Wastewater treatment method comprising electrooxidation step to maximize biogas production

Abstract

The present invention relates to a method and facility for treating wastewater and associated sludge, which is capable of removing carbon and nitrogen and maximizing biogas production. The method comprises: (a) a step of treating the wastewater, which produces a first effluent (2) having a reduced content of carbonaceous substances and a second effluent (3) having an increased content of carbonaceous substances; (b) a step of treating at least a portion of said first effluent, which produces a third effluent having a reduced nitrogen content, the step being carried out without carrying out biological nitrification under aerobic conditions and comprising at least one electrooxidation step during which at least a portion of said first effluent is subjected to a reduction in nitrogen content, the step being carried out without carrying out biological nitrification under aerobic conditions. At least a portion of the ammonium ions contained in the first effluent are oxidized to nitrate and / or nitrite, and / or dinitrogen; (c) a step of anaerobically digesting the second effluent to produce biogas (7) and a digest (8).

Description

Technical Field

[0001] The present invention relates to a method for treating wastewater (sewage) and associated sludge, in particular to remove carbon and nitrogen and maximize biogas production. Background Art

[0002] Wastewater (sewage) treatment is generally a three-step treatment process: a primary treatment step, a secondary treatment step, and a tertiary treatment step.

[0003] The primary treatment step generally allows to reduce the solid and / or organic content of the wastewater to be treated. This generally involves a sedimentation (precipitation) step, possibly assisted by the pre-addition of coagulants and flocculants, during which the wastewater is placed in a storage tank or a sedimentation tank. The solids contained in the wastewater are thus deposited at the bottom of the tank, from which they are collected, while lighter substances like grease and oil are present on the surface of the wastewater in the tank and recovered. This step thus produces the so-called primary sludge, and an effluent with a lower solid content. These primary sludges are generally treated by anaerobic digestion to produce biogas, a high-energy gas whose main components are methane and carbon dioxide.

[0004] The secondary treatment step allows to reduce the carbon and / or nitrogen and / or phosphorus content of the effluent with a lower solid content output from the first treatment step. During this step, the organic matter, nitrogen compounds and / or phosphorus compounds are assimilated or decomposed by aerobic and / or anaerobic and / or anoxic bacteria. This therefore involves a biological treatment step, which is most often implemented in a reactor with a free culture (so-called "activated sludge" process).

[0005] The tertiary treatment step is designed to further clean the water before dumping it into sensitive ecosystems, or to reuse it. This step may involve removal of phosphorus and / or micropollutants and / or disinfection and / or filtration.

[0006] During the secondary treatment step, the biological processes most commonly used to remove nitrogen compounds from wastewater generally utilize a process of nitrification followed by denitrification (N / DN), ie, the conversion of ammonia into dinitrogen.

[0007] Nitrification is an aerobic oxidation reaction that requires active aeration in which a specialized group of autotrophic bacteria converts ammonia or ammonium nitrogen (denoted as NH4 or NH4 + ) is oxidized to:

[0008] Nitrite nitrogen, also known as nitrite, NO2 or NO2 - ;

[0009] Then there is nitrate nitrogen, which is also called nitrate, NO3 or NO3 - .

[0010] Denitrification consists in anoxic reduction, during which specialized groups of heterotrophic bacteria (which may be anaerobic) combine the oxidation of organic substrates with the reduction of nitrates to nitrous oxide (N2O) or nitrogen gas (dianitrogen, N2).

[0011] At the end of the nitrification / denitrification step, the nitrogen content must comply with limits that depend on regulations, which may significantly affect the design of the treatment to be carried out. Generally, the lower the nitrogen content limit, the longer the nitrification step must be and the stronger aeration (high oxygen demand) required. Moreover, it is difficult to achieve low nitrogen contents by biological denitrification treatments, which also require large amounts of biodegradable carbon, usually from an external supply, when the amount of biodegradable carbon available in the effluent is insufficient relative to the amount of nitrogen oxides to be denitrified.

[0012] The sludge retention time (or SRT, i.e. "sludge retention time") is one of the key parameters in the design of a treatment chain, since the growth rate of autotrophic nitrifying bacteria is lower than that of the denitrifying heterotrophic microorganisms and must be maintained in the system for efficient nitrification. Furthermore, this growth rate decreases with the operating temperature. Therefore, low temperatures and / or low nitrogen discharge limits require extended aeration, as well as increased age, sludge retention time and hydraulic retention time of the produced sludge, which determine the size of the plant. If longer sludge retention times allow good development of autotrophic nitrifying bacteria, less biomass is formed under these conditions: this is called operating the system at low load. Conversely, shorter sludge retention times limit or even prevent the growth of nitrifying bacteria, thereby limiting or even preventing denitrification, but allowing an increase in the biomass formed: this is called operating the system at high load.

[0013] However, aerated sludges produced from nitrification treatments with long aeration (“low load” operation) have a lower methanogenic potential than sludges from “high load” operation, which is reflected in lower anaerobic digester performance during their subsequent treatment and, therefore, lower biogas production. Therefore, it is necessary to use “young” sludges to obtain a higher methanogenic potential and increase biogas production, but under these conditions, the treatment of nitrogen is weak or even non-existent.

[0014] Strict nitrogen discharge limits result not only in high construction costs due to long sludge retention time and hydraulic retention time, but also in high operating costs due to the addition of reagents (carbonate to increase alkalinity during autotrophic nitrification, methanol as external carbon source during heterotrophic denitrification, phosphate source in case of nutrient deficiency), high oxygen demand (strong aeration) and high pumping flows (internal and external recirculation).

[0015] As the wastewater industry moves towards resource recovery and reuse of carbon, maximizing biogas energy recovery becomes essential to improve the energy balance of wastewater treatment facilities. However, the current design paradigm of the nitrification / denitrification step of the wastewater treatment chain seems incompatible with increasingly stringent regulations on nitrogen discharge limits and with the goal of maximizing energy recovery through biogas production. In fact, in order to achieve the minimum nitrogen removal limit, enough carbon must be left at the output of the primary treatment to obtain sufficient denitrification during secondary treatment, which limits the possibility of capturing carbon in the sludge output of the primary treatment for biogas production.

[0016] In particular, for a primary treatment step with defined carbon collection performance, a downstream secondary treatment producing activated sludge at low loads has a lower methanogenic potential than a downstream secondary treatment producing activated sludge at high loads (also called "high rate activated sludge" or "HRAS"), in which the carbon is not processed by a reactor that achieves biological nitrification. In fact, at low loads, for longer sludge ages, the heterotrophic bacteria do not have enough food, so they consume their reserves (endogenous respiration), which reduces the methanogenic potential. Whereas at high loads, no nitrification occurs, so there is no need to work at longer sludge ages, so the sludge produced is younger, the sludge yield is greater, and its methanogenic potential is also greater.

[0017] Therefore, the limitation of carbon recovery at the output of primary treatment and the low methanogenic potential of the sludge from the nitrification output of secondary treatment do not allow for maximizing energy recovery through biogas production while reducing the nitrogen content at the output of secondary treatment.

[0018] Finally, the actual processing implements numerous intermediate steps to achieve the electron transfer that allows the reduction of the nitrogen compound to dinitrogen:

[0019] - Convert electricity into blown air (via a supercharger) for aeration of the environment;

[0020] - Transfer oxygen (20% of air) to the environment (wastewater);

[0021] - Transfer of dioxygen from the environment (wastewater) to bacteria;

[0022] - Use bacteria to convert oxygen to oxidize ammonium ions to nitrate / nitrite via electron transfer.

[0023] During each of these steps, energy losses due to conversion are observed, which makes the process more energy intensive than necessary.

[0024] Finally, the control of biological nitrogen treatments is complicated because the performance of these treatments is controlled indirectly: the activity of the bacteria is usually regulated by the dissolved oxygen content in the medium, which itself is controlled by the air injection command and therefore the blower flow rate. Moreover, these treatments are only effective after a period of growth of the biomass. Moreover, during the biological nitrification step at low loads, filamentous bacteria may be produced, which may cause malfunctions (especially loss of sludge settling properties, resulting in leakage of suspended matter at the clarified output) due in particular to swelling and foam formation.

[0025] Therefore, there is a need for a wastewater treatment method that can maximize biogas production during sludge treatment and nitrogen pollution treatment without adding reagents, or reducing the amount of added reagents, and is not affected by the carbon content of the wastewater to be treated (i.e., regardless of the C / N ratio). There is also a need for wastewater treatment that is easier to implement and control. Summary of the invention

[0026] A first subject of the present invention relates to a method for treating wastewater containing nitrogen in the form of ammonium ions and carbonaceous substances, the method comprising:

[0027] (a) a wastewater treatment step to produce a first effluent having a reduced carbonaceous matter content and a second effluent having an increased carbonaceous matter content;

[0028] (b) a treatment step of treating at least a portion of the first effluent to produce a third effluent having a reduced nitrogen content; and

[0029] (c) an anaerobic digestion step of the second effluent to produce biogas and digestate.

[0030] According to the present invention, step (b) of the method is carried out without implementing biological nitrification under aerobic conditions and comprises at least one electrooxidation step during which at least a portion of the ammonium ions contained in the first effluent are oxidized to nitrite and / or nitrate, and / or dinitrogen.

