Aerated biological filtration method for water treatment with reduced carbon source and aeration requirements aimed at reducing the nitrogen content (NGL) of the water

Abstract

The present invention relates to a biological filtration method for reducing the total nitrogen content of water loaded with nitrogenous pollutants, characterized in that it comprises a first step of nitritation and filtration carried out in a first aerated biological reactor, a second step of deammonification, denitrification and filtration carried out in a second non-aerated biological reactor, and a step of evaluating the ratio of the content of nitrite to the content of ammoniacal nitrogen of the water at the outlet of the first reactor.If this ratio is greater than a predetermined stoichiometric value, the method according to the invention comprises a step of adding the water to be treated to the water coming from the first reactor in order to obtain, at the inlet of the second reactor, a mixture in which the ratio of the content of nitrite to the content of ammoniacal nitrogen is close to the stoichiometric ratio of the anammox reaction.

Description

Detailed Description of the Invention

[0001] FIELD OF THE INVENTION The present invention relates to the technical field of biological treatment of water, in particular wastewater, in particular industrial and municipal wastewater. More particularly, the present invention relates to a biological filtration method for nitrogen-laden water, in which a portion of the water to be treated is used to adjust the stoichiometry of the anammox reaction before it enters a reactor in which this reaction takes place.

[0002] [Prior Art] Biological wastewater treatment methods are currently being implemented to reduce nitrogen pollution content.

[0003] These methods are based on various reaction mechanisms between the nitrogen products and the bacterial population present in the treatment reactor.

[0004] For example, the nitrification-denitrification process is based on the implementation of an aerobic phase and an anoxic phase, which are carried out in the same reactor or in separate reactors. The supply of oxygen in the aerobic phase is carried out by the addition of ammoniacal nitrogen (NH + ) to nitrite (NO2 - ) and AOB (ammonia oxidizing bacteria) which can convert nitrite to nitrate (NO3 - The anoxic phase promotes the development of an autotrophic nitrifying biomass consisting of NOB (nitrite-oxidizing bacteria) that can convert nitrate to nitrite and then to molecular gaseous nitrogen (dinitrogen, N2) using organic carbon, either contained in the wastewater or derived from external organic carbon sources such as methanol, in the absence of aeration.

[0005] This method is particularly effective but expensive because it requires the supply of large amounts of oxygen and possibly exogenous organic carbon sources.

[0006] There is also a nitritation (also called "nitrate shunt") method, in which operating conditions are adjusted to promote the development of AOB biomass to the detriment of NOB. This method allows for reduced oxygen consumption relative to the nitrification-denitrification method.

[0007] Finally, there is a nitritation-deammoniorization method that uses a specific bacterial population known as anammox (from anaerobic ammonium oxidation) without aeration during deammoniorization. Anammox bacteria are autotrophic and can convert nitrite and ammonia nitrogen into gaseous nitrogen (N) and a small amount of nitrate (approximately 11%), eliminating the need to add an organic carbon source to the reactor. This method therefore allows for a reduction in the supply of organic carbon and, therefore, water treatment costs.

[0008] US2018257966A1 discloses a wastewater treatment system including a biological filtration tank, a nitritation tank, and an anammox tank. The biological filtration tank performs biological filtration as a pretreatment method for influent wastewater to remove solids and organic matter. The nitritation tank performs a nitritation process on wastewater from the biological filtration tank, returning a portion of the wastewater to the biological filtration tank to provide electron acceptors necessary for organic matter removal in the biological filtration tank. The anammox tank performs an anaerobic ammonium oxidation process on filtered wastewater from the biological filtration tank and the nitritation tank. However, under practical conditions, the nitritation tank may not only produce nitrite but also nitrate. These nitrates are not treated in the next step, so at the end of the treatment process, the water also contains nitrate.

[0009] WO 2018 / 009348 A1 discloses a method for treating wastewater, including denitrification, using an electron donor. The electron donor, specifically an exogenous carbon source, is added to a reactor dedicated to deammonification, containing heterotrophic biomass and anammox bacteria. The amount of electron donor added is adjusted according to the amount of nitric oxide measured at the reactor outlet. Therefore, an adjustment time is required between measuring the nitrogen product in the water, detecting a deviation from the expected value, and restoring appropriate deammonification conditions in the reactor after adding the electron donor.

