Method for treating wastewater by consolidating sludge in a batch activated sludge reactor

Abstract

The present invention relates to a method for treating wastewater (20) containing carbon contaminants, nitrogen contaminants, and phosphorus contaminants in a sequencing batch activated sludge reactor (SBR), the SBR comprising: a chamber capable of accommodating a wastewater-sludge mixture having various boundary surfaces; a sludge bed containing PAOs at the bottom of the chamber and defining a sludge boundary surface above it; - means for identifying a minimum and a maximum boundary surface for extracting sludge in the chamber; - extraction means capable of extracting sludge at various interfaces between the minimum extraction interface and the maximum extraction interface; Including, The method comprises: - a step (101) of feeding the SBR, during which the amount of wastewater (20) to be treated is introduced into a sludge bed near the bottom of the chamber (101); a reaction sequence (102) At a minimum, there is an initial anaerobic step in which PAOs capture carbon contaminants and release phosphorus compounds (103); Optionally, a second step of denitrification under anoxic conditions (104), a third aeration step (105) in which dephosphorization of the wastewater by PAOs is carried out; a reaction sequence (102) comprising: a settling step (106) in which the sludge accumulates at the bottom of the chamber and the contents of the chamber clear near its surface; a recovery step (107) in which a clarified fraction is withdrawn from the contents of the chamber, said recovery step (107) and the supply step (101) being carried out simultaneously; - extracting (108) at least a portion of the light sludge at a predetermined interface; Includes:

Description

[Technical Field]

[0001] The present invention relates to the technical field of biological treatment of municipal and industrial wastewater, and more particularly to a technology known as sequencing batch reactor (SBR). [Background technology]

[0002] SBRs perform various treatment steps in a batchwise manner, in particular a settling phase that allows "activated" sludge to be separated from the treated water.

[0003] The so-called "activated sludge" method uses biological purification for wastewater treatment. It is a purification method using suspended cultures of bacteria. Its principle involves the bacterial decomposition of suspended or dissolved organic matter in wastewater. A high level of biodegradation is achieved by homogenizing the medium and by good aeration, which allows the bacteria to reach the particles. Thus, during the settling phase, the sludge is deposited in a reactor.

[0004] The activated sludge process aims to remove carbon and nitrogen pollution, as well as to remove and recover phosphorus from phosphorus pollution. Therefore, a cell culture medium rich in heterotrophic cells is required to ensure the elimination of carbon pollution. However, bacterial growth requires the presence of nutrients, particularly nitrogen and phosphorus, present in wastewater, which must also be removed.

[0005] Nitrogen treatment generally involves nitrification followed by denitrification (N / DN) processes. Nitridation is an oxidation reaction using autotrophic bacteria, ammonia nitrogen, or ammonium, often referred to as N-NH4. -Nitrite, also known as nitrite, N-NO2, -Then nitrate nitrogen, also known as nitric acid, N-NO3 Use.

[0006] In a known manner, the bionitriding process involves the addition of ammonium ions (NH +) is oxidized to nitrite ions (NO2 - ), and then nitrate ions (NO3 - This step is usually carried out under aerobic conditions using autotrophic microorganisms capable of converting nitrite into nitrate. This step is usually carried out in two substeps: nitritation and nitrification: NH + 4⇒NO2 - ⇒NO3 -

[0007] Denitrification involves the reduction of nitrate produced during the nitrification reaction to gaseous nitrogen (also referred to as dinitrogen, N2) using denitrifying bacteria. Biological denitrification is typically carried out under anoxic conditions using heterotrophic microorganisms that can first reduce the nitrate produced during the process to nitrite, and then reduce the nitrite to gaseous nitrogen (N2).

[0008] More specifically, nitrification can be divided into two substeps: a first step of nitritation in the presence of oxygen, followed by a second step of nitrification, also in the presence of oxygen. Nitritization involves the oxidation of ammonium to nitrite using autotrophic nitrite bacteria, known as AOB, or "Ammonia Oxidizing Bacteria," primarily in the genus Nitrosomonas. Nitrification involves the oxidation of nitrite to nitrate using other autotrophic bacteria, known as NOB, or "Nitrite Oxidizing Bacteria," primarily in the genus Nitrobacter.

[0009] Denitrification can also be divided into two substeps: the denitrification step, which converts nitrates to nitrites, and the denitrification step, which converts these nitrites to gaseous nitrogen. Each of these two substeps is carried out using heterotrophic bacteria and requires large amounts of biodegradable carbon. In fact, denitrification requires approximately 2.9 kilograms of carbon in the form of 5-day biological oxygen demand (DBO5) to reduce one kilogram of N-NO3 to dinitrogen.

[0010] To reduce the amount of energy and carbon required to process nitrogen, other metabolic routes can be envisaged: nitritation-denitrification and partial nitritation-deammoni- onionization.

[0011] The nitritation-denitrification process, also known as the "nitrite shunt," aims to stop nitrogen oxidation at the nitrite stage and avoid nitrate production; therefore, it shunts the "nitrate portion" of the cycle. Therefore, for nitritation-denitrification to occur, NOB (nitrite-oxidizing bacteria) must be suppressed in favor of AOB (ammonia-oxidizing bacteria). Prior art studies have shown that this process can reduce oxygen demand by 25%, and only 1.7 kilograms of carbon in the form of DBO5 are required to reduce 1 kilogram of N-NO2 to dinitrogen for denitrification. This represents an approximately 40% reduction in carbon demand compared to conventional nitrification-denitrification processes.

[0012] As is known, nitritation is carried out under aerobic conditions by the addition of ammonium ions (NH4 + ) is oxidized to nitrite ions (NO2 - Denitrification is carried out using autotrophic microorganisms that can convert nitrite ions (NO2 - This is done using heterotrophic microorganisms that can reduce nitrate (N) to dinitrogen (N2).

[0013] Another method, called partial deammonification or nitritation / anammox (NP / A), utilizes the nitritation reaction described above, but then involves anaerobic autotrophic bacteria called anammox, or "ANaerobic AMMonium Oxidation," which consumes ammonium and nitrite to produce N2, without the need for oxygen or biodegradable carbon.

[0014] The first step in deammonification is partial nitritation (NP), which involves oxidizing a portion (57%) of the ammonium ions to nitrite. The second step is carried out by anammox anaerobic bacteria. This reaction converts approximately 11% of the nitrogen load to nitrate, increasing the theoretical maximum removal rate to 89%.

[0015] The same microbial community as that in N / DN, namely anaerobic oxidizing bacteria (AOB), is also involved in partial nitritation. In this case, (i) only a portion of the ammonium is oxidized, whereas 100% oxidation of NH4 is required in the N / DN process, and (ii) the target molecule is NO2, not NO3, resulting in a lower oxidation level. According to the prior art, the oxygen savings for this treatment route are approximately 50% compared to conventional nitritation and denitrification processes.

[0016] Furthermore, because AOB and anammox bacteria are autotrophs, the entire NP / A process does not require any biodegradable carbon. No external (i.e., exogenous) carbon needs to be added to perform the nitrogen treatment. Therefore, the treatment cannot remove any carbon that may be present.

[0017] As is known, partial nitritation treatment is carried out under aerobic conditions to produce ammonium ions (NH4 + ) is oxidized to nitrite ions (NO2 - Anaerobic oxidation is carried out using autotrophic microorganisms that can convert nitrite ions (NO2 - ) (anammox bacteria) in the presence of ammonium ions (NH4 + This is done using autotrophic microorganisms that can oxidize nitrous oxide (NOx) to dinitrogen (N2).

[0018] Biological phosphorus removal (i.e., treatment of phosphorus by biological routes) is achieved by sequentially performing treatment steps under anaerobic and aerobic conditions. In fact, certain bacteria called polyphosphate-accumulating bacteria (PAOs) have unique characteristics that allow them to overaccumulate phosphorus when exposed to alternating anaerobic and aerobic conditions. PAOs release phosphate under anaerobic conditions, and when subsequently transferred to aerobic conditions, they accumulate a greater amount of phosphate than that released under anaerobic conditions.