[0031] The specific sequence of steps described, and in particular the use of at least one step of eliminating nitrogen by electrooxidation, allows a less complex implementation of the treatment method compared to biological treatment of nitrogen by nitrification / denitrification. In fact, the control of the electrooxidation step can be carried out directly by controlling the applied current density and the flow rate of the effluent to be treated, and does not require a growth period of the biomass.

[0032] The sequence also achieves lower cost implementation than biological denitrification treatment methods due to reduced use of chemicals, smaller overall energy requirements, and favorable biogas production due to the electro-oxidation treatment requiring less run time to achieve full or partial nitrification (shortened hydraulic retention time) and fewer intermediates for electron transfer.

[0033] Moreover, electro-oxidation is a treatment method with less risk of failure compared to biological nitrification (no risk of failure due to the production of filamentous bacteria, foam formation or sludge bulking). Electro-oxidation also allows very low nitrogen levels to be achieved in the treated water, not limited by the initial carbon content, and allows a reduction in the production of nitrous oxide, a reaction intermediate of the biological reactions of ammonia oxidation and nitrate reduction, which is a greenhouse gas.

[0034] Since the carbon present in the first effluent is not essential for the operation of step (b), step (a) of treating the wastewater can be carried out under conditions that maximize the carbon content in the second effluent, which can optimize the biogas produced by anaerobic digestion during step (c).

[0035] Advantageously, the treatment step (a) may comprise at least one step for treating the carbonaceous material selected from a physical treatment step (a1) and a step (a3, a4) of biologically treating the carbonaceous material, optionally preceded by a physico-chemical treatment step (a2).

[0036] The physical and / or physico-chemical treatment makes it possible to reduce the content of solids, possibly flocculated organic matter and possibly phosphorus in the wastewater to be treated, so as to thereby reduce the content of carbonaceous substances in the first effluent.

[0037] The use of physico-chemical treatment upstream of physical treatment can, among other things, increase the rate of treatment, which enables the use of smaller and therefore less expensive facilities.

[0038] Advantageously, the physical treatment step may be chosen from a sedimentation step, a flotation step and a filtration step, and the physico-chemical treatment step may be chosen from a coagulation-flocculation step, a flocculation alone and an electrocoagulation followed by flocculation step, or a combination of these steps.

[0039] The treatment step (a) may comprise at least one step (a3) ​​of biologically treating the carbonaceous matter, in particular under conditions which are not conducive to nitrification. In practice, this involves treating (i.e. eliminating) only the biodegradable soluble carbonaceous matter (i.e. non-particulate carbonaceous matter) in the effluent to be treated, to produce a first effluent with a reduced carbonaceous matter content and a second effluent with an increased carbonaceous matter content.

[0040] Biological treatment of carbonaceous materials can be carried out under anoxic or aerobic conditions.

[0041] In one embodiment, step (b) may include the step of completely electro-oxidizing at least a portion of the ammonium ions to dinitrogen.

[0042] In another embodiment, step (b) may include the step (b1) of partially electro-oxidizing at least a portion of the ammonium ions into nitrates and / or nitrites.

[0043] Advantageously, at least part of the effluent resulting from said partial electro-oxidation step (b1) may be conveyed upstream of or into step (a3) ​​of anoxic biological treatment of carbonaceous matter of treatment step (a).

[0044] In such anoxic biological treatment step (a3), the recycling of a portion of the partially oxidized effluent enables maximal denitrification and elimination of carbon to achieve the production of a sludge with potentially high methanogenic organisms (which forms the second effluent). In fact, the recycling in the anoxic biological treatment (a3) ​​of step (a) makes it possible to reduce the carbon present in the wastewater entering the biological treatment step (a3) ​​and to reduce the carbon present in the partially oxidized effluent recycled in this step (a3) ​​(which has become biodegradable by the partial electro-oxidation step), while providing the oxygen required for this reduction by the nitrate / nitrite produced during the partial electro-oxidation step (b1), which makes it possible to reduce the aeration demand of the carbon biological treatment step (a3).

[0045] In a variant, step (b) may comprise a partial electrooxidation step (b1) in which a portion of the ammonium ions are oxidized to nitrate and / or nitrite, for example in which only half of the ammonium ions are oxidized to nitrate and / or nitrite, and a subsequent step (b3) of anoxic biological treatment (Anammox step) in which the ammonium ions are oxidized by anaerobic autotrophic bacteria. The partial electrooxidation step (b2) is then incomplete.

[0046] In case the incomplete partial electro-oxidation step (b1) is followed by the Anammox step (b3), at least a portion of the effluent produced by this step (b3) may be returned upstream of or into the anoxic biological treatment step (a3) ​​of the carbonaceous material in the treatment step (a).

[0047] An advantage of carrying out the Anammox step (b3) at the output of the incomplete partial oxidation step (b1) is that the remaining ammonium ions are oxidized while reducing the energy required compared to carrying out step (b) with only one or more electrooxidation steps.

[0048] In another variation, step (b) may comprise a step (b1) of partially electro-oxidizing at least a portion, preferably all, of the ammonium ions into nitrates and / or nitrites, followed by a step (b2) of completely electro-oxidizing at least a portion, preferably all, of the nitrates and / or nitrites into dinitrogen.

[0049] In yet another variant, step (b) may comprise a step (b1) of partially electro-oxidizing a portion (e.g. half) of the ammonium ions to nitrate and / or nitrite, followed by a step (b3, Anammox step) of anoxic biological treatment by oxidation of the ammonium ions using anaerobic autotrophic bacteria, followed by a step (b2) of complete electro-oxidation of at least a portion, preferably all, of the nitrate and / or nitrite to dinitrogen. The purpose of the step (b2) of complete electro-oxidation of nitrate and / or nitrite to dinitrogen is to complete the elimination of total nitrogen and to reach legislative targets or prescribed total nitrogen limits. Prior to this complete electro-oxidation step (b2), the purpose of the Anammox step (b3) is to oxidize part of the ammonium ions, so as to thereby reduce the energy consumption required for the step (b2) of complete electro-oxidation of nitrate and / or nitrite to dinitrogen, and to reduce the overall energy consumption used to remove nitrogen during step (b).

[0050] Advantageously, during the electro-oxidation step (b), (b1) or (b2), water present in the effluent may be electrolyzed so that dihydrogen is produced at the cathode and dioxygen is produced at the anode. The dihydrogen and / or dioxygen may then be recovered and, optionally, conveyed upstream of or in the step (a3) ​​of biological treatment of carbonaceous matter of step (a).

[0051] Advantageously, the treatment method may also include a step (d) of treating the third effluent produced by treatment step (b) to produce a fourth effluent, the treatment step (d) comprising at least one treatment selected from a treatment for removing suspended matter, a treatment for removing phosphorus compounds, a treatment for removing micropollutants (particularly organic and / or metal pollutants), and a treatment for removing microorganisms.

[0052] The purpose of step (d) of treating the third effluent is to further clean the water so that it complies with discharge standards when discharged into sensitive ecosystems, or so that it can be reused.

[0053] Advantageously, the processing method may further comprise a control step, in which:

[0054] (i1) determining the content of nitrogen present in the third effluent or the fourth effluent and in at least one effluent to be extracted, the at least one effluent to be extracted being selected from the first effluent, the effluent of the step of partial electrooxidation of ammonium ions, and the effluent of the anoxic biological treatment step (b3) carried out by oxidation of ammonium ions using anaerobic autotrophic bacteria;

[0055] Then,

[0056] (i2) determining an amount of the at least one effluent to be extracted in order to reach a nitrogen content limit in the third effluent or the fourth effluent, extracting the amount of the at least one effluent to be extracted, and mixing it with the third effluent or the fourth effluent; and / or

[0057] (i3) determining an amount of effluent from step (b1) of partial electro-oxidation of ammonium ions to be sent to the anoxic biological treatment step (a3) ​​of step (a), and sending said amount of effluent to said anoxic biological treatment step (a3) ​​of step (a), said amount corresponding to the amount of nitrate and / or nitrite required for the anoxic biological treatment of carbonaceous matter.

[0058] The purpose of the control step comprising the sequence (i1)(i2) is to reduce the amount of effluent treated by step (b) while complying with the nitrogen emission standards in the third effluent, which makes it possible to reduce the size of the facility and / or the cost of treatment. The control step comprising the sequence (i1)(i3) can optimize the recycling of the effluent produced by the partial electro-oxidation step (b1) to provide the nitrate / nitrite required for the reduction of the carbon initially contained in the wastewater in step (a3). Step (i1) may also include, in particular, determining the amount of carbonaceous matter contained in the wastewater to be treated entering step (a), and during step (i3), the amount of effluent may be determined based on its nitrate and / or nitrite content and the carbonaceous matter content of the wastewater to be treated. The control step comprising the sequence (i1)(i3) can also optimize the method by minimizing the amount of nitrogen to be treated by the complete electro-oxidation step (b2). The control step may implement two sequences of steps (i1)(i2) and (i1)(i3) or only one of the two sequences.

[0059] Advantageously, the treatment method may also comprise at least one step (e) of treating at least a portion of the liquid portion of the digestate produced in the digestion step (c), the treatment step being selected from an electrocoagulation treatment step (e0), an electrooxidation treatment step (e1) during which at least a portion of the ammonium ions contained in the liquid portion are oxidized to nitrite and / or nitrate and / or dinitrogen, a step (e2) of anoxic biological treatment by oxidizing ammonium ions using anaerobic autotrophic bacteria (Anammox step), and a sequence of two steps (e1) (e2) with or without a preceding step (e0).