[0010] Therefore, there is a need for technologies that do not require exogenous carbon supplies or that require a reduced amount compared to existing solutions. Indeed, these exogenous carbon supplies represent a high cost item in wastewater treatment.

[0011] There is also a need for a technology that makes it possible to predict poor performance of deammonification, to prevent the production of treated water from failing to meet health and / or regulatory requirements during more or less long adjustment times.

[0012] [Object of the Invention] One object of the present invention is to propose a method for treating nitrogen-laden water, in which the consumption of oxygen and / or carbon source is further reduced with respect to the solutions known in the prior art.

[0013] Another objective is to propose a method for treating nitrogen-laden water in which optimization of the deammonification conditions is readily implemented.

[0014] The object of the present invention is therefore to propose a method for treating nitrogen-laden water that is more economical and at least as effective as the methods known from the prior art.

[0015] Summary of the Invention These objectives, as well as others that will become apparent hereinafter, are achieved by the present invention.

[0016] The present invention proposes a biological filtration method for reducing the total nitrogen content (NGL) of water loaded with nitrogenous pollutants, which requires no or little external supply of carbon sources. Furthermore, the method according to the present invention makes it possible to optimize the deammonification process independently of the values ​​of nitric oxide or ammonia nitrogen measured at the end of the method according to the present invention.

[0017] The process according to the invention comprises a first step of nitritation and filtration, and a second step of deammoniation, denitration and filtration.

[0018] The first step of nitritation and filtration involves passing the water to be treated through a first aerated biological reactor having a bed of filtration media and containing autotrophic biomass consisting primarily of AOB, to remove ammonia nitrogen (NH4 + ) is partly nitrite (NO2 - This first step results in a nitrite-rich, nitrate-rich solution at the outlet of the first reactor. - ) can be obtained as filtered water.

[0019] The second deammonification, denitrification, and filtration step involves passing the nitrite-rich, nitrate-poor water from the first reactor upflow through a second, non-aerated biological reactor having a first stage containing a transfer medium for receiving a bacterial biomass consisting primarily of anammox and heterotrophic bacteria, and a second stage containing a bed of filtration medium.

[0020] During the second step, another portion of the ammoniacal nitrogen, the nitrite originating from the first reactor, and the nitrite produced by the heterotrophic bacteria is mainly converted by anammox bacteria to molecular nitrogen and to a small amount of nitrate (deammoni- onation).

[0021] Furthermore, during this second step, the nitrate originating from the first reactor and the small amount of nitrate produced by the anammox bacteria are converted to nitrite by heterotrophic bacteria (denitrification).

[0022] Furthermore, during the second step, the water coming from the first stage is filtered again in the second stage.

[0023] The method according to the invention also comprises the step of assessing the ratio of the nitrite content to the ammoniacal nitrogen content of the water as it leaves the first reactor.

[0024] The method according to the invention further comprises the step of adding water to be treated to the water coming from the first reactor in order to obtain, at the inlet of the second reactor, a mixture having a ratio of nitrite to ammoniacal nitrogen content close to the stoichiometric ratio of the anammox reaction, if the ratio of the nitrite content to the ammoniacal nitrogen content of the water leaving the first reactor is greater than a predetermined stoichiometric value.

[0025] The method according to the invention is carried out with a reduced or even zero exogenous supply of carbon source.

[0026] By feeding the water coming from the first reactor with water to be treated that contains ammonia nitrogen, it is possible to restore the ratio of the nitrite content to the ammonia nitrogen content at the inlet of the second reactor to a value close to or equal to the stoichiometric ratio of the anammox reaction, thereby creating conditions that are optimal for the deammonification activity of the anammox bacteria.

[0027] By adding the water to be treated containing a carbon source to the water coming from the first reactor, the presence of suspended particles and soluble organic matter makes it possible to provide the amount of organic carbon necessary for the proper activity of the heterotrophic bacteria present in the second reactor for treating nitrates. The suspended particles are filtered in the second reactor, and the soluble organic matter is consumed by the heterotrophic bacteria present in the second reactor and is no longer present in the treated water upon exiting the second reactor. Thus, the method of the present invention cleverly makes it possible to create favorable conditions for the activity of heterotrophic bacteria without requiring an external supply of carbon, or only a reduced supply of said carbon as possible. Therefore, the method of the present invention is more economical and at least as effective as methods known from the prior art.

