Separation liquid treatment apparatus, water treatment system, and separation liquid treatment method

Abstract

To provide a separation liquid treatment device that can remove and recover not only phosphorus but also nitrogen to a large extent from organic wastewater, and that reduces the power consumption of aeration equipment when performing biological treatment. [Solution] A separation liquid treatment apparatus for treating organic sludge generated in the process of purifying organic wastewater containing nitrogen components with aerobic microorganisms, after anaerobic digestion treatment of the organic sludge, before returning the separated liquid to the purification process, comprising a reaction tank for storing part or all of the separation liquid and adding and mixing phosphoric acid and magnesium salts to the stored separation liquid.

Description

[Technical Field]

[0001] The present invention relates to a separation liquid treatment apparatus, a water treatment system, and a separation liquid treatment method. [Background technology]

[0002] A water treatment system is known in which organic wastewater is treated by sending it in the order of primary sedimentation tank, biological treatment tank, and final sedimentation tank, while the sludge generated in the primary and final sedimentation tanks is treated in an anaerobic digester. In this water treatment system, magnesium hydroxide is added to the separated liquid (desorbed liquid) from which solid matter has been separated from the effluent of the anaerobic digester to crystallize phosphorus compounds such as magnesium ammonium phosphate (MAP), and the crystallized material is separated and recovered. Patent Document 1 describes storing the crystallized phosphorus compounds in a washing device and washing them, and controlling the amount of phosphorus compounds transferred from the washing device based on the measurement results of the amount of phosphorus compounds stored. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-158515 [Overview of the project] [Problems that the invention aims to solve]

[0004] The separated liquid described above contains a large amount of ammonia nitrogen. Even if phosphorus compounds are crystallized and separated and recovered from this separated liquid, the remaining liquid still contains a large amount of ammonia nitrogen. This liquid is returned to the primary sedimentation tank and treated in a biological treatment tank, but since the nitrogen load in the biological treatment tank is not reduced, the operating costs required for the aeration equipment in the biological treatment tank are not reduced, and thus the cost of treating organic wastewater cannot be reduced. Furthermore, in the water treatment system described above, phosphorus is recovered from organic wastewater as solid phosphorus compounds, but nitrogen (ammonia nitrogen) is not recovered as a solid, so there is a problem in that fertilizer resources are not effectively recovered from organic wastewater.

[0005] The present invention aims to provide a separation liquid treatment device, a water treatment system, and a separation liquid treatment method that reduce the operating costs of aeration equipment in biological treatment tanks by removing and recovering phosphorus and nitrogen from the separation liquid, and further enable the effective utilization of nitrogen as a fertilizer resource. [Means for solving the problem]

[0006] A separation liquid treatment apparatus according to one aspect of the present invention is a separation liquid treatment apparatus that processes organic sludge generated in the process of purifying organic wastewater containing nitrogen components with aerobic microorganisms, after anaerobic digestion treatment of the organic sludge, before returning the separated solid liquid to the purification process, and comprises a reaction tank for storing part or all of the separation liquid and adding and mixing phosphoric acid and magnesium salt to the stored separation liquid.

[0007] A water treatment system according to one aspect of the present invention comprises: a primary sedimentation tank into which water to be treated, which is organic wastewater containing nitrogen components, is introduced; a biological treatment tank that purifies the supernatant water sent from the primary sedimentation tank by aerobic microorganisms; a final sedimentation tank to which the wastewater from the biological treatment tank is sent; an anaerobic digestion tank into which the organic sludge settled in the primary sedimentation tank and the organic sludge settled in the final sedimentation tank are introduced and the organic sludge is subjected to anaerobic digestion treatment; and a separation liquid treatment device that treats the separation liquid obtained by solid-liquid separation of the wastewater from the anaerobic digestion tank, wherein the separation liquid treatment device comprises: a reaction tank that stores part or all of the separation liquid and adds phosphate and magnesium salt to the stored separation liquid and mixes it; and a return path that returns the wastewater from the reaction tank to the primary sedimentation tank.

[0008] A method for treating separated liquid according to one aspect of the present invention is a method for treating the separated liquid obtained by anaerobic digestion of organic sludge generated in the process of purifying organic wastewater containing nitrogen components with aerobic microorganisms, before returning it to the purification process, and includes adding and mixing phosphoric acid and magnesium salts to part or all of the separated liquid. [Effects of the Invention]

[0009] According to the present invention, by removing and recovering phosphorus and nitrogen from the separated liquid, the nitrogen load in the biological treatment is reduced even when the remaining liquid is returned to the biological treatment. As a result, the operating costs required for aeration in the biological treatment can be reduced, and consequently, the treatment costs of organic wastewater can be reduced. Furthermore, since the nitrogen recovered as solid matter can be used as a fertilizer resource, fertilizer resources can be effectively recovered from organic wastewater. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows a schematic example of a water treatment system according to the embodiment, and a schematic diagram showing a schematic example of a separation liquid treatment apparatus according to the first embodiment. [Figure 2] This is a schematic diagram showing an example of a separation liquid treatment method according to the present invention. [Figure 3] This is a schematic diagram showing an example of a separation liquid processing apparatus according to the second embodiment. [Figure 4]This is a schematic diagram showing an example of a separation liquid processing apparatus according to the third embodiment. [Figure 5] This is a schematic diagram showing an example of a separation liquid processing apparatus according to the fourth embodiment. [Figure 6] This is a schematic diagram showing an example of a separation liquid processing apparatus according to the fifth embodiment. [Figure 7] The measurement results for Example 1 are shown below. (A) is a graph showing the change in the concentration of ammonia nitrogen in the treated solution with respect to the reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the treated solution with respect to the reaction time. [Figure 8] The measurement results for Example 1 are shown below. (A) is a graph showing the change in magnesium concentration in the treated solution with respect to reaction time, and (B) is a graph showing the change in pH value in the treated solution with respect to reaction time. [Figure 9] The measurement results for Example 1 are shown below. (A) is a graph showing the change in the ratio of ammonia nitrogen present in the precipitate to dissolved in the treated solution with respect to the reaction time, and (B) is a graph showing the change in the ratio of phosphate phosphorus present in each substance in the precipitate to dissolved in the treated solution with respect to the reaction time. [Figure 10] The measurement results for Example 1 are shown below. (A) is a graph showing the change in the ratio of magnesium present in each substance in the precipitate to magnesium dissolved in the treated solution with respect to the reaction time, and (B) is a graph showing the change in the ratio of magnesium present in each substance in the precipitate to magnesium dissolved in the treated solution with respect to the reaction time. [Figure 11] The measurement results for Example 2 are shown below. (A) is a graph showing the change in the concentration of ammonia nitrogen in the treated solution with respect to the reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the treated solution with respect to the reaction time. [Figure 12] The measurement results for Example 2 are shown below. (A) is a graph showing the change in magnesium concentration in the treated solution with respect to reaction time, and (B) is a graph showing the change in pH value in the treated solution with respect to reaction time. [Figure 13] These are the measurement results in Example 2, wherein (A) is a graph showing the change over reaction time in the ratio of the ammonia nitrogen present in the precipitate and the ammonia nitrogen dissolved in the liquid to be treated, and (B) is a graph showing the change over reaction time in the ratio of the phosphate phosphorus present in each substance in the precipitate and the phosphate phosphorus dissolved in the liquid to be treated. [Figure 14] These are the measurement results in Example 2, wherein (A) is a graph showing the change over reaction time in the ratio of the magnesium present in each substance in the precipitate and the magnesium dissolved in the liquid to be treated, and (B) is a graph showing the change over reaction time in the ratio of the magnesium present in each substance in the precipitate and the magnesium dissolved in the liquid to be treated. [Figure 15] These are the measurement results in Example 3, wherein (A) is a graph showing the change in the concentration of ammonia nitrogen in the liquid to be treated over reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the liquid to be treated over reaction time. [Figure 16] These are the measurement results in Example 3, wherein (A) is a graph showing the change in the concentration of magnesium in the liquid to be treated over reaction time, and (B) is a graph showing the change in the pH value of the liquid to be treated over reaction time. [Figure 17] These are the measurement results in Example 3, wherein (A) is a graph showing the change over reaction time in the ratio of the ammonia nitrogen present in the precipitate and the ammonia nitrogen dissolved in the liquid to be treated, and (B) is a graph showing the change over reaction time in the ratio of the phosphate phosphorus present in each substance in the precipitate and the phosphate phosphorus dissolved in the liquid to be treated. [Figure 18] These are the measurement results in Example 3, wherein (A) is a graph showing the change over reaction time in the ratio of the magnesium present in each substance in the precipitate and the magnesium dissolved in the liquid to be treated, and (B) is a graph showing the change over reaction time in the ratio of the magnesium present in each substance in the precipitate and the magnesium dissolved in the liquid to be treated. [Figure 19]These are the measurement results in Comparative Example 1, where (A) is a graph showing the change in the concentration of ammonia nitrogen in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the liquid to be treated with respect to reaction time. [Figure 20] These are the measurement results in Comparative Example 1, where (A) is a graph showing the change in the concentration of magnesium in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the pH value of the liquid to be treated with respect to reaction time. [Figure 21] These are the measurement results in Comparative Example 2, where (A) is a graph showing the change in the concentration of ammonia nitrogen in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the liquid to be treated with respect to reaction time. [Figure 22] These are the measurement results in Comparative Example 2, where (A) is a graph showing the change in the concentration of magnesium in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the pH value of the liquid to be treated with respect to reaction time. [Figure 23] These are the measurement results in Comparative Example 3, where (A) is a graph showing the change in the concentration of ammonia nitrogen in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the concentration of phosphate phosphorus in the liquid to be treated with respect to reaction time. [Figure 24] These are the measurement results in Comparative Example 3, where (A) is a graph showing the change in the concentration of magnesium in the liquid to be treated with respect to reaction time, and (B) is a graph showing the change in the pH value of the liquid to be treated with respect to reaction time. [Figure 25] These are the measurement results in Comparative Example 4, which is a graph showing the relationship with the treatment time required for the treatment of removing a predetermined amount of ammonia nitrogen for each experiment. Mode for Carrying Out the Invention

[0011] The embodiments are described below. The method of biologically purifying organic wastewater containing nitrogen components using aerobic microorganisms is widely used in wastewater treatment such as urban sewage as a nitrification-type activated sludge process. Most urban sewage treatment facilities consist of a primary sedimentation tank, a reaction tank (biological treatment tank), a final sedimentation tank, an anaerobic digester, a sludge dewatering machine, etc. Approximately 60% of the solid matter contained in urban sewage is separated by gravity in the primary sedimentation tank and reduced in volume by methane fermentation in the anaerobic digester as primary sludge. Dissolved components and remaining solids contained in the supernatant water of the primary sedimentation tank are biologically decomposed in the subsequent biological treatment tank.