[0060] Advantageously, the electrocoagulation treatment step (e0) may comprise a sub-step of precipitating struvite by electrochemical dissolution of a sacrificial anode comprising magnesium, combined with a sub-step of separating the precipitated struvite.

[0061] The purpose of this treatment step (e) is to treat the nitrogen contained in the liquid portion of the digestate produced in the ammonium-rich digestion step (c), which in particular allows the treated liquid portion to be fed back into the main wastewater supply line of the process, into step (a) or upstream of step (a).

[0062] Another subject of the present invention relates to a treatment plant for treating wastewater containing nitrogen in the form of ammonium ions and carbonaceous substances, which is particularly useful for carrying out the method according to the invention. The treatment plant according to the invention comprises:

[0063] a first wastewater treatment unit comprising a wastewater supply conduit, a first discharge conduit for discharging a first effluent having a reduced carbonaceous matter content, and a second discharge conduit for discharging a second effluent having an increased carbonaceous matter content;

[0064] a second treatment unit comprising a supply conduit connected to the first conduit of the first treatment unit, and a discharge conduit for discharging a third effluent having a reduced nitrogen content, the second treatment unit comprising at least one electro-oxidation treatment reaction zone but not an aerobic biological treatment reaction zone;

[0065] - A third anaerobic digestion treatment unit comprising a supply conduit connected to the second conduit of the first treatment unit, a biogas discharge conduit, and a digestate discharge conduit.

[0066] Advantageously, the first unit may comprise at least one reaction zone selected from a physical treatment reaction zone (optionally coupled to a physico-chemical treatment reaction zone) and a biological treatment reaction zone.

[0067] Advantageously, the second processing unit may include:

[0068] - at least one first electro-oxidation treatment reaction zone, and at least one second reaction zone selected from electro-oxidation treatment reaction zones and non-aerated biological treatment reaction zones, each second reaction zone being connected to the first reaction zone by a discharge conduit for discharging an effluent output from the first reaction zone; or

[0069] - at least one first electro-oxidation treatment reaction zone, at least one second non-aerated biological treatment reaction zone, and at least one third electro-oxidation treatment reaction zone, each second reaction zone is connected to the first reaction zone by a discharge pipe for discharging the effluent output from the first reaction zone (especially generated thereby), and each third reaction zone is connected to the second reaction zone by a discharge pipe for discharging the effluent output from the second reaction zone.

[0070] Advantageously, the treatment facility may comprise a recirculation conduit connecting the output of the at least one first electro-oxidation treatment reaction zone or the at least one second non-aerated biological treatment reaction zone to the input of the biological treatment unit zone of the first unit.

[0071] Advantageously, the second treatment unit may comprise at least one discharge conduit of the electro-oxidation reaction zone selected from a dihydrogen discharge conduit and a dioxygen discharge conduit.

[0072] The processing facility further comprises at least one further processing unit selected from the group consisting of:

[0073] a fourth treatment unit comprising a supply conduit connected to the discharge conduit of the second treatment unit and a discharge conduit for discharging a fourth effluent, and comprising at least one reaction zone selected from a treatment reaction zone for removing suspended matter, a treatment reaction zone for removing phosphorus compounds, a treatment reaction zone for removing micropollutants, and a treatment reaction zone for removing microorganisms;

[0074] -A fifth treatment unit, comprising a supply pipe connected to a discharge pipe for discharging the liquid part of the digestate of the third unit, and a discharge pipe for discharging the effluent, which discharge pipe is optionally connected to the supply pipe of the first unit, and further comprising at least one reaction zone, which at least one reaction zone is selected from an electrocoagulation treatment reaction zone, an electro-oxidation treatment reaction zone, and a non-aerated biological treatment reaction zone (Anammox reaction zone) for oxidizing ammonium ions using anaerobic autotrophic bacteria, the latter two reaction zones may or may not be preceded by an electrocoagulation treatment reaction zone, and the output of the electro-oxidation treatment reaction zone is connected to the input of the non-aerated biological treatment reaction zone.

[0075] The electrocoagulation treatment reaction zone may include, inter alia, an electrochemical reactor equipped with a sacrificial anode comprising magnesium and a solid-liquid separation device.

[0076] Advantageously, the treatment facility may be equipped with a control system comprising at least one measuring device for measuring the content of ammonium ions and / or nitrates and / or nitrites, at least one fluid moving device, and a control unit configured to:

[0077] - determining the content of nitrogen present in the third effluent or the fourth effluent and in at least one effluent to be extracted, the at least one effluent to be extracted being selected from the first effluent, the effluent of the at least one first electro-oxidation treatment reaction zone, and the effluent of the at least one non-aerated biological treatment reaction zone of the first unit;

[0078] Then,

[0079] - determining the amount of the at least one effluent to be extracted in order to reach the nitrogen content limit in the third effluent or the fourth effluent, and controlling the at least one fluid moving device to extract the at least one effluent to be extracted in said amount and mix it with the third effluent or the fourth effluent; and / or

[0080] -Determining the amount of effluent from at least one first electro-oxidation treatment reaction zone to be transported to the non-aerated biological treatment reaction zone of the first treatment unit, and controlling the at least one fluid moving device to transport the amount of the effluent to the non-aerated biological treatment reaction zone of the first unit, the amount corresponding to the amount of nitrate and / or nitrite required for the non-aerated biological treatment of carbonaceous materials.

[0081] Definition / Abbreviation

[0082] Anammox: ANaerobic AMMOnium OXidation Anaerobic ammonium oxidation (anaerobic oxidation of ammonium). During this reaction, ammonium is converted into gaseous nitrogen under anaerobic conditions (absence of oxygen) by using nitrite as an electron acceptor. The reaction is carried out in the presence of anaerobic autotrophic bacteria (they do not require free or dissolved O2).

[0083] BMP: methanogenic potential, which corresponds to the maximum yield of methane produced by a compound during anaerobic degradation. It is generally expressed in terms of the volume of methane produced per gram of volatile substrate material (NmL).

[0084] HRT (hydraulic retention time): hydraulic retention time.

[0085] N / DN: Nitrification / denitrification.

[0086] Refractory Carbon: Carbon that cannot be removed by purifying biomass in wastewater treatment methods because the compound is too complex.

[0087] Complete electro-oxidation step: In this step, complete electrochemical oxidation of the ammonium ion species present is achieved (complete oxidation of ammonium ions to dinitrogen, complete oxidation of nitrites / nitrates to dinitrogen).

[0088] Partial electrooxidation step: In this step, partial electrochemical oxidation of the substances present is achieved, for example partial electrochemical oxidation of ammonium ions to nitrates and / or nitrites.

[0089] A (complete or partial) electro-oxidation step is incomplete (exhaustive) when only a portion of the ions present in the effluent are oxidized.

[0090] Biological treatment under anoxic conditions refers to treatment carried out in an environment without supply of O2 (no aeration) but with the presence of oxygen in a combined form (e.g. nitrate, sulfate or other forms) in the environment. In contrast, treatment under aerobic conditions is carried out in an environment with supply of oxygen O2.

[0091] Biological treatment can be carried out in fixed culture, where bacteria grow in the form of biofilm on the surface of the support material, or in free (free) culture (also called activated sludge), where bacteria grow freely in enclosure (flocs). In the case where biological treatment is carried out in free culture (i.e. "activated sludge"), it then includes the step of separating the bacterial culture (i.e. sludge) from the treated liquid effluent. The sludge is generally sent back to the biological treatment. The separation can be carried out in a clarifier (settler) or in a filter using a microfiltration or ultrafiltration membrane. In the case where a series of bioreactors with free cultures are installed (continuous multi-pass biological treatment), the separation of biomass can be carried out downstream of the last reactor.

[0092] “Wastewater” means municipal wastewater, the origin of which is mainly domestic wastewater, but part of which may come from industrial wastewater or even industrial wastewater, especially wastewater from the agro-food industry or any other industry that produces wastewater with carbonaceous materials and nitrogen.

[0093] Struvite is a magnesium ammonium phosphate salt with the chemical formula NH4MgPO4·6H2O. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Other characteristics and advantages of the invention will emerge from a reading of the following description of several specific embodiments of the invention given by way of illustration and not limitation, with reference to the accompanying drawings, in which:

[0095] [ Figure 1 ] Figure 1 is a schematic diagram of a processing facility according to one embodiment of the present invention.

[0096] [ Figure 2 ] Figure 2 is a schematic diagram of a treatment plant according to an alternative first embodiment of the present invention.

[0097] [ Figure 3 ] Figure 3 is a schematic diagram of a treatment facility according to an alternative second embodiment of the present invention.

[0098] [ Figure 4 ] Figure 4 is a schematic diagram of a treatment facility according to an alternative third embodiment of the present invention.

[0099] [ Figure 5 ] Figure 5 is a schematic diagram of a treatment facility according to an alternative fourth embodiment of the present invention.

[0100] [ Figure 6 ] Figure 6 is a schematic diagram of a treatment facility according to an alternative fifth embodiment of the present invention. DETAILED DESCRIPTION

[0101] method

[0102] The method according to the invention is a method for treating a substance containing ammonium ions (NH4 + ) is a method for treating wastewater containing nitrogen and carbonaceous substances, which is also called a method for treating nitrogen and carbonaceous substances in wastewater. These wastewaters often contain suspended particles which can also be removed by the method according to the invention.

