EP4222118A1

EP4222118A1 - Method for treating a wastewater effluent by densifying sludge in a sequencing batch reactor

Info

Publication number: EP4222118A1
Application number: EP21783302.9A
Authority: EP
Inventors: Françoise PETITPAIN PERRIN; Alexis DAUNAY
Original assignee: Suez International SAS
Current assignee: Suez International SAS
Priority date: 2020-10-02
Filing date: 2021-10-01
Publication date: 2023-08-09
Also published as: CN117203167A; AU2021352125A1; JP2023543902A; KR20230088734A; WO2022069705A1; FR3114808A1; IL301834A; US20230373829A1; CA3194563A1; MX2023003757A

Abstract

The invention relates to a method for treating a wastewater effluent (20) in a sequencing batch reactor (SBR). The SBR includes a chamber for containing a wastewater-sludge mixture and extraction means capable of extracting sludge at variable levels. The method comprises: - a supply step (101), during which the SBR is supplied in the sludge bed, near the bottom of the chamber; - a reaction sequence (102) comprising a first anaerobic step (103), optionally a second anoxic denitrification step (104), and a third aeration step (105); - a decanting step (106); - a recovery step (107), during which a clarified fraction of the contents of the chamber is drawn off, said recovery (107) and supply (101) steps taking place simultaneously; and - an extraction step (108), during which at least part of the light sludge is extracted at a predetermined level.

Description

METHOD FOR TREATMENT OF WASTEWATER EFFLUENT BY DENSIFIED SLUDGE IN A BATCH SEQUENCE REACTOR

[0001] The invention lies in the technical field of the biological treatment of municipal and industrial waste water and relates more specifically to the technology known as Sequenced Biological Reactor (also known by its Anglo-Saxon acronym SBR for Sequencing Batch Reactor).

[0002] An SBR operates in sequence with different treatment steps, and in particular a settling phase which makes it possible to separate the so-called "activated" sludge from the treated water.

[0003] A so-called “activated sludge” process uses biological purification in its wastewater treatment. It is a mode of purification by free cultures. The principle is to degrade organic matter, suspended or dissolved in wastewater, by bacteria. A good level of biodegradation is obtained thanks to a homogenization of the medium allowing bacteria to access the particles and good aeration. Then, the sludge settles in the bottom of the reactor during the settling phase.

An activated sludge process aims to eliminate carbon pollution and nitrogen pollution, eliminate or recover the phosphorus included in the phosphorus pollution. To ensure the elimination of carbon pollution, a bacterial culture rich in heterotrophic cells is therefore required. But bacterial growth requires the presence of nutrients, in particular sources of nitrogen and phosphorus, such as those contained in effluents, the elimination of which is also necessary.

[0005] The treatment of nitrogen generally uses nitrification and then denitrification (N/DN) processes. Nitrification is an oxidation reaction by autotrophic bacteria, of ammoniacal or ammonium nitrogen, often denoted N-NH ₄ , into: nitrous nitrogen, also known as nitrite, N-NO ₂ , then nitric nitrogen, also known as nitrate, N-NO ₃ . In known manner, the biological nitrification treatment is carried out under aerobic conditions by autotrophic microorganisms capable of oxidizing ammonium ions (NH4 ⁺ ) to nitrite ions (NO ₂ ') then to nitrate ions (NO ₃ ') . This step is usually carried out in two sub-steps of nitritation and nitration:

NH ⁺ ₄ ^ NO ₂ ' ^NO ₃ -

[0007] Denitrification consists of a reduction in gaseous nitrogen (or dinitrogen also denoted N ₂ ), by denitrifying bacteria, of the nitrates produced during the nitrification reactions. The biological denitrification treatment is typically carried out under anoxic conditions, by heterotrophic microorganisms capable of reducing the nitrate ions produced during the first treatment into nitrite ions, then the nitrite ions into gaseous nitrogen (N2).

[0008] More precisely, the nitrification consists of two sub-steps: a first step of nitritation in the presence of oxygen followed by a second step of nitration also in the presence of oxygen. Nitritation consists of the oxidation of ammonium to nitrite by nitriting autotrophic bacteria, known as AOB or "Ammonia Oxidizing Bacteria", the predominant genus of which is Nitrosomonas. Nitratation consists of the oxidation of nitrite to nitrate by other autotrophic bacteria, known as NOB or "Nitrite Oxidizing Bacteria", the predominant genus of which is Nitrobacter.

[0009] The denitrification can also be broken down into two sub-steps: a denitrification step which will transform the nitrates into nitrites, and a denitrification step which will transform these nitrites into gaseous nitrogen. Each of these two substeps is carried out by heterotrophic bacteria and requires large amounts of biodegradable carbon. Denitrification indeed requires approximately 2.9 kilograms of carbon in the form of 5-day Biological Oxygen Demand (BODs) to reduce one kilogram of N-NO ₃ to nitrogen.

[0010] To reduce the quantities of energy and carbon used for the treatment of nitrogen, other metabolic pathways can be envisaged: nitritation-denitritation and partial nitritation-de-ammonification.

[001 1] The nitritation-denitritation process, also called "nitrate shunt", seeks to stop the oxidation of nitrogen at the nitrite stage by avoiding the production of nitrates, hence the shunt of the "nitrate part of the cycle. To implement the nitritation-denitritation, it is therefore necessary to repress NOB (Nitrite Oxidizing Bacteria) in favor of AOB (Ammonia Oxidizing Bacteria). According to the state of the art, this process allows a saving of 25% on the need for oxygen and requires only 1.7 kilograms of carbon in the form of BOD5 to reduce one kilogram of N-NO2 to dinitrogen. This represents a saving of about 40% on carbon requirements compared to a conventional nitrification-denitrification process.

[0012] In known manner, the nitritation treatment is carried out under aerobic conditions by autotrophic microorganisms capable of oxidizing ammonium ions (NH4+) to nitrite ions (NO2-). The denitritation treatment is carried out under anoxic conditions by heterotrophic micro-organisms capable of reducing nitrite ions (NO2-) to dinitrogen (N2).

Another process, called deammonification or partial nitritation/Anammox (NP/A) uses the nitritation reaction described above but then involves anaerobic autotrophic bacteria, called Anammox for "ANaerobic AMMonium Oxidation", which consume the ammonium and nitrite to produce N ₂ without the need for oxygen and biodegradable carbon.

[0014] The first step in deammonification is partial nitritation (NP). It consists of the oxidation of a fraction (57%) of the ammonium ion into nitrite. The second stage is carried out by Anammox anaerobic bacteria. In this reaction, approximately 11% of the nitrogen charge is transformed into nitrate, which brings the theoretical maximum elimination rate to 89%.

[0015] The same bacterial population, aerobic oxidizing bacteria (AOB), as that of N/DN, is involved in partial nitritation. In this case, (i) only a fraction of the ammonium is oxidized, unlike the N/DN process which requires 100% oxidation of the NH ₄ and (ii) the level of oxidation is reduced because the targeted molecule is the NO ₂ and not NO3. According to the state of the art, the oxygen savings for this treatment route reach approximately 50% compared to a conventional treatment of nitrification and denitrification.

[0016] Furthermore, since the AOB and Anammox bacteria are autotrophic populations, the entire NP/A process can be carried out without any biodegradable carbon. No addition of external (or exogenous) carbon is necessary to carry out the nitrogen treatment. This treatment therefore does not make it possible to eliminate the carbon that may be present.

[0017] In known manner, the partial nitritation treatment is carried out under aerobic conditions by autotrophic microorganisms capable of oxidizing ammonium ions (NH4+) to nitrite ions (NO2-). The anaerobic oxidation treatment is carried out under anaerobic conditions by autotrophic micro-organisms capable of oxidizing ammonium ions (NH4+) to dinitrogen (N2) in the presence of nitrite ions (NO2-) (Anammox bacteria).