[0019] As a result, the concentration of phosphate in the chamber of the SBR can be controlled by the intervention of phosphorus-rich PAOs by adjusting the anaerobic / aerobic conditions of the chamber.

[0020] Regardless of the treatment method used, SBR technology is limited in terms of its size by the settleability of the sludge. In fact, one of the factors that limits the activated sludge concentration of an SBR, which itself represents its capacity to treat a pollution load, is the settleability of the sludge, which is commonly expressed using the Mohlman index. The Mohlman index is an index of the settleability of the sludge. This index defines the amount of activated sludge that settles in 30 minutes, relative to the mass of dry residue of this sludge (or the concentration of suspended solids, also indicated as MES); the lower this index, the higher the settleability of the sludge.

[0021] As the sludge density increases, the settling phase proceeds more rapidly and the overall duration of the treatment cycle decreases, thereby increasing the same-day pollution throughput by running more cycles.

[0022] Generally, denser sludge means that you can work at a higher concentration while still achieving good settling properties (index), and therefore more pollution can be treated with the same amount of work.

[0023] The first reactor design, called the Sequencing Batch Reactor (SBR), uses two different volumes, which are alternately used for reaction and decantation, with water being transported from the reaction compartment to the decantation compartment (Seghers Unitank design). However, this type of SBR has been improved, and most SBR biological reactors are now designed with a single volume, in which the various steps of treatment occur continuously. These reactors are generally variable level reactors, i.e., the raw water feed phase and the treated water recovery phase are separated in time, so that the liquid level in the reactor drops as treated water is withdrawn.

[0024] "Constant level" SBRs are also known, which allow the duration of each treatment sequence to be reduced while still maintaining the effectiveness of the treatment. Such reactors are described, for example, in document WO 2016 / 020805.

[0025] In an SBR reactor, the most settleable, i.e., heaviest, sludge is generally found at the bottom of the sludge bed. However, during each cycle, it is this sludge that is extracted at the end of the settling period, which tends to select for the lightest, least settleable sludge.

[0026] The SBR system described in WO 2004 / 024638 aims to overcome this problem. It involves a constant liquid level SBR method, which achieves aerobic granular sludge, the particular feature of which is its very fast settling (settling velocity of more than 10 m / h). However, generating fines in municipal wastewater, i.e. low concentrations of pollutants (carbon, nitrogen, phosphorus), takes time, and its stability in response to influent load and temperature changes has not been proven so far.

[0027] International application WO 2019 / 053114 proposes to further improve the SBR method described in WO 2004 / 024638 by proposing an SBR that allows the use of means to identify the minimum and maximum boundaries of sludge extraction within the SBR chamber, for selective extraction of granular sludge exhibiting the best settling properties.

[0028] Therefore, there is a need for a more competitive, i.e., more powerful, method for treating activated sludge using an SBR that is operable for all types of sludge, including non-fines. Moreover, the method of the present invention advantageously treats wastewater volumes equivalent to or even greater than those of prior art methods, while requiring a limited footprint. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] International Publication No. 2016 / 020805 Brochure [Patent Document 2] International Publication No. 2004 / 024638 Pamphlet [Patent Document 3] International Publication No. 2019 / 053114 Brochure Summary of the Invention [Problem to be solved by the invention]

[0030] The present invention aims to overcome all or some of the above problems by proposing a method called "sludge consolidation", which makes it possible to achieve high settling rates regardless of the nature of the sludge (granular or not), and advantageously also with non-granular sludge. The sludge is consolidated in a constant level SBR by optimizing the production of microorganisms that are prone to settling, which is due to a combination of several factors: -Supply through sludge beds, - the order of sequences carried out in wastewater treatment that allows the generation of specific microbial populations, especially PAOs (phosphate-accumulating bacteria), that exhibit good settling properties; and - Sludge extraction strategy by extracting the least settleable sludge in each cycle, allowing the sludge with the best settleability to remain in the reactor. [Means for solving the problem]

[0031] To this end, the object of the present invention is a method for treating wastewater containing carbon contaminants, nitrogen contaminants, and phosphorus contaminants in a sequencing batch activated sludge reactor (SBR), said SBR comprising: a chamber capable of accommodating a wastewater-sludge mixture having various boundaries, each boundary being defined by a sludge concentration and / or density; a sludge bed containing PAOs at the bottom of the chamber and defining a sludge boundary surface above it; - means for identifying a minimum and a maximum boundary surface for extracting sludge in the chamber; - extraction means capable of extracting sludge at various interfaces between the minimum extraction interface and the maximum extraction interface; Including, The method comprises: - feeding the SBR, during which the amount of wastewater to be treated is introduced into a sludge bed near the bottom of the chamber, preferably through a distributor network covering the bottom of the chamber; a reaction sequence, At a minimum, there is an initial anaerobic step in which the PAOs capture carbon contaminants and release phosphorus compounds; Optionally, a second step of (partial and / or complete) denitrification under anoxic conditions, which is carried out only if the NOx concentration is higher than a predetermined threshold value; a third aeration step in which dephosphorization of the wastewater by PAOs is carried out, the aeration being controlled so as to simultaneously carry out either (partial or complete) nitration or (partial or complete) nitritation; a reaction sequence comprising: a settling step in which the sludge accumulates at the bottom of the chamber and the contents of the chamber clear near its surface; a collection step in which clarified liquid is withdrawn from the contents of the chamber, said collection and dispensing steps being carried out simultaneously so that the liquid level of the contents of the chamber is kept substantially constant during the collection and dispensing steps;

[0032] and extracting at least a portion of the light sludge at a predetermined interface between the minimum extraction interface and the maximum extraction interface, preferably near the sludge blanket. According to one particular embodiment, the method of the invention comprises the steps described above and, if applicable, one or more optional steps described below.

[0033] Advantageously, the treatment method according to the invention further comprises a step of measuring the sludge blanket, and the step of extracting at least a portion of the light sludge is carried out when the measured value of the sludge blanket is substantially equal to a predetermined distance from the sludge extraction interface.

[0034] Advantageously, the step of extracting at least a portion of the light sludge is carried out during the feeding step and / or during the settling step.

[0035] Advantageously, the treatment method according to the invention comprises the step of injecting air into the chamber during the reaction sequence.

[0036] Advantageously, the third aeration step is followed by a post-denitrification step under anoxic conditions, preferably carried out when the third step is a full or partial nitritation step, or by a denitrification step under anoxic conditions, preferably carried out when the third step is a full or partial nitritation step, or by a deammoniation step under anoxic conditions, preferably carried out when the third step is a partial nitritation step.

[0037] Advantageously, the settling step is preceded by a step of injecting air into the chamber.

[0038] Advantageously, the treatment method according to the invention includes the step of compacting the sludge using a compaction device in a chamber.

[0039] Advantageously, the treatment method according to the invention comprises a step of controlling the duration of the third aeration step depending on the pollutant (particularly carbon, nitrogen and phosphorus pollutant) interface of the wastewater.

[0040] "Granular sludge" is characterized by a settling velocity greater than 10 m / h and a sludge index ("sludge volume index", measured according to standard NF EN 14702-1 of July 2006) lower than 35 mL / g (as described in particular on page 3 of WO 2004 / 024638). Sludge that does not simultaneously meet these two conditions is not considered granular sludge. For example, non-granular sludge is sludge with a settling velocity of 10 m / h or less. Consequently, for granular sludge, the sludge index at 5 minutes is equal to the sludge index at 30 minutes.

[0041] "Consolidated sludge", also called gravimetric sludge, is characterized by a sludge index in the range of 35-100 mL / g, preferably 40-80 mL / g, more preferably 40-70 mL / g, and a settling velocity in the range of 2.0-9.0 m / h. It is also characterized by a mass ratio of 10%-50% (preferably 20%-40%) of particles with a particle size of 100 μm (up to 1,000 μm, preferably 200-500 μm) and a high mass ratio (50%-90%) of biological flocs with a particle size of less than 100 μm (advantageously less than 200 μm). This consolidated sludge also has a mass ratio of 8 kg MES.m -2 .h -1 Higher than or equal to, preferably 8.5 kg MES.m -2 .h -1 It can also be characterized by a critical mass flow rate criterion higher than or equal to that of the sludge. It is a mixture of solids, liquids, and microorganisms, including phosphorus-rich polyphosphate-accumulating bacteria. This heavy sludge exhibits very good decantability.

