An aerated biological filtration process for treating water to reduce its nitrogen content (NGL) with reduced carbon source and aeration requirements

Abstract

The present invention relates to a biological filtration process of water loaded with nitrogenous pollutants aimed at reducing the total nitrogen content, characterized in that it comprises a first step of nitritation and filtration carried out in a first aerated biological reactor, a second step of deamination, denitration and filtration carried out in a second non-aerated biological reactor, and a step of evaluating the ratio between the nitrite content and the ammonia nitrogen content of said water as it leaves said first reactor. When said ratio is greater than a predetermined stoichiometric value, the process according to the invention comprises a step of adding water to be treated to the water coming from the first reactor, so as to obtain at the inlet of the second reactor a mixture having a ratio between the nitrite content and the ammonia nitrogen content close to the stoichiometric ratio of the Anammox reaction.

Description

Technical Field

[0001] This invention belongs to the technical field of biological water treatment, particularly wastewater, especially industrial and municipal wastewater. More specifically, this invention relates to a biological treatment method for nitrogen-loaded water, wherein a portion of the water to be treated is used to adjust the stoichiometry of the reaction before entering a reactor in which an Anammox reaction occurs. Background Technology

[0002] Biological wastewater treatment methods are commonly used to reduce the levels of nitrogenous pollutants.

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

[0004] For example, nitrification-denitrification methods are based on the implementation of aeration and anoxic phases, which are either carried out in the same reactor or in separate reactors. The oxygen supply during the aeration phase promotes the development of autotrophic nitrifying bacterial biomass, which is capable of converting ammonia nitrogen (NH4) into nitrogen. + ) is converted into nitrite (NO2) - AOB (ammonia-oxidizing bacteria) and bacteria that can convert nitrite to nitrate (NO3) - The NOB (nitrite-oxidizing bacteria) composition of the wastewater is enhanced by the absence of an anaerobic phase, which promotes the development of denitrification biomass capable of reducing nitrate to nitrite and then to molecular gaseous nitrogen (nitrogen, N2), thanks to the organic carbon contained in the wastewater or organic carbon derived from external organic carbon sources such as methanol.

[0005] Although this method is particularly effective, it requires a large supply of oxygen and potentially exogenous organic carbon sources, making it very expensive.

[0006] There is also a nitrification method, also known as "nitrate avoidance," in which operating conditions are regulated in a way that promotes the growth of AOB biomass and is harmful to NOB bacteria. Compared to nitrification-denitrification methods, this method allows for reduced oxygen consumption.

[0007] Finally, there is a nitrification-deammoniation method that utilizes a special bacterial group called Anammox (derived from ANaerobic AMMonia Oxidation) in the absence of aeration during the deammoniation process. Anammox bacteria are autotrophic and capable of converting nitrite and ammonia nitrogen into gaseous nitrogen (N2) and a small amount of nitrate (approximately 11%) without the addition of an organic carbon source to the reactor. This method thus allows for a reduction in the supply of organic carbon and consequently lowers water treatment costs.

[0008] Document US2018257966A1 discloses a wastewater treatment method comprising a biological filter, a nitrification tank, and an anaerobic ammonia oxidation tank. The biological filter performs biological filtration as a pretreatment process for the input wastewater, removing solids and organic matter. The nitrification tank performs a nitrification process on the wastewater originating from the biological filter and provides the electron acceptors needed to remove organic matter from the biological filter by returning a portion of the wastewater to the biological filter. The anaerobic ammonia oxidation tank performs an anaerobic ammonium oxidation process on the filtered wastewater from the biological filter and the nitrification tank. However, under practical conditions, the nitrification tank may produce not only nitrite but also nitrate. Since these nitrates are not treated in subsequent steps, the water will still contain nitrates at the end of the treatment process.

[0009] Document WO2018 / 009348A1 discloses a method for treating wastewater, which includes denitrification using an electron donor. The electron donor (particularly an exogenous carbon source) is added to a reactor containing heterotrophic substances and Anammox bacteria (specifically for ammonia removal). The amount of electron donor supplied is adjusted based on the amount of oxidized nitrogen measured at the reactor outlet. Therefore, an adjustment period is required between the measurement of nitrogenous products in the water and the detection of deviations from the desired value, and the restoration of suitable ammonia removal conditions in the reactor after the addition of the electron donor.