[0028] According to a particular embodiment, the predetermined stoichiometric value is between 1 and 2.5, preferably between 1.1 and 2, more preferably between 1.2 and 1.5.

[0029] Therefore, the supply of ammoniacal nitrogen from the water to be treated is implemented as soon as the stoichiometric value deviates from the anammox reaction stoichiometric ratio due to an imbalance in favor of nitrite. The predetermined stoichiometric value is maintained to allow for adequate activity of the anammox bacteria, allowing for fluctuations in the ammoniacal nitrogen content so as not to adversely affect the proper performance of deammoniation in the second reactor.

[0030] According to one embodiment, the nitrite content of the water as it leaves the first reactor is measured using a probe placed at the outlet of the first reactor.

[0031] According to one embodiment, the ammoniacal nitrogen content of the water as it leaves the first reactor is measured using a probe placed at the outlet of the first reactor.

[0032] These probes, placed at the outlet of the first reactor, allow a rapid assessment of the content of nitrogen products in the water intended to enter the second reactor, and the information they provide allows a rapid, i.e., almost instantaneous, decision to add water to be treated in order to re-equilibrate the content of nitrite relative to the content of ammoniacal nitrogen in the water entering the second reactor.

[0033] According to one embodiment, the method according to the invention further comprises measuring the ammoniacal nitrogen content of the water to be treated using a probe located upstream of the first reactor.

[0034] Such a probe also makes it possible to quickly read the content of ammoniacal nitrogen in the water to be treated, allowing to better regulate the amount of water to be treated that is added to the water coming from the first reactor.

[0035] According to one embodiment, the autotrophic biomass in the first reactor is immobilized on a filtration medium.

[0036] In these conditions, nitrification and filtration occur simultaneously due to the filtration medium and the bacteria present on the medium.

[0037] According to another embodiment, the first reactor comprises a first stage containing a transfer medium and a second stage containing a bed of filtration medium.

[0038] Under these conditions, nitrification occurs primarily in the first stage. However, autotrophic biomass can also develop on the second-stage filtration media, allowing nitrification to continue in the second stage. The second-stage filtration media allows the water in the first reactor to be filtered regardless of whether bacterial biomass develops on its surface. This solution is advantageous because it also improves the effectiveness of the nitrification reaction and can be easily implemented in existing facilities that include two reactors in series.

[0039] According to a particular embodiment, the filtration medium of the first reactor and / or the second reactor has a particle size of 2 to 6 mm and a filtration rate of 15 to 100 kg / m 3 It is a fixed bed of particles with a bulk density of .

[0040] Such particle size allows biomass to be stored and particulate contamination to be retained. As a result, when the water to be treated is added to the water coming from the first reactor, it is possible to effectively filter suspended particles and related particulate organic matter present in the water to be treated during its passage through the first reactor, as well as suspended particles and related particulate organic matter present in the water contained in the second reactor. Such particles in the medium (fixed bed) have a density lower than that of water. Therefore, such particles spontaneously settle at the top of the reactor by floating, which also allows the reactor to be cleaned by gravity washing.

[0041] According to a preferred alternative of this embodiment, the particles of the medium (fixed bed) are made of polystyrene.

[0042] This material is advantageous because it is economical and durable.

[0043] According to one embodiment, the transfer medium of the second reactor and / or, if applicable, the transfer medium of the first reactor has a concentration of 900 to 1200 kg / m 3 , preferably 920 to 980 kg / m 3 and includes a surface that is protected from collisions with surfaces of other moving media.

[0044] Such media allow anammox and heterotrophic bacterial biomass to develop despite the movements caused by the upflow of nitrite-rich and nitrate-poor water. Such movements can actually cause collisions between the media, detaching part of the biomass located outside the collision-protected surface.

[0045] According to one embodiment, the water to be treated enters a precipitator before introducing the water into the first reactor.