[0103] The nitrogen present in wastewater is mainly in the form of ammonium ions. However, it may also be present in the form of organic nitrogen, which is eventually converted into ammonium ions by bacteria through ammoniation.

[0104] The wastewater treatment method comprises a wastewater treatment step (a) which produces a first effluent having a reduced carbonaceous matter content and a second effluent having an increased carbonaceous matter content; and a treatment step (b) comprising at least one electro-oxidation step which electro-oxidizes at least a portion of the first effluent to produce a third effluent having a reduced nitrogen content; and a step (c) which anaerobically digests the second effluent to produce biogas and digestate.

[0105] Thus, step (a) is a step of removing carbonaceous matter, step (b) is a step of removing nitrogen, and step (c) is a step of generating biogas.

[0106] The following alternative arrangements of the individual steps of the method can be combined depending on the determined processing objectives.

[0107] Wastewater treatment step (a)

[0108] The wastewater treatment step (a) produces a first effluent having a reduced carbonaceous matter content relative to the wastewater to be treated, and a second effluent having an increased carbonaceous matter content relative to the wastewater to be treated.

[0109] The treatment step is a first treatment step, which may comprise at least one treatment step selected from a physical treatment step (a1) (optionally preceded by a physico-chemical treatment step (a2)) and a biological treatment step (a3, a4), or a combination of these steps.

[0110] The physical treatment step (a1) can be selected from a sedimentation step, a flotation step or a filtration step. The significance of step (a1) is to remove solid particles. The physical treatment step (a1) thus produces a sludge corresponding to the second effluent with an increased carbonaceous matter content and an effluent corresponding to the first effluent with a reduced carbonaceous matter content.

[0111] The physico-chemical treatment step (a2) generally comprises a coagulation (or electrocoagulation) step followed by a flocculation step. This type of treatment is usually carried out in the presence of chemical reagents (e.g. coagulants and / or flocculants). The coagulant can be added to the water to be treated, or it can be formed on the spot (electrocoagulation). The flocculant is usually added to the coagulated water. It is also possible to consider only a flocculation step.

[0112] When step (a1) is present, a physico-chemical treatment step (a2) is carried out upstream thereof. Adding a flocculant, or a coagulant and a flocculant upstream of the physical treatment can improve the separation of the first effluent and the second effluent by also removing flocculated colloidal organic matter, and accelerate the process, which can result in a reduction in the size of the facility.

[0113] Preferably, the physical treatment step (a1) is a sedimentation step, with or without a prior physico-chemical treatment step (a2), in particular with or without prior coagulation / flocculation.

[0114] The treatment step (a) may further comprise at least one step (a3) ​​of biologically treating the carbonaceous material.

[0115] The biological treatment step (a3) ​​can be carried out under anoxic or aerobic conditions and is suitable for removing carbonaceous materials present in the treated wastewater. Treatment under anoxic conditions allows the removal of biodegradable carbonaceous materials by denitrification, i.e. without the need to add oxygen by aeration. When the biological treatment is carried out under anoxic conditions, upstream of or in the biological treatment step (a3) ​​under anoxic conditions, the portion of the effluent produced by step (b) containing nitrates and / or nitrites is sent back to upstream or in step (a), which allows the removal of residual nitrogen during the biological treatment of carbon. Treatment carried out under aerobic conditions allows the removal of residual biodegradable carbonaceous materials. The ordering of anoxic and then aerobic conditions makes it possible to limit the air intake for the overall removal of carbon, thereby optimizing the energy requirements of the biological treatment step (a3).

[0116] Typically, the biological treatment step (a3) ​​is carried out under conditions of limited nitrification, that is to say with a low sludge age (low sludge retention time). The purpose of this step is to treat only carbonaceous substances, without treating the nitrogen present in the wastewater. To this end, the skilled person will be able to select suitable conditions by specifically controlling one or more of the following parameters: sludge retention time (which is selected in particular according to the ambient temperature), hydraulic retention time, aeration, oxygen supply, etc. In particular, a high-load activated sludge process can be used to implement the biological treatment step (a3) ​​or a denitrifying biofilter.

[0117] Thus, the biological treatment step (a3) ​​produces a sludge corresponding to the second effluent having an increased content of matter, and an effluent corresponding to the first effluent having a reduced content of carbonaceous matter.

[0118] Preferably, the biological treatment step (a3) ​​is carried out under anoxic conditions. Alternatively, the biological treatment step (a3) ​​is carried out in two parts, the first part is carried out under anoxic conditions and the second part is carried out under aerobic conditions. The biological treatment is carried out first under anoxic conditions and then under aerobic conditions, so that the residual biodegradable carbon can be processed and a sludge with high methane production potential is produced.

[0119] The treatment step (a) may also include at least one step (a4) of anaerobic biological treatment in a free culture of carbonaceous matter, in order to advantageously biologically treat (remove) a portion of the phosphorus contained in the effluent. In the case where step (a4) is followed by step (a3), these steps are carried out in a free culture. Step (a3) ​​then includes a separation step, for example, carried out in a clarifier. The separated activated sludge is then sent back to step (a4).

[0120] In a first embodiment, the processing step (a) may include:

[0121] - at least one physical treatment step (a1) or a physico-chemical treatment step (a2), or a sequence of at least one physico-chemical treatment step (a2) and at least one preceding physical treatment step (a1) such as for example a sedimentation or filtration step with or without coagulation / flocculation;

[0122] This is followed by at least one biological treatment step (a3) ​​for removing carbonaceous substances present in the effluent from the physical treatment step (a1) or the physico-chemical treatment step (a2).

[0123] The sludges from the various steps (a1), (a2), (a3) ​​can then be combined to form a second effluent having an increased content of carbonaceous matter.

[0124] In a second embodiment, the processing step (a) may include:

[0125] - at least one physical treatment step (a1) or a physico-chemical treatment step (a2), or a sequence of at least one physico-chemical treatment step (a2) and at least one physical treatment step (a1);

[0126] - followed by at least one anaerobic biological treatment step (a4) for removing the phosphorus present in the effluent;

[0127] This is followed by at least one biological treatment step (a3) ​​for removing the carbonaceous substances present in the effluent under anoxic and / or aerobic conditions.

[0128] Advantageously, sludges from the physical treatment step (a1 ) and / or the physico-chemical treatment step (a2) and the biological treatment steps (a3), (a4) are combined to form a second effluent having an increased content of carbonaceous matter.

[0129] A person skilled in the art can select step (a), and in particular one or more of the above steps (a1), (a2), (a3), (a4) according to a number of factors, in particular the size of the plant, the amount of wastewater to be treated, and in particular the nitrogen and carbon content in the wastewater. A person skilled in the art can also select suitable implementation conditions for step (a) to maximize the content of carbonaceous matter present in the second effluent.

[0130] Electro-oxidation treatment step (b)

[0131] The first effluent from treatment step (a) is then treated by electro-oxidation to produce a third effluent having a reduced nitrogen content. During step (b), at least a portion of the ammonium ions contained in the first effluent are oxidized to nitrates and / or nitrites, and / or dinitrogen.

[0132] Electrooxidation, also known as anodic oxidation or electrochemical oxidation, is an advanced oxidation process. Electrooxidation can be direct or indirect. Electrooxidation is direct when electrons are exchanged directly between the electrode surface and ions adsorbed at the electrode surface (ammonium ions). Electrooxidation is indirect when electrons are exchanged with the aid of an intermediate oxidant. These oxidants can be generated at the electrode surface by transferring electrons to ions present in the water (chloride, sulfate) or directly to water (electrolysis of water). In wastewater, the main oxidant generated at the electrode surface is the hydroxyl radical (HO - ), sulfate (SO4 - ), hypochlorous acid (HClO), or even ozone (O3) or hydrogen peroxide (H2O2). For example, the treatment of ammonium ions can be carried out by oxidizing ammonium ions to nitrates and / or nitrites at the anode and simultaneously reducing nitrites and / or nitrates to N2 at the cathode. Alternatively, the ammonium ions can be directly oxidized to N2 at the anode. The electrolysis of water results in the production of H2 (gas) at the cathode and O2 (gas) at the anode. Such electrolysis can occur whether the electro-oxidation is partial or complete.

[0133] Electro-oxidation is a well known process and will not be described in further detail. Electro-oxidation is usually controlled by varying the current density applied between the electrodes and the flow rate (residence time) of the effluent entering the electro-oxidation chamber.

[0134] During the electro-oxidation step, organic matter still present, in particular refractory carbonaceous substances and / or organic micropollutants, can be removed by partial or complete indirect electro-oxidation, which allows obtaining low levels of carbon in the treated water.

[0135] Furthermore, reaction intermediates (intermediate oxidants), which are essentially non-selective oxidants, have an effect on microorganisms, which allows partial or even complete disinfection of the treated water to be achieved.

[0136] Step (b) may comprise or consist of a step of complete electro-oxidation of ammonium ions to dinitrogen.

[0137] Alternatively, step (b) may comprise (or consist of) one or more electro-oxidation steps, such as a step of partial electro-oxidation of at least a portion of the ammonium ions to nitrate and / or nitrite, followed by a step of complete electro-oxidation of at least a portion of the nitrate and / or nitrite to dinitrogen, optionally with an intermediate anaerobic ammonium oxidation (Anammox) step.

[0138] Thus, in one embodiment, the nitrogen removal step (b) may comprise the step (b1) of partially electro-oxidizing at least a portion of the ammonium ions into nitrates and / or nitrites.

