Method for producing nitrogen-containing concentrate from digested liquid

Abstract

To provide a method of producing a nitrogen-containing concentrated liquid from digestive juice, the method capable of efficiently performing an ammonium sulfate generation reaction from ammonia nitrogen in the digestive juice without using a coagulant in a dehydration step of the digestive juice.SOLUTION: A method of producing a nitrogen-containing concentrated liquid from digestive juice includes the steps of: (a) mixing an alcohol-based antifoam agent with the digestive liquid; (b) adjusting pH by adding sulfuric acid to the digestive juice obtained in the step (a); and (c) concentrating the digestive juice obtained in the step (c) to obtain the nitrogen-containing concentrated liquid by separating condensed water therefrom.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a nitrogen-containing concentrate from a digestive fluid. [Background technology]

[0002] The residual liquid after methane fermentation, the digested effluent, has a solids concentration of approximately 3–5%. Conventional wastewater treatment requires dehydration using chemicals such as flocculants and separation into solids and separated liquid. This dehydration process requires high costs for chemicals such as flocculants, resulting in poor economic efficiency. Furthermore, the separated liquid after dehydration contains significant BOD (biochemical oxygen demand) sources such as ammonia. Therefore, it cannot meet the discharge standards for public rivers or sewers. It requires advanced treatment methods such as nitrification, denitrification, flocculation, and activated carbon. The initial and running costs, complex flow, and operational management required for digested effluent treatment have hindered the widespread adoption of methane fermentation facilities. Furthermore, approximately 70% of the nitrogen in the digested effluent is ammoniacal nitrogen, which exists in aqueous solution. Therefore, the nitrogen component migrates to the separated liquid after dehydration, limiting the nitrogen content of the solids. As a result, the resulting solids have little value as fertilizer. In response to this, for example, Patent Document 1 describes removing solids from methane fermentation residual liquid using a screen with wedge wires, and then adjusting the pH of the resulting separated liquid to an acidic level. This fixes the ammonia component in the separated liquid, and the pH-adjusted separated liquid is then evaporated and concentrated to produce liquid fertilizer with a stable nitrogen component. Patent Document 1 also describes that sulfuric acid is preferable as an acid for adjusting the pH, and the addition of sulfuric acid converts the ammoniacal nitrogen component in the separated liquid into ammonium sulfate, which is fixed in the liquid fertilizer. On the other hand, the digested liquid, which is the residual liquid from methane fermentation, is saturated with carbon dioxide produced during methane fermentation, so the addition of sulfuric acid or other substances causes rapid and large amounts of foaming in the digested liquid.The large amounts of foaming in the digested liquid hinder the progress of the ammonium sulfate production reaction caused by the addition of sulfuric acid, and the time required for the foaming to disappear is the rate-limiting factor in the digested liquid treatment system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-34870 Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above circumstances, an object of the present invention is to provide a method for producing a nitrogen-containing concentrated liquid from a digestive liquid, which can efficiently carry out a reaction to produce ammonium sulfate from ammoniacal nitrogen in the digestive liquid without using a flocculant in the dehydration step of the digestive liquid. [Means for solving the problem]

[0005] To solve the above problems, the present inventors came up with the idea of ​​using an antifoaming agent to prevent foaming during the addition of sulfuric acid to produce ammonium sulfate. After extensive investigation, they discovered that mixing an antifoaming agent into the digestive liquor prior to the step of adding sulfuric acid to fix the ammoniacal nitrogen in the digestive liquor as ammonium sulfate can significantly suppress foaming during the addition of sulfuric acid. Furthermore, the present inventors discovered that, among various types of antifoaming agents, alcohol-based antifoaming agents exhibit significantly superior antifoaming effects. The present invention was completed based on this finding and includes the following aspects.

[0006] One aspect of the present invention is [1] A method for producing a nitrogen-containing concentrated liquid from a digestive liquid, (a) mixing an alcohol-based antifoaming agent with the digestive liquid; (b) adding sulfuric acid to the digestion liquid obtained in the step (a) to adjust the pH; (c) a step of concentrating the digested liquid obtained in the step (b) by separating the nitrogen-containing concentrated liquid from the condensed water; The present invention relates to a manufacturing method comprising the steps of: Here, the manufacturing method of the present invention is as follows: [2] The manufacturing method according to [1] above, The digested liquid is characterized in that it is obtained by methane fermentation. In one embodiment, the manufacturing method of the present invention is [3] The manufacturing method according to [1] or [2] above, The digestive fluid is characterized in that it is obtained by solid-liquid separation without using a flocculant. In one embodiment, the manufacturing method of the present invention is [4] The manufacturing method according to any one of [1] to [3] above, The method is characterized in that the alcohol-based antifoaming agent in the step (a) is added to the digestive liquid so that the concentration is in the range of 20 ppm to 1000 ppm. In one embodiment, the manufacturing method of the present invention is [5] The manufacturing method according to any one of [1] to [4] above, The pH of the digestive fluid adjusted in the step (b) is within the range of pH 4.0 to pH 6.0. In one embodiment, the manufacturing method of the present invention is [6] The manufacturing method according to any one of [1] to [5] above, The amount of sulfuric acid to be added in the step (b) is determined based on the evaporation residue, ammonia nitrogen, or M alkalinity of the digested liquid. In one embodiment, the manufacturing method of the present invention is [7] The manufacturing method according to any one of [1] to [6] above, The amount of sulfuric acid added in the step (b) is The amount of 20% sulfuric acid to be dropped is 5.8 to 7.8 mL per 1 g of M alkalinity based on the M alkalinity of the digested liquid. It is characterized by: In one embodiment, the manufacturing method of the present invention is [8] The manufacturing method according to any one of [1] to [7] above, the step (a) is a step of continuously flowing the digestion liquid and the alcohol-based defoaming agent into a mixing tank, and continuously flowing the digestion liquid sufficiently mixed with the alcohol-based defoaming agent into a pH adjustment tank, The step (b) is a step of adjusting the pH of the digested liquid continuously flowing in from the mixing tank by adding sulfuric acid to the pH adjustment tank, and continuously discharging the pH-adjusted digested liquid into a concentration raw water tank. Manufacturing method. In one embodiment, the manufacturing method of the present invention is [9] The manufacturing method according to any one of [1] to [8] above, (d) A step of drying the nitrogen-containing concentrate obtained in the step (c) is further included.