[0012] The dissolved components and nitrogen components of the residual solids are decomposed into ammonia nitrogen by general bacteria in the biological treatment tank, and then oxidized to nitrate nitrogen by nitrifying bacteria that proliferate in the aerobic section of the biological treatment tank (nitrification). The slurry (activated sludge) of these microorganisms is separated by gravity in the final sedimentation tank, and most of it is returned to the biological treatment tank as return sludge from the bottom of the final sedimentation tank. A portion of the gravity-separated activated sludge is then introduced into the anaerobic digester as excess sludge to reduce its volume. The supernatant water from the final sedimentation tank is disinfected with hypochlorous acid, etc., and then discharged into the water system. In the anaerobic digester, approximately 50% of the introduced primary sludge and excess sludge are decomposed by methane fermentation microorganisms. Consequently, about 50% of the nitrogen components of the sludge are redissolved in the anaerobic digester as ammonia nitrogen.

[0013] Digested sludge discharged from anaerobic digesters containing ammonia nitrogen is separated into dewatered cake and liquefied liquid in a sludge dewatering machine. In typical urban sewage treatment facilities, the dewatered cake is transported off-site for final disposal. Essentially, the liquefied liquid contains almost all of the redissolved ammonia nitrogen. Since this liquefied liquid is returned to the primary sedimentation tank, the redissolved ammonia nitrogen becomes a nitrogen load in the biological treatment tank. In the biological treatment tank, this sludge-derived nitrogen load accounts for approximately 1 / 5 of the nitrogen load derived from sewage. Therefore, sludge-derived nitrogen cannot be ignored in the operation of wastewater treatment facilities.

[0014] In the nitrification reaction, approximately 4.53 times the amount of oxygen per unit weight of nitrogen is required stoichiometrically (NH4).+ +2O2→2H + +NO3 - (+2H2O). The oxygen (bound oxygen) from nitrate rhizomes produced by nitrification is used as an oxygen source for denitrifying bacteria in the anaerobic section upstream of the biological treatment tank (organic matter + bound oxygen from nitrate rhizomes → carbon dioxide + molecular nitrogen + water). In principle, the oxygen consumed by nitrification can be reused stoichiometrically for the biological oxidation of sewage organic matter through denitrification. However, in a typical biological treatment tank flow, an anaerobic section is installed upstream and an aerobic section downstream, so the only liquid introduced into the anaerobic section is the returned sludge from the final sedimentation tank.

[0015] In typical final sedimentation tanks, the flow rate of returned sludge is approximately half the flow rate of sewage flowing into the biological treatment tank, meaning that at best only half of the nitrates generated in the aerobic section can be reused. The remaining bound oxygen is lost as nitrates from the supernatant water of the final sedimentation tank into the treated water. While increasing the flow rate of returned sludge can increase the reuse of nitrates, this directly leads to increased operating costs for the return pump. However, a multi-stage "step-type nitrification-denitrification method" that pairs anaerobic and aerobic sections can maximize the reuse of nitrates. However, this requires a fundamental modification of existing biological treatment tanks, and applying this to existing wastewater treatment facilities would require considerable construction and investment. For these reasons, there has been a need to establish a technology that minimizes the return of sludge-derived nitrogen (ammonia nitrogen) to the biological treatment tank.

[0016] Furthermore, the Anammox method is a technique that biologically denitrifies sludge by first bio-oxidizing approximately 50% of the ammonia nitrogen derived from the sludge to nitrite nitrogen, and then oxidizing the remaining ammonia nitrogen with that nitrite nitrogen (NH4). + +NO2 -(→N2 + 2H2O). While this can reduce the nitrogen load from sludge to the biological treatment tank, oxygen is still required for the biological oxidation of ammonia nitrogen to nitrite nitrogen, and the cost of the power used for aeration cannot be ignored. Furthermore, adopting this method necessitates the introduction and operation of a nitrite oxidation bioreactor and an Anammox bioreactor. The structure of a bioreactor, which requires three-phase separation of gas, solid, and liquid, is complex, and the reaction time takes several hours, so its introduction also requires considerable construction and investment. For this reason, there has been a desire to establish a technology that does not require biological treatment and removes sludge-derived nitrogen (ammonia nitrogen) from the separated liquid with a relatively simple structure.

[0017] The present invention has been made in consideration of the above-described content. Next, embodiments will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in order to make the configurations of the embodiments easier to understand, some parts are enlarged or emphasized, while others are omitted or simplified in the drawings, and the shape, scale, dimensions, etc., may differ from the actual product.

[0018] <First Embodiment> A water treatment system and a separation liquid treatment device according to the first embodiment will be described. Figure 1 is a schematic diagram showing an example of a water treatment system 100 and a separation liquid treatment device 50A according to the first embodiment. As shown in Figure 1, the water treatment system 100 comprises a primary sedimentation tank 10, a reaction tank 20, a final sedimentation tank 30, an anaerobic digester 40, and a separation liquid treatment device 50A.

[0019] The primary sedimentation tank 10 uses gravity to settle solid and suspended organic matter in the treated water W, which is nitrogen-containing organic wastewater, and separates it into solid-liquid water, which is the primary sludge W1 (primary sediment), and supernatant water S1. The primary sludge W1 is mostly water, but it also contains undecomposed organic matter such as carbohydrates, lipids, proteins, and inorganic matter such as sand and minerals. The supernatant water S1 contains dissolved organic matter and residual solid matter that did not settle as primary sludge W1.

[0020] The primary sedimentation tank 10 can be rectangular, circular, or other shapes. The bottom is sloped to allow sludge to settle. The material is selected considering durability and environmental impact, and examples include concrete, steel, fiber-reinforced plastic (FRP), and corrosion-resistant metals. The size is set appropriately according to the amount of water to be treated W. Examples of water to be treated W include general household sewage (wastewater) containing organic components, and wastewater from various factories. The primary sedimentation sludge W1 is sent to the anaerobic digester 40, and the supernatant water S1 is sent to the reaction tank 20.

[0021] The reaction tank 20 is a biological treatment tank that performs biological treatment. The reaction tank 20 utilizes aerobic microorganisms to decompose and remove dissolved components and residual solids from the supernatant water S1 sent from the primary sedimentation tank 10 (activated sludge method). Of these, the nitrogen components of the dissolved components and residual solids are decomposed into ammonia nitrogen by general bacteria in the biological treatment tank, and then oxidized to nitrate nitrogen by nitrifying bacteria that proliferate in the aerobic part of the biological treatment tank (nitrification). The supernatant water S1 that has been biologically treated in the reaction tank 20 is sent to the final sedimentation tank 30 as treated water S2.

[0022] In the reaction tank 20, oxygen is supplied to promote the activity of microorganisms. In this embodiment, an aeration device 21 is provided at the bottom of the reaction tank 20 to supply oxygen (air). The shape of the reaction tank 20 can be, for example, rectangular or circular, and the material can be, for example, concrete or corrosion-resistant metal. The size is set appropriately depending on the amount of supernatant water S1 to be treated. For example, if the amount of supernatant water S1 to be treated is large, multiple tanks may be arranged in parallel. The aeration device 21 is not particularly limited, and for example, a blower or a diffuser can be used.

[0023] The treated water S2 contains a slurry (activated sludge) of aerobic microorganisms that proliferated during the biological treatment carried out in the reaction tank 20. The final sedimentation tank 30 uses gravity to settle the microorganisms (activated sludge) and suspended matter contained in the treated water S2 sent from the reaction tank 20, and separates the sediment into excess sludge W2 (secondary sludge) and supernatant water S3. The excess sludge W2 has a high moisture content and contains microorganisms (cells such as bacteria and fungi), undecomposed organic matter, metabolic products of microorganisms, ammonia nitrogen, phosphorus, etc.

[0024] A portion of the excess sludge W2 is returned to the reaction tank 20 as return sludge from the bottom of the final sedimentation tank 30. The remaining excess sludge W2 that is not returned is sent to the anaerobic digester 40, where it is anaerobically digested together with the primary sedimentation sludge W1 described above to reduce its volume. The supernatant water S3 is disinfected with, for example, hypochlorous acid, and then discharged into the water system. The shape and material of the final sedimentation tank 30 are the same as those of the primary sedimentation tank 10.