[0046] This embodiment makes it possible to remove part of the suspended particles and associated particulate organic matter contained in the water to be treated that may settle at the bottom of the settler.

[0047] [Definition] In the context of the present invention, "anammox reaction" refers to a deammoniation reaction in which nitrite is converted to gaseous nitrogen and small amounts of nitrate by anammox bacteria in the presence of ammoniacal nitrogen. Based on material evaluation (Strous et al. 1999), the detailed stoichiometry of this reaction may be described as follows: NH4 + +1.32NO2 - +0.066HCO3 - +0.13H + ⇒1.02N2+0.26NO3 - +0.066CH2O 0.5 N 0.15 +2.03H2O (Equation 1) Therefore, within the meaning of the present invention, the "anammox reaction stoichiometry" refers to the molar ratio of the nitrite content to the ammoniacal nitrogen content, which is approximately 1.3, consistent with Equation 1 above. This ratio also corresponds to the mass ratio of nitrite nitrogen to ammoniacal nitrogen (1.3 mg N-NO2 / 1 mg N-NH4).

[0048] Unless otherwise specified, "stoichiometric amount" means the molar ratio of nitrite content to ammoniacal nitrogen content.

[0049] The method of the present invention allows for the supply of ammoniacal nitrogen to the water coming from the first reactor when the stoichiometric value reflects a stoichiometric imbalance in favor of nitrite. Therefore, the "predetermined stoichiometric value" of the present invention corresponds to the maximum allowable stoichiometric value at the inlet of the second reactor. The result of Equation 1 above is that the optimal stoichiometric value is approximately 1.3. Therefore, according to one embodiment, the predetermined stoichiometric value of the present invention is equal to 1.3.

[0050] However, the predetermined stoichiometric value may deviate from this value to accommodate acceptable variations in the nitrite and / or ammonia nitrogen content without significantly affecting the activity of the anammox bacteria present in the second reactor. Thus, the predetermined stoichiometric value may be between 1 and 2.5, preferably between 1.1 and 2, and more preferably between 1.2 and 1.5. In particular, the predetermined stoichiometric value may be about 1, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, or about 2.5.

[0051] Within the meaning of the present invention, "exogenous supply of carbon" means the addition of organic compounds, such as methanol, that do not come directly from the water being treated but are generally added to promote the activity of heterotrophic bacteria.

[0052] Within the meaning of the present invention, "nitrogen pollutants" means derivatives of nitrogen present in wastewater.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 shows a diagram of an installation suitable for carrying out the method according to the invention.

[0054] [Figure 2] FIG. 2 shows a diagram of another installation suitable for carrying out the method according to the invention.

[0055] [Figure 3] FIG. 3 shows a schematic diagram of the method according to the invention.

[0056] Detailed Description of the Invention The present inventors emphasize that it was possible to improve existing methods for treating water loaded with nitrogen contaminants, particularly by making them more economical. Indeed, the present inventors have successfully demonstrated that it is possible to use water loaded with nitrogen contaminants (water to be treated) to adjust the nitrite and ammonia nitrogen stoichiometry of the anammox reaction before it enters the reactor where the anammox reaction takes place. Additionally, the water loaded with nitrogen contaminants contains a carbon source that advantageously allows the activity of heterotrophic bacteria involved in denitrification to be promoted while limiting or even preventing the exogenous supply of carbon source. Thus, the method of the present invention can reduce oxygen consumption by up to 55% and the consumption of exogenous carbon sources by up to 100% compared to currently practiced methods.

[0057] The method according to the invention is a method for the biological filtration of water loaded with nitrogenous pollutants, in order to reduce the total nitrogen content (NGL, from N Global) of said water.

[0058] The method of the invention will now be explained in more detail by reference to the drawings, which are for illustrative purposes only and the purpose of these references is not to limit the scope of the invention.

[0059] [First reactor] The method according to the invention comprises a first step of nitrification reaction 101 and filtration 102, which takes place in a first aerated biological reactor 10 having a bed of filtration medium 12. Such reactors may include known means for injecting oxygen, in particular air, such as lamps located at the bottom of the first reactor.

[0060] The water 100 to be treated is conveyed by a pipe 1 to the inlet 13 of the first reactor 10 (100a).