[0007] Another aspect of the present invention is

[10] An apparatus for producing a nitrogen-containing concentrate from a digestive liquid, comprising: a mixing tank for mixing the digestive fluid and the antifoaming agent; A pH adjustment tank for adding sulfuric acid to the digestion liquid mixed with the antifoaming agent to adjust the pH. a concentrating means for concentrating the pH-adjusted digestive fluid; The present invention relates to an apparatus including: Here, the device of the present invention is

[11] The device according to

[10] above, the mixing tank is provided with a digestion fluid supply means for supplying a desired amount of digestion fluid and a defoaming agent supply means for supplying a desired amount of defoaming agent; The pH adjusting tank is characterized by being equipped with a sulfuric acid supply means. In one embodiment, the device of the present invention

[12] The device according to

[10] or

[11] above, Further comprising a solid-liquid separation means for separating the digestive liquid into solid and liquid, The solid-liquid separation means and the digestion liquid supply means are connected, and the separated liquid obtained by the solid-liquid separation means is sent to the mixing tank via the digestion liquid supply means. In one embodiment, the device of the present invention

[13] The device according to any one of

[10] to

[12] above, The mixing tank and the pH adjustment tank are directly connected to each other at their lower parts, and the digested liquid introduced into the mixing tank flows directly into the pH adjustment tank after a certain residence time in the mixing tank. In one embodiment, the device of the present invention

[14] The device according to any one of

[10] to

[13] above, The system further includes a digestion liquid storage tank, a defoaming agent storage tank, and a sulfuric acid storage tank. In one embodiment, the device of the present invention

[15] The device according to any one of

[10] to

[14] above, The apparatus further comprises a sulfuric acid dilution tank for adjusting the sulfuric acid to be added to the pH adjustment tank. In one embodiment, the device of the present invention

[16] The device according to any one of

[10] to

[15] above, The method further includes a drying means for drying the nitrogen-containing concentrated liquid obtained by the concentrating means, and is characterized in that the drying means and the concentrating means are connected, and the concentrated liquid is sent from the concentrating means to the drying means. [Effects of the Invention]

[0008] According to the method for producing a nitrogen-containing concentrated liquid from a digested liquid of the present invention, foaming that occurs when ammoniacal nitrogen in the digested liquid is fixed as ammonium sulfate can be defoamed in a short time with a smaller amount of defoaming agent. Furthermore, the method for producing a nitrogen-containing concentrate according to the present invention can provide a concentrate containing a high concentration of nitrogen. Furthermore, the condensed water separated during the production of the concentrate does not require wastewater treatment such as nitrification or denitrification. Therefore, the cost and treatment of the flocculant used in the production process of the nitrogen-containing concentrate, as well as the cost and treatment of the condensed water can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows a flow chart of one embodiment of the method for producing a nitrogen-containing concentrate from digested liquid according to the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an embodiment of an apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid according to the present invention. [Figure 3] FIG. 3 is a schematic diagram showing one embodiment of an apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid according to the present invention, which is an apparatus having a two-tank system in which a mixing tank and a pH adjustment tank are connected together. [Figure 4] FIG. 4 is a schematic diagram showing one embodiment of an apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid according to the present invention, which further includes a two-tank tank in which a mixing tank and a pH adjustment tank are connected, and a sulfuric acid dilution tank. [Figure 5] 5 is a graph showing the results of the post-foaming addition test (Comparative Example 1) described in the Examples below. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for the foam generated in the digestive liquid to disappear, and the pH change of the digestive liquid. [Figure 6] FIG. 6 is a photograph showing the state of the digestive fluid at the start (FIG. 4A) and when 3 ml of sulfuric acid was added dropwise (FIG. 4B) in the post-foaming addition test (Comparative Example 1) described in the Examples below. [Figure 7] 7 is a graph showing the results of the pre-addition test (Example 1) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 8] FIG. 8 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition (Example 1) described in the following Examples. [Figure 9] 9 is a graph showing the results of a pre-addition test (Example 2) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 10] FIG. 10 is a photograph showing the state of the digestive fluid when 5 ml (FIG. 10A) and 6 ml (FIG. 10B) of sulfuric acid were added dropwise in the prior addition test (Example 2) described in the following Example. [Figure 11]11 is a graph showing the results of a pre-addition test (Example 3) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 12] FIG. 12 is a photograph showing the state of the digestive fluid when 3 ml (FIG. 12A) and 5 ml (FIG. 12B) of sulfuric acid were added dropwise in the prior addition test (Example 3) described in the following Example. [Figure 13] 13 is a graph showing the results of a prior addition test (Comparative Example 2) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 14] FIG. 14 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition test (Comparative Example 2) described in the Examples below. [Figure 15] 15 is a graph showing the results of a prior addition test (Comparative Example 3) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 16] FIG. 16 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition test (Comparative Example 3) described in the Examples below. [Figure 17] 17 is a graph showing the results of a prior addition test (Comparative Example 4) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive fluid to disappear, and the pH change of the digestive fluid. [Figure 18] FIG. 18 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition test (Comparative Example 4) described in the Examples below. [Figure 19] 19 is a graph showing the results of a pre-addition test (Comparative Example 5) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive liquid to disappear, and the pH change of the digestive liquid. [Figure 20] FIG. 20 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition test (Comparative Example 5) described in the Examples below. [Figure 21]21 is a graph showing the results of a prior addition test (Comparative Example 6) described in the following Examples. The graph shows the relationship between the amount of sulfuric acid added, the time it takes for bubbles generated in the digestive liquid to disappear, and the pH change of the digestive liquid. [Figure 22] FIG. 22 is a photograph showing the state of the digestive fluid when 6 ml of sulfuric acid was added dropwise in the prior addition test (Comparative Example 6) described in the following Example. [Figure 23] FIG. 23 is a photograph showing the state of condensed water (FIG. 23A) and nitrogen-containing concentrated liquid (FIG. 23B) that are the subject of analysis in Example "II. Analysis of properties after digestive fluid treatment" below. [Figure 24] FIG. 24 is a graph showing the average titration results for each digestive fluid in Example "III. Relationship between sulfuric acid injection amount and digestive fluid properties" below. [Figure 25] FIG. 25 is a graph showing the relationship between the amount of sulfuric acid added dropwise and the evaporation residue measured in Example "III. Relationship between the amount of sulfuric acid added and the properties of the digested liquid" below. [Figure 26] FIG. 26 is a graph showing the relationship between the amount of sulfuric acid dripped and NH4-N measured in Example "III. Relationship between amount of sulfuric acid injected and properties of digested liquid" below. [Figure 27] FIG. 27 is a graph showing the relationship between the amount of sulfuric acid dripped and M alkalinity measured in the following Example "III. Relationship between sulfuric acid injection amount and properties of digested fluid." [Figure 28] FIG. 28 is a graph showing the change in the amount of sulfuric acid dropped and the pH when each alcohol-based defoaming agent was used in Example "IV. Examination of alcohol-based defoaming agents" below. [Figure 29] FIG. 29 is a graph showing the defoaming time at each pH point when each alcohol-based defoaming agent was used in Example "IV. Examination of Alcohol-Based Defoaming Agents" below. DETAILED DESCRIPTION OF THE INVENTION

[0010] One aspect of the present invention relates to a method for producing a nitrogen-containing concentrate from a digestive fluid. The method for producing a nitrogen-containing concentrate of the present invention comprises the following steps (a) to (c), as shown in FIG. 1: (a) A step of mixing an alcohol-based antifoaming agent with the digestive fluid (antifoaming agent mixing step) (b) A step of adding sulfuric acid to the digestion liquid obtained in step (a) to produce ammonium sulfate (pH adjustment step). (c) A step of concentrating the digested liquid obtained in step (b), which is a step of separating the nitrogen-containing concentrated liquid from the condensed water (concentration step).