[0042] "Lightweight sludge" is characterized by a sludge index greater than 100 mL / g and a settling velocity less than 2 m / h. It is also characterized by a mass fraction in the range of 15-50% of bioflocs with particle size less than 0.2 mm. This lightweight sludge is characterized by a mass fraction of 8 kg MES.m -2 .h -1 It can also be characterized by a critical mass flow criterion of less than 0.05. It is a mixture of solids, liquids, and microorganisms. This sludge contains little or no PAOs. This lightweight sludge is difficult to settle.

[0043] The "settling rate" is expressed in meters per hour (m / h). It can be determined from the Kinch curve, which is obtained by observing the decantation of a sample in a 1-liter test piece under gravity. It should be noted that, according to the July 2006 standard NF EN 14702-1, the Molhman Index (SVI, "Sludge Volume Index") or Sludge Index (raw sludge dilution, DSVI (diluted SVI)) is obtained from the Kinch curve value at 30 minutes. In pilot-scale or industrial reactors, the settling rate can be estimated from the change in the height of the settling blanket over time during the non-aerated sequence. The height of the sludge blanket can be measured continuously, for example with an ultrasonic probe. Alternatively, it can be measured intermittently, allowing manual sampling at predetermined intervals at various interfaces throughout the height of the reactor.

[0044] "Critical mass flow rate" is kg.m -2 h -1 It characterizes the amount of settled suspended solids (MES) per unit area and time and measures the droplet velocity that the sludge can have at a certain concentration. This critical mass flow rate is determined from the Kinch curve by successively diluting or concentrating the raw sludge multiple times.

[0045] The "biofloc ratio" is expressed as the % of the sludge weight that is associated with a certain size, e.g., the percentage less than 0.2 mm. This value can be obtained by screening a sludge sample through sieves of various mesh sizes (e.g., 200 μm / 400 μm / 500 μm / 800 μm / 1 mm / 1.25 mm). The MES (suspended solids) concentration of the resulting filtrate is then measured and added to the MES concentration (%) of the raw sludge.

[0046] The "biofloc size" corresponds to particle size, specifically the maximum particle size, which can be determined using statistical analysis based on micrographs.

[0047] Advantageously, the method of the present invention does not include the step of recirculating light sludge in a sequencing batch activated sludge reactor.

[0048] The invention will be better understood and further advantages will become apparent on reading the detailed description of embodiments given as examples, this description being illustrated by the accompanying drawings, in which: [Brief explanation of the drawings]

[0049] [Figure 1] 1 shows a schematic diagram of an example of a batch activated sludge reactor suitable for carrying out the treatment method of the present invention. [Figure 2] 1 shows a flow chart of the steps of a wastewater treatment method according to the present invention. [Figure 3] 1 shows a schematic diagram of the steps of a wastewater treatment method according to the present invention. [Figure 4] 1 shows a schematic diagram of a sequencing batch activated sludge reactor implemented in accordance with the method of the present invention. [Figure 5] 1 shows the selection of bacterial populations according to a reaction sequence using measurements carried out during the treatment method according to the invention. [Figure 6] 1 shows a schematic representation of the chamber and collection means of an SBR during the feeding and collection steps. [Figure 7] 1 shows a schematic of the chamber and collection means of the SBR during the settling step. DETAILED DESCRIPTION OF THE INVENTION

[0050] The drawings are not drawn to scale for clarity, and the same reference numbers are used for the same elements in different drawings.

[0051] FIG. 1 shows a schematic diagram of an exemplary sequencing batch activated sludge reactor suitable for carrying out the treatment method of the present invention. The method of the present invention is directed to treating wastewater 20 containing carbon, nitrogen, and phosphorus contaminants in a sequencing batch activated sludge reactor (SBR) 10. The SBR 10 includes a chamber 11 capable of containing a wastewater-sludge mixture 12 having various boundaries, each boundary defined by a sludge concentration and / or density. Each height within the chamber 11 corresponds to a sludge concentration and / or density of the contents 12. For example, several boundaries can be defined, designated N1, N2, N3, N4, N5, and N6. Each boundary can have a different sludge concentration and / or density than the other boundaries, or several boundaries can have the same sludge concentration and / or density. Finally, during a phase of the treatment method, as described in more detail below, all boundaries within the assembly have the same sludge concentration and / or density. The chamber 11 is advantageously supplied with the waste liquid 20 to be treated, preferably via a distributor mesh 21 which covers the bottom of the chamber, and with air 8, preferably via a distributor mesh 27 which covers the bottom of the chamber.

[0052] SBR 10 includes a sludge bed 13, shown schematically, containing PAOs 14, at the bottom of chamber 11, above which a sludge blanket boundary surface 15 is defined. SBR 10 includes means 16 for identifying a minimum boundary surface 17 and a maximum boundary surface 18 for extracting sludge within chamber 11. These boundaries are shown schematically in Figure 1, and their identification will be discussed below.

[0053] When wastewater is treated, the chamber 11 contains a wastewater-sludge mixture 12. As the sludge settles, treated water is in the upper part of the chamber of the reactor. This water can be withdrawn through an opening below the level of the surface 24 of the chamber 11 by means of a sampling system 200, which can remove the clarified fraction and which can include or consist of a submerged tube through which the water can be withdrawn and out of the chamber (arrow A). Other alternative embodiments of the recovery means are described below.

[0054] The heaviest and / or densest sludge particles are found at the bottom of chamber 11 and can be withdrawn from the bottom wall of the chamber. The remainder of the mixture is between these two and is in the form of layers, i.e., having a plurality of interfaces N1, N2, N3, N4, N5, N6, ..., each interface defined by a sludge concentration and / or density within the mixture 12.

[0055] The sludge blanket 15 is the boundary surface from which the sludge is present. It is defined by the height between the surface 24 of the chamber contents and the part of the assembly where the sludge is present. The boundary surface of the sludge blanket 15 can be determined, preferably continuously, by the determination means 16. Alternatively, it can be measured manually using a Secchi plate. The sludge blanket can be measured continuously. However, during the homogenization phase, it is meaningless to measure it, since the contents of the chamber are mixed and the sludge present has not yet settled.

[0056] The reactor 10 according to the present invention allows selective extraction of the sludge found in the mixture 12 which is the least likely to settle.

[0057] The SBR 10 comprises extraction means 19 (shown diagrammatically for ease of understanding), which are able to extract sludge 23 at various interfaces between the minimum extraction interface 17 and the maximum extraction interface 18 (arrow B). For example, but without limitation, the extraction means 19 may comprise an extractor 191, which comprises at least a first part having at least one opening 191a in the chamber 11 and a second part 191b able to extract sludge outside said chamber. The extraction means 19 may comprise modification means 192 able to vary the position of the opening 191a of said extractor 191, in particular the height of said opening between the minimum extraction interface 17 and the maximum extraction interface 18. The extractor 191 advantageously comprises a (suction) pump or a gravity valve (not shown) for extracting the sludge. Advantageously, the extractor 191 may comprise a set of tubes arranged at different heights in the chamber 11, each tube having a first end opening into the chamber 11 and a second end connected to the second part 191b of the extractor 191, the modifying means 192 comprising a set of valves capable of opening and closing said tubes. The extracting means can therefore extract sludge at one or more variable interfaces. For better clarity of the illustration, the extracting means 19 is shown on the left side of the SBR, while the second part 191b for drawing off the sludge is connected to the extracted sludge 23.