[0139] At the output of the partial electro-oxidation step (b1), at least a portion of the produced effluent can be sent to the treatment step (a). When the treatment step (a) comprises a biological treatment step (a3) ​​under anoxic conditions, recycling a portion of the produced effluent can optimize the energy requirements for carbon reduction.

[0140] Advantageously, the recovery is carried out upstream or in the step (a3) ​​of biological treatment of carbonaceous matter. Preferably, the recovery is carried out upstream or in the step (a3) ​​of biological treatment under anoxic conditions. In fact, the presence of nitrates and / or nitrites in the recovery (recycling) makes it possible to completely or partially dispense with the aeration usually necessary to reduce carbon emissions by non-nitrifying biological treatment.

[0141] The step (b1) of partial electrooxidation of ammonium ions may then be followed by a step (b2) of complete electrooxidation of at least a portion of the nitrate and / or nitrite to dinitrogen. During step (b2), at least a portion of the nitrate and / or nitrite is reduced to dinitrogen, however, a portion of the ammonium ions that were not oxidized during step (b1) may also be oxidized during this step.

[0142] The step (b2) of completely electro-oxidizing at least a portion of the nitrate and / or nitrite is intended to complete the removal of total nitrogen and reach the total nitrogen content limit predetermined by the operator or emission standard. This limit can be verified by directly measuring the content of ammonium ions and / or nitrate and / or nitrite with a suitable sensor and / or analyzer.

[0143] In an alternative third embodiment, step (b) may comprise a step (b1) of partially electro-oxidizing a portion of the ammonium ions, followed by a step (b3) of biologically treating a portion of the ammonium ions by oxidation using anaerobic autotrophic bacteria (also referred to as Anammox), and optionally followed by a step (b2) of completely electro-oxidizing at least a portion of the nitrate and / or nitrite to dinitrogen.

[0144] Thus, the Anammox treatment step (b3) is combined with the step (b1) of partially electrooxidizing ammonium ions to nitrates / nitrites. At the output of the partial oxidation step (b1), only a portion of the ammonium ions have been oxidized. The Anammox treatment step (b3) utilizes anaerobic autotrophic bacteria that consume ammonium ions and nitrites to produce N2 without oxygen and biodegradable carbon. Therefore, at the input of the Anammox treatment step (b3), ammonium ions and nitrites need to be provided by the incomplete partial oxidation step (b1). The combination of steps (b1) and (b3) can reduce the total energy consumption of nitrogen removal, especially the optional step (b2) of completely electrooxidizing nitrates / nitrites located downstream, which does not require oxidation of all ammonium ions not treated by step (b1) and all nitrates / nitrites formed by step (b1).

[0145] This embodiment also allows a better and more stable control of the NH4 / NOx ratio at the Anammox input, since the partial electrooxidation can be controlled by the applied current density. Thus, the partial electrooxidation step (b1) can be implemented to obtain at the output an effluent having a nitrite / ammonium ion concentration ratio that is favorable for its treatment by the Anammox bacteria. This ratio is, for example, between 0.8 and 1.8, preferably between 1.1 and 1.5 gN / gN.

[0146] However, the Anammox treatment step (b3) may not achieve a high ammonium ion removal rate, which may result in ammonium ions and nitrites passing through the output of the treatment, which must be converted to nitrates, or even partially converted to N2, in order to meet strict emission standards. It is then preferred that the Anammox treatment step (b3) is followed by a step (b2) of complete electro-oxidation of at least a portion of the remaining nitrates and / or nitrites and / or ammonium to dinitrogen.

[0147] Optionally, regardless of which embodiment of the present invention, especially step (b), H2 gas produced at the cathode during water electrolysis can be recovered for its utilization, and the water electrolysis may occur during the electro-oxidation step (b), especially during the step (b1) of partially electro-oxidizing ammonium ions into nitrate / nitrite and / or the step (b2) of completely electro-oxidizing at least a portion of nitrate and / or nitrite into dinitrogen.

[0148] Optionally, during the water electrolysis, the O2 gas produced at the anode can be recovered for its utilization or reinjected into the biological treatment step (a3) ​​for removing carbonaceous matter to reduce its energy requirement when it is carried out partially or completely under aerobic conditions, wherein the water electrolysis may occur during the electro-oxidation step (b), in particular during the step (b1) of partial electro-oxidation of ammonium ions to nitrate / nitrite and / or the step (b2) of complete electro-oxidation of at least a portion of nitrate and / or nitrite to dinitrogen.

[0149] Optional step (d) of treating the third effluent produced in step (b)

[0150] Optionally, the treatment step (b) is followed by a step (d) of treating the produced third effluent. The step (d) of treating the third effluent may include at least one treatment selected from a treatment for removing suspended matter, a treatment for removing phosphorus compounds, a treatment for removing micropollutants, and a treatment for removing microorganisms.

[0151] The treatment step for removing suspended matter may be a physical or physico-chemical treatment as described in step (a). It may involve, for example, a sedimentation, filtration or flotation step, with or without (preferably with) prior coagulation / flocculation.

[0152] The treatment step for removing phosphorus compounds may be a physical or physico-chemical treatment of the type described above, wherein a coagulant provided by a chemical reagent or by electrocoagulation is added to remove the phosphorus compounds.

[0153] The treatment steps for removing micropollutants or microorganisms may include at least one treatment selected from the following: electrocoagulation, advanced oxidation (for example ozonation or electrooxidation or by injection of strong oxidants, such as ferrate), an adsorption step on activated carbon, disinfection (for example with the help of oxidants, such as chlorine, peracid, ultraviolet light, peracid or chlorine).

[0154] The third effluent treatment step (d) is designed to further clean the water, or reuse the water when it is discharged into a sensitive ecosystem. The treatment step (d) can produce a fourth effluent having a nitrogen, carbonaceous matter, micropollutant and / or microbial content that meets the specifications required by the operator or regulations and can be discharged into nature or reused.

[0155] Optional control steps

[0156] The treatment method may further include a control step of controlling the wastewater treatment step (a) and the electro-oxidation treatment step (b).

[0157] The control step can control the amount of the first effluent entering the treatment step (b) and / or one of the steps (b1), (b2), (b3) of step (b). As a variant or in combination, the control step can control the amount of the effluent generated during the step (b1) of partial electrooxidation of ammonium ions that can be recovered in step (a).

[0158] During this control step, first (i1) the amount of nitrogen present in the third or fourth effluent and in at least one effluent to be extracted is determined, the at least one effluent to be extracted being chosen from the first effluent of step (a), the effluent of the step (b1) of partial electrooxidation of ammonium ions, and the effluent of the Anammox step (b3). The amount of nitrogen can be measured directly by a sensor for measuring the amount of ammonium ions and / or nitrate / nitrite. The amount of nitrogen can also be measured indirectly by an ammonia analyzer.

[0159] Then, (i2) the amount of the at least one effluent to be extracted is determined so as to reach the nitrogen limit content in the third effluent or the fourth effluent, and the at least one effluent to be extracted in said amount is extracted and mixed with the third effluent or the fourth effluent. For this purpose, the amount of nitrogen measured in the third effluent or the fourth effluent can be used to determine the amount of the at least one effluent to be extracted so that when it is combined with the third effluent or the fourth effluent, the total nitrogen content of the latter does not exceed the nitrogen limit content. The permitted nitrogen limit content (especially ammonium ions) can be selected according to the nitrogen emission limit permitted by law. Once the amount of the effluent to be extracted has been calculated based on the measurements carried out on the third effluent or the fourth effluent and the at least one effluent to be extracted, this amount is extracted to inject it into the third effluent or the fourth effluent.

[0160] During the step of controlling a portion of the effluent produced during the step (b1) of partially electro-oxidizing ammonium ions, (i3) determines the amount of effluent from the partial electro-oxidation step (b1) to be transported to the biological treatment step of step (a). The amount can be determined by measuring with a nitrate / nitrite / ammonia sensor, or by an analyzer. The amount corresponds to the content of nitrate and / or nitrite that can remove carbonaceous substances in the wastewater entering the biological treatment step (a3). In particular, pre-planning can be carried out when determining the amount of carbonaceous substances in the wastewater to determine the amount of effluent to be recovered. This amount of effluent is then transported to the biological treatment step (a3) ​​of step (a), preferably when this step is carried out under anaerobic conditions. Recovery (recycling) can also reduce the energy required to be used in the second electro-oxidation step (b2).

[0161] Anaerobic digestion step (c)

[0162] The second effluent from treatment step (a) is treated by an anaerobic digestion step (c) producing biogas and digestate.

[0163] Anaerobic digestion or methanogenesis corresponds to a series of biochemical reactions allowing methanogenic bacteria to transform the organic matter present in the digester into biogas corresponding mainly to a mixture of carbon dioxide and methane. The remaining substance is called digestate (or digestate).

[0164] The conditions under which this step (c) is carried out, in particular the temperature, the pH value and the residence time, may advantageously be chosen so as to maximize the biogas production.

[0165] The anaerobic digestion step (c) may also include, or be followed by, a solid-liquid separation step of the digestate, which allows the digestate to be separated into a solid portion and a liquid portion. The separation step may be a digestate dewatering step, such as, for example, a centrifugation or filtration step, which produces a solid portion (dewatered sludge) and a liquid portion.