[0025] The anaerobic digester 40 performs anaerobic digestion of the primary sludge W1 and excess sludge W2. The anaerobic digester 40 has a sealed structure and is equipped with a recovery device to recover methane gas and other substances generated by the anaerobic digestion process. The shape of the anaerobic digester 40 can be cylindrical, dome-shaped with a dome-shaped roof on top, or sloped-bottomed. The material of the anaerobic digester 40 can be the same as that of the primary sedimentation tank 10 or the final sedimentation tank 30. The size is appropriately designed according to the amount of primary sludge W1 and excess sludge W2 to be processed. The primary sludge W1 and excess sludge W2 that have undergone anaerobic digestion are discharged from the anaerobic digester 40 as digested sludge W3 and processed by the sludge dewatering machine 41.

[0026] The sludge dewatering machine 41 removes water from the digested sludge W3, reducing its volume. The sludge dewatering machine 41 separates the digested sludge W3 into a dewatered cake W4 and a separated liquid D (dehydrated liquid). The dewatered cake W4 contains water, undecomposed organic matter, nitrogen, and phosphorus. The separated liquid D contains water, ammonia nitrogen, phosphorus, etc. The dewatered cake W4 is removed and used, for example, as a raw material for fertilizer. The separated liquid D is sent to the separated liquid treatment device 50A for removal of ammonia nitrogen and phosphorus. It is not necessary to send all of the separated liquid D to the separated liquid treatment device 50A; a portion of the separated liquid D may be sent to the separated liquid treatment device 50A, and the remaining separated liquid D may be returned to the primary sedimentation tank 10. The sludge dewatering machine 41 is not particularly limited, and any known dewatering machine can be used. Examples include centrifugal dehydrators, screw press dehydrators, vacuum dehydrators, and filter presses.

[0027] The separation liquid treatment device of this embodiment is a device for treating organic wastewater in a wastewater treatment facility that purifies organic wastewater containing nitrogen components using aerobic microorganisms. It adds phosphoric acid and magnesium salts to part or all of the separation liquid discharged from the anaerobic digestion process, which is a treatment step for organic sludge generated in the wastewater treatment facility, to significantly precipitate and remove ammonia nitrogen from the separation liquid, and then returns the treated liquid to the wastewater treatment facility, thereby significantly reducing the aeration required in the wastewater treatment facility.

[0028] Chemically, it is known that ammonium ions in aqueous solutions combine with phosphate and magnesium ions to precipitate as solid struvite crystals (magnesium ammonium phosphate: MAP). On the other hand, when both phosphate and magnesium ions are present at high concentrations, the precipitation of magnesium phosphate (MgHPO4, Mg3(PO4)2) is also known to be more dominant than that of magnesium ammonium phosphate. Under such conditions, it is not possible to adequately remove ammoniacal nitrogen from the solution.

[0029] Furthermore, while magnesium ammonium phosphate is readily soluble in acids (and sparingly soluble in alkalis), magnesium hydroxide is readily soluble in weak acids, and its aqueous solution exhibits alkalinity. Therefore, in order to precipitate ammonia nitrogen as magnesium ammonium phosphate crystals using magnesium hydroxide and phosphate ions, an artificial operation is essential: first, the pH of the solution is lowered to dissolve the magnesium hydroxide, and then the pH is raised to precipitate the magnesium ammonium phosphate. This pH control is extremely complex, making it difficult to obtain the optimal operation a priori or theoretically.

[0030] As a result of further investigation into the above-mentioned matters, we found that in liquids containing high concentrations of ammonia nitrogen (approximately 40-50 mmol / L (40-50 mM)) produced by anaerobic digestion of sewage sludge, etc., mixing phosphoric acid (weakly acidic) and magnesium hydroxide (alkaline) into the liquid suppresses the precipitation of magnesium phosphate, and selective precipitation of magnesium ammonium phosphate proceeds without any artificial adjustment of the pH.

[0031] Although the chemical mechanism is not clear, the following observations have been made: (1) the precipitation of magnesium ammonium phosphate is slow unless the amount of magnesium hydroxide added is equal to or greater than the amount of ammonia nitrogen, and (2) the precipitation of magnesium ammonium phosphate is hindered if the amount of phosphate phosphorus in the solution is in excess of ammonia nitrogen. Therefore, it is considered essential for the efficient removal of ammonia nitrogen to be added in the form of a magnesium salt in an amount greater than the amount of ammonia nitrogen (moles) contained in the separated liquid to be treated, and for the initial presence of a level of phosphate (moles) equal to the amount of ammonia nitrogen (moles) to be removed.

[0032] In this embodiment, the separated liquid to be treated contains a high concentration of ammonia nitrogen, for example, generated by anaerobic digestion of sewage sludge, and may contain some suspended solids and dissolved organic matter. The added phosphoric acid is preferably in liquid form, such as an industrial chemical (e.g., 75% phosphoric acid), as it is inexpensive and easy to handle, but a solid phosphate salt that is weakly acidic may also be added to the separated liquid. The added magnesium salt is preferably magnesium hydroxide powder, as it is inexpensive and easy to handle, but other magnesium salts that exhibit weak alkalinity may also be used. Since magnesium hydroxide is slow-soluble, it is particularly preferable that it be in the form of a fine powder that dissolves easily in the separated liquid. During the reaction, the pH value of the liquid decreases instantaneously due to the addition of phosphoric acid, and then increases due to the dissolution of magnesium hydroxide.

[0033] For example, when phosphoric acid and magnesium hydroxide are added to the separated liquid discharged from a typical anaerobic digestion process, the pH drops from approximately 7.3 initially to around 5.0 immediately after the addition of phosphoric acid, and then rises to around 9.0 due to the dissolution of magnesium hydroxide. A series of studies revealed that there is no particular need to artificially control this pH value, and that the spontaneous fluctuation of pH is suitable for the removal of ammoniacal nitrogen. This is because the dissolution of magnesium hydroxide is promoted at the low pH in the initial stages of the reaction, and the rise in pH due to the dissolution of magnesium hydroxide in the later stages of the reaction promotes the precipitation of magnesium ammonium phosphate, an ammonia salt that is poorly soluble in alkali.

[0034] Therefore, to remove ammonia nitrogen from the separated liquid, it is particularly desirable to add phosphoric acid and magnesium hydroxide in batches (batch processing). However, in special cases where high-speed or continuous processing is required, magnesium ammonium phosphate may be precipitated by adding an appropriate acid or alkali (for example, an acid may be added in reaction vessel 50 to dissolve magnesium hydroxide, and then an alkali may be added in the subsequent first thickener (described later) to precipitate an alkali-insoluble ammonia salt).

[0035] The ammonia nitrogen removed from the separated liquid precipitates as a slurry mainly composed of magnesium ammonium phosphate (MAP), a salt that is sparingly soluble in alkali. Therefore, the amount of magnesium added (molar amount) must be equal to or greater than the amount of ammonia nitrogen to be removed. Note that if magnesium hydroxide is present in excess of ammonia nitrogen, precipitation will be accelerated, so it is preferable to add magnesium (molar amount) in amounts 1 to 2 times the amount of ammonia nitrogen to be removed.

[0036] Furthermore, if the phosphate ion concentration in the separated liquid is high, the added magnesium will precipitate as magnesium phosphate, reducing the reaction efficiency with ammonia nitrogen. For this reason, it is particularly preferable to set the amount of added phosphate (molar amount) so that the amount of phosphate (molar amount) remaining in the treated water after the ammonia nitrogen has precipitated and been removed from the separated liquid is about the same as or less than the amount of phosphate (molar amount) in the original separated liquid. As a result, almost all of the added phosphate and the phosphate present in the separated liquid precipitate as a slurry of magnesium ammonium phosphate.

[0037] Furthermore, chemically, the precipitation reaction generally proceeds on the surface of the precipitate (crystals). For this reason, it is preferable to leave at least a portion of the precipitated magnesium ammonium phosphate slurry in the tank and then introduce the separated liquid, phosphoric acid, and magnesium salt into the tank. This further accelerates the reaction.

[0038] Furthermore, some of the excess magnesium salt added will be present in the treatment solution as dissolved magnesium. High concentrations of dissolved magnesium can lead to the undesirable precipitation of magnesium phosphate, reducing the reaction efficiency between the added magnesium salt, phosphate, and ammoniacal nitrogen. Therefore, it is preferable to limit the amount of dissolved magnesium to approximately 10 mM at a weakly alkaline pH.

[0039] Furthermore, injecting magnesium salt and phosphoric acid at the same location can lead to localized increases in the concentration of magnesium salt and phosphoric acid, causing the precipitation of magnesium phosphate. For this reason, it is preferable to add the magnesium salt and phosphoric acid separately to the separation liquid to be treated. This separation can be achieved by providing separate injection points for magnesium salt and phosphoric acid in the tank, or by adding the magnesium salt or phosphoric acid separately over time.

[0040] The hydrological residence time of the anaerobic digester where the separated liquid is discharged is quite long, generally around 30 days. Therefore, short-term fluctuations in the nitrogen content of the sewage sludge being fed in are absorbed within the anaerobic digester. Consequently, it is not particularly necessary to frequently measure the water quality of the separated liquid and finely adjust the precipitation operating conditions. However, measuring the ammonia nitrogen concentration of the separated liquid, the pH value, magnesium concentration, ammonia nitrogen concentration, and phosphate concentration in the treated liquid, and automatically controlling the amount of magnesium salt and phosphate added, is preferable as it reduces the amount of these chemicals used.

[0041] Figure 1 is a schematic diagram showing an example of a separation liquid treatment apparatus 50A according to the first embodiment. As shown in Figure 1, the separation liquid treatment apparatus 50A comprises a reaction tank 50, a dewatering machine 501, a magnesium salt input device 60, a phosphoric acid input device 70, a control device 80, and measuring devices A and B. The separation liquid treatment apparatus 50A removes ammonia nitrogen and phosphoric acid contained in the separation liquid D. The separation liquid treatment apparatus 50A performs solid-liquid separation treatment by storing the separation liquid D and performing predetermined operations. After adding phosphoric acid and magnesium salt to part or all of the separation liquid D and performing a treatment to precipitate and remove phosphoric acid and ammonia nitrogen in the separation liquid D, the treated liquid D0 is returned to the primary sedimentation tank 10.