[0011] As described above, the method for producing a nitrogen-containing concentrate of the present invention includes the step (a) of mixing an alcohol-based antifoaming agent with a digested liquid. In this specification, the term "digestion liquid" refers to a methane fermentation residual liquid obtained after methane fermentation of organic waste. The digestion liquid that can be used in the present invention is a methane fermentation residual liquid containing ammonia and ammonium salts, and the origin of the organic waste and the methane fermentation method are not limited. The digested liquid can be the methane fermentation residual liquid obtained after methane fermentation. In this case, the digested liquid can be supplied, for example, from a storage tank for the methane fermentation residual liquid to a mixing tank for mixing with an antifoaming agent. The digested liquid is supplied to the mixing tank in a quantitative manner so as to obtain a desired amount.

[0012] The digestive fluid may also be a separated fluid obtained by solid-liquid separation. Therefore, one embodiment of the method for producing a nitrogen-containing concentrated fluid from a digestive fluid of the present invention includes a step of subjecting the digestive fluid to solid-liquid separation prior to step (a). Solid-liquid separation can be performed to separate solids with large particle sizes that may cause blockages in the concentration means or pump. Examples of solids to be removed in solid-liquid separation include, but are not limited to, substances with particle sizes or diameters of 20 mm or more. The solid-liquid separation means is not limited as long as it can separate the solids in the digestive fluid, and examples of such means include a juicer and a centrifugal dehydrator. The method for producing a nitrogen-containing concentrate of the present invention does not require the use of a flocculant in the solid-liquid separation process, and therefore the digestive liquor does not contain a flocculant. In this specification, a flocculant refers to a substance that changes the properties of particles in the digestive liquor to aggregate or coarsen them so that water and solids can be separated during the dehydration process of the digestive liquor. Known flocculants include, but are not limited to, inorganic flocculants such as iron salts, aluminum salts, and calcium salts, and organic flocculants such as cationic polymer flocculants and anionic polymer flocculants. In a preferred embodiment, the digestive liquid is a digestive liquid after solid-liquid separation and does not contain a flocculant.

[0013] The term "alcohol-based defoaming agent" refers to a defoaming agent used to eliminate foam generated in a liquid, and is prepared with alcohol as the main component. Examples of the main alcohol component include, but are not limited to, higher alcohols having 12 to 30 carbon atoms, and straight-chain alcohols having 18 to 22 carbon atoms. Examples of higher alcohols include, but are not limited to, one or more selected from the group consisting of natural alcohols having 12 to 30 carbon atoms and synthetic alcohols having 12 to 30 carbon atoms. Examples of natural alcohols having 12 to 30 carbon atoms include saturated alcohols such as lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, eicosanol, docosanol, tetracosanol, hexaconol, octacosanol, and myricyl alcohol, and unsaturated alcohols such as oleyl alcohol. Examples of synthetic alcohols having 12 to 30 carbon atoms include linear primary alcohols or branched primary alcohols synthesized by the Ziegler method, mixtures of these alcohols with different carbon numbers, and linear secondary alcohols produced by air oxidation of paraffin. The defoaming agent may be a single alcohol or a combination of two or more alcohols. The defoaming agent may contain, or may not contain, an alcohol with fewer than 12 carbon atoms or an alcohol with more than 30 carbon atoms. While not limited to the following, the higher alcohol may be contained in an amount of, for example, 5 to 90 wt. % of the total weight of the defoaming agent. In addition to alcohol, the alcohol-based defoaming agent may further contain known components of alcohol-based defoaming agents, such as inorganic salts, surfactants (e.g., anionic surfactants, nonionic surfactants), fatty acid esters, natural fats and oils, mineral oils, hydrocarbons, and water. The alcohol-based defoaming agent that can be used in the present invention is not limited, and any known alcohol-based defoaming agent can be used as long as it is added to the digestive liquor before the addition of sulfuric acid to inhibit foaming and / or provide a defoaming effect upon the addition of sulfuric acid.Examples of such alcohol-based defoamers include the higher alcohol-based defoamers disclosed in JP 2011-215235 A, JP 2012-143700 A, JP 2014-079699 A, JP 2018-51513 A, JP 2021-098156 A, and JP 2015-054259 A. The form of the defoaming agent is not particularly limited, and any form of defoaming agent can be used, such as oil type, oil compound type, solution type, emulsion type, self-emulsifying type, etc., but emulsion type is preferred. The defoaming agent may contain additives (such as separation inhibitors, preservatives, emulsifiers) that are preferred for each form. Commercially available alcohol-based defoaming agents that can be used in the present invention include, but are not limited to, Kuriles 653 (Kurita Water Industries), Dappo H-312 (San Nopco Ltd.), Bismer FS series (Nissin Chemical Research Institute Co., Ltd.), SN-650 (Taki Chemical Co., Ltd.), FALC-108 (Kubota Kasui Co., Ltd.), AE-3100 (Mitsubishi Chemical Aqua Solutions Co., Ltd.), Pronal EM-38N (Toho Chemical Industry Co., Ltd.), and EL-101 (E-Life Co., Ltd.).

[0014] The antifoaming agent is preferably added to the digestive fluid in a range of 20 ppm to 1000 ppm, more preferably in a range of 50 ppm to 500 ppm. In a more preferred embodiment, the antifoaming agent is added to the digestive fluid to a concentration of 100 ppm. If the amount of antifoaming agent added is less than 20 ppm, a desirable antifoaming effect cannot be obtained, and if it exceeds 1000 ppm, the cost increases, which is undesirable. Furthermore, after adding the antifoaming agent to the digestive liquid, it is preferable to thoroughly mix it using a stirring means. The stirring treatment is preferably carried out until the antifoaming agent is uniformly dispersed in the digestive liquid. The digestive liquid is stirred, for example, for 5 minutes or more (for example, about 5 to 10 minutes). By stirring the digestive liquid sufficiently, foaming during the production of ammonium sulfate can be suppressed. The stirring means is not limited as long as it can mix the antifoaming agent and the digestive liquid, and a known stirrer can be used.

[0015] The method for producing a nitrogen-containing concentrate of the present invention includes, after the above step (a), "(b) a step of adding sulfuric acid to the digested liquid obtained in step (a) to adjust the pH." The digested liquid that has been thoroughly mixed with the antifoaming agent in the mixing tank is sent to the pH adjustment tank, where ammonium sulfate is produced from the ammoniacal nitrogen in the digested liquid. It is preferable to use sulfuric acid to produce ammonium sulfate, as the use of sulfuric acid can reduce costs and also lower the possibility of equipment corrosion compared to the use of hydrochloric acid or the like. When sulfuric acid is used, it can be supplied to the pH adjustment tank as, for example, 10 to 40 wt% sulfuric acid. If the concentration of sulfuric acid supplied is high, the foaming force will be intense, while if the concentration of sulfuric acid is low, it will take time for the ammonium sulfate production reaction to proceed. Those skilled in the art can appropriately set a preferred concentration by taking into consideration the balance between the foaming state when sulfuric acid is added and the time required for the sulfuric acid production reaction. In a preferred embodiment, the concentration of sulfuric acid supplied to the pH adjustment tank is 15 to 25 wt%. Sulfuric acid may be supplied until the pH of the digested liquid reaches, for example, a range of pH 4.0 to pH 6.0. In a preferred embodiment, sulfuric acid is supplied until the pH of the digested liquid reaches a range of 4.5 to 5.5, and in a more preferred embodiment, sulfuric acid is supplied until the pH of the digested liquid reaches 5.0. Because the volatilization rate of ammonia (the rate at which ammonia is mixed into the condensed water) is the same at pH 4.0 and pH 5.0, a pH of 5 is preferable because it allows for reductions in the amount of sulfuric acid used and the amount of antifoaming agent. However, adjusting the pH to less than 4.0 is undesirable because it lowers the pH of the nitrogen-containing concentrate, which may cause problems when used as fertilizer, and adjusting the pH to greater than 6.0 is undesirable because ammonia nitrogen is not sufficiently fixed and volatilizes.