Biological dephosphatation (/.e. treatment of phosphorus by biological means) is carried out by the succession of a treatment step in anaerobic condition and a treatment step in aerobic condition. Indeed, certain bacteria called polyphosphate-accumulating organisms (also known by the acronym Polyphosphate-Accumulating Organisms or PAO) have the characteristic of overaccumulating phosphorus when subjected to alternating anaerobic and aerobic conditions. The PAOs release phosphates during their stay in anaerobic conditions, and then passing into aerobic conditions, they accumulate a quantity of phosphates greater than that released in anaerobic conditions.

[0019] Consequently, by adapting the anaerobic/aerobic conditions of the enclosure, the concentration of phosphates in the enclosure of the SBR is controllable thanks to the intervention of the PAOs charged with phosphorus.

[0020] Regardless of the treatment technology used, the SBR technology is limited in its dimensioning by the settleability of the sludge. Indeed, one of the factors limiting the concentration of activated sludge in an SBR, itself representing a potential for treating a polluting load, is the settleability of the sludge generally expressed by the Mohlman index. The Mohlman index is the index of sludge settling ability. This index defines the volume of activated sludge decanted in half an hour in relation to the mass of dry residue (or the concentration of suspended matter, also denoted SS) of this sludge: the lower the index, the better the capacity sludge settling. [0021] The denser the sludge, the faster the settling phase and the shorter the overall duration of the treatment cycle, which makes it possible to treat more pollution in the same day by carrying out a higher number of cycles.

[0022] Generally, denser sludge makes it possible to work with higher concentrations while allowing good decantability (index) and therefore to treat more pollution in the same volume of work.

A first design of a so-called sequenced reactor (SBR) uses two different volumes which are used alternately in reaction and in settling, the water being transferred from the reaction compartment to the settling compartment (Unitank process by Seghers). However, this type of SBR reactor has been improved, and most biological reactors of the sequenced type (SBR) are currently designed with a single volume, in which the various stages of the treatment take place successively. These reactors are generally at variable level: the raw water supply phase and the treated water recovery phase are separated over time, so that when the treated water is recovered, the water level in the reactor drops.

Also known are so-called constant-level SBR reactors, which make it possible to reduce the time of each treatment sequence, while maintaining the efficiency of the treatment. Such a reactor is described for example in the document WO2016020805.

[0025] In SBR type reactors, the most easily settled sludge - that is to say the heaviest sludge - is generally found in the lower part of the sludge bed. However, it is this sludge which is extracted at each cycle at the end of the settling period, which tends to select the lightest sludge, which is also the least settable.

The SBR process described in WO2004/024638 aims to overcome this problem. This is a constant level SBR process, which uses aerobic granular sludge, the particularity of which is to settle very quickly (settling speed greater than 10 m/h). However, the formation of granules with an urban/municipal effluent - that is to say with a low concentration of pollution (carbon, nitrogen, phosphorus) - takes a long time, and its stability according to incoming loads and temperature variations. has not been demonstrated to date. [0027] International application WO2019/053114 proposes to further improve the SBR process described in WO2004/024638 by proposing an SBR reactor allowing, using means for determining a minimum level and a maximum level of extraction of sludge in the SBR enclosure, to selectively extract granular sludge with the best decantability.

There is therefore a need for a more competitive SBR activated sludge treatment process, that is to say more intense, and capable of operating with any type of sludge, including non-granular sludge. In addition, the method of the invention advantageously makes it possible to treat a volume of wastewater identical to, or even greater than, those of the methods of the prior art, but with a restricted footprint.

The invention aims to overcome all or part of the problems mentioned above by proposing a so-called "densified sludge" process, making it possible to obtain high sludge settling speeds, whatever the nature of the sludge (granular or not), and advantageously with non-granular sludge. Sludge densification is obtained in a constant-level SBR by optimizing the production of easily decantable microorganisms, thanks to the combination of several factors:

- feed through the sludge bed,

- the order of the sequences used in the treatment of wastewater, allowing the development of specific populations of microorganisms, with good settleability, in particular PAOs (Phosphate Accumulating Organisms), and

- the sludge extraction strategy, which makes it possible to keep the sludge with the best settleability in the reactor, by extracting the least settleable sludge at each cycle.

To this end, the subject of the invention is a process for treating a waste water effluent comprising carbon pollution, nitrogen pollution and phosphorus pollution, in a sequenced batch reactor (SBR), said SBR comprising : - an enclosure capable of containing a waste water-sludge mixture comprising different levels, each level being defined by a concentration and/or a density of sludge,

- a bed of sludge, comprising PAO, located at the bottom of the containment, above which a level of mud veil is defined,

- means for determining a minimum level and a maximum level of sludge extraction in the enclosure,

- extraction means capable of extracting sludge at variable levels between the minimum extraction level and the maximum extraction level, said method comprising:

- an SBR supply step, during which a volume of effluent to be treated is introduced near the bottom of the enclosure, into the bed of sludge, preferably via a distribution network covering the bottom of the enclosure ,

- a reaction sequence comprising: o at least a first anaerobic stage, during which the PAOs capture carbon pollution and release phosphorus compounds, o optionally, a second stage, in anoxic conditions, of denitrification (partial and/or total), this stage being implemented only in the event of a NOx concentration greater than a predetermined threshold, o a third aeration stage, making it possible to carry out the dephosphatation of the effluent by the PAOs, the aeration being controlled so as to simultaneously carry out either nitrification (partial or total), or nitritation (partial or total),

- a settling stage, during which sludge settles at the bottom of the enclosure and the contents of the enclosure clarifies near its surface,

- a recovery step, during which a clarified fraction of the contents of the enclosure is evacuated, said recovery and supply steps taking place simultaneously, so as to maintain the level of the contents of the enclosure substantially constant during resume and power stages, and

[0031] a step of extracting at least part of the light sludge to a predefined level between the minimum extraction level and the maximum extraction level, preferably close to the veil of sludge. According to one embodiment In particular, the method of the invention consists of the above steps, and where appropriate one or more optional steps described below.

[0032] Advantageously, the treatment method according to the invention further comprises a step of measuring the sludge veil, and the step of extracting at least part of the light sludge is carried out when the measurement of the sludge veil is substantially equal to a predefined distance from the sludge extraction level.

[0033] Advantageously, the step of extracting at least part of the light sludge is carried out during the feed step and/or during the settling step.

Advantageously, the treatment method according to the invention comprises during the reaction sequence, a step of injecting air into the enclosure.

Advantageously, the third aeration step is followed by a step, in anoxia, of post-denitrification, preferably implemented when the third step is a step of total or partial nitrification; or the third aeration step is followed by a step, in anoxia, of denitritation, preferably implemented when the third step is a step of total or partial nitritation; or the third aeration step is followed by a step, in anoxia, of deammonification, preferably implemented when the third step is a partial nitritation step.

[0036] Advantageously, the settling step is preceded by a step of injecting air into the enclosure.

Advantageously, the treatment method according to the invention comprises a step of densification of the sludge by a densification device inside the enclosure.

Advantageously, the treatment method according to the invention comprises a step of controlling the duration of the third aeration step according to the level of pollution (in particular carbon, nitrogen and phosphorus pollution) of the effluent from waste water.

A "granular sludge" is characterized by a settling speed greater than 10 m/h, and a sludge index ("sludge volume index", measured according to standard NF EN 14702-1 of July 2006) less than 35 mL/g (as mentioned in particular in application W02004/024638, page 3). A sludge which does not fulfill these two conditions simultaneously is not considered as a granular sludge. For example, a non-granular sludge is a sludge having a settling speed less than or equal to 10 m/h. Therefore, for a granular sludge, the sludge index at 5 minutes is equal to the sludge index at 30 minutes.

A "densified sludge", also called heavy, is characterized by sludge indices of between 35 and 100 mL/g, preferably between 40 and 80 mL/g, even more preferably between 40 and 70 mL/g , and settling velocities between 2.0 and 9.0 m/h. It is also characterized by a mass proportion of 10 to 50% (preferably 20 to 40%) of particles with a particle size greater than 100 μm (up to 1000 μm, preferably between 200 μm and 500 μm), and a high mass proportion (between 50% and 90%) of biological flocs with a particle size of less than 100 μm (advantageously less than 200 μm). This densified sludge can also be characterized by the limit mass flow criterion which is greater than or equal to 8 kg MES.m' ² .h' ¹ , preferably greater than or equal to 8.5 kg MES.m' ² .h' ¹ . It is a mixture of solids, liquids and microorganisms, said microorganisms including polyphosphate accumulating organisms loaded with phosphorus. This heavy sludge has very good settleability.