[0042] The reaction vessel 50 is a stirring-type vessel equipped with a stirring blade M. The stirring blade M may be replaced with a rake R, which will be described in the second embodiment later. In the reaction vessel 50, phosphoric acid and magnesium salt are added to the separated liquid D from the magnesium salt adding device 60A and the phosphoric acid adding device 70A, which will be described later, and the mixture is stirred and reacted with the stirring blade M.

[0043] Subsequently, the stirring blade M is stopped and the mixture is allowed to stand, allowing for solid-liquid separation into a liquid treatment solution D0 and precipitate P0 by gravity. The pH value of the separated liquid D in the reaction vessel 50 is preferably around 7.3 to 9.0. The precipitate P0 consists of solid magnesium ammonium phosphate (MAP) and magnesium phosphate crystals (hereinafter sometimes referred to as "MAP, etc."). The shape and material of the reaction vessel 50 can be the same as those of the primary sedimentation tank 10 or the final sedimentation tank 30.

[0044] The reaction vessel 50 is equipped with a measuring device A. Measuring device A measures, for example, the pH value, magnesium salt concentration, ammonia nitrogen concentration, and phosphate concentration of the treatment liquid D0 in the reaction vessel 50. Measuring device A can use known pH sensors and concentration measuring devices. For example, pH sensors include glass electrode type, ion-selective electrode type, and solid sensor. Concentration measuring devices include conductivity meters and spectrophotometers. Furthermore, either a pH sensor or a concentration measuring device may be provided, or both may be provided.

[0045] The measuring device B is located at the outlet side of the sludge dewatering machine 41, where the separated liquid D is sent to the reaction tank 50, but it may also be located at the inlet side of the reaction tank 50. An example of measuring device B is a concentration estimation device that measures the pH value, ammonia nitrogen concentration, and phosphoric acid concentration in the separated liquid D. The same type of device used for measuring device B as for measuring device A is employed.

[0046] The solid-liquid separated treatment liquid D0 in the reaction tank 50 is returned to the primary sedimentation tank 10 via the return path L1. Meanwhile, the precipitate P0, which has precipitated as crystals such as MAP in the reaction tank 50, settles to the bottom of the reaction tank 50 by gravity. Since the settled precipitate P0 contains water, it is sent to the dewatering machine 501, where it is separated into solid matter P01 (MAP, etc.) and dewatered liquid D01. The solid matter P01 is used as fertilizer, etc., after drying and grinding. The dewatered liquid D01 has a reduced amount of ammonia nitrogen and is returned to the primary sedimentation tank 10 via the return paths L2 and L1.

[0047] In this embodiment, the return path L2 is merged with the return path L1, but the return path L2 may be made independent of the return path L1, and the dewatered liquid D01 may be returned directly to the primary sedimentation tank 10. The dewatering machine 501 is the same as the sludge dewatering machine 41.

[0048] The magnesium salt addition device 60A(60) is a device that adds a predetermined amount of magnesium salt to the separated liquid D introduced into the reaction vessel 50. Separated liquid D contains ammonia nitrogen (NH4-N), and it is preferable to add magnesium salt in an amount equal to or greater than the molar amount of ammonia nitrogen in separated liquid D, and more preferably 1 to 2 times the molar amount of ammonia nitrogen in separated liquid D. The molar amount of ammonia nitrogen (NH4-N) in separated liquid D can be determined from the ammonia nitrogen concentration measured by measuring device B.

[0049] Examples of magnesium salts include magnesium hydroxide (powder) and magnesium chloride. The ammonia nitrogen concentration and magnesium salt concentration in the treatment solution D0 are measured by measuring device A. The amount of magnesium salt to be added is determined by sending the measured values ​​from measuring devices A and B to the control device 80, which will be described later, and setting the most appropriate amount to add based on the measured values.

[0050] The phosphate addition device 70A(70) is a device that adds a predetermined amount of phosphate to the separated liquid D introduced into the reaction vessel 50. Separated liquid D contains ammonia nitrogen (NH4-N), but it is particularly preferable to add phosphate so that the molar amount of phosphate in the processing liquid D0 is about the same as or less than the molar amount of phosphate in the separated liquid D. The molar amounts of ammonia nitrogen (NH4-N) and phosphate in separated liquid D can be determined from the ammonia nitrogen concentration and phosphate concentration measured by measuring device B.

[0051] Furthermore, the molar amount of phosphoric acid contained in the processing solution D0 can be determined from the phosphoric acid concentration measured by measuring device A. Examples of phosphoric acid include liquid orthophosphoric acid. The amount of phosphoric acid to be added is determined by sending the measured values ​​from measuring devices A and B to the control device 80, which will be described later. The control device 80 processes the data and sets the most appropriate amount to be added based on the measured values.

[0052] Regarding the addition of magnesium salt and phosphoric acid to the reaction vessel 50, they may be added simultaneously, but it is preferable to add them separately to different locations in the reaction vessel 50. This is because adding magnesium salt and phosphoric acid to the same location will locally increase the concentrations of magnesium salt and phosphoric acid, resulting in the precipitation of a large amount of magnesium phosphate. Alternatively, the magnesium salt and phosphoric acid may be added with a time delay. Furthermore, the magnesium salt and phosphoric acid themselves may be added separately in portions.

[0053] According to the separation liquid treatment apparatus 50A of this embodiment, not only is the amount of phosphoric acid in the separation liquid D reduced, but a larger amount of ammoniacal nitrogen can also be removed. The separation liquid D treated in the reaction tank 50 is returned to the primary sedimentation tank 10 as treatment liquid D0 and treated together with the water to be treated W in the reaction tank 20. At this time, since the amount of ammoniacal nitrogen in the treatment liquid D0 is reduced, the nitrogen load in the reaction tank 20 can be reduced, and the operating costs required for aeration can be reduced.

[0054] <Method for treating separated liquid> A separation liquid treatment method according to an embodiment will now be described. Figure 2 is a schematic diagram showing an example of a separation liquid treatment method when using the separation liquid treatment apparatus 50A. The separation liquid treatment method shown in Figure 2 can also be carried out using each of the separation liquid treatment apparatuses of the second to fifth embodiments described later.

[0055] First, as shown in Figure 2(A), separation liquid D containing ammonia nitrogen is added to the reaction vessel 50. Next, based on the measurement results from measuring devices A and B, the control device 80 determines the amount of magnesium salt and phosphoric acid to be added to the reaction vessel 50. Then, as shown in Figure (2)B, while driving the stirring blade M, the control device 80 adds magnesium salt, such as magnesium hydroxide and phosphoric acid, from the magnesium salt adding device 60A and the phosphoric acid adding device 70A to the reaction vessel 50 and mixes them with separation liquid D. Figure 2(B) shows the state after separation liquid D, magnesium salt, and phosphoric acid have been mixed. There are no particular limitations on the mixing time, but it is desirable to mix for 5 minutes or more.

[0056] Figure 2(C) shows the state in which MAP and other substances have precipitated. In this state, it is preferable to suppress the precipitation of magnesium phosphate. For this reason, in Figure 2(B), measures such as adding the magnesium salt and phosphoric acid to the reaction vessel 50 at different times or adding them to different locations in the reaction vessel 50 are taken. After mixing for a certain period of time, the drive of the stirring blade M is stopped and the mixture is allowed to stand to perform solid-liquid separation.

[0057] Figure 2(D) shows the state after solid-liquid separation in the reaction tank 50, where the treatment liquid D0 and precipitate P0 such as MAP are separated. The precipitate P0 settles and settles at the bottom of the reaction tank 50. After solid-liquid separation, the supernatant treatment liquid D0 is returned to the primary sedimentation tank 10 via the return path L1 (see Figure 1). On the other hand, it is preferable to send the precipitate P0 to the dewatering machine 501 (see Figure 1) with some of it remaining (without removing all of the precipitate P0). Alternatively, all of the precipitate P0 may be sent to the dewatering machine 501.

[0058] Figure 2(E) shows the state in which the treatment liquid D0 is returned from the reaction tank 50 to the primary sedimentation tank 10 via the return path L1 (see Figure 1), leaving a portion of the precipitate P0 at the bottom of the reaction tank 50. In this state, a new predetermined amount of separation liquid D is added as shown in Figure 2(A). After that, the process from Figure 2(B) to Figure 2(E) described above is repeated. In this way, the separation liquid D is treated as one cycle from Figure 2(A) to Figure 2(E).

[0059] The precipitate P0 contains magnesium salts, such as magnesium hydroxide, that were introduced from the magnesium salt input device 60A. Therefore, by leaving a portion of the precipitate P0 in the reaction tank 50, the amount of magnesium salt introduced from the magnesium salt input device 60A can be reduced when processing the new separated liquid D (see Figure 2(A)) introduced into the reaction tank 50. Furthermore, the separated liquid D (see Figure 2(D)) processed in the reaction tank 50 is returned to the primary sedimentation tank 10 as the treated liquid D0 and processed in the reaction tank 20. As the separated liquid processing method according to this embodiment reduces the ammonia nitrogen in the treated liquid D0, the nitrogen load in the reaction tank 20 can be reduced, and the operating costs required for aeration can be reduced.