[0061] For example, according to one embodiment shown schematically in FIG. 1 , water follows an upward flow into a first reactor 10 and passes through a filtration and nitrification reaction zone containing an autotrophic biomass, primarily consisting of AOB, immobilized on a bed 12 of filtration media.

[0062] In this configuration, the nitrification reaction 101 and filtration 102 occur at the same level within the reactor and occur simultaneously. Referring to Figure 3, the water to be treated 100 is directed to the inlet of the first reactor 10 (100a), and the nitrification reaction 101 and filtration 102 steps are carried out simultaneously and do not need to be directed from one stage of the first reactor to the other (101a).

[0063] For example, according to another embodiment shown diagrammatically in Figure 2, water enters a first reactor 10 following an upward flow and passes through a first stage containing a moving medium 11 on which autotrophic biomass, mainly consisting of AOB, is fixed, capable of carrying out a nitrification reaction 101. The water is then conducted to a second stage (101a) containing a bed of filtration medium 12, allowing the water to be filtered (102). Autotrophic biomass may also be generated on the bed of filtration medium in this second stage. In this case, filtration 102 is accompanied by nitrification activity.

[0064] Generally, the first reactor 10 may contain other autotrophic bacteria, such as NOB. However, the conditions in the first reactor, such as pH, aeration, applied load, and / or temperature, are adapted to favor the development of AOB within the autotrophic biomass, according to known techniques in the prior art. Maintaining a low density of NOB-type bacteria limits the conversion of nitrite to nitrate, according to the "nitrate shunt" principle. Thus, during the first step, a portion of the ammoniacal nitrogen contained in the water being treated is converted primarily to nitrite by AOB. The water obtained at the outlet 14 of the first reactor 10 is rich in nitrite and poor in nitrate at the end of the first step.

[0065] The first reactor 10 may also contain a heterotrophic bacterial biomass that contributes to the reduction of a large proportion of the dissolved organic carbon contained in the water being treated (oxidation of the dissolved organic carbon to CO2).

[0066] It should be noted that heterotrophic and autotrophic bacteria may occur in the first reactor on the bed of filtration media 12 and, if applicable, on the transfer media 11 .

[0067] The fixed bed 12 of filter particles makes it possible to retain the organic matter and suspended particles present in the water during the first step of the method according to the invention.

[0068] The nitrite-rich, nitrate-poor water reaches the outlet 14 (102a) of the first reactor 10. The ratio of the nitrite content to the ammonia nitrogen content of the water as it leaves the first reactor 10 (14) is then evaluated (103).

[0069] [Second Reactor] The water is conducted by pipe 2 toward the inlet 23 of the second unaerated biological reactor 20 (103a). The second step of the method of the present invention, deammonification, denitrification, and filtration, takes place in the second reactor 20. The water at the inlet 23 of the second reactor 20 passes through the second reactor 20 in an upward flow. It passes through a first stage 21 containing a transfer medium that receives a bacterial biomass consisting of anammox bacteria and heterotrophic bacteria. In this first stage 21, deammonification and denitrification occur together in the presence of a carbon source (104). Another portion of the ammoniacal nitrogen, the nitrite originating from the first reactor and produced by the heterotrophic bacteria, is converted by the anammox bacteria mainly to molecular nitrogen and a small amount of nitrate (deammonification). At the same time, in the first stage 21, the nitrates coming from the first reactor and the small amount of nitrates produced by the anammox bacteria are converted to nitrites by heterotrophic bacteria (denitration), which are then used by the anammox bacteria.

[0070] Thus, the water at the outlet of the first stage 21 contains primarily molecular nitrogen. The water then proceeds to the second stage 22 (104a), which contains a bed of filtration media, where it undergoes a filtration step 105. Note that bacterial biomass may also develop on the filter bed of the second stage, allowing deammonification and denitrification to continue simultaneously with filtration in the second stage.

[0071] [Medium] Preferably, the transfer medium of the first and / or second reactor has a flow rate of 900 to 1200 kg / m 3 , preferably 920 to 980 kg / m 3 and includes a surface protected from collisions with surfaces of other moving media. Such moving media are, for example, the moving media described in patent application published under WO2012 / 136654.