[0058] The means 16 for identifying the minimum and maximum interfaces 17 and 18 for extracting the sludge 23 in the chamber 11 can include a measuring means 161 capable of measuring the concentrations at various interfaces of the wastewater-sludge mixture. For example, a sludge blanket probe can measure the surface of the sludge bed. An MES (suspended solids) probe can measure the concentration of the sludge. Several probes can be positioned throughout the height of the chamber to measure the concentration of suspended solids at various interfaces. These measurements are used to identify the interfaces 17, 18. The means 16 can include a selecting means 162 capable of selecting a maximum and a minimum sludge concentration value. The selection can be made by an operator or based on a calculation related to the sludge age. The means 16 can include an estimating means 163 capable of estimating the minimum extraction interface corresponding to the selected maximum concentration value and the maximum extraction interface corresponding to the selected minimum concentration value.

[0059] The measuring means 161 can include, for example, one or more measuring probes, in particular concentration probes, which allow the concentration of sludge in the mixture to be measured. The measuring probe 161 is immersed in the mixture as shown. This can be a fixed or variable immersion depth depending on the type of probe selected. Alternatively, as mentioned above, there can be several measuring probes across the height of the chamber. The measuring probes 161 are connected to selection means 162, which make it possible to check whether the measurement result corresponds to the sludge to be extracted, and to estimation means 163, which make it possible to associate the measurement with the corresponding interface. These identification means 16 are connected to the sludge extraction means 19, more particularly to means 192 for varying the extraction interface, mainly to select the extraction interface. The varying means 192 can vary the height of the opening 191a of the extractor 191, or selectively extract at a constant extraction interface and at variable times depending on changes in the contents, for example during settling, waiting, feed / recovery steps, during the anaerobic step, depending on sludge blanket measurements, or even non-selectively during the aeration step.

[0060] For example, but not by way of limitation, the measuring means 161 of the identifying means 16 may include an ultrasonic sensor immersed below the surface of the wastewater-sludge mixture. The ultrasonic sensor may cause ultrasonic waves to be transmitted into the mixture (thus acting as a transmitter) and then received again (thus acting as a receiver) after traveling a distance within the wastewater-sludge mixture. The sensor is connected to the selecting means 162 and the estimating means 163.

[0061] Figure 2 shows a flow chart of the steps of a method for treating wastewater according to the present invention. The treatment method according to the present invention comprises: a step 101 of feeding the SBR 10, during which the amount of wastewater 20 to be treated is introduced into the sludge bed 13 near the bottom of the chamber 11, preferably through a distributor mesh 21 covering the bottom of the chamber 11, so that the wastewater to be treated mixes with the sludge in the sludge bed; a reaction sequence 102, at least a first anaerobic step 103 in which the PAOs 14 capture carbon contaminants and release phosphorus compounds; an optional second step 104 of (pre-) denitrification under anoxic conditions, advantageously carried out when the concentration of NOx is higher than a predetermined threshold; a third aeration step 105 in which dephosphorization of the wastewater by PAOs 14 is carried out and the aeration is controlled so as to simultaneously carry out either (partial or complete) nitration or (partial or complete) nitritation; a reaction sequence 102 comprising: a settling step 106 during which the sludge settles at the bottom of the chamber 11 and the contents of the chamber 11 become clear near its surface 24; a recovery step 107 in which clarified liquid 22 is withdrawn from the contents of the chamber, said recovery step 107 and said supply step 101 being carried out simultaneously so that the liquid level of the contents of the chamber 11 remains substantially constant during the recovery step 107 and the supply step 101; and Step 108 of extracting at least a portion of the light sludge 23 at a predetermined interface between the minimum extraction interface 17 and the maximum extraction interface 18, preferably in the vicinity of the sludge blanket 15. Includes:

[0062] Typically, feeding step 101 is performed under anaerobic or even anoxic conditions. In this latter case, anoxic step 101 allows for denitrification or denitrification. Anaerobic step 103 is performed under anaerobic conditions, and aeration step 105 is performed under aerobic conditions. Preferably, settling step 106 is performed at least partially under anoxic conditions.

[0063] The second step 104 may involve a step 117 of measuring the NOx concentration in the chamber.

[0064] The treatment method according to the invention can also optionally include a fourth anaerobic denitrification or denitrification or deammoniation step 111. More specifically, three basic alternative embodiments are envisaged: according to a first alternative embodiment, this third step 105 includes full or partial nitritation and the anaerobic step 111 includes denitrification (post-denitrification); according to a second alternative embodiment, the third step 105 includes full or partial nitritation and the anaerobic step 111 includes denitrification (post-denitrification); and finally, according to a third alternative embodiment, the third step 105 includes partial nitritation and the anaerobic step 111 includes deammoniation (a method known as "anammox"). The fourth step 111 can be associated with a step 117bis of measuring the NOx concentration in the chamber.

[0065] The feeding through sludge bed step 101 allows sludge to come into contact with the raw water to be treated. A volume of wastewater 20 to be treated is introduced through the sludge bed where the PAOs reside. In this way, the particulate and soluble fractions of the introduced volume are accessible to the bacteria. The anaerobic condition step 103 allows the PAOs to capture carbonaceous contaminants and release phosphate compounds. The aeration step 105 allows the PAOs to dephosphorize the chamber contents. The reaction sequence 102 contributes to the development of PAOs that exhibit good settling properties. During the settling step 106, the sludge settles to the bottom of the chamber by gravity. Heavy sludge and PAOs settle more quickly than light sludge. They are added to the sludge bed. Light sludge does not settle as well; it remains suspended above the sludge bed in the chamber contents for a longer period of time.

[0066] Extracting at least a portion of the light sludge (step 108) allows the least settleable sludge to be extracted periodically, or at least at predetermined times, e.g., during each cycle. However, extraction does not necessarily occur during each cycle, depending on operational constraints. For example, extraction may not occur on weekends. As a result, only sludge exhibiting good settleability remains in the SBR chamber. In addition to treating contaminants present in the incoming wastewater, the combination of the operation of the PAOs, which produce denser sludge, and the operation of the light sludge extraction, consolidates the sludge present in the chamber. As a result, the method of the present invention, referred to as a sludge consolidation method, can achieve high sludge settling rates regardless of the nature of the sludge present in the SBR chamber.

[0067] If the reaction sequence 102 includes a second step 104, it may include a step 110 of injecting air into the chamber 11. Injecting air into the chamber before step 104 allows the biomass to suspend and mix better with the oxidized nitrogen-rich supernatant (nitrate NO3 and nitrite NO2), thereby improving the efficiency of denitrification in the feeding step 104 and also the efficiency of the first anaerobic condition step 103. It should be noted that this step 110 is optional if the optional second step 104 is performed in response to the NOx concentration measurement results.

[0068] The settling step 106 can be preceded by a step 112 of injecting air into the chamber 11. Injecting air into the chamber before the settling step homogenizes the contents of the chamber and exposes the sludge to oxidized nitrogen species. Additionally, the injection of air also allows for the degassing of dinitrogen present in the reactor contents.

[0069] Furthermore, the treatment method according to the invention can include a step 113 of compacting the sludge using a compaction device 30 inside or outside, preferably inside, the chamber 11. The compaction device 30 can be a screen of suitable size downstream or upstream of the sludge extraction means, in order to retain the largest flocs and therefore improve the selection of the particles most susceptible to settling, i.e., their retention in the chamber. Alternatively, or in addition, the step of compacting the sludge can include adding ballast (such as zeolite).

[0070] Advantageously, the treatment method according to the invention can be adapted to the level of contamination of the wastewater 20, in particular the NH4 and / or NO2 of the contents of the chamber. - and / or NO3 - The method includes a step 114 of controlling the duration of the third aeration step 105 in response to the concentration of the contaminant in the raw water. More specifically, the contaminant in the raw water is indirectly measured immediately after the contents of the chamber have been aerated at least once.