[0016] In one embodiment of the method for producing a nitrogen-containing concentrate of the present invention, the amount of sulfuric acid to be added to the digested liquid can be determined from the evaporation residue, ammoniacal nitrogen, or M alkalinity of the digested liquid. By measuring the evaporation residue, ammoniacal nitrogen, or M alkalinity of the digested liquid in advance, the amount of sulfuric acid required for pH adjustment can be calculated based on the description of Example III and the results of Figures 25 to 27 of the present application. For example, when adjusting the pH of the digested liquid to 4.8, The amount of 20% sulfuric acid to be added per 1 g of M alkalinity based on the M alkalinity of the digested liquid is 5.8 to 7.8 mL. It can be said that: It is preferable to supply sulfuric acid from a sulfuric acid supply port connected to the bottom or lower part of the pH adjustment tank containing the digestion liquid. Supplying sulfuric acid from the lower part of the digestion liquid can efficiently promote the reaction. After adding sulfuric acid to the digestive liquid, it is preferable to mix it thoroughly using a stirring means. The digestive liquid is preferably stirred for 5 minutes or more (for example, 5 to 10 minutes). This makes it possible to fix the nitrogen (especially ammoniacal nitrogen) contained in the digestive liquid without volatilizing it. After pH adjustment, the digested liquid can be sent to the concentrated raw water tank via overflow.

[0017] The method for producing a nitrogen-containing concentrate of the present invention includes, after step (b), "(c) a step of concentrating the digested liquid obtained in step (b), which involves separating the nitrogen-containing concentrate from condensed water." In step (c), the digested liquid from which ammonium sulfate has been produced is sent from a pH adjustment tank or a raw concentrate tank to a concentrating means. The digested liquid is concentrated by the concentrating means and separated into a nitrogen-containing concentrate and condensed water. At this time, the ammoniacal nitrogen contained in the digested liquid is transferred to the concentrate. In a preferred embodiment, the nitrogen-containing concentrate obtained in step (c) can contain ammoniacal nitrogen that is 1.5 times or more, 2 times or more, and more preferably 2.5 times or more concentrated compared to the ammoniacal nitrogen in the digested liquid before concentration. For example, in a preferred embodiment, the nitrogen-containing concentrate obtained by the production method of the present invention can contain 5,000 mg / kg or more of nitrogen. A known reduced-pressure concentrating device can be used as the concentrating means for step (c). Hot water at about 90°C, for example, can be used as a heat source for the reduced-pressure concentrating device. Furthermore, by using a heat pump to reuse the latent heat of the condensed water and thereby increasing thermal efficiency, it is possible to configure the system so that condensation can be performed using only the surplus heat source of the generator. The condensed water obtained from the concentration process has low solids (SS) and nitrogen content, meets the general wastewater standards set by the Ministry of the Environment, and can be discharged into rivers and sewers. In one embodiment, the condensate obtained by the method of the present invention has a SS (solids) of less than 100 mg / L, preferably less than 50 mg / L, and more preferably less than 30 mg / L. In another embodiment, the condensate obtained by the method of the present invention has a tn (total nitrogen) of less than 100 mg / L, preferably less than 50 mg / L, and more preferably less than 30 mg / L. In another embodiment, the condensate obtained by the method of the present invention has a BOD (biochemical oxygen demand) of less than 100 mg / L, preferably less than 50 mg / L, and more preferably less than 30 mg / L. In another embodiment, the condensate obtained by the method of the present invention has a COD Mn (Chemical oxygen demand) is less than 100 mg / L, preferably less than 50 mg / L, and more preferably less than 30 mg / L.

[0018] The nitrogen-containing concentrate obtained through the above step (c) can be used as a liquid fertilizer as it is, or can be dried to form a dry fertilizer. Therefore, in one embodiment, the method of producing a nitrogen-containing concentrate from digested fluid of the present invention further comprises a step (d) of drying the nitrogen-containing concentrate obtained in step (c). This makes it possible to provide the nitrogen-containing solid as a dried fertilizer. A known drying device can be used as a drying means in step (d).

[0019] In another aspect, the present invention provides an apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid (digested liquid treatment apparatus), which comprises a mixing tank for mixing the digested liquid with an antifoaming agent, a pH adjustment tank for adjusting the pH of the digested liquid by adding sulfuric acid to the digested liquid mixed with the antifoaming agent, and a concentrating means for concentrating the pH-adjusted digested liquid.

[0020] In one embodiment of the apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid of the present invention, the mixing tank is equipped with a digested liquid supply means for supplying a desired amount of digested liquid, an antifoaming agent supply means for supplying a desired amount of antifoaming agent, and an agitation means, and the pH adjustment tank is equipped with a sulfuric acid supply means and an agitation means. The digested liquid supply means may be a configuration such as a combination of a digested liquid storage tank, a pump, and a flow meter, as exemplified in FIG. 2. The antifoaming agent supply means may be a configuration such as a combination of an antifoaming agent storage tank, a pump, and a flow meter, as exemplified in FIG. 2. The sulfuric acid supply means may be a configuration such as a combination of a sulfuric acid storage tank, a pump controlled by a pH control panel, and a pH meter. With this configuration, it is possible to supply the antifoaming agent in a preferred range to a desired amount of the digestive liquid, and to thoroughly mix the digestive liquid and the antifoaming agent in the mixing tank before adding sulfuric acid.

[0021] In one embodiment, the apparatus for producing a nitrogen-containing concentrated liquid from a digested liquid of the present invention further includes a solid-liquid separation means for separating the digested liquid into solid and liquid. The solid-liquid separation means is connected to the digested liquid supply means, and the separated liquid obtained by the solid-liquid separation means is sent to the mixing tank via the digested liquid supply means. As described above, the solid-liquid separation means is not limited as long as it can separate the solids in the digested liquid, and known juice extractors, centrifugal dehydrators, etc. can be used. This configuration allows large-sized solids contained in the digestion liquid to be removed in advance, improving the efficiency of the subsequent defoaming agent mixing step and pH adjustment step.

[0022] In one embodiment, the apparatus for producing a nitrogen-containing concentrate from a digested liquid of the present invention further includes a drying means for drying the nitrogen-containing concentrate obtained by the concentrating means. The drying means is connected to the concentrating means, and the nitrogen-containing concentrate obtained by the concentrating means can be sent to the drying means. The drying means is not limited as long as it can dry the nitrogen-containing concentrate into a solid, and a known dryer can be used. This configuration allows the nitrogen-containing concentrate to be provided as a dry or solid product.

[0023] One embodiment of the apparatus of the present invention will now be described with reference to Figure 2. Note that the drawings referred to are used to explain the technical features that can be adopted by the present invention, and the apparatus of the present invention is not limited to the configuration shown in the drawings. The digested fluid treatment apparatus 1 shown in Figure 2 comprises a digested fluid storage tank 2, an antifoaming agent storage tank 3, a mixing tank 4, a sulfuric acid storage tank 5, a pH adjustment tank 6, a concentrated raw water tank 7, and a reduced pressure concentration means 8.