[0060] <Second Embodiment> A separation liquid processing apparatus 50B according to the second embodiment will now be described. Components identical to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted or simplified. Figure 3 is a schematic diagram showing an example of the separation liquid processing apparatus 50B according to the second embodiment. As shown in Figure 3, the separation liquid processing apparatus 50B is located downstream of the reaction tank 50 of the first embodiment and includes a first thickener 51, a dewatering machine 511, a magnesium salt input device 60B (60), and a phosphate input device 70B (70). Note that in Figure 3, the descriptions of measuring devices A and B are omitted.

[0061] The separation liquid treatment device 50B stores the wastewater containing precipitate P0 that has settled at the bottom of the reaction tank 50 in the first thickener 51 and performs solid-liquid separation by carrying out predetermined operations. The separation liquid treatment device 50B removes ammonia nitrogen and phosphoric acid contained in the wastewater containing precipitate P0. The separation liquid treatment device 50B adds phosphoric acid and magnesium salt to part or all of the wastewater containing precipitate P0 to precipitate and remove phosphoric acid and ammonia nitrogen from the wastewater, and then returns the treated liquid D1 to the primary sedimentation tank 10.

[0062] The first thickener 51 is a tank equipped with a rake R. In the first thickener 51, phosphoric acid and magnesium salt are added to the wastewater stored in the first thickener 51 from the magnesium salt adder 60B and the phosphoric acid adder 70B, and the wastewater is separated into a solid-liquid mixture: a liquid treatment solution D1 and precipitate P1. The pH value of the wastewater in the first thickener 51 at this time is preferably around 7.3 to 9.0. The rake R collects the precipitate P1 at the bottom of the first thickener 51. The precipitate P1 is MAP, etc. The shape and material of the first thickener 51 can be the same as those of the reaction tank 50, primary sedimentation tank 10, or final sedimentation tank 30.

[0063] The first thickener 51 may be equipped with measuring devices similar to those of measuring devices A and B. By providing measuring devices, the amount of phosphoric acid and magnesium salt added to the first thickener 51 can be adjusted by the control device 80. The magnesium salt adder 60B and phosphoric acid adder 70B are the same as those used in the magnesium salt adder 60A and phosphoric acid adder 70A of the first embodiment. The wastewater stored in the first thickener 51 still contains ammonia nitrogen and phosphoric acid. Therefore, based on the measurement results of the measuring devices, an appropriate amount of phosphoric acid and magnesium salt may be added to the wastewater (added on), which can cause precipitates such as MAP P1 to precipitate and reduce the amount of ammonia nitrogen and phosphoric acid in the supernatant water, the treated liquid D1.

[0064] The treated liquid D1, which has been separated into solid and liquid form in the first thickener 51, is returned to the primary sedimentation tank 10 via the return path L3. Meanwhile, the precipitate P1, which has precipitated as crystals such as MAP in the first thickener 51, settles to the bottom of the first thickener 51 by gravity. Since the settled precipitate P1 contains water, it is sent to the dewatering machine 511, where it is separated into solid matter P11 (MAP, etc.) and dewatered liquid D11. The solid matter P11 is used as fertilizer after drying and grinding. Since the solid matter P11 contains even more nitrogen and phosphorus than the solid matter P01 of the first embodiment, it is suitable as a fertilizer.

[0065] The dewatered liquid D11 has a reduced amount of ammonia nitrogen and is returned to the primary sedimentation tank 10 via return pathways L4, L3, and L1. In this embodiment, return pathway L4 is merged with return pathway L3, and return pathway L3 is further merged with return pathway L1. However, return pathways L4 and L3 may be made independent of return pathway L1, and the dewatered liquid D11 may be returned directly to the primary sedimentation tank 10. The dewatering machine 511 is the same as that used in dewatering machine 501.

[0066] According to this embodiment, the amount of ammoniacal nitrogen in the treatment liquid D1 and dewatered liquid D11 returned to the primary sedimentation tank 10 is reduced compared to the treatment liquid D0 and dewatered liquid D01 of the first embodiment. Therefore, the nitrogen load in the reaction tank 20 can be further reduced, and the operating costs required for aeration can be further reduced.

[0067] <Third Embodiment> A separation liquid processing apparatus 50C according to the third embodiment will now be described. Components identical to those in the first and second embodiments will be denoted by the same reference numerals, and their descriptions will be omitted or simplified. Figure 4 is a schematic diagram showing an example of the separation liquid processing apparatus 50C according to the third embodiment. As shown in Figure 4, the separation liquid processing apparatus 50C includes a second thickener 52, a dewatering machine 521, a magnesium salt input device 60C(60), and a phosphate input device 70C(70) downstream of the first thickener 51 of the second embodiment. Note that in Figure 4, the descriptions of measuring devices A and B are omitted.

[0068] The separation liquid treatment device 50C stores the wastewater containing precipitate P1 that has settled at the bottom of the first thickener 51 in the second thickener 52 and performs solid-liquid separation by performing predetermined operations. The separation liquid treatment device 50C removes ammonia nitrogen and phosphoric acid contained in the wastewater. The separation liquid treatment device 50C adds phosphoric acid and magnesium salt to part or all of the wastewater to precipitate and remove phosphoric acid and ammonia nitrogen from the wastewater, and then returns the treated liquid D2 to the primary sedimentation tank 10.

[0069] The second thickener 52 adds phosphoric acid and magnesium salt from the magnesium salt input device 60C and the phosphoric acid input device 70C to the stored wastewater, separating the wastewater into a liquid treatment solution D2 and precipitate P2. The pH value of the wastewater in the second thickener 52 is preferably around 7.3 to 9.0. The rake R collects the precipitate P2 at the bottom of the second thickener 52. The precipitate P2 is MAP, etc. The shape and material of the second thickener 52 are the same as those of the first thickener 51.

[0070] The second thickener 52 may be equipped with measuring devices similar to those of measuring devices A and B. By providing measuring devices, the amount of phosphoric acid and magnesium salt added to the second thickener 52 can be adjusted by the control device 80. The magnesium salt adder 60C and phosphoric acid adder 70C are the same as those used in the magnesium salt adder 60B and phosphoric acid adder 70B of the second embodiment. The wastewater from the first thickener 51 still contains ammonia nitrogen and phosphoric acid. Therefore, based on the measurement results of the measuring devices, an appropriate amount of phosphoric acid and magnesium salt may be added to the wastewater (added on top of the existing solution). By adding on top of the existing solution, precipitates such as MAP P2 can be precipitated, further reducing the amount of ammonia nitrogen and phosphoric acid in the supernatant water, which is the treated liquid D2.

[0071] The treated liquid D2, which has been separated into solid and liquid form in the second thickener 52, is returned to the primary sedimentation tank 10 via the return path L5. Meanwhile, the precipitate P2 that has precipitated as MAP crystals in the second thickener 52 settles to the bottom of the second thickener 52 by gravity separation. Since the settled precipitate P2 contains water, it is sent to the dewatering machine 521, where it is separated into solid matter P21 (MAP, etc.) and dewatered liquid D21. The solid matter P21 is used as fertilizer after drying and grinding. Since the solid matter P21 contains even more nitrogen and phosphorus than the solid matter P11 of the second embodiment, it can be used as a fertilizer with high nitrogen and phosphorus content.

[0072] The dewatered liquid D21 has a reduced amount of ammonia nitrogen and is returned to the primary sedimentation tank 10 via return paths L6, L5, L3, and L1. In this embodiment, return path L6 is merged with return path L5, return path L5 is merged with return path L3, and return path L3 is further merged with return path L1. However, return paths L6, L5, and L3 may be made independent of return path L1, and the dewatered liquid D11 may be returned directly to the primary sedimentation tank 10. The dewatering machine 511 is the same as the dewatering machine 501.

[0073] According to this embodiment, the amount of ammoniacal nitrogen in the treatment liquid D2 and dewatered liquid D21 returned to the initial sedimentation tank 10 is further reduced compared to the treatment liquid D0 and dewatered liquid D01 of the first embodiment and the treatment liquid D1 and dewatered liquid D11 of the second embodiment. Therefore, the nitrogen load in the reaction tank 20 can be reduced even further than in the first and second embodiments, and the operating costs required for aeration can be further reduced.

[0074] Furthermore, the precipitates P0, P1, and P2, such as MAP, that precipitate in the first to third embodiments are concentrated and their particle size is increased by sedimentation separation by gravity, making subsequent processes after removal, such as filtration and drying, easier.

[0075] <Fourth Embodiment> A separation liquid treatment apparatus 50D according to the fourth embodiment will now be described. Components identical to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted or simplified. Figure 5 is a schematic diagram showing an example of the separation liquid treatment apparatus 50D according to the fourth embodiment. As shown in Figure 5, the separation liquid treatment apparatus 50D is equipped with a storage tank 90 in front of the reaction tank 50, as in the separation liquid treatment apparatus 50A of the first embodiment. The storage tank 90 is a tank for temporarily storing the separation liquid D separated by solid-liquid separation by the sludge dewatering machine 41 (see Figure 1). Note that the descriptions of measuring devices A and B are omitted in Figure 5.

[0076] A valve V1 is provided between the storage tank 90 and the reaction tank 50. The valve V1 adjusts the amount of separation liquid D sent to the reaction tank 50. The shape of the storage tank 90 is not particularly limited and can be cylindrical, square, polygonal, dome-shaped, etc. As for the material, known metals or resins that have a predetermined strength and are corrosion-resistant to the separation liquid D can be used. The valve V1 is not particularly limited as long as it can adjust the amount of separation liquid D introduced from the storage tank 90 to the reaction tank 50, and known valves can be used. The opening and closing of the valve V1 may be controlled by the control device 80.