[0071] 3 shows a schematic representation of the steps of the wastewater treatment method according to the invention. During step 101 of feeding the SBR with wastewater to be treated and step 107 of withdrawing the clarified fraction of the chamber contents, the chamber is filled with wastewater 20, forming a mixture 12, and the contaminants are subjected to biological treatment. During this phase, wastewater is introduced into the chamber. The liquid level in the chamber is kept constant, for example by opening the treated water valve (clarified fraction). In other words, treated water is withdrawn at the same time as raw water (wastewater) is fed. The flow rate of the treated water is always the same as the feed flow rate.

[0072] At this stage, denitrification (exogenous denitrification under anoxic conditions at the bottom of the sludge bed and endogenous denitrification under anoxic conditions at the top of the chamber) and biological phosphorus removal processes begin. The biological treatment of the wastewater primarily occurs during reaction sequence 102: During the aeration step 105, carbon is removed and ammoniacal nitrogen is nitrified, phosphorus is released during the anaerobic step 103 and reabsorbed during the aeration step 105; -Denitrification takes place during a specific anoxic period. If the settling and feeding times are insufficient, there is a pre-denitrification period (exogenous denitrification under anoxic conditions) and / or a post-denitrification period (exogenous denitrification).

[0073] Next, a settling step 106 is performed. During this step, the treated water is separated from the sludge by static settling only. Some biological activity occurs when the liquid contacts the sludge layer, resulting in endogenous denitrification. During this step, the chamber feeding step 101 and chamber withdrawal step 107 cannot be performed. The chamber contents are allowed to settle, allowing the sludge to settle. At the end of the settling step 106, sludge exhibiting good settling properties (heavy sludge) is found at the bottom of the chamber, while sludge with poor settling properties (light sludge) is suspended in the chamber contents, between the bottom of the chamber and the sludge blanket. The clarified fraction is located in the upper part of the chamber, near its surface 24. At the end of the settling step 106, excess biological sludge can be extracted to preserve the age of the sludge required for nitrification and / or nitritation, depending on the temperature, which can be measured during the temperature measurement step 118. Alternatively, excess biological sludge can be selectively extracted during settling step 106, and / or during feeding step 101 and recovery step 107, and / or during anaerobic step 103 and / or waiting step 116. Sludge can also be non-selectively extracted during aeration step 105.

[0074] The step 108 of extracting at least a portion of the light sludge 23 is carried out at a predetermined interface between the minimum extraction interface 17 and the maximum extraction interface 18, preferably near the sludge blanket 15. In fact, the light sludge is located at the interface of the sludge blanket. The predetermined interface for the extraction of the light sludge is not necessarily a constant interface over time. This interface may vary depending on the biological treatment and on the flow rate of the wastewater introduced into the chamber of the SBR. The extraction means 19 allows extraction at any interface. The light sludge can thus be extracted at various interfaces during the cycle of the treatment method. From a practical point of view, several fixed extraction interfaces, for example three, can be defined. Furthermore, it is possible to select which of the three interfaces is used for extraction depending on the results of measurements of the sludge concentration and / or density at various interfaces of the wastewater-sludge mixture in the chamber and / or on the results of measurements of the sludge blanket. For this purpose, the method according to the invention may include a step 109 of measuring the sludge blanket 15, and the step 108 of extracting at least a portion of the light sludge is carried out when the measurement result of the sludge blanket 15 is substantially equal to a predetermined distance from the extraction interface of the sludge.

[0075] Since the sludge bed interface changes over time, the sludge extraction interface is advantageously set between two interfaces in the chamber height, between the bottom and mid-height for heavy sludge, or throughout the chamber height for light sludge. For example, the extraction interface can be located 50 cm above the chamber bottom to remove excess old sludge (which may be mineralized), and other extraction points can be located throughout the chamber height. In Figure 3, the bold arrows indicate open inlets / outlets, which can channel the corresponding flows depending on the phase of the method.

[0076] FIG. 4 shows a schematic diagram of a batch activated sludge reactor 10 implemented in accordance with the present invention. The various phases described above occur within the same chamber and are separated in time. As a result, step 101 of feeding the chamber with wastewater is managed intermittently. However, to ensure continuous treatment of the wastewater, multiple chambers can be operated simultaneously, with alternating feeding. The principles of the present invention apply equally to multiple chambers.

[0077] During the feeding step 101, raw water is dispersed at the bottom of the chamber, for example through a network of perforated pipes 21. After the settling step 106, simultaneously with the feeding step 101, the supernatant clarified liquid is withdrawn from the upper part of the chamber, for example using a network of perforated collecting pipes. Particularly advantageous means for recovering the clarified fraction are described below.

[0078] Light sludge can be selectively extracted right at the sludge blanket interface during the settling step 106, and / or during the feeding step 101 and recovery step 107, and / or during the first anaerobic condition step 103, thereby removing the lightest sludge particles.

[0079] Non-selective sludge extraction (especially heavy but also light sludge) can also be envisaged when the contents 12 are homogenous during the aeration step 105 and / or during step 110 and / or during step 112.

[0080] 5A, 5B, 5C and 5D show the selection of bacterial populations according to a reaction sequence using measurement results, carried out during the treatment method according to the invention.

[0081] A strict anaerobic sequence followed by an aerobic sequence following the feeding of raw water (easily biodegradable carbon) through a sludge bed selects for phosphorus-removing bacteria (PAOs) that are able to accumulate phosphate in the form of intracellular polyphosphate granules.

[0082] Figure 5A shows the release of P-PO4 (anaerobic) and subsequent resorption during the aeration period (aerobic). The curve labeled 40 clearly demonstrates the behavior of bioremoval, with significant release of P-PO4 as soon as the reactor is placed under anaerobic conditions. A rise in the curve is observed, followed by a decline as soon as aeration is performed, corresponding to the resorption of the released P-PO4 and that provided by the raw water. This corresponds to the bioaccumulation of phosphorus.

[0083] Figure 5B shows nitrification (the decline of the NH curve and the rise of the NO curve), endogenous denitrification (the first part of the decline of the NO curve), and exogenous denitrification (the second part of the decline of the NO curve after feeding). The curves clearly show the advantage of exogenous denitrification for enhancing the denitrification reaction over endogenous denitrification, with a much steeper slope and therefore higher kinetics after feeding an easily biodegradable carbon-rich feed. In addition to this bacterial group, PAOs produce exopolymers, which naturally tend to compact the flocs. These dense flocs are not granular sludge, and the settling velocity of this sludge is 2-10 m / h, preferably 3-6 m / h, and its Mohlman index (i.e., sludge index) is approximately 65 mL / g. Granular sludge always has particles (or fines) larger than 200 micrometers, whereas in this case, the compacted sludge may contain a certain percentage of particles smaller than 200 micrometers.

[0084] To further increase the proportion of dense flocs in the sludge, the treatment method according to the invention applies a sludge extraction method that allows the removal of the lightest sludge, resulting in a faster settling rate, since only sludge with good settling properties remains in the chamber.

[0085] The method according to the invention may also include a waiting phase 116 associated with the feeding, settling or aeration step.

[0086] Considering that lighter sludge is found at the top of the sludge bed, particularly at the end of the settling step 106, and / or during the waiting step 116, and / or during the feeding step 101, and / or during the recovery step 107, and / or during the first anaerobic condition step 103 (the heaviest sludge having fallen to the bottom from the start of settling), the sludge is extracted at (or slightly below) the interface of the sludge blanket at the end of the settling step 106, and / or during the waiting step 116, and / or during the feeding step 101, and / or during the recovery step 107, and / or during the first anaerobic condition step 103.

[0087] The light sludge can also be extracted from the beginning of settling, but at a higher interface within the reactor. This extraction can also be carried out at any interface of the chamber at the end of aeration, since the contents are homogenous throughout the height of the chamber and therefore contain light sludge. It is also conceivable that the light sludge is extracted at the very beginning or during the feed stage, as the light sludge rises first, or during the anaerobic reaction sequence.

[0088] The method of the present invention is based on the combined selection of the extraction time of the light sludge and the height at which this extraction takes place. The selected height is also related to the age of the sludge that should be retained in the reactor by the duration and extraction flow rate. The target sludge age can be determined from measurements of the temperature of the water / sludge mixture in the reactor.