[0072] According to a preferred embodiment, the filtration medium of the first and / or second reactor has a particle size of 2 to 6 mm and a filtration rate of 15 to 100 kg / m3 The apparatus comprises a fixed bed of particles having a bulk density of 0.01 to 0.01 MPa. Such particles allow for the retention of particle contamination. In addition, their density is lower than that of water, allowing for the particles to be washed under gravity. Preferably, the particles are made of polystyrene. According to one variant, the particles are made of expanded polystyrene.

[0073] [Treated water] The water exiting the second reactor 20 (105a) is treated water 106. This treated water is conducted by pipe 3 from the outlet 24 of the second reactor 20. This treated water may be transported to a storage area, an area for further processing, or an area for distribution, depending on its use.

[0074] 〔bypass〕 If the ratio of the nitrite content to the ammoniacal nitrogen content of the water, evaluated (103) at the outlet 14 of the first reactor 10, is greater than a predetermined stoichiometric value (103b), the water to be treated 100 is added (103c) to the water coming from said first reactor 10 by means of the so-called bypass pipe 4. This makes it possible to obtain, at the inlet 23 of the second reactor 20, a mixture whose ratio of the nitrite content to the ammoniacal nitrogen content is close to the stoichiometric ratio of the anammox reaction.

[0075] According to one embodiment, the bypass 4 is a pipe connecting a pipe 1 for conducting the water to be treated 100 to the first reactor 10 with a pipe 2 for conducting the water from the first reactor 10 to the second reactor 20. The bypass 4 may be equipped with a valve (not shown) for controlling the ingress of the water to be treated in the pipe 1 and / or a valve (not shown) for controlling the egress of the water to be treated in the pipe 2.

[0076] Thus, in the method according to the invention, the water at the outlet 14 of the first reactor 10 may be different from the water at the inlet 23 of the second reactor 20 .

[0077] The conditions in the first reactor 10 are adjusted according to known means to allow the effective conversion of ammoniacal nitrogen, mainly to nitrite, by the biomass. These known means are, for example, ammoniacal nitrogen aeration and an added load in the first reactor 10. Adjustment of the conditions in the first reactor 10 is necessary when the nitrite content of the water is too low relative to the ammoniacal nitrogen content, in particular when the ratio of the nitrite content to the ammoniacal nitrogen content is significantly lower than the predetermined stoichiometric value.

[0078] As mentioned above, the predetermined stoichiometric value may be between 1 and 2.5, preferably between 1.1 and 2, and more preferably between 1.2 and 1.5. In particular, the predetermined stoichiometric value may be about 1, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, or about 2.5.

[0079] Since the water to be treated 100 contains a carbon source, the addition (103c) of the water to be treated to the water coming from the first reactor 10 also makes it possible to provide the carbon source necessary for the activity of the heterotrophic bacteria in the first stage 21 of the second reactor 20. Therefore, the method according to the invention is carried out with as little or as little external carbon source supply as possible, or even zero. As shown in the examples, the carbon consumption is significantly reduced by the method according to the invention compared to known methods. Another advantageous result of the method according to the invention is that the amount of sludge formed by the external supply of a carbon source is also reduced. However, it may be desirable to supply an external carbon source, for example, if the water to be treated does not contain a sufficient amount of said carbon source to allow satisfactory activity of the heterotrophic bacteria. To enable this supply, the second reactor 20 can advantageously be equipped with a pipe that conveys the carbon source to the first stage 21. By carbon source, we mean a readily biodegradable carbon substrate, such as methanol.

[0080] The evaluation of the ratio of the nitrite content to the ammoniacal nitrogen content (103) is carried out from the measured values ​​of the nitrate and nitrite contents. This evaluation may be carried out by known calculation devices, such as, for example, computer-implemented calculation tools. Such a computer can advantageously control the opening and closing of valve(s) that can be equipped with a bypass 4, if such valve(s) are present.

[0081] The measurement of the nitrite content may be carried out by any known means. According to one embodiment, the measurement of the nitrite content is carried out by a probe 31. The use of the probe 31 is advantageous as it allows the measurement of the nitrite content in the water to be carried out continuously. Such probes are commercially available, for example the "OPUS" nitrite probe sold by Trios.