[0077] The separated liquid D is temporarily stored in the storage tank 90, and only the amount required for processing is introduced into the reaction tank 50. Therefore, even if the separated liquid D is discharged continuously, by introducing only the amount required for processing into the reaction tank 50, it is possible to process the separated liquid D in a batch process in the reaction tank 50. Furthermore, even if multiple reaction tanks 50 are installed, the separated liquid D can be sequentially sent to each reaction tank 50. As a result, the processing efficiency of the separated liquid D can be improved. The storage tank 90 and valve V1 described above can also be applied to the second embodiment, the third embodiment, and the embodiments described below.

[0078] <Fifth Embodiment> A separation liquid processing apparatus 50F according to the fifth embodiment will now be described. Note that components identical to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted or simplified. Figure 6 is a schematic diagram showing an example of the separation liquid processing apparatus 50F according to the fifth embodiment. As shown in Figure 6, the separation liquid processing apparatus 50F comprises a valve V2, a separation liquid processing apparatus 50A, and a separation liquid processing apparatus 50E. The separation liquid processing apparatus 50E has the same configuration as the separation liquid processing apparatus 50A. In the separation liquid processing apparatus 50F, the separation liquid processing apparatus 50A and the separation liquid processing apparatus 50E are installed in parallel. Note that in Figure 6, the descriptions of measuring devices A and B are omitted.

[0079] The separation liquid processing apparatus 50E comprises a reaction tank 53, a dewatering machine 531, a magnesium salt input device 60A, a phosphoric acid input device 70A, a control device 80, and measuring devices A and B. The reaction tank 53 corresponds to the reaction tank 50 of the separation liquid processing apparatus 50A. The reaction tank 53 may be identical to the reaction tank 50, or it may have a different shape and dimensions. The dewatering machine 531 corresponds to the dewatering machine 501 of the separation liquid processing apparatus 50A. The dewatering machine 531 may be identical to the dewatering machine 501, or it may have a different configuration from the dewatering machine 501. Measuring devices A and B have the same configuration as in the first embodiment, so they are not shown and their description is omitted, but the separation liquid processing apparatus 50E also includes measuring device A.

[0080] In the reaction tank 53, phosphoric acid and magnesium salts are added to part or all of the introduced separation liquid D, and solid-liquid separation is performed to separate the treated liquid D3 from precipitates P3 such as MAP. The treated liquid D3 is returned to the primary sedimentation tank 10 via the return path L11. The precipitates P3 are sent to the dewatering machine 531, where solid-liquid separation is performed to separate solid matter P31 (MAP, etc.) from dewatered liquid D31. The solid matter P31 is used as fertilizer after drying and grinding, and the dewatered liquid D31 is returned to the primary sedimentation tank 10 via the return path L21 and the return path L11. In this embodiment, the return path L21 is merged with the return path L11, but the return path L21 may be kept separate from the return path L11, and the dewatered liquid D31 may be returned directly to the primary sedimentation tank 10.

[0081] The separation liquid processing device 50F switches the flow of separation liquid D to either the separation liquid processing device 50A or the separation liquid processing device 50E via valve V2. The switching of valve V2 may be controlled by control device 80. Separation liquid D is supplied sequentially to the separation liquid processing device 50A and the separation liquid processing device 50E via valve V2. Therefore, even when separation liquid D is discharged continuously, batch processing can be performed in both the separation liquid processing device 50A and the separation liquid processing device 50E.

[0082] In this embodiment, by arranging a configuration similar to that of the separation liquid treatment device 50A in parallel, even when the discharge volume of separation liquid D is large, the separation liquid D can be efficiently processed while batch processing is performed in the separation liquid treatment devices 50A and 50E. In this embodiment, two separation liquid treatment devices 50A and 50E are used, but a configuration with three or more separation liquid treatment devices may be arranged. In this embodiment, a dewatering machine 501 and 531 are provided for each separation liquid treatment device 50A and 50E, but a configuration in which precipitates P0 and P3 are dewatered by a single dewatering machine (for example, only the dewatering machine 501) may be used. Furthermore, one or both of the separation liquid treatment devices 50A and 50E may be configured to apply the second or third embodiment described above. That is, the configuration of the first thickener 51, second thickener 52, etc. (including the configuration of the later stages) described in the second and third embodiments may be provided downstream of the reaction tanks 50 and 53. [Examples]

[0083] Next, examples will be described, but the present invention is not limited to the examples described below. [Example 1] The separated liquid discharged from the anaerobic digestion process at the sewage treatment plant was filtered through filter paper to obtain a treatment solution containing 50 mM ammonia nitrogen and 6 mM phosphate phosphorus. This treatment solution was introduced into a treatment tank, and magnesium hydroxide was added to the treatment solution at a molar ratio of 1.6 times that of ammonia nitrogen (Mg / N = 1.6). Then, 44 mM phosphorus was added so that the amount of phosphorus in the treatment solution was equal to the molar ratio of ammonia nitrogen. Next, the ammonia nitrogen, phosphate phosphorus, and magnesium dissolved in the treatment solution, as well as the pH value of the treatment solution, were measured over time while the treatment solution was slowly stirred. The results are shown in Figures 7 to 10. In addition to the time-dependent concentrations of each component, the graphs for Comparative Examples 1 to 3 and Examples 1 to 3 also show the 10% equivalent concentration of ammonia nitrogen and phosphate phosphorus contained in the initial sample water (90% of the components in the sample water removed) as a horizontal line (target).

[0084] [Example 2] The same treatment as in Example 1 was carried out, except that magnesium hydroxide was added to the same treatment solution as in Example 1 at a molar ratio of 1.2 times that of ammonia nitrogen (denoted as Mg / N = 1.2). The results are shown in Figures 11 to 14.

[0085] [Example 3] The same treatment as in Example 1 was carried out, except that magnesium hydroxide was added to the same treatment solution as in Example 1 at a molar ratio of 2.0 times that of ammonia nitrogen (denoted as Mg / N = 2.0). The results are shown in Figures 15 to 18.

[0086] [Comparative Example 1] The separated liquid discharged from the anaerobic digestion process at the sewage treatment plant was filtered through filter paper to obtain a treatment solution containing 50 mM ammonia nitrogen and 6 mM phosphate phosphorus. This treatment solution was introduced into a treatment tank, and magnesium hydroxide was added to it in the same mole ratio as the ammonia nitrogen (Mg / N = 1.0). Next, the ammonia nitrogen, phosphate phosphorus, and magnesium dissolved in the treatment solution, as well as the pH value of the treatment solution, were measured over time while the treatment solution was slowly stirred. The results are shown in Figures 19 to 20.

[0087] [Comparative Example 2] The separated liquid discharged from the anaerobic digestion process at the sewage treatment plant was filtered through filter paper to obtain a treatment liquid containing 50 mM ammonia nitrogen and 6 mM phosphate phosphorus. This treatment liquid was introduced into a treatment tank, and magnesium hydroxide was added to the treatment liquid in the same mole ratio as the ammonia nitrogen (Mg / N = 1.0). Then, 44 mM phosphorus was added so that the amount of phosphorus in the treatment liquid was equal to the molar ratio of the ammonia nitrogen (P / N = 1.0). Next, the ammonia nitrogen, phosphate phosphorus, and magnesium dissolved in the treatment liquid, as well as the pH value of the treatment liquid, were measured over time while the treatment liquid was slowly stirred. The results are shown in Figures 21 and 22.

[0088] [Comparative Example 3] The separated liquid discharged from the anaerobic digestion process of a sewage treatment plant was filtered through filter paper to obtain a liquid to be treated containing 50 mM ammonia nitrogen and 6 mM phosphate phosphorus. This liquid to be treated was charged into a treatment tank, magnesium hydroxide was added to the liquid to be treated at a molar amount 1.6 times that of the ammonia nitrogen (denoted as Mg / N=1.6), and then 94 mM phosphoric acid was added so that the phosphoric acid in the liquid to be treated reached a molar amount 2 times that of the ammonia nitrogen (denoted as P / N=2.0). Next, the same treatment as in Comparative Example 2 was performed. The results are shown in Figure 23 to Figure 24.

[0089] In Comparative Example 1, almost no ammonia nitrogen concentration was removed from the liquid to be treated (see Figure 19(A)). Since the phosphoric acid concentration in the liquid to be treated became almost zero within 3 minutes after the start of the reaction (see Figure 19(B)), the ammonia nitrogen during this period was removed from the liquid as magnesium ammonium phosphate. A slight decrease in ammonia nitrogen occurred even after this, which was due to the increase in pH accompanying the dissolution of magnesium hydroxide (Mg(OH)2→Mg 2+ +2OH - ) caused volatilization of ammonia (NH4 + +OH - →NH3+H2O, generating easily volatilizable NH3 from poorly volatilizable NH4 + ). In this comparative example, even after a reaction time of 180 minutes, about 40 mM of ammonia nitrogen remained in the liquid to be treated (see Figure 19(A)), failing to meet the target removal level of 5 mM (90% removal rate).

[0090] When comparing Example 1 with Comparative Example 2, in Comparative Example 2, when magnesium hydroxide was added in the same molar amount as ammonia nitrogen (Mg / N=1.0), the ammonia nitrogen concentration decreased slowly, but the reaction was slow, and even after a reaction time of 180 minutes, approximately 15 mM of ammonia nitrogen remained in the solution (see Figure 21(A)), failing to meet the removal target of 5 mM (removal rate of 90%). In addition, approximately 10 mM of phosphate phosphorus remained in the solution after 180 minutes (Figure 21(B)), which was approximately 1.6 times the concentration of phosphate phosphorus present in the treated solution. The soluble magnesium remained between 2-8 mM (see Figure 22(A)). The pH of the solution, which instantaneously dropped to pH=5.3 immediately after the addition of phosphate, remained weakly acidic to neutral due to the dissolution of magnesium hydroxide (Figure 22(B)).