[0024] The digested liquid as a methane fermentation residual liquid is stored in the digested liquid storage tank 2. The digested liquid storage tank 2 is connected to the mixing tank 4 by piping. The digested liquid in the digested liquid storage tank 2 is supplied quantitatively to the mixing tank 4 by a pump 21 and a flow meter 31. The antifoaming agent is adjusted to a desired concentration in the antifoaming agent storage tank 3 and stored therein. The antifoaming agent storage tank 3 is equipped with an agitation means 51 and is connected to the mixing tank 4 by piping. The antifoaming agent in the antifoaming agent storage tank 3 is supplied quantitatively to the mixing tank 4 by a pump 22 and a flow meter 32. The mixing tank 4 is equipped with an agitation means 52 and mixes the digested liquid and the antifoaming agent. The mixing tank 4 is connected to the pH adjustment tank 6 by piping, and the digested liquid mixed with the antifoaming agent is sent to the pH adjustment tank 6. In the sulfuric acid storage tank 5, sulfuric acid is adjusted to a desired concentration and stored. The sulfuric acid storage tank 5 is connected to the pH adjustment tank 6 by piping, and sulfuric acid in the sulfuric acid storage tank 5 is sent to the pH adjustment tank 6 by a pump 23. The pH adjustment tank 6 is equipped with an agitation means 53 and a pH meter 41. The pH meter 41 and pump 23 are controlled by a pH control panel, and sulfuric acid is sent to the pH adjustment tank 6 to achieve the desired pH. The pH adjustment tank 6 is connected to the concentrated raw water tank 7 by piping, and the digested liquid overflowing from the pH adjustment tank 6 is sent to the concentrated raw water tank 7. The concentrated raw water tank 7 is equipped with an agitation means 54, and is connected to the reduced pressure concentration means 8 by piping. The digested liquid in the concentrated raw water tank 7 is sent to the reduced pressure concentration means 8 by control of a flow regulator and a control valve. The reduced pressure concentration means 8 separates the digested liquid into a nitrogen-containing concentrated liquid and condensed water.

[0025] Another embodiment of the apparatus of the present invention is shown in FIG. 3. The digested fluid treatment apparatus 1 shown in FIG. 3 comprises a digested fluid storage tank 2, an antifoaming agent storage tank 3, a two-tank tank consisting of a mixing tank 4 and a pH adjustment tank 6 connected together, a sulfuric acid storage tank 5, a concentrated raw water tank 7, and a vacuum concentration means 8. The antifoaming agent and digested fluid are introduced into the upper part of the two-layer mixing tank 4. The mixing tank 4 can be designed to have a sufficient residence time for the digested fluid to mix with the antifoaming agent therein. The digested fluid thoroughly mixed with the antifoaming agent is then sent from the bottom of the mixing tank 4 to the pH adjustment tank 6, where the pH is adjusted with sulfuric acid. The pH adjustment tank 6 can be designed to have a sufficient residence time for the digested fluid to be adjusted to the desired pH. Since a constant amount of digested fluid and antifoaming agent is continuously introduced into the mixing tank 4, the digested fluid adjusted to the desired pH in the pH adjustment tank 6 overflows and is sent to the concentrated raw water tank 7. As in the digested fluid treatment apparatus shown in Figure 3, the mixing tank 4 and the pH adjusting tank 6 may be connected to form a two-tank system. This two-tank system is preferable because it reduces costs compared to separate tanks.

[0026] Another embodiment of the apparatus of the present invention is shown in Figure 4. The digested fluid treatment apparatus 1 shown in Figure 4 includes a digested fluid storage tank 2, an antifoaming agent storage tank 3, a two-tank tank consisting of a mixing tank 4 and a pH adjustment tank 6 connected together, a sulfuric acid storage tank 5, a sulfuric acid dilution tank 9, a concentrated raw water tank 7, and a reduced-pressure concentration means 8. The sulfuric acid dilution tank 9 can dilute the sulfuric acid to a desired concentration. As in the digested fluid treatment apparatus shown in Figure 4, a sulfuric acid dilution tank may be further included. Two or more sulfuric acid dilution tanks may also be included. The inclusion of the sulfuric acid dilution tank 9 allows the use of concentrated sulfuric acid (98%), thereby reducing the amount of sulfuric acid to be brought in and leading to space-saving operation of the apparatus, which is preferable.

[0027] The present invention will be described in detail below using examples, but the present invention is not limited to the following embodiments. [Example]

[0028] (I. Antifoam Test) In this example, sulfuric acid was added dropwise to the digestion liquid, and after foaming was confirmed in the digestion liquid, an alcohol-based defoaming agent was added after foaming (Comparative Example 1). The amount of defoaming agent added and the defoaming time were then confirmed. In addition, the amount of antifoaming agent added and the defoaming time when sulfuric acid was added dropwise after an alcohol-based antifoaming agent was added to the digestion liquid in advance were confirmed (pre-addition test group: Examples 1 to 4), and compared with the post-foaming addition group. Furthermore, in order to verify the defoaming effect of the silicone-based defoaming agent, tests were carried out in the same manner as in the pre-addition test group using the silicone-based defoaming agent (Comparative Examples 2 to 6).

[0029] 1-1. Reagents The digested fluid used was obtained after methane fermentation of livestock waste. The analysis results of the digested fluid are shown in Table 1. Before use, the digested fluid was sieved to remove floating matter so as not to affect pH measurement or stirring operations. [Table 1]

[0030] The sulfuric acid used for titration was 96% concentrated sulfuric acid diluted to 20%. The defoaming agents used were "Kuriles (registered trademark) 653" (manufactured by Kurita Water Industries Ltd.) as an alcohol-based defoaming agent, and "Kuriles (registered trademark) S-117" (manufactured by Kurita Water Industries Ltd.) and "KM-73" (manufactured by Shin-Etsu Silicones Co., Ltd.) as silicone-based defoaming agents.

[0031] 1-2. Test method The post-foaming addition test was conducted as follows: 150 ml of digestion solution was transferred to a 500 ml beaker, and while stirring, sulfuric acid was added dropwise in 1 ml increments until the digestion solution reached a pH of 4. If foaming occurred during the addition of sulfuric acid, the addition was stopped and antifoaming agent was added in small amounts, and the time required for foaming to disappear was recorded. After foaming had disappeared, sulfuric acid was again added dropwise in 1 ml increments until the digestion solution reached a pH of 4, and the time required for the addition of antifoaming agent after foaming and for foaming to disappear was recorded. This process was repeated until the digestion solution reached a pH of approximately 4. The pre-addition test was carried out as follows: 150 ml of digested fluid was transferred to a 500 ml beaker, and a certain amount of antifoaming agent was added to the digested fluid in advance. After adding the antifoaming agent, the digested fluid was stirred and thoroughly mixed. Next, sulfuric acid was added dropwise in 1 ml increments while stirring until the digested fluid reached a pH of 4. If foaming occurred during the addition of sulfuric acid, the addition was stopped and stirring was continued until the foaming disappeared, and the time from foaming to disappearance was recorded. After the foaming disappeared, sulfuric acid was added again in 1 mL increments until the digestion solution reached a pH of 4. If foaming occurred, the addition of sulfuric acid was stopped and stirring was continued until the foaming disappeared, and the time from foaming to disappearance was recorded. This process was repeated until the digestion solution reached a pH of around 4. The defoaming time was the time required from the formation of a foam layer until the liquid surface became visible.