A “light sludge” is characterized by sludge indices greater than 100 mL/g and settling speeds less than 2 m/h. It is also characterized by a proportion by mass of biological flocs of size less than 0.2 mm of between 15 and 50%. This light sludge can also be characterized by the limit mass flow criterion which is less than 8 kg suspended solids/m ² /h. It is a mixture of solids, liquids and microorganisms. This mud contains little or no PAO. This light mud is difficult to settle.

[0042] The settling speed is expressed in meters/hour (m/h). It can be determined from the Kynch curve, which is obtained by observing the decantation by gravity of a sample in a 1 L test tube. It should be noted that the value at 30 minutes of the Kynch curve makes it possible to obtain what is called the Molhman index (SVI in English, for “Sludge Volume Index”) or the sludge index (dilution of raw sludge, DSVI in English, for “dilute SVI”), according to standard NF EN 14702-1 - July 2006. On a pilot or industrial reactor, the settling rate can be deduced from the evolution of the height of the veil of sludge at course of time, during a non-aerated sequence. The measurement of the height of the sludge veil can be carried out continuously, for example using an ultrasound probe. Alternatively, it can be discontinuous, it will then be possible to take manual samples at different levels on the height of the reactor at predetermined intervals.

The limit mass flow is expressed in kg.m′ ² h′ ¹ . It characterizes the quantity of solid matter in suspension (also denoted MES) that can be settled per unit area and time, and measures the rate of fall that a sludge is capable of having at a given concentration. The limiting mass flux is determined from the Kynch curve, by carrying out several successive dilutions or concentrations of the raw sludge.

[0044] The proportion of biological flocs is expressed in % of sludge weight, associated with a size - for example, the percentage of less than 0.2 mm. This value can be obtained by sieving a sludge sample on sieves with different mesh sizes (for example 200 μm / 400 μm / 500 μm / 800 μm / 1 mm / 1.25 mm). We then measure the suspended solids (SS) concentration of the filtrate obtained, which is then related to the suspended solids concentration of the raw sludge (in %).

The size of the biological flocs corresponds to a particle size, in particular the maximum size of the particles. It can be determined by a statistical analysis from microscopic photographs.

Advantageously, the method of the invention does not include a step for recirculating the light sludge in the sequenced batch reactor.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, description illustrated by the attached drawing in which:

FIG. 1 schematically represents an example of a sequenced batch reactor adapted to the implementation of the treatment method of the invention;

FIG. 2 represents a flowchart of the steps of the process for treating a waste water effluent according to the invention;

Figure 3 schematically shows the steps of the process for treating a waste water effluent according to the invention; FIG. 4 schematically represents a sequenced batch reactor implemented according to the method of the invention;

Figures 5A, 5B, 5C, 5D illustrate the selection of the bacterial population according to the reaction sequence by measurements carried out during the treatment method according to the invention;

[0053] Figure 6 schematically shows the enclosure of the SBR and recovery means during the supply and recovery steps;

Figure 7 schematically shows the enclosure of the SBR and recovery means during the settling step.

In these figures, for the sake of clarity, the scales are not respected. Furthermore, the same elements will bear the same references in the different figures.

FIG. 1 schematically represents an example of a sequenced batch reactor suitable for implementing the treatment method of the invention. The method of the invention is aimed at the treatment of a waste water effluent comprising carbon pollution, nitrogen pollution and phosphorus pollution, in a sequenced batch reactor (SBR 10). The SBR 10 comprises an enclosure 11 capable of containing a waste water-sludge mixture 12 comprising different levels, each level being defined by a concentration and/or a density of sludge. At each height in the enclosure 11 corresponds a concentration and/or density of sludge of the content 12. For example, it is possible to define several levels denoted N1, N2, N3, N4, N5, N6. Each of the levels can have a different concentration and/or density of sludge from the other levels, or several levels can have the same concentration and/or density of sludge. Finally, during one phase of the treatment process, as will be explained in more detail below, all levels as a whole have the same sludge concentration and/or density. The enclosure 11 is supplied with effluent to be treated 20 advantageously by a distribution network 21, preferably covering the bottom of the enclosure, and with air 8 by a distribution network 27, preferably covering the bottom of the enclosure.

The SBR 10 comprises a bed of sludge 13, shown schematically, comprising PAOs 14, located at the bottom of the enclosure 11, above which is defined a veil of sludge level 15. The SBR 10 comprises means 16 for determining a minimum level 17 and a maximum level 18 of extraction of the sludge in the enclosure 11 . In Figure 1, these levels are shown schematically. Their determination will be detailed below.

During the treatment of waste water, the enclosure 11 contains a mixture 12 of waste water-sludge. When the sludge has settled, the treated water is located in the upper part of the reactor enclosure. The water can be withdrawn via an opening below the level of the surface 24 of the enclosure 11 by a sampling system 200 capable of sampling the clarified fraction, and comprises or consists of an immersed pipe through which the water can be sucked and taken outside the enclosure (arrow A). Another variant of recovery means is detailed below.

The heaviest and/or dense sludge particles are found at the bottom of enclosure 11 and they can be drawn off at the bottom wall of the enclosure. Between the two, there is the rest of the mixture, which is in the form of a stratification, that is to say which has several levels N _1; N ₂ , N ₃ , N ₄ , N ₅ , N ₆ ..., each level being defined by a concentration and/or a density of sludge in the mixture 12.

The veil of mud 15 is the level from which there is mud. It is defined by the height between the surface 24 of the contents of the enclosure and the presence of mud in the whole. The level of the veil of sludge 15 can be determined by the means 16 for determining, preferably continuously. Alternatively, it can be measured manually using a Secchi disk. The measurement of the sludge layer can be done permanently. However, it is not useful to carry out the measurement during the homogenization phases since the contents of the enclosure are mixed, and the sludge present has not yet settled.

The reactor 10 according to the invention makes it possible to selectively extract the sludges least able to settle which are found in the mixture 12.

[0062] The SBR 10 comprises extraction means 19 capable of extracting sludge 23 (shown schematically for understanding purposes) at variable levels between the minimum extraction level 17 and the maximum extraction level.

18 (arrow B). By way of example and without limitation, the means of extraction

19 may comprise an extractor 191 comprising at least a first part having at least one opening 191 a inside the enclosure 11 and a second part 191 b able to bring out the sludge outside of said enclosure. The extraction means 19 may comprise variation means 192 capable of varying the position of the opening 191a of said extractor 191, in particular the level of said opening between the minimum extraction level 17 and the extraction level maximum 18. The extractor 191 advantageously comprises a pump (suction) or a gravity valve (not shown) for extracting the sludge. Advantageously, the extractor 191 can comprise a set of tubes arranged at different levels in the enclosure 11, each tube having a first end presenting an opening inside the enclosure 11 and a second end connected to the second part 91 b of the extractor 191, and variation means 192 comprising a set of valves capable of opening or closing said tubes. The extraction means thus allow the extraction of the sludge at one or more variable levels. For better readability of the figure, the extraction means 19 are represented on the left part of the SBR, but the second part 191 b of the sludge outlet is to be connected to the extracted sludge 23.