[0166] Optionally, upstream of the anaerobic digestion step (c), at least one pretreatment step of the second effluent may be performed to improve its yield. The pretreatment step may be selected from chemical, mechanical, biological and thermal pretreatment steps.

[0167] The chemical pretreatment step may be an acidic or alkaline hydrolysis or an advanced oxidation.During the chemical pretreatment the sludge may be heated to a temperature below 100°C.

[0168] The mechanical pretreatment step may be a disintegration step by ultrasound, microwaves or electrokinesis.

[0169] The biological pretreatment step is, for example, a fermentation / hydrolysis step under mesophilic (30-42°C) or thermophilic (45-70°C) conditions with a residence time of about 1 to 3 days.

[0170] Finally, the thermal pretreatment step may be a thermal hydrolysis process (THP). The thermal hydrolysis process (THP) is a process in which the sludge is heated to a temperature generally between 140°C and 180°C for a treatment time of 30 minutes to 60 minutes.

[0171] Optionally, a post-treatment step may also be implemented at the output of step (c) of treating the second effluent by anaerobic digestion. In fact, the digested sludge obtained in the anaerobic digestion step (c) contains a large amount of non-biodegradable organic matter that can be used to generate additional energy. The post-treatment step is usually a hydrothermal carbonization (HTC) process. The process is usually operated in a non-oxidizing atmosphere at a temperature of 180°C to 280°C for several minutes to several hours. The wet dehydrated sludge is treated with pressurized steam, and the process produces a solid carbonaceous part and a liquid part. The liquid part can be sent back to the anaerobic digestion step (c) to increase the biogas production.

[0172] An optional additional step (e) of treating the liquid portion of the digestate produced in step (c)

[0173] In one embodiment, the step (c) of anaerobic digestion of the second effluent may be followed by an additional step (e) of treating at least a portion of the liquid portion of the digestate resulting from the digestion step (c). The effluent resulting from the additional step (e) may then be sent back to the input of the process for recovery (recycling) of the effluent. Recovery (recycling) of this treated stream allows the process to be optimized by treating as much of the wastewater as possible and thereby reducing the load contained in these return streams.

[0174] The additional treatment step (e) may be selected from a step of electrocoagulation treatment (e0), an electrooxidation treatment step (e1), a biological treatment step (e2) using anaerobic autotrophic bacteria to oxidize ammonium ions (Anammox treatment), and a sequence of the latter two steps (e1), (e2) with or without a preceding step (e0). The solid portion of the biomass produced by the Anammox step (e2) may be fed back to the input of the digestion step (c).

[0175] An additional step (e) enables the treatment of the liquid fraction enriched in ammonium ions to reduce its nitrogen content so that it can be fed back to the main water pipeline at the input of step (a) or to step (a).

[0176] Preferably, the step of treating the liquid portion of additional step (e) is an electro-oxidation step to completely oxidize the ammonium ions to dinitrogen. In this arrangement, the electro-oxidation will also oxidize dissolved carbon and should not be affected by the variation in the collection rate of the sludge pre-treatment process. High temperature and high nitrogen content also provide conditions that are favorable for the electro-oxidation dynamics.

[0177] Alternatively, the step of treating the liquid portion of the additional step (e) is an electro-oxidation step followed by an Anammox treatment step. In this case, the electro-oxidation step is a step of partial electro-oxidation of the ammonium ions into nitrates / nitrites. As explained in the description of step (b), this embodiment leads to a better and more stable control of the NH4 / NOx ratio. The energy requirement is also improved since only a portion of the liquid portion of the digestate is subjected to electro-oxidation, which reduces the associated energy requirements.

[0178] Optionally, the additional step (e) comprises an electrocoagulation treatment step (e0) comprising a first sub-step of precipitation of the phosphorus and ammonium contained in the liquid part of the digestate in the form of struvite by carrying out electrocoagulation with the aid of a sacrificial anode comprising magnesium, combined with a sub-step of forming the struvite by separation, which may be, for example, filtration or sedimentation. This step (e0) has the advantage of reducing the amount of nitrogen to be oxidized by the subsequent steps, while producing a resource (struvite) with a high agronomic added value (fertilizer), without the need to add external chemical agents, since the magnesium required for precipitation comes from the electrocoagulation.

[0179] Description of the facility

[0180] Reference Figure 1 The facility 100 for treating wastewater containing nitrogen and carbonaceous materials in the form of mainly ammonium ions comprises a first wastewater treatment unit 110 suitable for implementing step (a) of the method, a second electro-oxidation treatment unit 120 suitable for implementing step (b) of the method, and a third anaerobic digestion treatment unit 130 suitable for implementing step (c) of the method.

[0181] The first wastewater treatment unit 110 is configured to be supplied with wastewater containing nitrogen and carbonaceous substances in the form of ammonium ions in part by a supply pipe 1, and is configured to produce a first effluent with a reduced carbonaceous substance content and a second effluent with an increased carbonaceous substance content, the first effluent being discharged into a first discharge pipe 2, and the second effluent being discharged into a second discharge pipe 3. The first treatment unit 110 can be a physical, physico-chemical or biological treatment unit. To this end, it can include one or more treatment reaction zones selected from a filtration reaction zone, a sedimentation reaction zone, a flotation reaction zone, a coagulation reaction zone, a flocculation reaction zone, an electrocoagulation reaction zone, and a biological treatment reaction zone (which has aeration for aerobic treatment, or does not have aeration for anoxic treatment). In particular, one or more reaction zones installed in parallel and / or in series can be provided to implement each of the physical treatment step (a1), the physico-chemical treatment step (a2) or the biological treatment step (a3, a4).

[0182] The reaction zone may comprise a reactor or a treatment chamber. When the reactor or treatment chamber performs the biological treatment in a free culture, the reaction zone may comprise a system for separation by means of sedimentation (clarifier) ​​or filtration.

[0183] exist Figure 1 In the example of, the first unit 110 may include one or more biological treatment reaction zones, such as a single sequencing batch reactor (which is also called an SBR reactor, Sequential Batch Reactor), a continuously supplied reactor with a suspended free culture (activated sludge), or a biofiltration reactor (a reactor using a thin and regularly renewed biofilm), or a separate (separate) plurality of reactors, especially with recirculation between them. The use of separate reactors allows continuous treatment of the effluent. In all cases, the present invention is not limited by the number of reactors used, in particular, multiple reactors each operating according to an aerated / non-aerated cycle may be provided, or multiple continuously supplied reactors or reactors comprising a sequential sequence of SBRs and continuously supplied reactors may be provided. The first treatment unit 110, when it contains an aerobic biological treatment reaction zone, will be sized to avoid biological nitrification.

[0184] The second electro-oxidation treatment unit 120 is configured to be supplied with the first effluent from the supply pipe 4 connected to the first discharge pipe 2 of the first treatment unit 110, and is configured to discharge the third effluent having a reduced nitrogen content through the discharge pipe 5. To this end, the second unit 120 includes at least one electro-oxidation reaction zone to implement the at least one electro-oxidation step. Figure 1 In the example of, the second treatment unit 120 includes one or more electro-oxidation reaction zones installed in series and / or in parallel. The one or more reaction zones can particularly implement complete or partial oxidation. Moreover, the second unit 120 does not include an aerobic biological treatment reaction zone. The second unit 120 may also include a dioxygen discharge pipeline 37 for discharging dioxygen from the electro-oxidation area and a dihydrogen discharge pipeline 38 for discharging dihydrogen from the electro-oxidation area.

[0185] The first discharge conduit 2 and the supply conduit 4 are also connected to an optional bypass conduit 13 (bypass conduit) via a valve 30. The discharge bypass conduit 13 is connected to the discharge conduit 5 of the third effluent.

[0186] The third anaerobic digestion treatment unit 130 includes a supply pipe 6 connected to the second pipe 3 of the first treatment unit 110, a biogas discharge pipe 7, and a digestate discharge pipe 8. The third unit 130 may include one or more anaerobic digestion reaction zones, which are particularly installed in series and / or in parallel.

[0187] Figure 2 and Figure 3 An alternative set-up of the plant is shown, in particular for carrying out the wastewater treatment step (a). Figure 2 and Figure 3 The wastewater treatment facilities 200 and 300 are shown respectively, which include a first wastewater treatment unit 110, a second electro-oxidation treatment unit 120, and a third anaerobic digestion treatment unit 130. These units 120 and 130 are relatively Figure 1 The reference numerals remain the same for these units and the pipes involved.

[0188] Reference Figure 2 The first wastewater treatment unit 110 comprises a wastewater physical treatment and / or physico-chemical treatment unit 111 capable of implementing step a1) or a2)+a1), and a biological treatment unit 112 capable of implementing step a3) of the method. The biological treatment unit 112 comprises one or more reaction zones. If the biological treatment is carried out in a free culture, the last reaction zone of the unit comprises a biomass separation system not shown in the figure, such as a clarification chamber.

[0189] The physical and / or physico-chemical treatment unit 111 is supplied with wastewater by a supply conduit 1 and comprises a discharge conduit 9 for discharging a portion of the second effluent and a discharge conduit 11 for discharging the produced effluent.

[0190] The biological treatment unit 112 comprises a supply conduit 12 connected to the discharge conduit 11 of the unit 111. It is also connected to a first discharge conduit 2 for discharging a first effluent and comprises a second discharge conduit 3 for discharging a portion of a second effluent. The first discharge conduit 2 is connected to a supply conduit 4 of a second unit 120 and optionally to a second discharge conduit 4 as described with reference to Figure 1 The bypass pipe 13. Finally, the unit 112 can receive the reference Figure 1 The pipe 37 contains dioxygen.