[0082] The measurement of the ammoniacal nitrogen content may be carried out by any known means. According to one embodiment, the measurement of the ammoniacal nitrogen content is carried out by a probe 32. The use of a probe is advantageous as it allows the measurement of the ammoniacal nitrogen content in the water to be carried out continuously. An example of a probe suitable for measuring the ammoniacal nitrogen content according to the present invention is the Ammonium Analyzer sold by Hach under the AMTAX brand.

[0083] According to one embodiment, the method according to the invention further comprises measuring the ammoniacal nitrogen content of the water 100 to be treated. This measurement may be carried out by any known means. In a particular embodiment, this measurement is carried out using a probe 33 placed upstream of the first reactor 10, for example on the pipe 1. An example of a probe suitable for measuring the ammoniacal nitrogen content according to the invention is the ammonium analyzer sold by Hach under the AMTAX brand.

[0084] According to a particular embodiment, the method according to the invention also comprises measuring the content of nitrates in the water at the outlet of the first reactor 10. This measurement may be carried out by any known means, in particular by means of a probe (not shown) placed at the outlet of the first reactor, for example on the pipe 2. This measurement makes it possible to quickly detect nitrates and thereby reduce the air supply in the first reactor in order to limit the development of NOB-type bacterial biomass.

[0085] The water to be treated can be subjected to one or more preliminary treatments before being introduced into the first reactor 10. In particular, the method according to the invention may comprise a preliminary step of passing the water to be treated through a precipitator in order to reduce the amount of suspended particles in the water to be treated before it enters the first reactor.

[0086] [Example] Other features and advantages of the present invention will become more apparent from the following examples, given for illustrative and non-limiting purposes.

[0087] A water treatment plant is configured to carry out the method of the present invention. Specifically, a first aerated biological reactor is installed, followed by a second unaerated biological reactor, connected by a pipe equipped with a probe for measuring the nitrite and ammonia nitrogen content. The pipe carrying the water to be treated to the first reactor is modified to also communicate with a bypass pipe. The bypass pipe joins the pipe connecting the two reactors together upstream of the inlet to the second reactor.

[0088] The first aerated biological reactor 10 contains autotrophic biomass consisting primarily of AOB immobilized on filtration media 12. It also contains heterotrophic biomass that allows for the reduction of dissolved organic carbon. The second non-aerated biological reactor 20 has a first stage containing a transfer media 21 that receives bacterial biomass consisting of anammox bacteria and heterotrophic bacteria, and a second stage containing a bed of filtration media 22 on which bacterial biomass may also be immobilized.

[0089] Water loaded with nitrogen pollutants 100 is introduced into the first reactor 10 (100a), and nitrogen aeration and loading conditions are configured to promote the nitrification reaction of ammoniacal nitrogen. At the outlet 14 of the first reactor, the water is rich in nitrite and poor in nitrate. The nitrite and ammoniacal nitrogen contents of the water at the outlet of the first reactor are measured by probes 31 and 32. The molar ratio of the nitrite content to the ammoniacal nitrogen content is measured, and when this ratio is greater than 1.7, the water to be treated 100 is injected into the bypass 4 (103c). The water to be treated is mixed with water coming from the first reactor 10 upstream of the inlet 23 of the second reactor 20, so that the ratio of the nitrite content to the ammoniacal nitrogen content of the mixture approaches the stoichiometric ratio for the anammox reaction.

[0090] The oxygen consumption and carbon source consumption are measured and correlated with the amount of nitrogen treated and compared with values ​​obtained by conventional methods.

[0091] [References] Strous M, Kuenen JG, Jetten MS. Key physiology of anaerobic ammonium oxidation. Appl Environ Microbiol. 1999 Jul;65(7):3248-50.doi:10.1128 / AEM.65.7.3248-3250.1999.PMID:10388731;PMCID:PMC91484. [Brief explanation of the drawings]

[0092] [Figure 1] 1 shows a diagram of an installation suitable for carrying out the method according to the invention; [Figure 2] 1 shows a diagram of another installation suitable for carrying out the method according to the invention; [Figure 3] 1 illustrates a schematic representation of a method according to the present invention.