[0063] The means 16 for determining the minimum level 17 and the maximum level 18 for extracting the sludge 23 in the enclosure 11 can comprise measurement means 161 capable of measuring the concentration at different levels of a waste water- sludge. For example, a mud blanket probe can measure the surface of the mud bed. A MES (Suspended Matter) probe is used to measure the concentration of the sludge. Several probes can be placed on the height of the enclosure in order to measure the concentration of suspended matter at different levels. These measurements are used to determine the levels 17, 18. The means 16 can comprise selection means 162 able to select a maximum sludge concentration value and a minimum sludge concentration value. The selection can be made by an operator or based on a calculation related to the age of mud. The means 16 may comprise deduction means 163 able to deduce a minimum extraction level corresponding to the selected maximum concentration value and a maximum extraction level corresponding to the selected minimum concentration value. The measurement means 161 can for example comprise one or more measurement probe(s), in particular concentration probe(s). Said measuring probe makes it possible to measure the concentration of sludge in the mixture. The measuring probe 161 is immersed in the mixture as shown. It can be at a fixed or variable immersion depth depending on the type of probe chosen. Or as said above, there may be several measurement probes on the height of the enclosure. The measuring probe 161 is connected to the selection means 162, which make it possible to check whether the measurement corresponds to sludge to be extracted or not, and to the deduction means 163 which make it possible to link the measurement to the corresponding level. These determining means 16 are connected to means 19 for extracting the sludge, more particularly to the means 192 for varying the level of extraction, mainly to select the level of extraction. The means of variations 192 vary the level of the opening 191a of the extractor 191, or it is possible to extract selectively at fixed levels of extraction and at variable instants according to the evolution of the content, for example during the step decantation, waiting, supply/recovery, anaerobic, depending on the measurement of the sludge veil, or even non-selectively during the aeration stage.

For example and in a non-limiting way, the measuring means 161 of the determining means 16 comprise an ultrasonic sensor immersed below the surface of the waste water-sludge mixture. The ultrasonic sensor makes it possible to send an ultrasonic wave into said mixture (it then functions as a transmitter) then to receive an ultrasonic wave in return after having traveled a given distance in the waste water-sludge mixture (it then functions as a receiver). The sensor is connected to selection means 162 and to deduction means 163.

FIG. 2 represents a flowchart of the steps of the process for treating a waste water effluent according to the invention. The treatment method according to the invention comprises:

- a step 101 of supplying the SBR 10, during which a volume of effluent to be treated 20 is introduced near the bottom of the enclosure 11, into the bed of sludge 13, preferably by a distribution network 21 covering the bottom of the enclosure 11, in order to mix the waste water to be treated with the sludge from the sludge bed, - a reaction sequence 102 comprising: o at least a first anaerobic stage 103, during which the PAOs 14 capture the carbonaceous pollution and release phosphorus compounds, o optionally, a second stage 104, in anoxic conditions, of (pre)-denitrification, this step being advantageously implemented in the event of a concentration of NOx greater than a predetermined threshold, o a third aeration step 105, making it possible to carry out the dephosphatation of the effluent by the PAOs 14, the aeration being controlled so as to simultaneously carry out either nitrification (partial or total), or nitritation (partial or total),

- a settling step 106, during which sludge settles at the bottom of the enclosure 11 and the contents of the enclosure 11 clarifies near its surface 24,

- a recovery step 107, during which a clarified fraction 22 of the contents of the enclosure is evacuated, said recovery 107 and supply 101 steps taking place simultaneously, so as to maintain the level of the contents of the enclosure 11 substantially constant during the recovery 107 and supply 101 steps, and

- a step 108 for extracting at least part of the light sludge 23 to a predefined level between the minimum extraction level 17 and the maximum extraction level 18, preferably close to the veil of mud 15.

[0067] Typically, the feeding step 101 is carried out under anaerobic conditions, or else anoxia. In the latter case, step 101 in anoxia makes it possible to denitrify or denitrify. The anaerobic step 103 is carried out anaerobically, the aeration step 105 is carried out aerobically. Preferably, the settling step 106 is carried out at least partially in anoxia.

The second step 104 can be linked to a step 117 for measuring the concentration of NOx in the enclosure.

The treatment method according to the invention may also optionally comprise a fourth step 111 anoxia of denitrification or denitritation or deammonification. More specifically, essentially three variants will be considered: according to the first variant, the third step 105 comprises a total or partial nitrification, and the anoxia step 111 is a denitrification (post-denitrification process); according to a second variant, the third step 105 comprises total or partial nitritation, and the anoxia step 111 is a denitritation (post-denitritation process); finally, according to a third variant, the third step 105 comprises a partial nitritation, and the anoxia step 111 is a deammonification (process called “ANAMMOX”). The fourth step 111 can be linked to a step 117bis for measuring the concentration of NOx in the enclosure.

The step 101 of feeding through the bed of sludge allows the sludge to come into contact with the raw water to be treated. The volume of waste water to be treated 20 is introduced through the sludge bed where the PAOs are located. Thus, the particles and the soluble fraction of the volume introduced are made accessible to bacteria. Thanks to the anaerobic step 103, PAOs capture carbon pollution and release phosphate compounds. The aeration step 105 enables the dephosphatation of the contents of the enclosure by the PAOs. The reaction sequence 102 contributes to the development of PAOs which exhibit good settleability. During settling step 106, the sludge is deposited by gravity in the bottom of the enclosure. Heavy muds and PAOs settle faster than light muds. They contribute to the sludge bed. Light sludge has poorer settleability. They remain suspended longer in the contents of the enclosure, above the sludge bed.

The step 108 of extracting at least part of the light sludge makes it possible to extract regularly or at the very least at predetermined times, for example at each cycle, the least decantable sludge. However, the extraction does not necessarily take place at each cycle depending on the operating constraints. For example, it is possible not to extract on weekends. As a result, only sludge with good settleability is kept in the SBR enclosure. In addition to treating the pollution present in the effluent introduced, the combination of the action of the PAO producing denser sludge and the extraction of the light sludge densifies the sludge present in the enclosure. As a result, the process of the invention, a so-called densified sludge process, makes it possible to obtain high sludge settling speeds, regardless of the nature of the sludge present in the enclosure of the SBR. [0072] During the reaction sequence 102, when the latter comprises a second step 104, there can be a step 110 of injecting air into the enclosure 11 . The injection of air into the enclosure before step 104 allows the suspension of the biomass for better mixing with the supernatant rich in oxidized nitrogen (nitrate NO3 and nitrite NO2), which improves the yield of the denitrification of the feed stage 104, and also the yield of the first anaerobic stage 103. It can be noted that this stage 110 is optional, if the optional second stage 104 is activated, according to the NOx concentration measurement.

The settling step 106 can be preceded by a step 112 of injecting air into the enclosure 11 . The injection of air into the enclosure before the settling stage allows homogenization of the contents of the enclosure and bringing the sludge into contact with the oxidized nitrogen species. In addition, the injection of air also makes it possible to degas the nitrogen present in the contents of the reactor.

In addition, the treatment method according to the invention may comprise a step 113 of densification of the sludge by a densification device 30 inside or outside the enclosure 11, preferably inside . The densification device 30 can be a sieve of suitable size downstream or upstream of the sludge extraction means in order to retain the largest flocs and thus improve the selection, that is to say their maintenance in enclosure, particles settling most easily. Alternatively or in addition, the sludge densification step can consist of adding ballast (such as zeolites).

Advantageously, the treatment method according to the invention comprises a step 114 of controlling the duration of the third aeration step 105 as a function of the level of pollution of the waste water effluent 20, in particular as a function the concentration of NH4 and/or NO ₂ ' and/or NO ₃ ' in the contents of the enclosure. More precisely, it is the pollution of the raw water which is measured indirectly as soon as the contents of the enclosure are aerated at least once.

FIG. 3 schematically represents the steps of the process for treating a waste water effluent according to the invention. During the steps 101 of supplying the SBR with effluent to be treated and 107 of taking up a clarified fraction of the contents of the enclosure, the enclosure is filled with waste water 20 and forms a mixture 12 and the pollution undergoes biological treatment. During this phase, the water residual is introduced into the enclosure. The level of liquid in the enclosure is kept constant by opening a treated water valve (clarified fraction) for example. In other words, the recovery of the treated water is done at the same time as the supply of raw water (waste water). The treated water flow is always the same as the supply flow.