[0010] Therefore, there is a need for a technology that requires no external carbon supply or a significantly reduced external carbon supply compared to existing solutions. In fact, these external carbon supplies represent a high-cost item in wastewater treatment.

[0011] A technology is also needed to predict the decline in ammonia removal performance in order to prevent the produced treated water from failing to meet health and / or regulatory requirements for a longer or more extended conditioning period. Summary of the Invention

[0012] The purpose of this invention

[0013] One object of the present invention is to provide a method for treating nitrogen-loaded water, wherein the consumption of oxygen and / or carbon sources is further reduced relative to solutions known in the prior art.

[0014] Another objective is to propose a method for treating nitrogen-loaded water, wherein the optimization of deammoniation conditions is carried out immediately.

[0015] Therefore, the object of the present invention is to provide a method for treating nitrogen-loaded water that is more economical and at least as effective as methods known in the prior art.

[0016] Overview of the Invention

[0017] These objectives, as well as other objectives that will become apparent below, are all achieved by virtue of the present invention.

[0018] This invention proposes a biological filtration method for water containing nitrogenous contaminants, aimed at reducing the total nitrogen (NGL) content of such water, requiring little or no external carbon source supply. Furthermore, the method according to the invention enables optimization of the ammonia removal process, regardless of the value of oxidized nitrogen or ammonia nitrogen measured at the end of the method according to the invention.

[0019] The method according to the invention includes a first step of nitritation and filtration, and a second step of deammonization, denitrification and filtration.

[0020] The first step of nitrification and filtration involves passing the water to be treated through a first aerated bioreactor, which has a filter media bed and contains autotrophic material mainly composed of AOB bacteria, by which the ammonia nitrogen (NH4) in the water to be treated is reduced. + A portion of it is converted into nitrite (NO2). - This first step enables the production of nitrite-rich and nitrate-poor (NO3)-poor samples at the outlet of the first reactor. - ) filtered water.

[0021] The second step of deammoniation, denitrification, and filtration involves passing nitrite-rich and nitrate-poor water from the first reactor through a second non-aerated bioreactor in an upflow. This non-aerated bioreactor has a first stage and a second stage. The first stage contains a moving medium containing bacterial biomass primarily composed of Anammox and heterotrophic bacteria, while the second stage contains a filter bed.

[0022] In the second step, another portion of the ammonia nitrogen, nitrite from the first reactor and nitrite produced by heterotrophic bacteria, is mainly converted into molecular nitrogen and a small amount of nitrate (deammoniation) by the Anammox bacteria.

[0023] Furthermore, during this second step, the nitrates originating from the first reactor and the small amount of nitrates produced by the Anammox bacteria are converted into nitrites (denitrification) by the heterotrophic bacteria.

[0024] In addition, during the second step, the water originating from the first stage is filtered again in the second stage.

[0025] The method according to the invention further includes the step of evaluating the ratio of nitrite content to ammonia nitrogen content in the water as it leaves the first reactor.

[0026] The method according to the invention further includes the step of adding water to be treated to water originating from the first reactor when the ratio of nitrite content to ammonia nitrogen content in the water as it leaves the first reactor is greater than a predetermined stoichiometric value, so as to obtain a mixture at the inlet of the second reactor having a nitrite to ammonia nitrogen content ratio close to the stoichiometric ratio of the Anammox reaction.

[0027] The method according to the invention is implemented by reducing or even eliminating the supply of exogenous carbon sources.

[0028] By supplying treated water containing ammonia nitrogen from the water in the first reactor, the nitrite to ammonia nitrogen ratio, close to or equal to the stoichiometric ratio of the Anammox reaction, can be restored at the inlet of the second reactor. These conditions are optimal for the deammoniation activity of Anammox bacteria.