[0191] Figure 3 and Figure 2 The difference is that an intermediate unit 113 capable of implementing step a4) of the method through one or more biological treatment reaction zones is added between units 111 and 112. Unit 113 is an anaerobic biological treatment unit, which includes a supply pipe 15 connected to the discharge pipe 11 of unit 111, and a discharge pipe 16 connected to the supply pipe 12 of unit 112. Unit 112 also includes a sludge recycling (recovery) pipe 34 connected to the anaerobic biological treatment unit 113. The recycling pipe 34 is present only when the biological treatment of units 112 and 113 is carried out in a free culture.

[0192] Figure 4 and Figure 5 An alternative set-up of the plant is shown, in particular for carrying out the electro-oxidation treatment step (b). Figure 4 and Figure 5 The wastewater treatment facilities 400 and 500 are shown respectively, which include a first wastewater treatment unit 110, a second electro-oxidation treatment unit 120, and a third anaerobic digestion treatment unit 130. These units 110 and 130 are relatively Figure 1 The reference numerals remain the same for these units and the pipes involved.

[0193] Reference Figure 4 The second electro-oxidation treatment unit 120 includes a partial electro-oxidation treatment unit 121 capable of implementing step b1) of the method for partially electro-oxidizing ammonium ions into nitrate / nitrite ions; and a complete electro-oxidation treatment unit 122 capable of implementing step b2) of the method for completely electro-oxidizing nitrate / nitrite ions into dinitrogen. Each unit 121, 122 includes one or more electro-oxidation reaction zones.

[0194] The partial electro-oxidation treatment unit 121 is supplied with a first effluent by a supply conduit 4 connected to the discharge conduit 2 of the unit 110 and comprises a discharge conduit 17 for discharging the effluent output from step b1). The discharge conduit 17 is here connected, via valves 30, 32, to at least one conduit, here to three conduits: the supply conduit 18 of the unit 122, an optional recirculation conduit 20 for recirculating a portion of the produced effluent upstream of the unit 110, and a bypass conduit 19 for bypassing a portion of the produced effluent. The bypass conduit 19 is connected to the bypass conduit 13 and to the discharge conduit 5 of the third effluent. The optional recirculation conduit 20 preferably sends the produced effluent to the first treatment unit 110 (at Figure 4 1 ).

[0195] The complete electro-oxidation treatment unit 122 comprises a supply conduit 18 connected to the exhaust conduit 17 of the unit 121 , and the third effluent it produces is discharged through the exhaust conduit 5 .

[0196] Figure 5 and Figure 4 The difference is that an intermediate unit 123 is added between units 121 and 122, which is capable of implementing step (b3) of the method. Unit 123 includes one or more non-aerated biological treatment reaction zones. Unit 123 is an Anammox treatment unit and includes a supply pipe 21 connected to the discharge pipe 17 of unit 121, and a discharge pipe 22 connected to the supply pipe 18 and bypass pipe 19 of unit 122. The supply pipe 21 of unit 123 is also connected to a bypass pipe 33 of a portion of the first effluent from the discharge pipe 2 of unit 110.

[0197] Figure 5 The facility shown has an optional fourth unit 124 capable of carrying out step (d) of treating the third effluent. The treatment unit 124 comprises a supply conduit 23 connected to the discharge conduit 5 of the unit 122, and a discharge conduit 24 for discharging the fourth effluent. The fourth unit may comprise one or more treatment reaction zones installed in series and / or in parallel.

[0198] Figure 6 An alternative arrangement of treatment facilities is shown, specifically downstream of an anaerobic digestion unit. Figure 6 6 shows a wastewater treatment facility 600, which includes a first wastewater treatment unit 110, a second electro-oxidation treatment unit 120, and a third anaerobic digestion treatment unit 130. Here, these units 110, 120 and 130 are relatively similar, except that unit 130 includes a discharge pipe 8' for discharging the liquid part of the produced digestate. Figure 1 The reference numerals remain the same for these units and the pipes involved.

[0199] Reference Figure 6 , the installation comprises a fifth unit 131 capable of implementing the additional step e) of the method.

[0200] The fifth unit 131 includes an optional electrocoagulation treatment unit 132 capable of implementing step e0), an electrooxidation treatment unit 133 capable of implementing step e1), and an optional Anammox treatment unit 134 capable of implementing step e2). Each unit may include one or more suitable treatment reaction zones installed in series and / or in parallel.

[0201] The unit 132 comprises a supply conduit 25 connected to the discharge conduit 8' of the unit 130, and a discharge conduit 26 for discharging the produced effluent.

[0202] In this embodiment, the third unit 130 includes a solid-liquid separation system (not shown) that allows the digestate to be separated into a solid portion and a liquid portion. The liquid portion is then discharged through the discharge pipe 8'. It should be noted that the solid-liquid separation system can be external to the third unit 130 and located between it and the fifth unit 131.

[0203] The unit 133 comprises a supply conduit 27 connected to the discharge conduit 26 of the unit 132, and a discharge conduit 28 for discharging the produced effluent.

[0204] Unit 134 comprises a supply conduit 35 connected to the discharge conduit 28 of unit 132 , and a discharge conduit 36 ​​which returns the effluent to the wastewater supply conduit 1 .

[0205] The above-mentioned processing facilities 100, 200, 300, 400, 500, 600 may also include a control system for controlling the method to implement steps (i1), (i2) and (i3) of the control step. Figures 1 to 6 The control system comprises at least one measuring device 29 for measuring the content of ammonium ions and / or nitrates and / or nitrites, at least one fluid moving device 30 for moving the fluid, and a control unit 31 .

[0206] The control unit 31 is configured as follows:

[0207] - performing step (i1) based on the measured quantity (value) received from said at least one determination device 29;

[0208] - Based on the amount determined in step (i1), and by controlling the at least one fluid moving device 30, performing step (i2)

[0209] - Based on the amount determined in step (i1), and by controlling the at least one fluid moving device 30, performing step (i3).

[0210] The at least one measuring device 29 may be one or more sensors of the nitrogen content of the effluent. The at least one measuring device 29 may be installed at the third effluent discharge conduit 5 or the fourth effluent discharge conduit 24, and at least one conduit selected from the first discharge conduit 2 for discharging the first effluent with a reduced carbonaceous matter content, the discharge conduit 17 for discharging the effluent output from the partial electro-oxidation step, and the discharge conduit 22 for discharging a portion of the effluent produced by the Anammox step b3).

[0211] The amount measured by the at least one measuring device 29 is sent to a control unit 31 which calculates the amount of fluid to be extracted through the bypass conduit and controls the movement of this amount. The control unit 31 may comprise a computer, or more generally, at least one processor or any other type of digital calculator. The control unit 31 may also comprise a plurality of processors or digital calculators, respectively, which form different means of the device and cooperate with each other.

[0212] The at least one fluid moving device 30 for moving the fluid may comprise one or more valves, for example a three-way or four-way valve, the third of which leads to the bypass duct 13 and optionally to the bypass duct 19. The at least one device 30 may also comprise one or more positive displacement pumps (or any pump combined with a frequency converter and a flow meter to regulate its flow rate) capable of extracting the calculated amount of fluid to be extracted. The bypass duct connected to the valve also forms a moving device in the sense of the present invention.

[0213] Reference Figure 4 and Figure 5 In order to control the recovery (recycling) of the effluent from the first electro-oxidation treatment unit, the control system includes a measuring device 29 for measuring the content of ammonium ions and / or nitrates and / or nitrites, a fluid moving device 32, and a control unit 31.

[0214] The measuring device 29 may be a sensor for the nitrogen content of the effluent. Here, it is installed at the discharge pipe 17 for discharging the effluent output from the partial electro-oxidation treatment unit 121.

[0215] The measured quantities are sent to the control unit 31 which calculates the quantity of recirculating fluid to be recovered corresponding to the nitrate and / or nitrite content required for the anoxic biological treatment for the removal of carbonaceous materials. The control unit 31 also controls the movement of the quantity of recirculating fluid to be recovered.

[0216] The device 32 for moving the fluid may be a three-way or four-way valve, one of the ways of which opens into the recirculation conduit 20. The device 32 may also be a positive displacement pump (or any pump combined with a frequency converter and a flow meter) capable of extracting the calculated amount to be recovered.

[0217] Reference Figures 1 to 6 The above-described various embodiments can be combined with each other according to the determined processing objectives.

Claims

1. A method for treating wastewater comprising nitrogen in the form of ammonium ions and carbonaceous matter, the method comprising: (a) a wastewater treatment step to produce a first effluent having a reduced carbonaceous matter content and a second effluent having an increased carbonaceous matter content, (b) a treatment step of treating at least a portion of said first effluent to produce a third effluent having a reduced nitrogen content, and (c) an anaerobic digestion step of said second effluent to produce biogas and digestate; The method is characterized in that The treatment step (b) is carried out without biological nitrification under aerobic conditions and comprises at least one electro-oxidation step during which at least a portion of the ammonium ions contained in the first effluent are oxidized to nitrite and / or nitrate, and / or dinitrogen.

2. The wastewater treatment method according to claim 1, characterized in that: The treatment step (a) comprises at least one treatment step for treating the carbonaceous material, which treatment step is selected from a physical treatment step (a1) and a biological treatment step (a3, a4) of the carbonaceous material. Optionally, there is a physico-chemical treatment step (a2) before the physical treatment step.