[0089] The treatment method according to the present invention can further include a step 109 of measuring the sludge blanket 15, and the step 108 of extracting at least a portion of the light sludge is performed when the measurement of the sludge blanket 15 is substantially equal to a predetermined distance from the sludge extraction boundary. The method of extracting light sludge is improved by measuring the sludge blanket and triggering the extraction of the light sludge at a certain interface when the sludge blanket interface is a predetermined distance from the sludge extraction boundary, regardless of whether this interface is reached during the settling step, the feeding step, or the anaerobic reaction sequence. This measurement, and optionally the temperature of the water / sludge mixture in the reaction vessel, can also take into account the instantaneous drop rate (or residue feed rate) and the duration required for extraction, preferably incorporating dynamic sludge age considerations, to complete its self-optimized extraction mode. By proceeding in this way, the sludge extraction can eliminate the lightest sludge slightly above the sludge blanket, more specifically in its upper part, in each sequence by appropriately calibrating the sludge blanket probe.

[0090] The method of the present invention takes into account the daily variations in flow rate that may occur in the chamber. At night, the feed flow rate is low, the difference between the feed rate and the settling rate is large, and the sludge blanket quickly approaches the extraction point. Conversely, during peak daily hydraulic activity, the difference between the feed rate and the settling rate is small, and the sludge blanket falls more slowly. By using the sludge blanket measurements to control the extraction time and its duration, adjusting the extraction time between cycles ensures that the lightest sludge is always extracted at a given interface.

[0091] By combining the reaction sequence and the feeding and recovery steps of the settling step with the step of extracting light sludge, it is possible to obtain sludge with a density higher than that of conventional activated sludge. As a result, sludge with a Mohlman index of 65 mL / g (+ / - 10 mL / g) can be obtained very stably at a settling velocity of more than 2 m / h but less than 10 m / h, approximately 3 m / h to 6 m / h. The method of the present invention is based on this combination, which allows the production of a compacted but non-granular sludge.

[0092] Figure 5C shows the stability of the sludge index at values ​​below 75 mL / g during pilot testing, demonstrating a compacted sludge with good settling properties. Results are shown for 91 days (horizontal axis).

[0093] The obvious advantage of this consolidation is that it allows two opposing flows, i.e. raw water supply and sludge settling, to be managed safely at the same time, with raw water supply rates higher than 2 m / h applied, while sludge is not drawn into the treated water.

[0094] Experiments with various feed rates (less than 4 m / h) showed that the settling rate decreased during feeding, but decantation continued during raw water feeding.

[0095] Figure 5D shows the sludge blanket at a feed rate of 17 m3 / h, or 2,266 m / h. The upper curve is the descending portion, during settling ( * The graph shows the decrease in sludge blanket during the phase indicated by (#) and the phase indicated by (#) which is the feed phase. The graph shows that the settling rate is much faster than the feed rate and the sludge blanket continues to decrease during the feed phase.

[0096] Although the duration of the various sequences in an SBR reactor is generally constant, the method according to the invention also allows, by fitting appropriate sensors and probes, to adjust the duration of the reaction sequences 102 in real time in order to take into account changes in pollutant concentration and water dynamic flow rate as a function of time (filling time) or to take into account the dilution of the wastewater associated with rainfall. Furthermore, a waiting phase allows for synchronization of the cycles.

[0097] In particular, by setting up an NH4 measurement in the reactor, which may or may not be supplemented by a measurement of NOx (especially NO2), its changes can be monitored during the aeration nitriding phase and stopped as soon as a predetermined value is reached.

[0098] The advantage is that the aeration period can be shortened when the water is diluted (night or rainfall water movement points). The shortened aeration period length also optimizes energy consumption and allows more cycles to be performed per day, thus treating more pollutants compared to operation with a constant aeration time. Conversely, during pollutant peaks, the duration of the aeration phase can be increased to allow the NH4 to be converted to the specified value at the filling point for longer than at low loads, thus ensuring performance capabilities at peak NH4 concentrations.

[0099] Finally, the treatment method according to the present invention can include step 117 of measuring the NOx concentration in the chamber, so that this value is low enough before proceeding to the feeding and recovery steps to allow phosphorus to be released by the phosphorus removal bacteria under anaerobic conditions, thus ensuring proper biological phosphorus removal. This measurement is then made at the end of step 106 or, preferably, at the end of step 105. If the measured NOx concentration is still too high, additional steps of treating the nitrogen can be carried out to reach the desired NOx concentration threshold.

[0100] The overall cycle duration and feed duration are generally fixed, allowing multiple chambers to be fed sequentially. The feed duration is also fixed, and the overall cycle duration is generally four times the feed duration. This means that the sum of the reaction sequence duration and the settling time is three times the feed duration. However, the method of the present invention is also applicable to variable cycle durations.

[0101] The method of the invention therefore offers great flexibility: in particular, the duration of the steps, in particular the settling step, the feed and recovery step and the anoxic step, can be adjusted depending on the hydrodynamic conditions and the load to be treated.

[0102] The present invention also relates to a facility for treating wastewater containing carbon, nitrogen, and phosphorus contaminants, the facility including a sequencing batch activated sludge reactor (SBR), the SBR comprising: a chamber capable of containing a wastewater-sludge mixture 12 comprising various boundaries, each boundary being defined by the concentration and / or density of the sludge; a sludge bed 13 at the bottom of the chamber, comprising PAOs 14, on which a sludge blanket interface 15 is defined; means 16 for determining a minimum boundary surface 17 and a maximum boundary surface 18 for extracting sludge in the chamber; extraction means 19 capable of extracting at least a portion of the light sludge 23 at a predetermined interface between a minimum extraction interface and a maximum extraction interface; - a device for feeding the SBR with the quantity of wastewater to be treated into a sludge bed near the bottom of the chamber, preferably through a distributor network covering the bottom of the chamber, preferably near the sludge blanket; a device for recovering a clarified fraction of the contents of the chamber; means for aerating the chamber; Includes:

[0103] The facility is arranged and equipped to carry out the aforementioned processing methods.

[0104] In the present invention, the term "recovery" is used synonymously with the term "discharge" and is intended to essentially refer to the discharge of treated water from the chamber.

[0105] Figure 6 shows a schematic representation of an embodiment of the chamber and recovery means of an SBR during the feeding and recovery steps, and Figure 7 shows a schematic representation of the chamber and recovery means of an SBR during the settling step. Throughout the remainder of the description, the term recovery / reuse shall be understood as evacuation / evacuate, drain / draining. Aeration of the contents of the chamber is preferably carried out with air 8 via a distributor net 27 covering the bottom of the chamber 11. In this embodiment of the invention, the means 200 for recovering the clarified fraction of the contents 12 of the chamber 11 comprises: a recovery duct 201 extending below the surface 24 of the contents 12 of the chamber 11 between the interior 25 and the exterior 26 of the chamber, at least one channel 202 hydraulically connecting the contents 12 of the chamber 11 with a collection duct 201; a collection hole 203 through which the clarified fraction of the contents 12 of the chamber 11 is released; an air duct 204 hydraulically or energetically connecting the recovery duct 201 to the atmosphere; a recovery duct 201 including an exhaust valve 205 on the air duct 204 that can be in an open or closed position, allowing the air blocking the recovery duct to be released to the atmosphere; an air / water blocking device 216 on the collection duct 201, which can be blocked by air upstream of the air / water blocking device 216 in the collection duct 201 and can be blocked by water downstream of the air / water blocking device 216; an air injector 207 connected to the recovery duct 201 and intended to supply pressurized and / or compressed air to the recovery duct 201;

[0106] The recovery means 200 may include an air injector 207 (advantageously including a check valve) connected between the exhaust valve 205 of the air duct 204 and the air / water blocking device 216 and intended to supply pressurized / compressed air to the recovery duct 201.

[0107] Air / water occlusion device 216 may be a valve, preferably electrically operated, that can assume an open or closed position, or a U-shaped siphon that may or may not be primed. Throughout the remainder of the description, air / water occlusion device 216 is said to be open when the valve is in the open position or the siphon is primed, and closed when the valve is closed or the siphon is not primed.