[0029] By supplying treated water containing a carbon source from the water in the first reactor, the amount of organic carbon required for the good activity of heterotrophic bacteria present in the second reactor for nitrate treatment can be supplied due to the presence of suspended particles and soluble organic matter. The suspended particles will be filtered out in the second reactor, and the soluble organic matter will be consumed by the heterotrophic bacteria present in the second reactor and will no longer be present in the treated water upon leaving the second reactor. Therefore, ingeniously, the method according to the invention makes it possible to create conditions favorable to the activity of heterotrophic bacteria without requiring an exogenous carbon supply, or requiring only a minimal carbon supply. The method according to the invention is thus more economical and at least as effective as methods known in the prior art.

[0030] According to a particular embodiment, the predetermined stoichiometric value is between 1 and 2.5, preferably between 1.1 and 2, and more preferably between 1.2 and 1.5.

[0031] Therefore, once this stoichiometric value deviates from the stoichiometric ratio required for the Anammox reaction due to an imbalance favoring nitrite, the supply of ammonia nitrogen from the treated water is adjusted. This predetermined stoichiometric value allows for tolerance of variations in ammonia nitrogen content that remain acceptable for the good activity of Anammox bacteria and do not adversely affect the good deammoniation performance in the second reactor.

[0032] According to one embodiment, the nitrite content of the water as it leaves the first reactor is measured by means of a probe placed at the outlet of the first reactor.

[0033] According to one embodiment, the ammonia nitrogen content of the water as it leaves the first reactor is measured by means of a probe placed at the outlet of the first reactor.

[0034] Because these probes are positioned at the outlet of the first reactor, they enable a rapid assessment of the nitrogenous product content in the water intended to enter the second reactor. The information provided by these probes will allow for a rapid (i.e., almost instantaneous) decision to add treated water to rebalance the nitrite and ammonia nitrogen content in the water entering the second reactor.

[0035] According to one embodiment, the method according to the invention further includes measuring the ammonia nitrogen content of the water to be treated by means of a probe located upstream of the first reactor.

[0036] This probe also enables rapid reading of the ammonia nitrogen content in the water to be treated, and allows for better adjustment of the amount of water to be added to the water from the first reactor.

[0037] According to one embodiment, the autotrophic biomass in the first reactor is fixed on the filter medium.

[0038] Under these conditions, nitrification and filtration occur simultaneously due to the filter medium and the bacteria present on it.

[0039] According to another embodiment, the first reactor includes a first stage containing a moving medium and a second stage containing a filter media bed.

[0040] Under these conditions, nitrification primarily occurs in the first stage. Naturally, it is possible that the autotrophic biomass also develops on the filter media in the second stage, and nitrification can continue in the second stage. The filter media in the second stage allows for the filtration of water from the first reactor, regardless of whether bacterial biomass develops on its surface. This solution is advantageous because it also allows for improved nitrification efficiency and can be readily implemented in existing equipment comprising two reactors with two stages in series.

[0041] According to a particular embodiment, the filter media of the first reactor and / or the second reactor has a particle size of 2-6 mm and a bulk density of 15-100 kg / m³. 3 A fixed bed of particles.

[0042] This particle size allows for the storage of biomass and the trapping of particulate contaminants. Therefore, it can effectively filter suspended particles and related particulate organic matter present in the water: the water to be treated as it passes through the first reactor, and the water contained in the second reactor after the water to be treated has been added to the water from the first reactor. The density of these media particles (fixed bed) is less than that of water. Therefore, through flotation, they spontaneously position themselves at the top of the reactor, which also makes it possible to clean them by gravity washing.

[0043] According to a preferred variant of this embodiment, the media particles (fixed bed) are made of polystyrene.

[0044] This material is advantageous because it is economical and resistant.

[0045] According to one embodiment, the moving medium in the second reactor and / or, if applicable, the first reactor has a density of 900-1200 kg / m³. 3 Preferred weight: 920-980 kg / m³ 3 And includes surfaces that prevent collisions with other moving media.

[0046] This medium allows Anammox bacterial and heterotrophic bacterial biomass to develop, although the upwelling of nitrite-rich and nitrate-poor water induces movement. This movement can indeed lead to collisions between the media, which can separate a portion of the biomass located outside the surface, protecting it from impact.