At this stage, denitrification (exogenous denitrification in anoxic condition at the bottom of the sludge bed and endogenous denitrification in anoxic condition at the upper level of the containment) and the bio-dephosphatation process begin. The biological treatment of the effluent takes place mainly during the reaction sequence 102:

- The carbon is eliminated and the ammoniacal nitrogen undergoes nitrification during the aeration step 105;

- The phosphorus is released during the anaerobic step 103, and reabsorbed during the aeration step 105;

- Denitrification takes place during specific anoxic periods. If the sedimentation and feeding time is not sufficient, there is a predenitrification period (exogenous denitrification under anoxic conditions) and/or a post-denitrification period (endogenous denitrification).

[0078] Then takes place step 106 of decantation. It is during this stage that the treated water is separated from the sludge by static sedimentation only. Some biological activity takes place when the liquid undergoes endogenous denitrification in contact with the sludge layer. During this step, steps 101 of supply and 107 of recovery in the enclosure are not authorized. The contents of the enclosure are at rest to allow the settling of the sludge. At the end of the settling step 106, the sludge with good settleability (heavy sludge) is found in the bottom of the enclosure, and the sludge with poor settleability (light sludge) is found in suspension in the contents of the enclosure, between the bottom of the enclosure and the veil of mud. The clarified fraction is located in the upper part of the enclosure, close to its surface 24. At the end of the settling step 106, the excess biological sludge can be extracted to maintain the age of the sludge necessary for nitrification and/or nitritation as a function of temperature, which can be measured during a step 118 of measuring temperature. Alternatively, the excess biological sludge can be selectively extracted during the settling step 106, and/or during the supply step 101 and the recovery step 107, and/or during the anaerobic step 103 and/or waiting 116. The sludge can be extracted non-selectively during the aeration step 105.

The step 108 of extracting at least part of the light sludge 23 is carried out at a predefined level between the minimum extraction level 17 and the maximum extraction level 18, preferably close to the veil of mud. 15. Indeed, it is at the level of the veil of mud that the light muds are found. The predefined level of light sludge extraction is not necessarily a fixed level over time. This level will change depending on the biological treatment and the flow of waste water introduced into the SBR enclosure. The extraction means 19 allow extraction at any level. The extraction of light sludge can thus be done at variable levels during cycles of the treatment process. From a practical point of view, it is possible to define several fixed levels of extraction, for example three. And according to the measurement of the concentration and/or the density of sludge at different levels of the waste water-sludge mixture in the enclosure and/or the measurement of the veil of sludge, it can be chosen at which of the three levels the extraction is done. To do this, the method according to the invention may comprise a step 109 of measuring the veil of sludge 15, and the step 108 of extracting at least part of the light sludge is carried out when the measurement of the veil of sludge 15 is substantially equal to a predefined distance from the sludge extraction level.

Since the level of the sludge bed can vary over time, sludge extraction levels are advantageously installed in the height of the enclosure between the bottom and the middle of the height for heavy sludge and between two levels on the height of the enclosure for light sludge. For example, an extraction level can be located 50 cm above the bottom of the enclosure to eliminate sludge that is too old (mineralized), the other extraction points can be located on the height of the enclosure. In FIG. 3, the arrows represented in bold indicate the open inlets/outlets allowing the flow of the corresponding flux according to the phase of the process. FIG. 4 schematically represents a sequenced batch reactor 10 implemented according to the method of the invention. The different phases presented above take place in the same enclosure and are separated in time. Consequently, step 101 of supplying effluent to the enclosure is managed intermittently. However, in order to ensure continuous treatment of the effluents, several chambers operate in parallel and are fed alternately. The principle of the invention applies similarly to several enclosures.

[0082] During the supply step 101, the raw water is distributed to the bottom of the enclosure, for example through a network 21 of perforated pipes. After step 106 of decantation, and at the same time as step 101 of supply, the supernatant clarified water is withdrawn from the upper part of the enclosure using, for example, a network of perforated recovery pipes . Particularly advantageous means for recovering the clarified fraction are described below.

[0083] The light sludge can be extracted selectively during the settling step 106 and/or during the supply step 101 and 107 recovery and/or during the first anaerobic step 103 just at the level of the veil of sludge to effect the removal of the lightest sludge particles.

[0084] A non-selective extraction of sludge (particularly heavy but also light) is also possible during the aeration step 105 and/or during step 110 and/or during step 112, when the content 12 is homogeneous. .

Figures 5A, 5B, 5C, 5D illustrate the selection of the bacterial population as a function of the reaction sequence by measurements carried out during the treatment method according to the invention.

[0086] The supply of raw water (easily biodegradable carbon) through the sludge bed followed by a strict anaerobic sequence then an aerobic sequence leads to the selection of phosphate-depleting bacteria (PAOs) capable of accumulating phosphates under form of intracellular polyphosphate granules.

FIG. 5A represents the release (anaerobic) followed by the reabsorption of P-PO4 during the aeration period (aerobic). The curve referenced 40 clearly demonstrates the functioning of the biological dephosphatation with a significant release of P-PO4 as soon as the reactor is in anaerobic condition. We observe an increase in the curve followed by a decrease as soon as the ventilation works, decrease which corresponds to the reabsorption of the released P-PO4 and that provided by the raw water. This corresponds to the biological overaccumulation of phosphorus.

FIG. 5B represents nitrification (decrease in the NH4 curve and increase in the NOx curve), with endogenous denitrification (first part of the decrease in the NO _X curve) and exogenous denitrification (second part of the decrease in the NO _X curve after feeding). The curve clearly highlights the interest of exogenous denitrification for the intensification of the denitrification reaction compared to endogenous denitrification with a much steeper slope and therefore higher kinetics after the diet rich in easily biodegradable carbon. This bacterial population as well as the PAOs generate exopolymers which naturally tend to densify the flocs. These dense flocs are not granular sludge, the settling speed of these sludges is between 2 to 10 m/h, preferably between 3 and 6 m/h and their Mohlman index (or sludge index) around 65 mL /g. A granular sludge has particles (or granules) whose size is always greater than 200 micrometers whereas here the densified sludge can contain a proportion of particles whose size is less than 200 micrometers.

To further increase the fraction of dense flocs in the sludge, the treatment method according to the invention applies a sludge extraction strategy which makes it possible to eliminate the lightest sludge. This results in a faster settling rate because only sludge with good settleability remains in the enclosure.

The method according to the invention can also comprise a waiting phase 116 coupled with the feeding, settling or anaerobic stages.

[0091] Considering that the light sludge is found at the top of the sludge bed, in particular at the end of settling step 106 and/or during the waiting step 116, and/or during the supply step 101 and / or during the recovery stage 107 and/or during the first anaerobic stage 103 (the heaviest have fallen to the bottom from the start of settling), the sludge is extracted at the level of the veil of sludge (or slightly below) at the end of settling 106, and/or during the waiting step 116 and/or during the feeding 101 and/or during the recovery step 107 and/or during the first anaerobic step 103. It is also possible to extract the light sludge from the start of settling but at a higher level in the reactor. It is also possible to carry out this extraction at the end of aeration, at any level of the enclosure since the content is homogeneous over the entire height of the enclosure and therefore presents light sludge. It can also be envisaged to extract the light sludge at the very start of the feed or during the feed because the light sludge is the first to rise, or during the anaerobic reaction sequence.

The method of the invention is based on the choice combining the moment of extraction of light sludge and the height at which this extraction is carried out. The height chosen is also related to the age of sludge that one wishes to maintain within the reactor by the duration and the extraction rate. The target sludge age can be determined from a measurement of the temperature of the water/sludge mixture in the reactor.

The treatment method according to the invention may further comprise a step 109 of measuring the veil of sludge 15, and the step 108 of extracting at least part of the light sludge is carried out when the measurement of the veil of sludge 15 is substantially equal to a predefined distance from the sludge extraction level. The sludge light extraction strategy is enhanced by sludge blanket measurement to trigger sludge light extraction at a given level, when the sludge blanket level is within a predefined distance from the sludge extraction level , whether this level is reached during the settling step or during the feed step or during the anaerobic reaction sequence. Thanks to this measurement, and possibly that of the temperature of the water/sludge mixture in the reactor, it is also possible to take into account the instantaneous rate of fall (or residual rate in feed) and the duration necessary for the extraction to perfect this self-optimized extraction mode, preferably integrating the notion of dynamic sludge age. By proceeding in this way, the extraction of the sludge makes it possible to eliminate in each sequence the lightest sludge which is slightly above the veil of sludge, on its upper part more precisely, by calibrating the probe appropriately veil of sludge.