3. The wastewater treatment method according to claim 2, characterized in that: The physical treatment step (a1) is selected from a sedimentation step, a flotation step and a filtration step, and the physico-chemical treatment step (a2) is selected from a coagulation-flocculation step, a single flocculation step and a step of electrocoagulation followed by flocculation.

4. The wastewater treatment method according to any one of claims 1 to 3, characterized in that: The step (b) comprises the step of completely electro-oxidizing at least a portion of the ammonium ions into dinitrogen.

5. The wastewater treatment method according to any one of claims 1 to 3, characterized in that: The step (b) comprises the step (b1) of partially electro-oxidizing at least a portion of the ammonium ions into nitrates and / or nitrites.

6. The wastewater treatment method according to claim 5, characterized in that: The step (b) comprises: (i) the partial electro-oxidation step (b1) in which a portion of the ammonium ions are oxidized to nitrate and / or nitrite, and a subsequent anoxic biological treatment step (b3) in which the ammonium ions are oxidized by anaerobic autotrophic bacteria; or (ii) the partial electro-oxidation step (b1) in which at least a portion of the ammonium ions are oxidized to nitrate and / or nitrite, and a subsequent step (b2) of completely electro-oxidizing at least a portion of the nitrate and / or nitrite to dinitrogen; or (iii) the partial electro-oxidation step (b1), in which at least a portion of the ammonium ions are oxidized to nitrate and / or nitrite, and a subsequent anoxic biological treatment step (b3) of oxidizing the ammonium ions by using anaerobic autotrophic bacteria, and thereafter a step (b2) of completely electro-oxidizing at least a portion of the nitrate and / or nitrite to dinitrogen.

7. The wastewater treatment method according to claim 5 or 6, characterized in that: At least a portion of the effluent produced by the partial electro-oxidation step (b1) or the anoxic biological treatment step (b3) is conveyed upstream of or into the anoxic biological treatment step (a3) ​​of the carbonaceous material in the treatment step (a).

8. The wastewater treatment method according to any one of claims 1 to 7, characterized in that: During the electro-oxidation step (b), (b1) or (b2), water present in the effluent is electrolyzed so that dioxygen is produced at the cathode and dihydrogen is produced at the anode, and the dihydrogen and / or the dioxygen are recovered and, optionally, the dioxygen is conveyed upstream of or into the step (a3) ​​of biological treatment of carbonaceous matter in the treatment step (a).

9. The wastewater treatment method according to any one of claims 1 to 8, characterized in that: The method also includes a step (d) of treating the third effluent produced by the treatment step (b) to produce a fourth effluent, wherein the treatment step (d) includes at least one treatment selected from: a treatment for removing suspended matter, a treatment for removing phosphorus compounds, a treatment for removing micropollutants, and a treatment for removing microorganisms.

10. The wastewater treatment method according to any one of claims 1 to 9, characterized in that: The method further comprises a control step, in which: (i1) determining the content of nitrogen present in the third effluent or the fourth effluent and in at least one effluent to be extracted, the at least one effluent to be extracted being selected from the first effluent, the effluent of the step (b1) of partial electrooxidation of ammonium ions, and the effluent of the anoxic biological treatment step (b3) of oxidizing ammonium ions by using anaerobic autotrophic bacteria; then, (i2) determining an amount of the at least one effluent to be extracted in order to reach a nitrogen content limit in the third effluent or the fourth effluent, extracting the amount of the at least one effluent to be extracted, and mixing it with the third effluent or the fourth effluent; and / or (i3) determining an amount of effluent from step (b1) of partial electro-oxidation of ammonium ions to be conveyed to the anoxic biological treatment step (a3) ​​of said step (a), which amount corresponds to the amount of nitrate and / or nitrite required for the anoxic biological treatment of said carbonaceous material, and conveying said amount of effluent to the anoxic biological treatment step (a3) ​​of said step (a).

11. The wastewater treatment method according to any one of claims 1 to 10, characterized in that: The method further comprises at least one treatment step (e) for treating at least a part of the liquid part of the digestate produced in the digestion step (c), the treatment step being selected from: an electrocoagulation treatment step (e0), an electrooxidation treatment step (e1), during which at least a part of the ammonium ions contained in the liquid part are oxidized into nitrite and / or nitrate and / or dinitrogen, a step (e2) of anoxic biological treatment by oxidizing the ammonium ions using anaerobic autotrophic bacteria, and a sequence of the two steps (e1) (e2) with or without the step (e0) preceding it.

12. The wastewater treatment method according to claim 11, characterized in that: The electrocoagulation treatment step (e0) comprises a sub-step of precipitating struvite by electrochemically dissolving a sacrificial anode containing magnesium, which is combined with a sub-step of separating the precipitated struvite.

13. A treatment facility (100, 200, 300, 400, 500, 600) for treating wastewater containing nitrogen in the form of ammonium ions and carbonaceous matter, comprising: a first wastewater treatment unit (110) comprising a wastewater supply conduit (1), a first discharge conduit (2) for discharging a first effluent having a reduced carbonaceous matter content, and a second discharge conduit (3) for discharging a second effluent having an increased carbonaceous matter content; - a second treatment unit (120) comprising a supply conduit (4) connected to the first conduit (2) of the first treatment unit (110), a discharge conduit (5) for discharging a third effluent having a reduced nitrogen content, the second treatment unit comprising at least one electro-oxidation treatment reaction zone but not an aerobic biological treatment reaction zone; - A third anaerobic digestion treatment unit (130) comprising a supply conduit (6) connected to the second conduit (3) of the first treatment unit (110), a biogas discharge conduit (7), and a digestate discharge conduit (8).

14. The treatment facility according to claim 13, characterized in that The first unit comprises at least one reaction zone selected from: a physical treatment reaction zone and a biological treatment reaction zone, and optionally the physical treatment reaction zone is connected to the physical-chemical treatment reaction zone.

15. The treatment facility according to claim 13 or 14, characterized in that The second processing unit comprises: - at least one first electro-oxidation treatment reaction zone, and at least one second reaction zone selected from the electro-oxidation treatment reaction zone and the non-aerated biological treatment reaction zone, each second reaction zone being connected to the first reaction zone by a discharge pipe for discharging an effluent output from the first reaction zone; or - at least one first electro-oxidation treatment reaction zone, at least one second non-aerated biological treatment reaction zone, and at least one third electro-oxidation treatment reaction zone, each second reaction zone is connected to the first reaction zone via a discharge pipe for discharging the effluent produced by the first reaction zone, and each third reaction zone is connected to the second reaction zone via a discharge pipe for discharging the effluent output from the second reaction zone.

16. The treatment facility according to claim 15, characterized in that The treatment facility includes a recirculation conduit connecting the output of the at least one first electro-oxidation treatment reaction zone or the at least one second non-aerated biological treatment reaction zone to the input of the biological treatment reaction zone of the first unit.

17. The treatment facility according to any one of claims 13 to 16, characterized in that The treatment facility comprises at least one further treatment unit selected from the group consisting of: a fourth treatment unit (124), comprising a supply conduit connected to the discharge conduit (5) of the second treatment unit, and a discharge conduit for discharging a fourth effluent, and comprising at least one reaction zone selected from the group consisting of: a treatment reaction zone for removing suspended matter, a treatment reaction zone for removing phosphorus compounds, a treatment reaction zone for removing micropollutants, and a treatment reaction zone for removing microorganisms; - A fifth treatment unit (131), comprising a supply pipe connected to a discharge pipe (8') for discharging the liquid part of the digestate of the third unit, and a discharge pipe (36) for discharging effluent, wherein the discharge pipe (36) is optionally connected to the supply pipe (1) of the first unit (110), and further comprising at least one reaction zone selected from an electrocoagulation treatment reaction zone, an electro-oxidation treatment reaction zone, and a non-aerated biological treatment reaction zone for oxidizing ammonium ions using anaerobic autotrophic bacteria, the latter two reaction zones being preceded by or without an electrocoagulation treatment reaction zone, and the output of the electro-oxidation treatment reaction zone being connected to the input of the non-aerated biological treatment reaction zone.

18. The treatment facility according to any one of claims 13 to 17, characterized in that The treatment facility is equipped with a control system, which includes at least one measuring device for measuring the content of ammonium ions and / or nitrates and / or nitrites, at least one fluid moving device, and a control unit, which is configured to: - determining the content of nitrogen present in said third effluent or said fourth effluent and in at least one effluent to be extracted, said at least one effluent to be extracted being chosen from said first effluent, the effluent of said at least one first electro-oxidation treatment reaction zone, and the effluent of said at least one non-aerated biological treatment reaction zone of said first unit; Then, - determining the amount of the at least one effluent to be extracted in order to reach the nitrogen content limit in the third effluent or the fourth effluent, and controlling the at least one fluid moving device to extract the at least one effluent to be extracted in said amount and mix it with the third effluent or the fourth effluent; and / or - Determining the amount of effluent from the at least one first electro-oxidation treatment reaction zone to be transported to the non-aerated biological treatment reaction zone of the first treatment unit, and controlling the at least one fluid moving device to transport the amount of the effluent to the non-aerated biological treatment reaction zone of the first unit (110), the amount corresponding to the amount of nitrate and / or nitrite required for the non-aerated biological treatment of the carbonaceous material.

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