[0047] According to one embodiment, the water to be treated passes through a settling tank (décanteur) before being introduced into the first reactor.

[0048] This implementation scheme enables the removal of some of the suspended particles and related particulate organic matter contained in the water to be treated, which can settle to the bottom of the settling tank.

[0049] definition

[0050] In the context of this invention, the "Anammox reaction" refers to a deamination reaction in which nitrite is converted into gaseous nitrogen and a small amount of nitrate by Anammox bacteria in the presence of ammoniacal nitrogen. Based on bilansmatières (Strous et al., 1999), the detailed stoichiometry of this reaction can be written as follows:

[0051]

[0052] Therefore, within the meaning of this invention, "stoichiometric ratio of the Anammox reaction" refers to the molar ratio of nitrite content to ammonia nitrogen content, which, according to Equation 1 above, is approximately 1.3. This ratio also corresponds to the mass ratio of nitrite nitrogen to ammonia nitrogen (1.3 mg N-NO2 / 1 mg N-NH4).

[0053] Within the meaning of this invention, unless explicitly stated otherwise, "stoichiometric value" refers to the molar ratio of nitrite content to ammonia nitrogen content.

[0054] The method according to the invention enables the supply of ammonia nitrogen to the water from the first reactor when the stoichiometric value reflects an imbalance in the stoichiometric coefficient favoring nitrite. Therefore, the "predetermined stoichiometric value" according to the invention corresponds to the maximum acceptable stoichiometric value at the inlet of the second reactor. As can be seen from Equation 1 above, the optimal stoichiometric value is approximately 1.3. Therefore, according to one embodiment, the predetermined stoichiometric value according to the invention is equal to 1.3.

[0055] However, this predetermined stoichiometric value can deviate from the value to cover acceptable variations in nitrite and / or ammonia nitrogen content without significantly affecting the activity of Anammox bacteria present in the second reactor. Therefore, the predetermined stoichiometric value can be 1-2.5, preferably 1.1-2, more preferably 1.2-1.5. Specifically, the predetermined stoichiometric value can be approximately 1, approximately 1.1, approximately 1.2, approximately 1.3, approximately 1.4, approximately 1.5, approximately 1.6, approximately 1.7, approximately 1.8, approximately 1.9, approximately 2.0, approximately 2.1, approximately 2.2, approximately 2.3, approximately 2.4, or approximately 2.5.

[0056] Within the meaning of this invention, "exogenous carbon supply" refers to the addition of organic compounds, such as methanol, that are not directly derived from the water to be treated but are typically added to the water to promote the activity of heterotrophic bacteria.

[0057] Within the meaning of this invention, "nitrogenous pollutants" refers to nitrogen derivatives present in wastewater. Attached Figure Description

[0058] [ Figure 1 ] Figure 1 A schematic diagram of an apparatus suitable for implementing the method of the present invention is shown.

[0059] [ Figure 2 ] Figure 2 A schematic diagram of another apparatus suitable for implementing the method of the present invention is shown.

[0060] [ Figure 3 ] Figure 3The method according to the invention is illustrated schematically. Detailed Implementation

[0061] Detailed description of the invention

[0062] The inventors have demonstrated that existing methods for treating water loaded with nitrogenous contaminants can be improved, particularly made more economical. In fact, the inventors have ingeniously shown that water loaded with nitrogenous contaminants (the water to be treated) can be used to adjust the stoichiometry of nitrite and ammonia nitrogen in the Anammox reaction before it enters the reactor where the Anammox reaction occurs. Furthermore, the water loaded with nitrogenous contaminants contains a carbon source, which advantageously promotes the activity of heterotrophic bacteria responsible for denitrification while limiting or even eliminating the supply of exogenous carbon sources. Therefore, with the method of the present invention, oxygen consumption can be reduced by up to 55% and exogenous carbon source consumption by up to 100% compared to currently implemented methods.

[0063] The method according to the invention is a biological filtration method for water loaded with nitrogen-containing contaminants, the purpose of which is to reduce the total nitrogen content (“NGL”, derived from N Global) of the water.