[0091] On the other hand, in Example 1, when magnesium hydroxide was added at 1.6 times the molar amount of ammonia nitrogen (Mg / N=1.6), the decrease in ammonia nitrogen concentration was clearly faster than in Comparative Example 2, and even after a reaction time of about 20 minutes, the ammonia nitrogen concentration remaining in the solution had decreased to about 10% of the initial concentration (see target line in Figure 7(A)). At this time, the concentration of soluble phosphate phosphorus in the solution also decreased accordingly (see Figure 7(B)). The soluble magnesium remained at 6-9 mM (see Figure 8(A)), and the pH was 6.4 immediately after the addition of phosphate. The pH of the treated solution rose to 9.0 after 180 minutes (see Figure 8(B)).

[0092] Furthermore, in Example 1, after 180 minutes, the precipitated ammonia nitrogen was almost entirely present as magnesium ammonium phosphate (MAP) (see Figure 9(A)). Although most of the precipitated phosphate phosphorus was magnesium ammonium phosphate, a small amount of magnesium phosphate was also present (Figure 9(B)). Approximately 20 mM of added magnesium hydroxide remained in the solid magnesium (see Figures 10(A) and 10(B)). Since it is not possible to distinguish between Mg3(PO4)2 (magnesium phosphate) and MgHPO4 (magnesium hydrogen phosphate) in the precipitated magnesium phosphate, two graphs were created assuming that each precipitated individually (see Figures 10(A) and 10(B)). According to this, the amount of magnesium precipitated as magnesium phosphate was at most 2-3 mM (see Figures 10(A) and 10(B)).

[0093] It is generally believed that when phosphoric acid and magnesium salts are dissolved in water, magnesium phosphate crystals immediately precipitate. Therefore, when phosphoric acid and magnesium salts are added to a liquid containing ammoniacal nitrogen, they precipitate first, and it was thought that an extremely large amount of phosphoric acid and magnesium salts would be added to fix and precipitate the ammonium in the liquid as magnesium ammonium phosphate. This invention involves diligently investigating the type of magnesium salt that is suitable for selectively precipitating magnesium ammonium phosphate, and has found that magnesium hydroxide powder is optimal. This is based on the principle of using magnesium hydroxide powder, which is poorly soluble in water, to suppress the reaction between phosphoric acid and magnesium, thereby minimizing the precipitation of magnesium phosphate crystals. As a result, the added phosphoric acid and magnesium salt (magnesium hydroxide powder) react with the ammoniacal nitrogen in the liquid and precipitate almost entirely as magnesium ammonium phosphate.

[0094] Comparing Example 2 with Comparative Example 2, in Example 2, when magnesium hydroxide was added at 1.2 times the molar amount of ammonia nitrogen (Mg / N=1,2), the decrease in ammonia nitrogen concentration was slightly faster than in Comparative Example 2 (see Figure 21(A)), and even after a reaction time of approximately 180 minutes, the ammonia nitrogen concentration remaining in the solution decreased to about 15% of the initial concentration (see Figure 11(A)). At this time, the concentration of soluble phosphate phosphorus in the treated solution also decreased accordingly (see Figure 11(B)). The soluble magnesium also gradually decreased from an initial 8 mM to 3 mM after 180 minutes (see Figure 12(A)). Because less magnesium hydroxide, which serves as the alkali source, was added than in Example 1, the pH value in the treated solution remained below 8 (Figure 12(B)).

[0095] Furthermore, in Example 2, after 180 minutes, most of the precipitated ammoniacal nitrogen existed as magnesium ammonium phosphate (see Figure 13(A)). However, among the precipitated phosphate phosphorus, magnesium phosphate was slightly more abundant than in Example 1, reaching 2-3 mM after 180 minutes (see Figure 13(B)). This indicates that if there is not enough added magnesium hydroxide, magnesium will react with phosphate phosphorus rather than ammoniacal nitrogen, resulting in unnecessary precipitation.

[0096] Approximately 10 mM of added magnesium hydroxide remained in the solid magnesium (see Figures 14(A) and 14(B)). The precipitated magnesium was almost entirely composed of magnesium ammonium phosphate and the remaining magnesium hydroxide (see Figures 14(A) and 14(B)). Similar to Example 1, since Mg3(PO4)2 (magnesium phosphate) and MgHPO4 (magnesium hydrogen phosphate) could not be distinguished from the precipitated magnesium phosphate, two graphs were created assuming that each precipitated individually (see Figures 14(A) and 14(B)). According to this, the amount of magnesium wasted as magnesium phosphate was greater than in Example 1, reaching 4-5 mM (see Figures 14(A) and 14(B)).

[0097] In Example 3, when magnesium hydroxide was added at 2.0 times the molar amount of ammonia nitrogen (Mg / N=2.0), the decrease in ammonia nitrogen concentration was even faster than in Example 1 (see Figure 15(A)), and even with a reaction time of 5 minutes or less, the ammonia nitrogen concentration remaining in the solution decreased to about 10% of the initial level. At this time, the concentration of soluble phosphate phosphorus in the solution also decreased accordingly (see Figure 15(B)). The soluble magnesium gradually increased from an initial 6-9 mM, reaching 12 mM after 60 minutes (see Figure 16(A)). Because more magnesium hydroxide, which acts as an alkali source, was added than in Example 1, the pH value in the solution rose to above 9 after 30 minutes (see Figure 16(B)).

[0098] In Example 3, after 180 minutes, most of the precipitated ammonia nitrogen existed as magnesium ammonium phosphate (see Figure 17(A)). However, the amount of magnesium phosphate in the precipitated phosphate phosphorus was slightly higher than in Example 1, reaching the same level as Example 2 (3 mM) after 60 minutes (see Figure 17(B)). This indicates that when the amount of added magnesium hydroxide is high, the magnesium reacts with phosphate phosphorus rather than ammonia nitrogen, resulting in unnecessary precipitation, similar to when the amount is low. Approximately 45 mM of added magnesium hydroxide remained in the solid magnesium (see Figures 18(A) and (B)).

[0099] This high concentration of magnesium hydroxide accelerated the precipitation of ammonia nitrogen. The precipitated magnesium consisted almost entirely of magnesium ammonium phosphate and residual magnesium hydroxide (see Figures 18(A) and 18(B)). Similar to Example 1, since Mg3(PO4)2 (magnesium phosphate) and MgHPO4 (magnesium hydrogen phosphate) could not be distinguished from the precipitated magnesium phosphate, two graphs were created by considering each as having precipitated individually (see Figures 14(A) and 14(B)). According to this, the amount of magnesium wasted as magnesium phosphate was less than in Example 2, at 3-4 mM (see Figures 18(A) and 18(B)).

[0100] In Comparative Example 3, when magnesium hydroxide was added at 1.6 times the molar ratio of ammonia nitrogen (Mg / N=1.6) and phosphoric acid was added so that the amount of phosphate phosphorus in the treated solution was twice the molar ratio of ammonia nitrogen (P / N=2.0), the decrease in ammonia nitrogen concentration was significantly slower than in Example 1, and even after a reaction time of 180 minutes, the ammonia nitrogen concentration remaining in the solution remained at about 20% of the initial level (see Figure 23(A)). At this time, the concentration of soluble phosphate phosphorus in the treated solution decreased slightly in correspondence (see Figure 23(B)). The soluble magnesium initially rose to about 17 mM, and then gradually decreased to about 15 mM (Figure 24(A)).

[0101] The pH value of the treated solution dropped to pH=3 immediately after the addition of phosphoric acid. As a result, the magnesium hydroxide, which is the alkali source, dissolved rapidly, and the pH quickly reached around pH=6.1, which is in the weakly acidic range, and remained at this pH value thereafter. This acidic-weakly acidic pH value is due to the higher amount of phosphoric acid, which is the acid source, compared to Example 1. Consequently, in Comparative Example 3, the pH was considerably lower than in Example 1, which was performed in a weakly alkaline environment (see Figure 24(B)), and the precipitation of magnesium ammonium phosphate, an ammonia salt that is poorly soluble in alkali (but acid-soluble), was suppressed.

[0102] [Comparative Example 4] In Comparative Example 4, the precipitated slurry was left intact (the remaining slurry), and the process of adding the treatment solution, magnesium hydroxide powder, and phosphoric acid to the remaining slurry was repeated. This will be explained in detail below. (Experiment 1: First attempt) The separated liquid discharged from the anaerobic digestion process at the sewage treatment plant was filtered through filter paper to obtain a liquor containing 50 mM ammonia nitrogen and 6 mM phosphate phosphorus. This liquor was introduced into a treatment tank, and magnesium hydroxide was added to the liquor in the same molar ratio as the ammonia nitrogen (Mg / N = 1.0). Then, 44 mM phosphorus was added so that the phosphorus in the liquor after magnesium hydroxide addition was equal to the ammonia nitrogen (P / N = 1.0). Next, the liquor was slowly stirred. The procedures for slow stirring after the addition of magnesium hydroxide and phosphorus were the same as in Experiment 1 for Experiments 2 to 5. (Experiment 2: 2 times) After removing the supernatant water following Experiment 1, the remaining slurry (precipitation) in the treatment tank was mixed with the treatment solution again. Magnesium hydroxide was then added to this mixture in the same mole ratio as ammonia nitrogen (Mg / N = 1.0). Finally, phosphoric acid was added to the treatment solution after the magnesium hydroxide was added so that the amount of phosphoric acid in the treatment solution was equal to the same mole ratio as ammonia nitrogen (P / N = 1.0). (Experiment 3: 3 times) After removing the supernatant water following Experiment 2, the remaining slurry (precipitation) in the treatment tank was mixed with the treatment solution again. Magnesium hydroxide was then added to this mixture in the same mole ratio as ammonia nitrogen (Mg / N = 1.0). Finally, phosphoric acid was added to the treatment solution after the magnesium hydroxide addition so that the amount of phosphoric acid in the treatment solution was equal to the same mole ratio as ammonia nitrogen (P / N = 1.0). (Experiment 4: 4 times) After removing the supernatant water following Experiment 3, the remaining slurry (precipitation) in the treatment tank was mixed with the treatment solution again. Magnesium hydroxide was then added to this mixture in the same molar ratio as ammonia nitrogen (Mg / N=1.0). Finally, phosphoric acid was added to the treatment solution after the magnesium hydroxide was added so that the amount of phosphoric acid in the treatment solution was equal to the same molar ratio as ammonia nitrogen (P / N=1.0). (Experiment 5: 5 times) After removing the supernatant water following Experiment 4, the remaining slurry (precipitation) in the treatment tank was mixed with the treatment solution again. Magnesium hydroxide was then added to this mixture in the same mole ratio as ammonia nitrogen (Mg / N = 1.0). Finally, phosphoric acid was added to the treatment solution after the magnesium hydroxide was added so that the amount of phosphoric acid in the treatment solution was equal to the same mole ratio as ammonia nitrogen (P / N = 1.0).