[0108] The recovery means 200 may include an air injector 207 connected between the exhaust valve 205 of the air duct 204 and the air / water blocking device 216 and intended to supply pressurized / compressed air to the recovery duct 201. The air for closing the recovery duct may alternatively originate from the air source used in the treatment method. More specifically, the air injector 207 may be dedicated to air / water blocking. In this case, it includes a check valve. The air injector 207 may also not be dedicated to air / water blocking, i.e., the air injector may originate from the air source and lead to the chamber. In this case, the recovery means 200 further includes a closing valve 206 for providing the blocking function. The air injector 207 is not necessarily connected to the air duct 204, but is systematically connected to the recovery duct 101 to close it with air / water.

[0109] The air injector 207 can operate intermittently or continuously during the aeration step 105.

[0110] The exhaust valve 205 corresponds to the vent valve.

[0111] The means 210 for controlling the recovery means 200 aim to fill the recovery duct 201 with air and to completely empty it of the clarified fraction contained therein, so that it remains filled with air during the aeration step 105 and the settling step 106, and that the air contained in the recovery duct 201 is released via the clarified fraction 22 during the supply step 101 and the recovery step 107. More specifically, the control means 210 are configured to activate the valve 205 and the blocking device 216 as required, so that the recovery duct 201 is completely empty of the clarified fraction present in the recovery duct 201 and is kept filled with air during the aeration and settling phases. Air can be supplied continuously. It can also be supplied from an external air source, i.e., an air source not dedicated to air / water blocking but designed for aeration of the chamber. In the case of an external air source, a gate valve 206 is required. If the recovery means 200 comprises a dedicated air injector 207 for air / water occlusion, said injector can inject pressurized and / or compressed air into the recovery duct 201. It should be noted that this dedicated air injector 207 has a check valve (not shown). In other words, the recovery duct 201 is then air occluded, i.e. it is filled with air, which cannot escape because the air / water occlusion device 216 and the exhaust valve 205 are closed. During the aeration phase, the liquid level of the contents of the chamber increases as air is introduced into the chamber, causing the liquid level of the contents to rise. However, since the recovery duct is filled with air, this content cannot enter the duct. This has the advantage of avoiding the loss of sludge from the system (the presence of sludge is important for compaction) and the contamination of the recovery duct and of the clarified liquid leaving through the holes 203 (which is important with regard to tertiary treatment to be implemented downstream and / or with regard to rejection criteria), and the channels 202 make it possible to compensate for the rise in the water level in the aerated reactor due to gas retention, which also compensates for imperfect levelness of the piping.

[0112] The contents build up in the channel 202 when discontinuous air injections are made but are unable to enter the recovery duct 201. This configuration ensures that, by controlling the recovery means, only the clarified fraction enters the recovery duct, eliminating the risk of the contents being contaminated by the sludge that has entered it.

[0113] It is important to emphasize that the collection ducts extend below the surface 24 of the chamber contents. They are therefore permanently immersed in the chamber contents. The channels 202 are tubes with inlets, permanently immersed, and filled with the chamber contents (clarified liquid during the feed / collection and anaerobic steps) or with air (during the reaction steps, including the aeration step, and the settling step). In other words, the contents of the channels change depending on the current sequence. The channels 202 have a dual role: they provide access to the clarified fraction towards the collection ducts 201 during the feed / collection steps, and they also do not access the collection ducts 201 but form a buffer volume that accommodates the chamber contents when the chamber contents level rises due to aeration. The transition from accessing the collection ducts to serving as a buffer volume is achieved by the injection / release of pressurized and / or compressed air and the opening / closing of the blocking and exhaust valves, depending on the progress of the treatment method. The injection / release of pressurized and / or compressed air and the opening / closing of the blocking device and the exhaust valve are controlled by the control means 210 of the recovery means 200 .

[0114] In one embodiment, the air / water blocking device 216 includes a U-shaped siphon 208 between the air duct 204 and the recovery hole 203. When air is injected, the siphon and the clarified liquid contained in the recovery duct are replaced with air up to a height equivalent to the end of one or more channels. By this means, the siphon is intended to hydraulically separate the contents of the chamber from the clarified liquid outside the chamber and is therefore not primed. By extending the height of the siphon, it is possible to compensate for the rise in the height of the surface 24 during the aeration step. The presence of a siphon is not mandatory, and other embodiments are possible, which will be described later. The siphon can be associated with a closing valve 206, also controlled by the control means 210, if the air for filling the recovery duct is obtained from the air for treatment (air injector 207 not dedicated to blocking air). The recovery hole 203 is the hole through which the treated water is discharged.

[0115] The recovery holes 203 are advantageously located above the level of the recovery duct 201. Furthermore, the recovery duct 201 advantageously includes an exhaust duct 211. Again, other embodiments are possible, which will be described later.

[0116] In this embodiment of the recovery means, the method of the present invention includes a step 107 of recovering a clarified fraction 22 of the contents of chamber 11 after a settling step 106 in which sludge accumulates at the bottom of chamber 11 and the contents of chamber 11 become clarified near its surface 24, said recovery step 107 and supply step 101 being carried out simultaneously so that the liquid level of the contents of chamber 11 is kept substantially constant during the recovery step 107 and the supply step 101.

[0117] The treatment method according to the invention may also include a waiting phase 116 associated with the feeding, settling or anaerobic step.

[0118] According to the present invention, the treatment method comprises: a step 120 of controlling the recovery means 200, during which the recovery duct 201 is filled with air so as to empty it of all the clarified fraction 22 it contains, and to keep the recovery duct 201 filled with air during the reaction sequence 102 and, preferably, the settling step 106, and optionally during the waiting step; a step 123 of extracting, by means of the clarified fraction 22, the air contained in the recovery duct 201 during the supply step 101 and the recovery step 107; Includes:

[0119] If the air injection is not continuous during the air injection step, the method may include a step 121 after step 120 and before step 123 of at least partially filling at least one channel 202 with the contents 12 of the chamber 11 during the aeration step 105.

[0120] Furthermore, the treatment method includes two other steps between steps 120 and 123 that keep the collection duct filled with air. As mentioned above, step 120 of filling the collection duct 201 with air is performed by injecting air while simultaneously draining the clarified liquid. At the start of the first aeration step 105, valve 205 is closed, air / water blocking device 216 is said to be closed, and the air injection device (air injector 207) is operating.

[0121] Next, the method includes a step 122 of keeping the collection duct 201 filled with air by injecting air. During the aeration step 105, the valve 205 is closed, the air / water blocking device 216 is said to be closed, and the air injection device 207 is activated.

[0122] The method then includes a step 122bis of keeping the collection duct full of air without injecting air. During the aeration step 105 and the settling step 106, the valve 205 is closed, the air / water blocking device 216 is said to be closed, and the air injection device 207 is deactivated.

[0123] Next, a step 123 is performed in which the air contained in the recovery duct is evacuated and at the same time filled with clarified liquid. During the feeding step 101, the recovery step 107 and the anaerobic condition step 103, the valve 205 is open, the obturator 216 is said to be open and the air injector 207 is deactivated.

[0124] Finally, then, if the injection of air is not continued during the aeration step 105, in particular to save energy, a step 121 can be carried out (although this step is not intended to be so) of at least partially filling at least one channel 202 with the contents 12 of the chamber 11 during the aeration step 105. In this case, it is possible to reinject air in order to refill the recovery duct 201, this being step 122. This can be done simply by adjusting the frequency and duration of the air injection, or more precisely by incorporating a liquid level measurement probe that makes it possible to detect whether air should be reinjected during the aeration step 105 and step 122 should be triggered.

[0125] During the reaction sequence, including the aeration step, the collection duct is kept filled with air. Preferably, it is also kept filled with air during the settling step. Indeed, if the collection duct is not filled with air at the start of settling, the sludge blanket will not have enough time to settle below the entrance to the channel 202, which will cause contamination of the collection duct with sludge.