[0064] The method of the present invention will be described in more detail with reference to the accompanying drawings, which are for illustrative purposes only and are not intended to limit the scope of the invention.

[0065] First reactor

[0066] The method according to the invention includes a first step of nitrification 101 and filtration 102, which are carried out in a first aerated bioreactor 10 having a filter media bed 12. Such a reactor may include known devices for injecting oxygen (especially air), such as a ramp located at the bottom of the first reactor.

[0067] The water to be treated 100 is introduced into the inlet 13 of the first reactor 10 through pipe 1, 100a.

[0068] According to one implementation scheme, such as Figure 1 As shown, water flows upward through the first reactor 10 and through the filtration and nitrification zone, which contains autotrophic material mainly composed of AOB bacteria fixed on the filter media bed 12.

[0069] In this configuration, nitration 101 and filtration 102 occur at the same level in the reactor, and simultaneously. (Reference) Figure 3 The water to be treated 100 is directed 100a to the inlet of the first reactor 10, where the steps of nitrification 101 and filtration 102 will be carried out simultaneously, and it is unnecessary to direct it from the first stage 101a to another stage in the first reactor.

[0070] According to another implementation scheme, such as Figure 2 As shown, water flows upward through the first reactor 10 and through a first stage containing a moving medium 11 on which autotrophic material, primarily composed of AOB bacteria capable of nitrification 101, is immobilized. The water is then directed 101a to a second stage containing a filter media bed 12 to enable water filtration 102. In this second stage, the autotrophic material can also develop on the filter media bed. In this case, filtration 102 is accompanied by nitrification activity.

[0071] Typically, the first reactor 10 may contain other autotrophic bacteria, such as NOB bacteria. However, according to techniques known in the prior art, conditions within the first reactor, such as pH, aeration, applied load, and / or temperature, are adjusted to promote the predominant development of AOB bacteria within the autotrophic biomass. Based on the principle of "nitrate avoidance," maintaining a low density level of NOB-type bacteria limits the conversion of nitrite to nitrate. Therefore, during the first step, a portion of the ammonia nitrogen contained in the water to be treated is primarily converted to nitrite by AOB bacteria. At the end of the first step, the water obtained at the outlet 14 of the first reactor 10 is nitrite-rich and nitrate-poor.

[0072] The first reactor 10 may also contain heterotrophic bacterial biomass, which helps to reduce most of the dissolved organic carbon contained in the water to be treated (by oxidizing dissolved organic carbon into CO2).

[0073] It should be noted that heterotrophic and autotrophic bacteria can develop on the filter media bed 12 in the first reactor and, if applicable, on the moving media 11.

[0074] The filter particle fixed bed 12 enables the interception of organic matter and suspended particles present in the water during the first step of the method of the present invention.

[0075] Water rich in nitrite and poor in nitrate reaches outlet 14 of the first reactor 10 at 102a. Then, the ratio of nitrite content to ammonia nitrogen content of the water leaving the first reactor 10 at 103 is evaluated.

[0076] Second reactor

[0077] Water is guided 103a through pipe 2 to inlet 23 of the second non-aerated bioreactor 20. The second steps of deammoniation, denitrification, and filtration according to the method of the invention are carried out in the second reactor 20. Water at inlet 23 of the second reactor 20 flows upward through the second reactor 20. It passes through a first stage 21 containing a moving medium that holds bacterial biomass composed of Anammox bacteria and heterotrophic bacteria. In this first stage 21, deammoniation and denitrification occur together due to the presence of a carbon source 104. Another portion of the ammonia nitrogen, nitrite from the first reactor and nitrite produced by the heterotrophic bacteria, is mainly converted into molecular nitrogen and a small amount of nitrate by the Anammox bacteria (deammoniation). Simultaneously, in the second stage 21, nitrate from the first reactor and a small amount of nitrate produced by the Anammox bacteria are converted into nitrite by the heterotrophic bacteria (denitrification). These nitrites are then used by the Anammox bacteria.

