (3), and a discharge pipe (26b) of the tank bacterial bed (4) comprising a valve (14) for the evacuation of the bacterial bed (4), said ducts (26a, 26b) being connected to the common duct (21), so as to be able to define additional flow paths of the effluent, the opening of the valves (13,14) being controlled by said control means,

- a valve (28) placed on the pipe (18) connecting the two bacterial bed tanks (3,4).

4. System (1) according to claim 1 or 2, characterized in that the pipe connecting said bacterial bed (3,4) also allows the evacuation of effluents from each of said tanks (3,4) by a pipe (21b), and in that the segments (36a, 36b) of said pipe for discharging the effluents that are upstream of said common pipe (21b) are each provided with a valve (33,34) allowing the individual evacuation of each of said tanks (3,4) through said common pipe (21b).

5. System (1) according to any one of claims 1 to 4 characterized in that the support of the bacterial beds (3a, 4a) is a mineral material, and preferably pozzolan.

An effluent treatment process using the system (1) according to any one of claims 1 to 5, comprising the steps of:

a) bringing the effluent to be treated into the oxygenation tank (2),

b) extracting a portion of the effluent from the oxygenation vessel (2) to send it to the first bacterial bed (3), the valve (5) being open and the valve (7) being closed,

c) passing the effluent from the first bacterial bed (3) to the second bacterial bed (4) through line (18),

d) discharging effluent from the second bacterial bed (4) through line (25b) and line (21), valve (10) being open and valve (9) closed, e) returning a portion X% of the effluent leaving the second bacterial bed (4) to the oxygenation tank (2) through the recirculation line (22), and simultaneously send the remaining portion (100-X)% of the effluent to a holding pond or to the natural environment via the discharge pipe (23), f) simultaneously with the previous steps, measure the level of effluent in the first bacterial bed (3) with the level probe (3c)

g) automatically initiate the cleaning and unclogging cycle of the system (1), either when a predetermined level measured by the level probes (3c) and / or (4c) is reached, or when a predetermined duration of uninterrupted operation of the system is reached.

7. Method according to claim 6 characterized in that the cleaning and declogging cycle of step g) comprises the steps of: h) optionally, closing the valve 27 and the valve 16, and completely opening the valve 15,

a) bringing the effluent to be treated into the oxygenation vessel 2,

b) extracting part of the effluent from the tank 2 to send it to the first bacterial bed 3 and the second bacterial bed 4, the valve 5 and the valve 7 being open,

c) evacuate the effluent of the bacterial bed tanks 3,4 by the lines 26a, 26b, the valves 13, 14 being open,

9. The method of claim 8 characterized in that the cleaning and declogging cycle of step e) comprises the successive steps of:

An effluent treatment method using the system (1) according to any one of claims 1 to 5, comprising the steps of:

a) bring the effluent to be treated into the oxygenation tank 2 by opening the valve 27, b) extract a portion of the effluent from the tank 2 to send it to the bacterial bed 3 by opening the valve 5 and closing the valve 6, and towards the bacterial bed 4 by closing the valve 7, and opening the valve 8,

c) evacuate the effluent from the bacterial bed 3 through line 36a and line 21b, by opening the valve 33 and closing the valve 9,

d) returning a portion X% of the effluent exiting the tank 3 to the tank 2 through the recirculation line 22b and the recirculation line 22, and simultaneously send the remaining portion (100-X)% of the effluent to a retention basin or to the natural environment via the discharge pipe 23b, by means of the pump 30 or by gravity, simultaneously with steps c) and d), evacuate the effluent from the bacterial bed 4 by the pipe 25b and the pipe 21, by opening the valve 10 and closing the valve 9 and the valve 34,