[0032] 1-3. Test conditions In the pre-addition test section, the antifoaming agent was added in advance at the concentration shown in the table below. When the digestive fluid foamed, resistance was created in the fluid, causing the agitation to stop, so the agitation speed was increased as appropriate. Table 2 below shows the initial agitation speed and the increased agitation speed for each test section. [Table 2]

[0033] 2.Results 2-1. Comparative Example 1 Figure 5 shows a graph illustrating the relationship between pH change and defoaming time when the antifoaming agent was added after foaming (Comparative Example 1). As shown in Figure 5, foaming was observed when the pH dropped below 7. When 3 ml of sulfuric acid was added dropwise, the pH reached 6.7, and a 10 mm-thick layer of foam formed. Flow of the digestion liquid was observed during stirring, but once the foam layer formed, the liquid stopped flowing. The stirrer speed was increased to 1,200 rpm. 333 ppm of antifoaming agent was added. Since defoaming occurred 30 seconds after the antifoaming agent was added, sulfuric acid was continued to be added dropwise. Although it took some time after the antifoaming agent was added, defoaming occurred simply by stirring. Figure 6 shows the state at the start and after 3 ml of sulfuric acid was added dropwise. As shown in Figure 6, in the test area where 333 ppm of antifoaming agent was added after foaming, it took a total of approximately 12.5 minutes for the defoaming process to reach pH 4.

[0034] 2-2. Example 1 FIG. 7 is a graph showing the relationship between pH change and defoaming time in Example 1 (pre-addition amount 1000 ppm). As shown in FIG. 7, when 6 ml of sulfuric acid was added dropwise, a layer of foam (approximately 5 mm) was formed. The pH at this time was 6.3. A fine layer of foam approximately 1 mm thick was also formed, but the fine layer of foam disappeared in 30 seconds. When 7 ml to 8 ml of sulfuric acid was added dropwise, a small amount of foam was formed, but the foam disappeared in 30 seconds. After 8 ml of sulfuric acid was added dropwise, the rotation speed was increased to 1000 rpm. The state after 6 ml was added is shown in FIG. 8. By mixing the antifoaming agent with the digestion liquid before adding sulfuric acid, the defoaming time could be significantly shortened compared to Comparative Example 1, in which the antifoaming agent was added after foaming.

[0035] 2-3. Example 2 FIG. 9 is a graph showing the relationship between pH change and defoaming time in Example 2 (pre-addition amount 100 ppm). As shown in FIG. 9, a layer of foam formed when 2 ml of sulfuric acid was added dropwise. When 2 ml of sulfuric acid was added dropwise, the stirring stopped, so the rotation speed was increased to 1,000 rpm. When 5 ml of sulfuric acid was added dropwise, a layer of foam about 3 mm thick formed. The pH at that time was 6.3. After foaming, the foam defoamed in 1 minute. When 6 ml of sulfuric acid was added dropwise, a layer of foam about 5 mm thick formed. The pH was 6.0. After foaming, the foam defoamed in 1 minute. As shown in FIG. 9, in this example, it took a total of about 5.5 minutes for the foam to defoam. FIG. 10 shows the state when 5 ml and 6 ml of sulfuric acid were added dropwise. Even though the amount of antifoaming agent used (100 ppm) was less than one-third of that used in Comparative Example 1 (333 ppm), by mixing the antifoaming agent with the digestion liquid before adding sulfuric acid, the defoaming time could be significantly shortened compared to Comparative Example 1, in which the antifoaming agent was added after foaming.

[0036] 2-4. Example 3 FIG. 11 is a graph showing the relationship between pH change and defoaming time in Example 3 (pre-addition amount 20 ppm). As shown in FIG. 11, a layer of foam formed when 2 ml of sulfuric acid was added dropwise. When 2 ml of sulfuric acid was added dropwise, the stirring stopped, so the rotation speed was increased to 1,000 rpm. When 3 ml of sulfuric acid was added dropwise, a layer of foam about 3 mm in size formed. The pH was 6.4. After foaming, the foam defoamed in 1 minute. When 5 ml of sulfuric acid was added dropwise, a layer of foam about 5 mm in size formed. The pH was 6.0. After foaming, the foam defoamed in 1 minute. The state when 3 ml and 5 ml of sulfuric acid were added dropwise is shown in FIG. 12. Even though the amount of antifoaming agent used (20 ppm) was less than one-fifteenth of that used in Comparative Example 1 (333 ppm), by mixing the antifoaming agent with the digestion liquid before adding sulfuric acid, the defoaming time could be significantly shortened compared to Comparative Example 1, in which the antifoaming agent was added after foaming.

[0037] 2-5. Comparative Example 2 FIG. 13 is a graph showing the relationship between pH change and defoaming time in Comparative Example 2 (pre-addition amount 10 ppm). As shown in FIG. 13, a layer of foam formed when 3 ml of sulfuric acid was added dropwise. A layer of foam about 2 mm thick also formed when 3 ml of sulfuric acid was added dropwise. The pH was 6.5. After foaming, the foam defoamed in 2 minutes. When 6 ml of sulfuric acid was added dropwise, a layer of foam 5 mm thick also formed. The pH at this time was 5.9. After foaming, the foam defoamed in 4 minutes. The state when 6 ml was added dropwise is shown in FIG. 14.

[0038] 2-6. Comparative Example 3 FIG. 15 is a graph showing the relationship between pH change and defoaming time in Comparative Example 3 (using silicone-based defoamer "CURIRES S-117"; pre-added amount 1000 ppm). As shown in FIG. 15, when 2 ml of sulfuric acid was added dropwise, a layer of foam (5 mm) formed. The pH was 6.8. Because stirring could not be confirmed from the side of the beaker, the rotation speed was increased to 750 rpm, and the foam defoamed in 3 minutes. After 3 ml of sulfuric acid was added dropwise, stirring could no longer be seen from the side of the beaker, so the rotation speed was increased to 1000 ppm. When 6 ml of sulfuric acid was added dropwise, a layer of foam about 5 mm thick also formed. The pH was 6.0. After foaming, the foam defoamed in 2 minutes. The state when 2 ml and 6 ml of sulfuric acid were added dropwise is shown in FIG. 16.

[0039] 2-7. Comparative Example 4 FIG. 17 is a graph showing the relationship between pH change and defoaming time in Comparative Example 4 (using silicone-based defoaming agent "KM-73"; pre-added amount 1000 ppm). As shown in FIG. 17, when 3 ml of sulfuric acid was added dropwise, a layer of foam (3 mm) was formed. The pH was 6.6. When 6 ml of sulfuric acid was added dropwise, a layer of foam about 5 mm was also formed. The pH was 6.0. After foaming, the foam defoamed in 5 minutes. The state when 3 ml and 5 ml of sulfuric acid were added dropwise is shown in FIG. 18.