[0078] The water at the outlet of the first stage 21 thus primarily contains molecular nitrogen. It then passes through the second stage 22, which contains a filter media bed, at step 104a, where filtration step 105 takes place. It should be noted that bacterial biomass can also develop on the filter bed in the second stage, allowing ammonia and denitrification to continue simultaneously with filtration in the second stage.

[0079] medium

[0080] Preferably, the density of the moving medium in the first reactor and / or the second reactor is 900-1200 kg / m³. 3 Preferred weight: 920-980 kg / m³ 3 It also includes a surface that prevents collisions with surfaces of other moving media. Such a moving media is, for example, the moving media described in patent application publication number WO2012 / 136654.

[0081] According to a preferred embodiment, the filter media of the first and / or second reactors consists of particles with a particle size of 2-6 mm and a bulk density of 15-100 kg / m³. 3 The particles are arranged in a fixed bed. Such particles allow for the trapping of particulate contaminants. Furthermore, their density is lower than that of water, which allows for the washing of particles by gravity. Preferably, these particles are made of polystyrene. According to one variant, these particles are made of expanded polystyrene.

[0082] treated water

[0083] The water leaving the second reactor 20 (105a) is treated water (106). This treated water is discharged from the outlet 24 of the second reactor 20 through pipe 3. This treated water can be directed to a storage area, a supplementary treatment area, or a distribution area, depending on its intended use.

[0084] bypass

[0085] When the ratio of nitrite to ammonia nitrogen in the water assessed 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 originating from the first reactor 10 via a so-called "bypass" pipe 4. This allows a mixture to be obtained at the inlet 23 of the second reactor 20, which has a nitrite to ammonia nitrogen ratio close to the stoichiometric ratio of the Anammox reaction.

[0086] According to one embodiment, bypass 4 is a conduit connecting conduit 1 for introducing water 100 to be treated into first reactor 10 and conduit 2 for introducing water from first reactor 10 into second reactor 20. Bypass 4 may be equipped with a valve (not shown) for controlling the entry of water to be treated into conduit 1, and / or a valve (not shown) for controlling the exit of water to be treated from conduit 2.

[0087] Therefore, 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.

[0088] The conditions in the first reactor 10 are adjusted according to known measures to enable the efficient conversion of ammonia nitrogen primarily into nitrite via biomass. These known measures include, for example, the application of ammonia nitrogen loading and aeration in the first reactor 10. Condition adjustment in the first reactor 10 is necessary when the nitrite content in the water becomes too low relative to the ammonia nitrogen content, particularly when the nitrite to ammonia nitrogen ratio becomes significantly lower than a predetermined stoichiometric value.

[0089] As previously mentioned, the predetermined stoichiometric value can be 1-2.5, preferably 1.1-2, and more preferably 1.2-1.5. In particular, the predetermined stoichiometric value can 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.

[0090] Since the water to be treated 100 contains a carbon source, its addition of 103c to the water from the first reactor 10 also enables the supply of the carbon source required for the heterotrophic bacteria activity in the first stage 21 of the second reactor 20. Therefore, the method according to the invention is implemented with reduced or even zero exogenous carbon source supply. As shown in the embodiments, carbon consumption is significantly reduced due to the method of 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 supply of exogenous carbon source is also reduced. However, it may be desirable to supply exogenous carbon source, for example, when the water to be treated does not contain sufficient carbon source to enable satisfactory heterotrophic bacteria activity. To make this supply possible, the second reactor 20 may advantageously be equipped with a conduit to introduce the carbon source into the first stage 21. The carbon source refers to a readily biodegradable carbon matrix, such as methanol.

[0091] The assessment 103 of the nitrite to ammonia nitrogen ratio is performed by measuring the nitrate and nitrite contents. This assessment can be performed using known computing devices, such as computer-based computational tools. Such a computer can advantageously control the opening and closing of valves equipped with bypasses 4, when they are present.

[0092] The measurement of nitrite content can be performed by any known method. According to one embodiment, the measurement of nitrite content is performed using probe 31. The use of probe 31 is advantageous because it allows for continuous measurement of nitrite content in water. Such probes are commercially available, such as the "OPUS" nitrite probe sold by Trios Corporation.