[0126] A particular feature of the present invention is that the recovery duct 201 is positioned below the surface 24 of the chamber contents, i.e., it is always submerged. In other words, the contents are controlled by steps (120, 122, 122bis, 123) of controlling the recovery means 200 depending on the step of the treatment method. As a result, only treated water can enter the recovery duct for recovery. Although the recovery duct is shown substantially horizontal, i.e., parallel to the surface 24 of the chamber contents, it can also be tilted, extending along an axis oblique to the plane of the surface 24. A first advantage is that the chamber volume is not limited, since the water level does not need to be lowered below the recovery duct to prevent raw water and sludge from entering during the aeration step 105. By controlling the recovery means, the recovery duct is filled with air just before the aeration step 105 of the reactor. In other words, during the phases of the chamber when the contents near the duct are not exclusively treated water, the recovery duct fills with air, i.e., it becomes blocked with air and therefore inaccessible to the chamber contents. Another special feature results from the channels 202 that hydraulically connect the contents of chamber 11 to the recovery duct 201. They are shown perpendicular to surface 24, but they can also be inclined downward. The channels 202 play a prominent role: by ensuring a hydraulic connection between the clarified fraction and the recovery duct, they allow the clarified fraction to be recovered, while also maintaining the elevation of the interface of the chamber contents during the aeration step. The channels 202 have two ends (visible in FIG. 4): a first end 221 and a second end 222 that are in direct contact with the recovery duct 201, thereby allowing flow between the recovery duct 201 and the channels 202. The channels 202, like the recovery duct 201, can have any cross-section, such as circular, rectangular, polygonal, etc.

[0127] The aeration step 105 results in a change in the liquid level of the chamber contents due to the injection of air into the chamber. During the aeration step 105, the channel 202 is at least partially filled with the chamber contents. This is a special case step 121 for methods where air injection into the collection duct is not continued. The filling height of the channel 202 corresponds to the rising height of the chamber contents. Because the channel 202 is dimensioned to have a height sufficient to accommodate the special case step 121, the contents 12 do not reach the second end 222 of the channel 202. The collection duct 201 itself remains filled with air. During the aeration step 105, the chamber contents are homogenous even at the surface 24. The channel 202 prevents these homogenous contents, including sludge, from entering the collection duct 201. The channel 202 forms a transition zone between the collection duct, which is blocked with air, and the chamber contents. The end 221 of the channel 202 may come into contact with water and sludge. The end 222 of the channel 202 does not come into contact with the sludge, so the recovery duct contains either air or treated water, depending on the phase, but not sludge.

[0128] The recovery 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 chamber is deposited at the bottom of the chamber 11 and the contents of the chamber 11 are clarified at its surface 24. The method then includes a step 123 of evacuating the air from the recovery duct 201. The valve 205 is in an open position, allowing clarified liquid to enter the recovery duct and for the air blocking the recovery duct to be evacuated via the valve 205 and the ventilation duct. The air blocking the recovery duct is now gone.

[0129] The air / water blocking device 216 is then set in the so-called open position and a new cycle begins, i.e. the feed step 101 is carried out simultaneously with the recovery step 107. By introducing a certain amount of wastewater into the chamber, the same amount is discharged, maintaining a substantially constant liquid level. As the recovery duct is not blocked by air, the recovery duct 201 and the channel 202 are filled with this amount of contents 12 located on the surface 24 of the chamber 11. This is the clarified fraction intended to be recovered.

[0130] By controlling the filling of the collection duct with air (step 120) and its blocking with air (step 122bis, optionally supplemented by step 122 if the air injection is not continuous), the timing of the flow of the contents into the collection duct can be precisely controlled. The collection duct can reach the contents of the chamber when they have clarified on its surface. However, during the aeration step when the contents are homogenous, i.e. when the contents of the chamber have not clarified in the vicinity of the collection duct, the collection duct cannot reach these contents. In other words, the method according to the invention allows precise control of what enters the collection duct. The wastewater treatment step successively involves a phase of blocking the collection duct with air and a phase of free-flowing water connection in which the contents of the chamber can circulate in the collection duct.

[0131] This alternative embodiment is therefore based on a step of controlling the means for refreshing the chamber of the SBR, during which the recovery duct is filled with air just before aeration takes place in the SBR, leaving the duct completely empty of the water (clarified liquid) contained therein. According to this alternative embodiment of the invention, the controlled filling of the recovery duct with air in accordance with the steps of the treatment method ensures that the activated sludge treated water recovery duct is not contaminated during aeration.

[0132] More generally, it will be apparent to those skilled in the art that various modifications can be made to the above-described embodiments in light of the teachings disclosed above. In the following claims, the terms used should not be understood to limit the claims to the embodiments described herein, but should be understood to include all equivalents thereof that the claims by their language are intended to cover and that are within the scope of one of ordinary skill in the art based on their general knowledge.

Claims

1. A method for treating wastewater (20) containing carbon contaminants, nitrogen contaminants, and phosphorus contaminants in a sequencing batch activated sludge reactor (SBR) (10), comprising: a chamber (11) capable of accommodating a wastewater-sludge mixture (12) having various boundaries, each boundary being defined by a sludge concentration and / or density; a sludge bed (13) containing a polyphosphate-accumulating bacterial population (14) at the bottom of said chamber (11) and defining a sludge blanket boundary surface (15) above it; - means (16) for determining a minimum extraction boundary (17) and a maximum extraction boundary (18) for extracting the light sludge (23) in said chamber (11); extraction means (19) capable of extracting said light sludge (23) at various interfaces between said minimum extraction interface (17) and said maximum extraction interface (18); Including, The method comprises: - a step (101) of feeding the SBR (10) during which the amount of wastewater (20) to be treated is introduced into the sludge bed (13) near the bottom of the chamber (11); a reaction sequence (102) in which - at least a first anaerobic step (103) in which the polyphosphate accumulating bacteria (14) capture the carbon contaminants and release phosphorus compounds; a third aeration step (105) to effect dephosphorization of the wastewater by the polyphosphate-accumulating bacteria (14), the aeration being controlled to simultaneously effect either (partial or complete) nitrification or (partial or complete) nitritation; a reaction sequence (102) comprising: a settling step (106) during which sludge accumulates at the bottom of the chamber (11) and the contents of the chamber (11) become clear near its surface (24); a recovery step (107) in which a clarified fraction (22) is withdrawn from the contents of the chamber, said recovery step (107) and the supply step (101) being carried out simultaneously, said interface of the contents of the chamber (11) being kept constant during said recovery step (107) and said supply step (101); - extracting (108) at least a portion of the light sludge (23) having a sludge index greater than 100 ml / g and a settling velocity less than 2 m / h at a predetermined interface between the minimum extraction interface (17) and the maximum extraction interface (18); Including, The method further comprises the step of measuring (109) the sludge blanket interface (15), wherein the step of extracting (108) at least a portion of the light sludge (23) is performed when the measurement of the sludge blanket interface (15) is equal to a predetermined distance from the sludge extraction interface.

2. 2. The method of claim 1, wherein the step (108) of extracting at least a portion of the light sludge (23) is carried out during the feeding step (101) and / or during the settling step (106).

3. 3. The method of claim 1, further comprising the step (110) of injecting air into the chamber (11) during the reaction sequence (102).

4. 4. The method according to claim 1, wherein the third aeration step (105) is followed by a step of post-denitrification (111) under anaerobic conditions, or the third aeration step (105) is followed by a denitrification step (111) under anaerobic conditions, or the third aeration step (105) is followed by a deammonification step (111) under anaerobic conditions.

5. The method according to any one of claims 1 to 4, wherein the settling step (106) is preceded by a step (112) of injecting air into the chamber (11).

6. The method of any one of claims 1 to 5, further comprising the step of compacting (113) the sludge using a compaction device (30) in the chamber (11).

7. 7. The method of claim 1, further comprising the step of controlling (114) the duration of the third aeration step (105) depending on the levels of carbon, nitrogen, and phosphorus contaminants in the wastewater (20).

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