The method of the invention makes it possible to take into account the daily variations in flow rate to which the enclosure may be subjected. During the night, the feed rate is low, the difference between the feed rate and the feed rate decantation is important, the veil of mud quickly approaches the point of extraction. Conversely, during daily hydraulic peaks, the difference between the feed rate and the settling rate is low, the descent of the veil of sludge is slowed down. The slaving of the moment and the duration of the extraction to the sludge blanket measurement makes it possible to ensure that the lightest sludge is always extracted at a given level by modifying the moment of extraction from cycle to cycle.

The combination of the feeding and recovery steps, the reaction sequence and the settling step with the light sludge extraction step results in the production of a denser sludge than that of a sludge activated conventional. The result is the very stable obtaining of a sludge having a settling speed greater than 2 m/h and less than 10 m/h, of the order of 3 m/h to 6 m/h and an index of Mohlman close to 65 mL/g (+/- 10 mL/g). The process of the invention is based on this combination which makes it possible to obtain a densified but non-granular sludge.

FIG. 5C illustrates the stability of the sludge index during pilot tests at a value of less than 75 mL/g, attesting to densified sludge with good settleability. The results are represented for a period of 91 days (x-axis).

[0098] The interest of this densification is indeed to be able to manage two opposite flows simultaneously and safely, the supply of raw water and the settling of the sludge, without causing sludge in the treated water while applying raw water supply velocities greater than 2 m/h.

[0099] Experimentation at different supply speeds (less than 4 m/h) shows that during the supply, the settling speed is slowed down but that the settling continues to take place during the raw water supply.

[0100] FIG. 5D represents the veil of sludge with a supply at 17 m3/h or 2,266 m/h. The upper curve shows partly decreasing the lowering of the sludge veil in the phase noted (*) during settling and in the phase noted (#) during feeding. On the graph, we see that the settling speed is much higher than the feed rate and that the sludge veil continues to lower during the feed. [0101] While the duration of the different sequences of an SBR type reactor is generally fixed, the method according to the invention also makes it possible to adapt, thanks to the installation of suitable sensors and probes, the duration of the reaction sequence. 102 in real time to take into account variations in pollution concentration and hydraulic flow depending either on the time of day (peak load) or to take into account the dilution of the effluent linked to rainy weather. In addition, a synchronization of the cycles by setting up a waiting phase could be put in place.

[0102] In particular the implementation of a measurement of NH4, supplemented or not by a measurement of NOx (in particular NO2), in the reactor can make it possible to follow its evolution during the aerated phase of nitrification and to stop it as soon as a predefined value is reached.

[0103] The advantage is to be able to reduce the aeration period when the water is diluted (night period or hydraulic peak in rainy weather). Reducing the duration of the aeration period also makes it possible to optimize energy consumption, and to carry out more cycles per day and therefore to treat more pollution compared to operation with a fixed aeration period. Conversely, during pollution peaks, the duration of the aeration phase will be increased, while being longer on load peaks than during low loads, to allow the transformation of NH ₄ to the value defined and thus securing performance in the event of NH ₄ concentration peaks.

Finally, the treatment method according to the invention may comprise a step 117 for measuring the concentration of NOx in the enclosure in order to ensure that this value is low enough before moving on to the step of supplying and recovery to allow the release of the phosphorus anaerobically by the phosphorus-removing bacteria and thus ensure the proper functioning of the biological phosphorus removal. This measurement will then be carried out at the end of step 106, or preferably at the end of step 105. If the concentration of NOx measured is still too high, an additional step of treatment of the nitrogen to reach the desired NOx concentration threshold.

[0105] The total duration of a cycle and the power supply duration are generally fixed in order to be able to manage a continuous power supply over several enclosures. The duration The feed time is also fixed, with the total cycle time typically being four times the feed time. This means that the sum of the reaction sequence time and the settling time is three times the feed time. Nevertheless, the method of the invention also applies to a variable cycle duration.

The method of the invention thus allows great flexibility. It is in particular possible to adapt the duration of the stages, in particular the settling stage, the supply and recovery stage, and the anoxia stage, depending on the hydraulic regime and the load to be treated.

The invention also relates to an installation for treating waste water effluent comprising carbon pollution, nitrogen pollution and phosphorus pollution. The installation comprises a sequenced batch reactor (SBR), said SBR 10 comprising:

- an enclosure capable of containing a mixture of 12 waste water-sludge comprising different levels, each level being defined by a concentration and/or a density of sludge,

- a bed of mud 13, comprising PAOs 14, located at the bottom of the enclosure, above which is defined a level of veil of mud 15,

- means 16 for determining a minimum level 17 and a maximum level 18 of sludge extraction in the enclosure,

- extraction means 19 capable of extracting at least part of the light sludge 23 to a predefined level between the minimum extraction level and the maximum extraction level,

- a device for supplying the SBR with a volume of effluent to be treated near the bottom of the enclosure, in the sludge bed, preferably via a distribution network covering the bottom of the enclosure, preferably near the wall mud,

- a device for recovering a clarified fraction of the contents of the containment,

- means of ventilation of the enclosure.

The installation is arranged and equipped for the implementation of the treatment method described above. In the present invention, the term "recovery" is used as a synonym for the term "emptying", and is essentially intended to indicate the evacuation of the treated water from the enclosure.

FIG. 6 schematically represents the enclosure of the SBR and an embodiment of the recovery means during the supply and recovery stages, and FIG. 7 schematically represents the enclosure of the SBR and the recovery means during the settling step. In what follows, the term recovery / recovery is to be understood as evacuation / evacuate and / or emptying / emptying. Aeration of the contents of the enclosure is done with air 8 via a distribution network 27, preferably covering the bottom of the enclosure 11 . In this embodiment of the invention, the recovery means 200 of the clarified fraction of the content 12 of the enclosure 11 comprise:

- a return duct 201 extending below the surface 24 of the contents 12 of the enclosure 11, between the interior 25 and the exterior 26 of the enclosure, comprising: o at least one channel 202 hydraulically connecting the contents 12 of the enclosure 11 and the return duct 201, o a return orifice 203 through which the clarified fraction of the contents 12 of the enclosure 11 is intended to be evacuated, o an air duct 204 connecting hydraulically or air the return duct 201 with the atmosphere,

- an air exhaust valve 205 on the air duct 204, capable of assuming an open position or a closed position, through which the air blocked in the return duct can be evacuated to the atmosphere,

- an air/water blocking device 216 on the return duct 201, able to block the air in the return duct 201 upstream of the air/water blocking device 216 and able to block the water downstream of the air/water lock 216,

- an air injector 207 connected to the return duct 201 and intended to supply the return duct 201 with pressurized and/or compressed air.

[0111] The recovery means 200 may comprise an air injector 207 (advantageously having a non-return valve) connected to the air duct 204 between the exhaust valve 205 and the air/water blocking device 216 and intended to supply the return duct 201 with pressurized/compressed air.

The air/water blocking device 216 can be a valve, preferably motorized, which can assume the open or closed position or a U-shaped siphon which can be primed or deprimed. In the following, the air/water blocking device 216 is said to be open if the valve is in the open position or the siphon primed, and is said to be closed if the valve is closed or the siphon deprimed.

[0113] The recovery means 200 may comprise an air injector 207 connected to the air duct 204 between the exhaust valve 205 and the air/water blocking device 216 and be intended to supply the recovery duct 201 with supercharged/compressed air. The air allowing the blockage of the return duct can alternatively come from the air source used in the treatment process. More specifically, the air injector 207 can be dedicated to air/water blockage. In this case, it includes a non-return valve. The air injector 207 can also be not dedicated to air/water blockage, that is to say the air injector can come from the air supply of the enclosure. In this case, the recovery means 200 further comprise a blocking valve 206 to ensure the blocking function. The air injector 207 is not necessarily connected to the air duct 204 but it is systematically connected to the return duct 101 to block it in air/water.