[0093] The measurement of ammonia nitrogen content can be performed by any known method. According to one embodiment, the measurement of ammonia nitrogen content is performed using probe 32. The use of the probe is advantageous because it allows for continuous measurement of the ammonia nitrogen content in the water. An example of a probe suitable for measuring ammonia nitrogen content according to the present invention is the ammonium analyzer sold by Hach under the trademark AMTAX.

[0094] According to one embodiment, the method according to the invention further includes measuring the ammonia nitrogen content of the water to be treated 100. This measurement can be performed by any known means. In a particular embodiment, the measurement is performed using a probe 33 located upstream of the first reactor 10 (e.g., on pipe 1). An example of a probe suitable for measuring ammonia nitrogen content according to the invention is the ammonium analyzer sold by Hach Corporation under the trademark AMTAX.

[0095] According to one particular embodiment, the method according to the invention further includes measuring the nitrate content in the water at the outlet of the first reactor 10. This measurement can be performed by any known means, particularly by a probe (not shown) placed at the outlet of the first reactor (e.g., on pipe 2). This measurement allows for rapid detection of nitrates and thus reduces the air supply in the first reactor, thereby limiting the development of NOB-type bacterial biomass.

[0096] The water to be treated may undergo one or more pretreatments before being introduced into the first reactor 10. In particular, in order to reduce the amount of suspended particles in the water to be treated before it enters the first reactor, the method according to the invention may include a preliminary step of passing the water to be treated through a settling tank.

[0097] Example

[0098] Other features and advantages of the invention will become more apparent from the following embodiments, which are given for illustrative purposes and not for limiting purposes.

[0099] A water treatment plant is set up to implement the method of the present invention. Specifically, a first aerated bioreactor, followed by a second non-aerated bioreactor, is installed, connected by pipes equipped with probes for measuring nitrite and ammonia nitrogen levels. The pipe introducing the water to be treated into the first reactor is modified to also connect to a "bypass" pipe. The bypass pipe is connected upstream of the inlet to the second reactor to a pipe that connects the two reactors together.

[0100] The first aerated bioreactor 10 contains autotrophic material, primarily composed of AOB bacteria, immobilized on filter media 12. It also contains heterotrophic material that enables the reduction of dissolved organic carbon. The second non-aerated bioreactor 20 has a first stage and a second stage. The first stage contains a moving medium 21 containing bacterial biomass composed of Anammox bacteria and heterotrophic bacteria, and the second stage contains a filter media bed 22 on which bacterial biomass can also be immobilized.

[0101] Water 100 loaded with nitrogenous contaminants is introduced into the first reactor 10 (100a), where nitrogen loading and aeration conditions are set to promote nitrification of ammonia nitrogen. At the outlet 14 of the first reactor, the water is rich in nitrite and poor in nitrate. The nitrite and ammonia nitrogen content in the water at the outlet of the first reactor are measured using probes 31 and 32. The molar ratio of nitrite to ammonia nitrogen is measured, and when this molar ratio is greater than 1.7, the water to be treated 100 is injected into bypass 4 (103c). This water to be treated is mixed with water from the first reactor 10 upstream of the inlet 23 of the second reactor 20 such that the ratio of nitrite to ammonia nitrogen in the mixture is close to the stoichiometric ratio of the Anammox reaction.

[0102] Oxygen consumption and carbon source consumption were measured, correlated with the amount of nitrogen treated, and compared with values ​​obtained by conventional methods.

[0103] References

[0104] Strous M, Kuenen JG, Jetten MS. Key physiology of anaerobic ammonium oxidation. Appl Environ Microbiol. 1999Jul; 65(7):3248-50.doi:10.1128 / AEM.65.7.3248-3250.1999.PMID:10388731; PMCID:PMC91484.