[0040] 2-8. Comparative Example 5 FIG. 19 is a graph showing the relationship between pH change and defoaming time in Comparative Example 5 (using silicone-based defoaming agent "CURIRES S-117"; pre-added amount 100 ppm). As shown in FIG. 19, when 3 ml of sulfuric acid was added dropwise, a layer of foam (5 mm) was formed. The pH was 6.4. The foaming disappeared 5 minutes after foaming. When 6 ml of sulfuric acid was added dropwise, a layer of foam about 5 mm thick was also formed. The pH was 5.5. The foaming disappeared 5 minutes after foaming. The state when 5 ml of sulfuric acid was added dropwise and when 6 ml of sulfuric acid was added dropwise is shown in FIG. 20.

[0041] 2-9. Comparative Example 6 FIG. 21 is a graph showing the relationship between pH change and defoaming time in Comparative Example 5 (using silicone-based defoaming agent "KM-73"; pre-added amount 100 ppm). As shown in FIG. 21, when 3 ml of sulfuric acid was added dropwise, a layer of foam (5 mm) was formed. The pH was 6.4. Foaming deactivated 2 minutes after foaming. When 4 ml of sulfuric acid was added dropwise, a layer of foam (5 mm) was formed. The pH was 6.2. Foaming deactivated 5 minutes after foaming. When 5 ml of sulfuric acid was added dropwise, a layer of foam (3 mm) was formed. The pH was 6.0. Foaming deactivated 4 minutes after foaming. As shown in FIG. 22, in this Comparative Example, it took a total of approximately 16 minutes for the foam that had formed to defoam. FIG. 22 shows the state when 3 ml and 4 ml of sulfuric acid were added dropwise. The results of Example 2 (alcohol-based defoamer; pre-added amount 100 ppm) and Comparative Example 6 (silicone-based defoamer; pre-added amount 100 ppm) show that the use of an alcohol-based defoamer can reduce the total time required for defoaming by about one-third compared to the use of a silicone-based defoamer.

[0042] (II. Analysis of properties after digestive fluid treatment) In this example, a nitrogen-containing concentrate and condensed water were obtained from the digested liquid using the method for producing a nitrogen-containing concentrate from the digested liquid according to the present invention, and the properties of the nitrogen-containing concentrate and condensed water were analyzed. 1. Vacuum concentration test of digested fluid An antifoaming agent was added to the digested fluid to a concentration of 100 ppm, and the mixture was thoroughly mixed. Then, while stirring, 20 wt% sulfuric acid was added to adjust the pH to 4. The pH-adjusted digested fluid contained ammonium sulfate, which was then subjected to vacuum evaporation and concentration using a rotary evaporator to obtain a nitrogen-containing concentrate and condensed water. The rotary evaporator was operated under the following conditions: operating pressure 20 kPa.A, constant temperature bath temperature 82°C, and rotation speed 70 rpm. The above vacuum concentration test was performed twice, and two samples for analysis were obtained.

[0043] 2.Results The properties of the nitrogen-containing concentrate and condensed water obtained as a result of the above test were analyzed. The digested fluid vacuum concentration test was conducted twice, and the properties of the nitrogen-containing concentrate and condensed water obtained in each test were analyzed. The results are shown in the table below (in the table, - indicates that data was not measured). The state of the nitrogen-containing concentrate and condensed water is also shown in Figure 23. [Table 3]

[0044] As shown in Table 3, the ammonia concentration of the raw digested liquor was 2300 mg / kg. On the other hand, the ammonia concentration in the condensed water after concentration was almost zero (less than 5 mg / L). In this test, the raw digested liquor was concentrated 2.5 times. Therefore, it is calculated that approximately 5700 mg / kg of ammoniacal nitrogen was fixed in the nitrogen-containing concentrated liquid. According to the method for producing a nitrogen-containing concentrate from a digested liquid of the present invention, the resulting nitrogen-containing concentrate contains a high concentration of ammonia nitrogen. Furthermore, the condensed water obtained together with the nitrogen-containing concentrate contains almost no ammonia, and can be directly discharged without requiring nitrification or denitrification treatment.

[0045] (III. Relationship between sulfuric acid injection amount and digestion fluid properties) In this example, the amount of sulfuric acid injected for concentrating the digested fluid was examined. The relationship between the amount of sulfuric acid injected for concentrating the digested fluid and the values ​​of ammonia nitrogen and M alkalinity was also examined.

[0046] 1-1. Reagents The digestate solutions used were those obtained after methane fermentation of livestock waste from Inagawa Farm (hereinafter referred to as Digestive Solution I), Kobayashi Farm (hereinafter referred to as Digestive Solution K), and Minnano Farm (hereinafter referred to as Digestive Solution M). Digestive Solutions I and K were separated using a mesh with 1 mm openings, and the passed-through digestive solution was used. Digestive Solution M was the digestive solution after separation and was used as is. The analysis results of the initial values ​​for the three types of digested fluids are shown in Table 4 below. The evaporation residue was measured in accordance with the measurement method specified in JIS K 0102 14.2. NH4-N was measured in accordance with the measurement method specified in JIS K 0102 42.1 42.3. M alkalinity was measured in accordance with the measurement method specified in 5.1.13 of the Sewerage Testing Method (Japan Sewage Works Association). As shown in Table 4, the evaporation residue, NH4-N (ammonia nitrogen), and t-VFA (total volatile fatty acids) were highest in digested fluid I, followed by digested fluid K, and lowest in digested fluid M. The alkalinity was highest in digested fluid I, followed by digested fluid M, and lowest in digested fluid K. [Table 4] In addition, 96% sulfuric acid was diluted with water to prepare 20% sulfuric acid, which was then used.

[0047] 1-2. Test method 150 ml of each digestion solution was transferred to a 500 ml beaker, and 100 ppm of CRYRES 653 was added to each digestion solution. While stirring at 1,000 rpm, 20% sulfuric acid was added dropwise until the pH reached 4.8. After the sulfuric acid addition, the digestion solution samples were analyzed. The test was performed twice for each digestion solution, and the average value was used as the analysis result.

[0048] 2.Results The titration results for the three types of digestive fluids up to pH 4.8 are shown in Table 5 below. The average titration results for each digestive fluid are shown in Figure 24. The sulfuric acid titration volume for digestive fluid I was 10.4 mL, the sulfuric acid titration volume for digestive fluid K was 9 mL, and the sulfuric acid titration volume for digestive fluid M was 9.7 mL. [Table 5]

[0049] Figure 25 shows the relationship between the amount of sulfuric acid added and evaporation residue, Figure 26 shows the relationship between the amount of sulfuric acid added and the amount of ammoniacal nitrogen (NH4-N), and Figure 27 shows the relationship between the amount of sulfuric acid added and M alkalinity. As shown in Figures 25 to 27, there was a proportional correlation between the amount of sulfuric acid added and each water quality item, and a calibration curve could be drawn. The sulfuric acid titration rate was 6-6.8% for a digestion liquid volume of 150 mL. Furthermore, the amount of sulfuric acid added per 1 g of M alkalinity was 1.2-1.6 mg H2SO4 / g alkalinity. The average values ​​of the digestive fluid analysis results before and after the test are shown in Table 6. [Table 6]

[0050] (IV. Consideration of Alcohol-Based Antifoaming Agents) 1-1. Reagents The digested liquid used was the digested liquid obtained after methane fermentation of livestock waste from Minna no Bokujo (digested liquid M). This digested liquid was used as is, since it was a digested liquid after solid-liquid separation. The antifoaming agents used were Kuriles 653, SN Deformer 170, FK Antifoamer FALC-108, or Dappo H312.