[0103] The concentration of ammonia nitrogen in the supernatant of each of the first five samples was measured, and the time it took for the ammonia nitrogen to decrease to 30% (17 mM), 20% (11 mM), and 10% (6 mM) of the initial concentration was recorded. Note that the time it took for the ammonia nitrogen to decrease to 30% of the initial concentration means that 70% of the ammonia nitrogen was removed. The time it took for the ammonia nitrogen to decrease to 20% means that 80% was removed. The time it took for the ammonia nitrogen to decrease to 10% means that 90% was removed. The results are shown in Figure 25.

[0104] When measuring the time it took for the ammonia nitrogen concentration in the treated liquid to decrease to 30% (17 mM) of the initial concentration and to 20% (11 mM), the treatment in which slurry was left for up to four cycles (Experiment 4) showed the shortest reaction time in all cases. In the first experiment (Experiment 1), it took about 60 minutes for the ammonia nitrogen concentration in the treated liquid to decrease to 30% of the initial concentration, and as long as 1200 minutes to remove it to 20%.

[0105] In Experiment 2, where the liquid to be treated was added again to the remaining slurry after Experiment 1 and subjected to the prescribed treatment, the removal rate of ammonia nitrogen from the liquid to be treated reached 70% and 80% in approximately 15 minutes and 75 minutes, respectively.

[0106] In Experiment 3, where the liquid to be treated was added again to the remaining slurry after Experiment 2 and the predetermined treatment was performed, the time was further shortened, and it took approximately 9 minutes and 30 minutes, respectively, for the removal rate of ammonia nitrogen from the liquid to be treated to reach 70% and 80%.

[0107] In Experiment 4, which had the shortest reaction time, it was sufficient to reach a 70% and 80% removal rate of ammonia nitrogen in the treated solution in about 5 minutes and 11 minutes, respectively. On the other hand, in Experiment 5, in which the treated solution was added again to the slurry from Experiment 4 and the predetermined treatment was performed, the decrease in ammonia nitrogen concentration was slower, and it took 40 minutes and 150 minutes, respectively, to reach a 70% and 80% removal rate of ammonia nitrogen in the treated solution.

[0108] Furthermore, to remove 90% of the ammonia nitrogen from the treated liquid, a reaction time of 1200 minutes was required under the conditions of Experiment 3, while 90 minutes was sufficient under the conditions of Experiment 4. Under the conditions of Experiment 5, 480 minutes were required. This indicates that by increasing the slurry concentration to four times the initial concentration (Experiment 4), the volume of the treatment tank used to remove ammonia nitrogen from the treated liquid can be significantly reduced compared to cases where the slurry concentration is lower than in Experiment 4 (Experiments 1-3) or higher than in Experiment 4 (Experiment 5).

[0109] In Experiment 5, where the slurry concentration was highest, the reason for the slow decrease in ammonia nitrogen concentration is still unclear, but it is possible that the generated struvite adhered to the surface of the added magnesium hydroxide powder, hindering the dissolution of the magnesium hydroxide. Therefore, it is thought that leaving a high concentration of the slurry containing precipitated struvite in the tank would have a counterproductive effect on the reaction. For this reason, in order to remove ammonia nitrogen rapidly by leaving the slurry in the tank and adding the next batch of water to be treated, it is necessary to remove a certain amount of slurry to sufficiently expose the surface of the magnesium hydroxide powder to the liquid.

[0110] Although embodiments and examples have been described above, the technical scope of the present invention is not limited to the embodiments and examples described above. It will be apparent to those skilled in the art that various modifications or improvements can be made to the embodiments and examples described above. Furthermore, such modified or improved forms are also included in the technical scope of the present invention. For example, in the water treatment system 100, the separation liquid treatment device 50A may be changed to separation liquid treatment devices 50B, 50C, 50D, and 50F. One or more of the requirements described in the embodiments and examples described above may be omitted. Also, the requirements described in the embodiments and examples described above can be combined as appropriate. Furthermore, the execution order of each operation shown in the embodiments and examples can be implemented in any order, as long as the result of the previous operation is not used in the subsequent operation. Also, even if the operations in the embodiments and examples described above are described using "first," "next," "followed," etc. for convenience, it is not necessary to perform them in this order. [Explanation of Symbols]

[0111] 10. Initial sedimentation tank 20... Reaction tanks 21. Aeration device 30. Final sedimentation tank 40. Anaerobic digester 41. Sludge dewatering machine 50A, 50B, 50C, 50D, 50E, 50F... Separation liquid treatment device 50, 53... Reaction tanks 51...First thickener 52...2nd thickener 60, 60A, 60B, 60C... Magnesium salt feeding device 70, 70A, 70B, 70C... Phosphate injection device 80... Control device 90... Storage tank 100...Water treatment system 501, 511, 521, 531...Dehydrator A, B...Measuring device D... Separation liquid D0, D1, D2, D3... Processing liquid D01, D11, D21, D31...Dehydration liquid L1, L2, L3 L4, L5, L6, L11, L21...Return path M... Stirring blade P0, P1, P2, P3...precipitates P01, P11, P21, P31... Solids R...Lake S1, S3...supernatant water S2... Treated water W1... Primary sedimentation sludge W2... Excess sludge W3... Digested sludge W4... Dehydrated Cake

Claims

1. A separation liquid treatment apparatus that processes organic sludge generated in the process of purifying organic wastewater containing nitrogen components using aerobic microorganisms, and then treats the separated liquid obtained by anaerobic digestion before returning it to the purification process, A separation liquid processing apparatus comprising a reaction vessel for storing part or all of the aforementioned separation liquid, and for adding and mixing phosphoric acid and magnesium salt to the stored separation liquid.

2. The separation liquid apparatus according to claim 1, further comprising a first thickener located downstream of the reaction tank for storing wastewater containing precipitates generated in the reaction tank and for allowing the precipitates to settle.

3. The separation liquid processing apparatus according to claim 2, wherein the first thickener adds and mixes the phosphoric acid and the magnesium salt to the stored wastewater.

4. The separation liquid processing apparatus according to claim 2 or 3, wherein a second thickener is provided downstream of the first thickener to store the wastewater from the first thickener and allow the precipitate to settle, and the second thickener adds and mixes the phosphoric acid and the magnesium salt to the stored wastewater.

5. A phosphoric acid input device for introducing the aforementioned phosphoric acid into the reaction vessel, A magnesium salt adding device for adding the magnesium salt to the reaction vessel, The phosphate injection device and the control device for controlling the phosphate injection device, The reactor comprises a measuring device for measuring at least one of the following: the concentration of ammonia nitrogen in the separated liquid introduced into the reactor, the concentration of phosphoric acid in the separated liquid, the pH value of the liquid in the reactor, the concentration of the magnesium salt in the liquid in the reactor, the concentration of ammonia nitrogen in the liquid in the reactor, and the concentration of phosphoric acid in the liquid in the reactor. The separation liquid processing apparatus according to claim 1, wherein the control device controls the amount of phosphoric acid added by the phosphoric acid adding device and the amount of magnesium salt added by the magnesium salt adding device based on the measurement results of the measuring device.

6. The primary sedimentation tank into which the treated water, which is organic wastewater containing nitrogen components, A biological treatment tank for purifying the supernatant water sent from the primary sedimentation tank by aerobic microorganisms, A final sedimentation tank to which the wastewater from the biological treatment tank is sent, The organic sludge settled in the primary sedimentation tank and the organic sludge settled in the final sedimentation tank are introduced into an anaerobic digester, and the organic sludge is subjected to anaerobic digestion treatment. The system includes a separation liquid processing device for processing the separated liquid obtained by solid-liquid separation of the wastewater from the anaerobic digester, The separation liquid processing apparatus includes a reaction tank for storing part or all of the separation liquid and adding and mixing phosphoric acid and magnesium salt to the stored separation liquid, A water treatment system comprising a return path that returns the wastewater from the reaction tank to the primary sedimentation tank.

7. A method for treating organic sludge generated in the process of purifying organic wastewater containing nitrogen components using aerobic microorganisms, after anaerobic digestion treatment of the organic sludge, and before returning the separated liquid (after solid-liquid separation) to the purification process, A method for treating a separated liquid, comprising adding and mixing phosphoric acid and magnesium salts to part or all of the separated liquid.

Images