Claims

1. 1. A biological filtration method for reducing the total nitrogen content (NGL) of water loaded with nitrogen contaminants, comprising: a first step of nitritation and filtration, consisting of passing the water to be treated through a first aerated biological reactor having a bed of filtration medium and containing an autotrophic biomass consisting mainly of AOB, in order to convert a portion of the ammoniacal nitrogen (NH 4 +) contained in the water to be treated into nitrites (NO ２ － ), the first step produces a nitrite-rich, nitrate-rich bioreactor at the outlet of the first aerated biological reactor. ３ － a first step, which makes it possible to obtain a filtered water poor in - following an upflow, the water rich in nitrite and poor in nitrate coming from the first aerated biological reactor, i) a first stage comprising a transfer medium receiving a bacterial biomass, consisting primarily of anammox bacteria and heterotrophic bacteria; ii) a second stage comprising a bed of filtration media; a second step of deammonification, denitrification and filtration, comprising passing the effluent through a second unaerated biological reactor having Meanwhile, another portion of the ammoniacal nitrogen is converted by anammox bacteria, mainly to molecular nitrogen, with a small amount being converted to nitrate (deammonification), from the nitrite originating from the first aerated biological reactor and the nitrite produced by the heterotrophic bacteria; Meanwhile, the nitrate from the first aerated biological reactor and the small amount of nitrate produced by the anammox bacteria are converted to nitrite by the heterotrophic bacteria (denitration); a second step in which the water from the first stage is filtered again in the second stage; - assessing the ratio of the nitrite content to the ammonia nitrogen content of the nitrite-rich, nitrate-poor water upon exiting the first aerated biological reactor; - if said ratio is greater than a predetermined stoichiometric value, adding the water to be treated to the water coming from the first aerated biological reactor in order to obtain, at the inlet of the second unaerated biological reactor, a mixture having a ratio of the nitrite content to the ammoniacal nitrogen content close to the stoichiometric ratio of the anammox reaction, wherein the step of adding the water to be treated to the water coming from the first aerated biological reactor, in addition to providing the amount of organic carbon necessary for the proper activity of the heterotrophic bacteria present in the second unaerated biological reactor to treat the nitrates, makes it possible to carry out the biological filtration method with a reduced or even zero exogenous supply of carbon source, A biological filtration method comprising:

2. 2. The biological filtration method of claim 1, wherein the predetermined stoichiometric value is between 1 and 2.

5.

3. 3. The biological filtration method according to claim 1 or 2, characterized in that the nitrite content of the nitrite-rich, nitrate-poor water as it leaves the first aerated biological reactor is measured using a probe placed at the outlet of the first aerated biological reactor.

4. 4. The biological filtration method according to claim 1, wherein the ammoniacal nitrogen content of the nitrite-rich, nitrate-poor water leaving the first aerated biological reactor is measured using a probe placed at the outlet of the first aerated biological reactor.

5. 5. The biological filtration method according to claim 1, further comprising measuring the ammonia nitrogen content of the water treated by the first aerated biological reactor using a probe located upstream of the first aerated biological reactor.

6. 6. The biological filtration method according to claim 1, wherein the autotrophic biomass in the first aerated biological reactor is immobilized on the filtration medium.

7. 6. The biological filtration method according to any one of claims 1 to 5, characterized in that the first aerated biological reactor comprises: i) a first stage containing a moving medium; and ii) a second stage containing a bed of the filtration medium.

8. 8. The biological filtration method according to any one of claims 1 to 7, characterized in that the filtration medium of the first aerated biological reactor and / or the second non-aerated biological reactor is a fixed bed of particles with a particle size of 2 to 6 mm and a bulk density of 15 to 100 kg / m3.

9. 9. The biological filtration method of claim 8, wherein the particles are made of polystyrene.

10. 10. Biological filtration method according to any one of claims 1 to 9, characterized in that the transfer medium of the second unaerated biological reactor and / or, if applicable, the transfer medium of the first aerated biological reactor has a density of 900 to 1200 kg / m 3 and comprises surfaces protected from collision with surfaces of other transfer media.

11. 11. The biological filtration method according to any one of claims 1 to 10, characterized in that the water to be treated by the first aerated biological reactor enters a settling vessel before introducing the water into the first aerated biological reactor.

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