The air injector 207 can operate intermittently during the aeration step 105 or continuously.

The exhaust valve 205 corresponds to a vent valve.

The control means 210 of the recovery means 200 aim to fill the recovery duct 201 with air until the recovery duct 201 is completely emptied of the clarified fraction contained in the recovery duct 201, at keep the return duct 201 filled with air during the aeration step 105 and during the settling step 106, and to evacuate the air contained in the return duct 201 with clarified fraction 22 during the step supply 101 and step 107 of recovery. More specifically, the control means 210 are configured to actuate the valve 205 and the blocking device 216 as needed so that the recovery pipe empties of the clarified fraction present in the recovery pipe. 201 and keep the return duct 201 filled with air during the aeration phase and the settling phase. Air can be supplied continuously. It can also come from an external air source, that is to say not dedicated to air/water blockage, and provided for the ventilation of the enclosure. In the case of an external air source, an isolation valve 206 is necessary. In the case where the recovery means 200 comprise an air injector 207 dedicated to blocking air/water, the latter can inject pressurized and/or compressed air into the recovery duct 201 . Note that this dedicated air injector 207 has a check valve (not shown in the figures). In other words, the return duct 201 is then blocked in air: it is filled with air which cannot then be evacuated due to the closing of the air/water blocking device 216 and the exhaust valve 205. During the aeration phase, the level of the contents of the enclosure increases due to the introduction of air into the enclosure and the level of the contents rises. The speaker content level rises. But the return duct being filled with air, this content cannot enter the duct. This has the advantages of avoiding a loss of sludge from the system (the presence of sludge being important to densify), and of avoiding contamination of the return pipe and of the clarified water leaving the orifice 203 (this is important vis-à-vis the tertiary treatment that should be implemented downstream, and/or vis-à-vis the discharge standards), the channels 202 make it possible to compensate for the gaseous retention raising the water level of the reactor by ventilation, they also compensate for an imperfect horizontality of the pipes.

The content rises in the channels 202 in the case of a discontinuous injection of air, but cannot enter the return duct 201. This configuration guarantees, thanks to the control of the return means, that enter only the clarified fraction into the return pipe, without any risk of contents containing sludge entering it.

It is important to emphasize that the return duct extends below the surface 24 of the contents of the enclosure. It is therefore permanently immersed in the contents of the enclosure. The channels 202, which are tubes with an inlet orifice, are permanently immersed and are filled with the contents of the enclosure (in clarified water (during the supply/recovery and the anaerobic phase) or in air (reaction stage including aeration stage, and settling stage).In other words, the content of the channels varies according to the current sequence.The channels 202 have a dual role: they form access to the clarified fraction towards the recovery duct 201 during the supply/recovery step, and they form a buffer volume, without access to the recovery duct 201, which contains the contents of the enclosure when the level of the contents of the enclosure increases due to aeration. The passage from the role of access to the recovery duct to that of buffer volume is done according to the progress of the treatment process, thanks to the injection/exhaust of supercharged and/or compressed air and the opening/closing of the blocking device and exhaust valve. The injection/exhaust of supercharged and/or compressed air and the opening/closing of the blocking device and of the exhaust valve are controlled by the control means 210 of the recovery means 200.

In one embodiment, the air/water blocking device 216 comprises a U-shaped siphon 208 between the air duct 204 and the return orifice 203. When the injection of air takes place, the clarified water contained in the siphon and in the return duct is replaced by air up to an equivalent height at the ends of the channel or channels. By this means, the siphon aims to hydraulically disconnect the contents of the enclosure from the clarified water outside the enclosure, it is thus defused. By extending the height of the siphon, it is also possible to compensate for the elevation of the level of the surface 24 during the aeration stage. The presence of a siphon is not mandatory and other embodiments are possible and will be presented below. The siphon can be associated with a blocking valve 206 which is also controlled by the control means 210 if the air to fill the return duct comes from the air for the treatment (air injector 207 not dedicated to blocking in air). The return orifice 203 is the orifice through which the treated water is evacuated.

The return orifice 203 is advantageously positioned above the level of the return duct 201. And advantageously, the return duct 201 comprises an exhaust duct 211 of air. Here again, other embodiments are possible and will be presented below.

[0121] With this embodiment of the recovery means, the method of the invention comprises, following the settling step 106, during which sludge is deposited at the bottom of the enclosure 11 and the contents of the enclosure 11 clarifies near its surface 24, a step 107 of recovering the clarified fraction 22 of the contents of the enclosure 11, said recovery 107 and supply 101 steps having take place simultaneously, so as to maintain the level of the contents of enclosure 11 substantially constant during the recovery 107 and supply 101 steps.

The treatment method according to the invention can also comprise a waiting phase 116 coupled with the feeding, settling or anaerobic stages.

According to the invention, the treatment method comprises:

- a step 120 for controlling the recovery means 200 during which the recovery duct 201 is filled with air until the recovery duct 201 is completely emptied of the clarified fraction 22 contained in the recovery duct 201 , and the return pipe 201 is kept filled with air during the reaction sequence 102 and preferably also during the settling step 106, and optionally waiting, and

- a step 123 of expulsion of the air contained in the recovery duct 201 by the clarified fraction 22 during the supply step 101 and the recovery step 107.

[0124] After step 120 and before step 123, the method may comprise a step 121 of at least partially filling the at least one channel 202 with the contents 12 of the enclosure 11 during step 105 d aeration, if the air injection is not continuous during the air injection steps.

Furthermore, the processing method comprises, between step 120 and step 123, two other steps of maintaining the air filling of the return duct. As mentioned previously, the step 120 of filling the return duct 201 with air takes place by injecting air and emptying it with clarified water simultaneously. The valve 205 is closed and the air/water blocking device 216 is said to be closed, the air injection device (the air injector 207) is in operation, at the start of the first aeration stage 105.

Next, the method comprises a step 122 of maintaining the air filling of the return duct 201 by injecting air. The valve 205 is closed and the air/water blocking device 216 is said to be closed, the air injection device 207 is in operation, during the aeration step 105.

Next, the method comprises a step 122bis of maintaining the filling of the return duct with air without injecting air. Valve 205 is closed and the air/water blocking device 216 is said to be closed, air injection device 207 is off, during the aeration 105 and settling 106 steps.

Next comes step 123 of expelling the air contained in the return duct and filling it with clarified water simultaneously. The valve 205 is open and the blocking device 216 is said to be open, the air injection device 207 is off, during the supply 101, recovery 107, anaerobic 103 stages.

[0129] And ultimately, if the injection of air is not continuous during step 105 of aeration, in particular to save energy, a step 121 of filling, at least partially, of the at least one channel 202 through the contents 12 of the enclosure 11 during the ventilation step 105 can take place (but this step is not intended in some way). In this case, it is possible to reinject air to refill the return duct 201, this is step 122. This can be done in a syncopated manner by adjusting a frequency and an injection duration of air or in a finer way by integrating a level measurement probe which makes it possible to detect whether it is necessary to reinject air and to trigger a step 122 during the aeration step 105.

The return duct is kept filled with air during the reaction sequence comprising the aeration step. Preferably, it is also kept filled with air during the settling step. Indeed, if the return duct was no longer filled with air at the start of settling, the veil of sludge would not have enough time to descend below the inlet orifices of the channels 202, which would cause the contamination of the return duct by sludge.