Claims

1. A biological filtration method for water intended to reduce the total nitrogen content (NGL) of water loaded with nitrogenous contaminants, characterized in that, The method includes: - The first step of nitrification and filtration involves passing the water to be treated through a first aerated bioreactor, which has a filter media bed and contains autotrophic material mainly composed of AOB bacteria, by virtue of which the ammonia nitrogen (NH4) in the water to be treated is reduced. + A portion of it is converted into nitrite (NO2). - The first step enables the production of nitrite-rich and nitrate-poor samples at the outlet of the first aerated bioreactor. - ) filtered water; - A second step of ammonia removal, denitrification, and filtration, wherein the water, rich in nitrite and poor in nitrate, originating from the first aerated bioreactor, is passed in an upflow through a second non-aerated bioreactor, the second non-aerated bioreactor having... i) The first stage, comprising a mobile medium containing bacterial biomass primarily composed of Anammox bacteria and heterotrophic bacteria, and ii) Second stage, which includes a filter media bed. In the second step, another portion of the ammonia nitrogen, nitrite from the first aerated bioreactor and nitrite produced by heterotrophic bacteria, is mainly converted into molecular nitrogen and a small amount of nitrate (deammoniation) by the Anammox bacteria. In the second step, nitrates from the first aerated bioreactor and a small amount of nitrates produced by the Anammox bacteria are converted into nitrites by the heterotrophic bacteria (denitrification). Furthermore, during the second step, the water originating from the first stage is filtered again in the second stage; - A step of assessing the ratio of nitrite content to ammonia nitrogen content in the water as it leaves the first aerated bioreactor; - When the ratio is greater than a predetermined stoichiometric value, the step of adding the water to be treated to the water originating from the first aerated bioreactor to obtain a mixture at the inlet of the second non-aerated bioreactor having a nitrite content to ammonia nitrogen content ratio close to the stoichiometric ratio of the Anammox reaction, the step of adding the water to be treated to the water originating from the first aerated bioreactor to enable the supply of the amount of organic carbon required for the good activity of heterotrophic bacteria present in the second non-aerated bioreactor for nitrate treatment, the method being implemented with reduced or even zero exogenous carbon source supply.

2. The biological filtration method according to claim 1, characterized in that, The predetermined stoichiometric value is between 1 and 2.

5.

3. The biological filtration method according to claim 1, characterized in that, The predetermined stoichiometric value is between 1.1 and 2.

4. The biological filtration method according to claim 1, characterized in that, The predetermined stoichiometric value is between 1.2 and 1.

5.

5. The biological filtration method according to any one of claims 1 or 2, characterized in that, The nitrite content of the water as it leaves the first aerated bioreactor is measured by means of a probe placed at the outlet of the first aerated bioreactor.

6. The biological filtration method according to any one of claims 1 or 2, characterized in that, The ammonia nitrogen content of the water as it leaves the first aerated bioreactor is measured by means of a probe placed at the outlet of the first aerated bioreactor.

7. The biological filtration method according to any one of claims 1 or 2, characterized in that, The method also includes measuring the ammonia nitrogen content of the water to be treated using a probe located upstream of the first aerated bioreactor.

8. The biological filtration method according to any one of claims 1 or 2, characterized in that, The autotrophic substances in the first aerated bioreactor are fixed on the filter medium.

9. The biological filtration method according to any one of claims 1 or 2, characterized in that, The first aerated bioreactor includes i) a first stage containing moving media and ii) a second stage containing the filter media bed.

10. The biological filtration method according to any one of claims 1 or 2, characterized in that, The filter media in the first aerated bioreactor and / or the second non-aerated bioreactor has a particle size of 2-6 mm and a bulk density of 15-100 kg / m³. 3 A fixed bed of particles.

11. The biological filtration method according to claim 10, characterized in that, The particles are made of polystyrene.

12. The biological filtration method according to any one of claims 1 or 2, characterized in that, The moving medium in the second non-aerated bioreactor and / or, if applicable, the first aerated bioreactor has a density of 900-1200 kg / m³. 3 And includes surfaces that prevent collisions with other moving media.

13. The biological filtration method according to any one of claims 1 or 2, characterized in that, The moving medium in the second non-aerated bioreactor and / or, if applicable, the first aerated bioreactor has a density of 920-980 kg / m³. 3 And includes surfaces that prevent collisions with other moving media.

14. The biological filtration method according to any one of claims 1 or 2, characterized in that, The water to be treated passes through a settling tank before being introduced into the first aerated bioreactor.

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