[0051] 1-2. Test method 150 ml of each digestion liquid was transferred to a 500 ml beaker, and 100 ppm of each antifoaming agent was added to each digestion liquid. While stirring at 1,000 rpm, 20% sulfuric acid was added dropwise until the pH reached 5.0. The time until the foaming disappeared when sulfuric acid was added dropwise and the thickness of the foam layer were measured, and the effectiveness of alcohol-based antifoaming agents from each manufacturer was compared. The condition for foaming to start was when bubbles could be seen on the liquid surface, and the condition for foaming to stop was when bubbles could no longer be seen on the liquid surface.

[0052] 2.Results Each antifoaming agent was added in advance to three digestive fluid samples (digestive fluid M: Minna no Bokujo) at 100 ppm. The relationship between the amount of 20% sulfuric acid added dropwise until the pH reached 5.0 and the pH is shown in Table 7 and Figure 28. As shown in Table 7 and Figure 28, when each alcohol-based antifoaming agent was added to the digestive fluid, there was no difference in the amount of sulfuric acid added dropwise until the pH reached 5.0, regardless of the antifoaming agent used. [Table 7]

[0053] The defoaming time for each defoaming agent when sulfuric acid was added dropwise is shown in Figure 29. As shown in Figure 29, when any of the alcohol-based defoaming agents was used, the defoaming time was less than 1 minute at each pH point. Thus, alcohol-based defoaming agents other than CRYLES 653 also showed favorable defoaming time results.

[0054] (V. Example of production of nitrogen-containing concentrate) A nitrogen-containing concentrate was produced from the digested fluid using the digested fluid treatment device shown in Figure 2. Specifically, in a mixing tank, an antifoaming agent was added to 38 L / h of digested liquor after methane fermentation (after solid-liquid separation) to achieve a concentration of 100 ppm, and the mixture was stirred for 5 minutes. The digested liquor with sufficient antifoaming agent mixed in was transferred to a pH adjustment tank, where 20% sulfuric acid was added to achieve a pH of 5 and the mixture was stirred for 5 minutes. After the pH adjustment, the digested liquor was transferred to a raw water concentration tank and separated into a nitrogen-containing concentrate and condensed water using a vacuum concentration device. The results of component analysis of the digested liquor used, as well as the resulting nitrogen-containing concentrate and condensed water, are shown in the table below. [Table 8] As shown in Table 8, the nitrogen-containing concentrate produced by the method of the present invention contained a high concentration of nitrogen. Such a concentrate containing a high concentration of nitrogen can be used as liquid fertilizer or dried to produce solid fertilizer. On the other hand, the condensed water separated by the concentration treatment of the digested liquid contains SS, TN, BOD, and COD. Mn All of these values ​​were low and met the general wastewater standards. [Explanation of symbols]

[0055] 1 Digestive fluid treatment equipment 2 Digestive fluid storage tank 3. Defoamer storage tank 4 Mixing tank 5. Sulfuric acid storage tank 6 pH adjustment 7 Concentrated raw water tank 8. Vacuum concentration means 9 Sulfuric acid dilution tank 21, 22, 23, 24 Pumps 31, 32 Flow meter 41 pH meter 51, 52, 53, 54, 55 Stirring means

Claims

1. A method for producing a nitrogen-containing concentrate from a digested liquid, (a) mixing an alcohol-based antifoaming agent with the digestive liquid; (b) adding sulfuric acid to the digestion liquid obtained in the step (a) to adjust the pH; (c) a step of concentrating the digested liquid obtained in the step (b) by separating a nitrogen-containing concentrated liquid from condensed water; A manufacturing method comprising:

2. The method of claim 1, The production method, wherein the digested liquid is obtained by methane fermentation.

3. The method of claim 1, The production method, wherein the digestive fluid is obtained by solid-liquid separation without using a flocculant.

4. The method of claim 1, The method for producing the digestive liquid, wherein the alcohol-based defoaming agent in the step (a) is added to the digestive liquid so as to have a concentration in the range of 20 ppm to 1000 ppm.

5. The method of claim 1, The production method, wherein the pH of the digestive fluid adjusted in the step (b) is within the range of pH 4.0 to pH 6.

0.

6. The method of claim 1, The production method, wherein the amount of sulfuric acid to be added in the step (b) is determined based on the evaporation residue, ammonia nitrogen, or M alkalinity of the digested liquid.

7. The method of claim 1, The amount of sulfuric acid added in the step (b) is an amount such that the amount of 20% sulfuric acid dropped per 1 g of M alkali amount based on the M alkalinity of the digested liquid is 5.8 to 7.8 mL.

8. The method of claim 1, the step (a) is a step of continuously flowing the digestion liquid and the alcohol-based defoaming agent into a mixing tank, and continuously flowing the digestion liquid sufficiently mixed with the alcohol-based defoaming agent into a pH adjustment tank, The step (b) is a step of adjusting the pH of the digested liquid continuously flowing in from the mixing tank by adding sulfuric acid to the pH adjustment tank, and continuously discharging the pH-adjusted digested liquid into a concentration raw water tank. Manufacturing method.

9. The method of claim 1, (d) A method for producing a nitrogen-containing concentrate, further comprising the step of drying the nitrogen-containing concentrate obtained in the step (c).

10. 1. An apparatus for producing a nitrogen-containing concentrate from a digested liquid, comprising: a mixing tank for mixing the digestive fluid and the antifoaming agent; A pH adjustment tank for adjusting the pH by adding sulfuric acid to the digestion liquid mixed with the antifoaming agent. a concentrating means for concentrating the pH-adjusted digestive fluid; 1. An apparatus comprising:

11. 11. The apparatus of claim 10, the mixing tank is provided with a digestion fluid supply means for supplying a desired amount of digestion fluid and a defoaming agent supply means for supplying a desired amount of defoaming agent; The pH adjusting tank is equipped with a sulfuric acid supply means. Device.

12. 11. The apparatus of claim 10, Further comprising a solid-liquid separation means for separating the digestive liquid into solid and liquid, The solid-liquid separation means and the digestion liquid supply means are connected, and the separated liquid obtained by the solid-liquid separation means is sent to the mixing tank via the digestion liquid supply means.

13. 11. The apparatus of claim 10, The mixing tank and the pH adjustment tank are directly connected to each other at their lower parts, and the digested liquid introduced into the mixing tank flows directly into the pH adjustment tank after a certain residence time in the mixing tank.

14. 11. The apparatus of claim 10, The apparatus further includes a digester fluid reservoir, a defoamer reservoir, and a sulfuric acid reservoir.

15. 15. The apparatus of claim 14, The apparatus further comprises a sulfuric acid dilution tank for adjusting the sulfuric acid to be added to the pH adjustment tank.

16. 16. The device according to any one of claims 10 to 15, The apparatus further comprises a drying means for drying the nitrogen-containing concentrate obtained by the concentrating means, said drying means and said concentrating means being connected, and said concentrate being sent from said concentrating means to said drying means.

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