[0131] The particularity of the invention lies in the positioning of the return duct 201 below the surface 24 of the contents of the enclosure, that is to say that it is always submerged. However, its content is controlled thanks to the step of piloting (120, 122, 122bis, 123) the recovery means 200 according to the steps of the processing method. As a result, only the treated water can enter the recovery duct in order to be recovered. The return duct is shown substantially horizontal, that is to say parallel to the surface 24 of the contents of the enclosure, but it could also be inclined and extend along an axis secant to the plane in which the surface is located. 24. The first advantage is not to limit the volume of the enclosure since it is not necessary to lower the water level below the return pipe to avoid the entry of untreated water and of sludge during the aeration step 105. Thanks to the control of the recovery means, the recovery duct is filled with air just before the aeration step 105 of the reactor. In other words, the return duct is filled with air, that is to say it is blocked with air and thus made inaccessible to the contents of the enclosure during the phases when the contents of the enclosure near the conduit is not just treated water. Another feature comes from the channel (or channels) 202 which hydraulically connects the contents of the enclosure 11 to the return duct 201. They are represented perpendicular to the surface 24, but can also be inclined downwards. The channel 202 plays a preponderant role: while providing the hydraulic connection between the clarified fraction and the recovery pipe to allow the recovery of the clarified fraction, it also allows during the aeration step to contain the rise in level of the contents of the enclosure. The channel 202 has two ends (visible in Figure 4): a first end 221 and a second end 222 in direct contact with the return duct 201, allowing the flow between the return duct 201 and the channel 202. The channel 202 can have any section: circular, rectangular, polygonal, etc., as can the return duct 201 .

The aeration step 105 causes a variation in the level of the contents of the enclosure due to the injection of air into the enclosure. During the aeration step 105, the channel (or channels) 202 fills at least partially with the contents of the enclosure. This is the particular case of step 121, for a method in which the injection of air into the return duct is not continuous. The filling height of the channels 202 corresponds to the elevation height of the contents of the enclosure. As the channels 202 are sized to be high enough to respond to the particular case of step 121, the content 12 does not reach the second end 222 of the channels 202. The return duct 201 remains filled with 'air. During step 105 of aeration, the content of the enclosure is homogeneous, even at the level of the surface 24. Thanks to the channels 202, this homogeneous content containing sludge does not enter the return duct 201 . The channels 202 form a transition zone between the return duct blocked in air and the contents of the enclosure. The ends 221 of the channels 202 can be in contact with water and sludge. The ends 222 of the channels 202 are never in contact with sludge. So, he is guaranteed that the return duct, depending on the phase, contains either air or treated water, but never sludge.

The return duct 201 is kept filled with air during the reaction sequence 102 and preferably the settling step 106, and optionally the waiting phase 116. This is step 122bis. At the end of settling, the sludge present in the enclosure is deposited at the bottom of the enclosure 11 and the contents of the enclosure 11 clarifies near its surface 24. The method then comprises a step 123 of expulsion of Air from the return duct 201. The valve 205 is in the open position and clarified water enters the return duct and allows the air blocked in the return duct to be expelled by the valve 205 and by the update duct. the atmosphere. Air is no longer blocked in the return duct.

Subsequently, the air/water blocking device 216 goes into the so-called open position and a new cycle begins: the supply step 101 takes place simultaneously with the recovery step 107. By introducing a volume of effluent into the enclosure, the same volume is drained in order to maintain a substantially constant level. As the return duct is no longer blocked in air, the return duct 201 and the channels 202 are filled with this volume of the contents 12 of the enclosure 11 located at the level of the surface 24. This is the fraction clarified that one wishes to resume.

[0135] Controlling the air filling of the return duct (step 120) and the blocking of air in the return duct (step 122bis, possibly supplemented by step 122 if the injection of air does not is not continuous) results in precise control of when content is fed into the resume path. The return duct is accessible to the contents of the enclosure when the contents of the enclosure are clarified at its surface. On the other hand, during the aeration stage where the content is homogeneous, that is to say when the content of the enclosure is not clarified at the level of the return duct, the return duct is not accessible to this content. In other words, the method according to the invention makes it possible to precisely control what enters the return duct. Depending on the steps in the treatment of waste water, there is a succession of air blockage phases of the return pipe and free hydraulic connection phases during which the contents of the enclosure can circulate in the return pipe. [0136] As a result, this variant is based on a step for controlling the recovery means of the SBR enclosure during which, just before the commissioning of the ventilation in the SBR, the recovery duct is filled of air until the pipe is completely emptied of the (clarified) water contained in the pipe. This variant of the invention guarantees non-contamination of the treated water return conduit by activated sludge during aeration thanks to controlled air filling of the return conduit according to the steps of the treatment process.

It will more generally appear to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching which has just been disclosed to them. In the following claims, the terms used should not be interpreted as limiting the claims to the embodiments set out in the present description, but should be interpreted to include all the equivalents which the claims are intended to cover by virtue of their formulation and the prediction of which is within the reach of those skilled in the art based on their general knowledge.

Claims

35 CLAIMS

1. Process for treating a waste water effluent (20) comprising carbon pollution, nitrogen pollution and phosphorus pollution, in a sequenced batch reactor (SBR 10), said SBR (10) comprising:

- an enclosure (11) capable of containing a waste water-sludge mixture (12) comprising different levels, each level being defined by a concentration and/or a density of sludge,

- a bed of sludge (13), comprising PAO (14), located at the bottom of the enclosure (11), above which is defined a level of veil of mud (15),

- means (16) for determining a minimum level (17) and a maximum level (18) of sludge extraction in the enclosure (11),

- extraction means (19) capable of extracting sludge (23) at variable levels between the minimum extraction level (17) and the maximum extraction level (18), said method comprising:

- a step (101) of supplying the SBR (10), during which a volume of effluent to be treated (20) is introduced near the bottom of the enclosure (11), into the bed of sludge (13) , preferably by a distribution network (21) covering the bottom of the enclosure (11),

- a reaction sequence (102) comprising: o at least a first anaerobic stage (103), during which the PAOs (14) capture the carbonaceous pollution and release phosphorus compounds, o optionally, a second stage (104), in anoxia , denitrification (partial and/or total), this step being implemented only in the event of a NOx concentration greater than a predetermined threshold, o a third step (105) of aeration, making it possible to carry out the dephosphatation of the effluent by the PAOs (14), the aeration being controlled so as to simultaneously carry out either nitrification (partial or total), or nitritation (partial or total), 36

- a settling step (106), during which sludge settles at the bottom of the enclosure (1 1 ) and the contents of the enclosure (1 1 ) clarifies near its surface (24),

- a recovery step (107), during which a clarified fraction (22) of the contents of the enclosure is evacuated, said recovery (107) and supply (101) steps taking place simultaneously, so as to maintain the level of the contents of the enclosure (1 1 ) substantially constant during the recovery (107) and supply (101) steps, and

- a step (108) for extracting at least part of the light sludge (23) having a sludge index greater than 100 mL/g and a settling speed less than 2 m/h at a predefined level between the level minimum extraction level (17) and the maximum extraction level (18), preferably close to the veil of mud (15).

2. Treatment method according to claim 1, further comprising a step (109) of measuring the veil of sludge (15), and in which the step (108) of extracting at least a part of the light sludge is performed when the measurement of the sludge blanket (15) is substantially equal to a predefined distance from the sludge extraction level.

3. A method of treatment according to any one of claims 1 or 2, wherein the step (108) of extracting at least a portion of the light sludge is carried out during the step (101) of feeding and / or during the settling step (106).

4. A method of treatment according to any one of claims 1 to 3, comprising, during the reaction sequence (102), a step (1 10) of injecting air into the enclosure (1 1).

5. A method of treatment according to any one of claims 1 to 4, wherein the third step (105) of aeration is followed by a step (1 1 1), in anoxia, of post-denitrification, preferably put in works when the third step (105) is a step of total or partial nitrification; or the third step (105) of aeration is followed by a step (1 1 1 ), in anoxia, of denitritation, preferably implemented when the third step (105) is a step of total or partial nitritation; or the third aeration step (105) is followed by a step (1 1 1 ), in anoxia, deammonification, preferably implemented when the third step (105) is a partial nitritation step.

6. A method of treatment according to any one of claims 1 to 5, wherein the step (106) of settling is preceded by a step (112) of injecting air into the enclosure (11).

7. Treatment method according to any one of claims 1 to 6, comprising a step (113) of densification of the sludge by a densification device (30) inside the enclosure (11).

8. Treatment method according to any one of claims 1 to 7, further comprising a step (114) of controlling the duration of the third aeration step (105) as a function of the level of carbonaceous, nitrogenous and phosphorus from waste water effluent (20).