Methane fermentation digestate processing system

Abstract

The object of the present invention is to provide a methane fermentation digestate concentration system for efficiently concentrating the liquid component of methane fermentation digestate to obtain liquid fertilizer. [Solution] The above objective is solved by a system for circulating screen permeate of methane fermentation digestate, comprising a storage means, a filtration means, and a circulation means, wherein the storage means is configured to contain the screen permeate, the filtration means is configured to filter the screen permeate in an upward flow, and the circulation means is configured to circulate the screen permeate between the storage means and the filtration means.

Description

Technical Field

[0001] The present invention relates to a treatment system for methanogenic digestion liquid.

Background Art

[0002] Organic resources derived from animals and plants are known as biomass and have attracted attention as renewable energy sources to replace fossil fuels. For example, it is known to biochemically convert waste biomass such as livestock excrement and food waste to produce biogas.

[0003] In the production of biogas, methanogenic fermentation technology is utilized. That is, waste-based resources are subjected to methanogenic fermentation in which they are digested by anaerobic microorganisms to decompose organic substances, thereby producing methane gas (CH4) as biogas.

[0004] In methanogenic fermentation, together with biogas, digestion liquid, which is a fermentation residue, is generated. The methanogenic digestion liquid is separated into a solid component and a liquid component by solid-liquid separation treatment, and the solid component is used as solid fertilizer. On the other hand, the liquid component of the methanogenic digestion liquid has a water content of 95% to 98% and lacks nutrient components for use as fertilizer. Therefore, there have been attempts to concentrate the liquid component of the methanogenic digestion liquid in order to cause eutrophication.

[0005] For example, Non-Patent Document 1 describes that methanogenic digestion liquid is separated by screen separation to obtain a screen permeate, and then the screen permeate is separated by MF membrane separation to obtain a membrane permeate and a membrane concentrate, and these are used as liquid fertilizers.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] The liquid component of methane fermentation digestate is not only poor in nutrients but also contains a large amount of insoluble solids, resulting in high viscosity. Therefore, when attempting to use the liquid component of methane fermentation digestate itself as liquid fertilizer, there is a problem of clogging at the discharge section of liquid fertilizer spreaders.

[0008] Furthermore, according to the inventors' investigation, as described in Non-Patent Literature 1, when the liquid component of methane fermentation digestate is subjected to screen separation and then to MF membrane separation, clogging of the MF membrane occurs, resulting in a significant decrease in concentration efficiency.

[0009] Furthermore, to date, there is little known about methods or systems for efficiently concentrating the liquid component of methane fermentation digestate to obtain liquid fertilizer.

[0010] Therefore, the problem that the present invention aims to solve is to provide a methane fermentation digestate concentration treatment system for efficiently concentrating the liquid component of methane fermentation digestate to obtain liquid fertilizer. [Means for solving the problem]

[0011] As a result of diligent research aimed at solving the above problems, the inventors of the present invention have found that by circulating the screen permeate between a storage means for containing the screen permeate of methane fermentation digestate and a filtration means for filtering the screen permeate in an upward flow, the methane fermentation digestate can be filtered and concentrated more efficiently.

[0012] Based on these ideas, the inventors, after repeated trial and error, succeeded in creating a circulation treatment system for screen permeates of methane fermentation digestate and a method for producing methane fermentation digestate filtrate, which solve the problems of the present invention. Furthermore, they found a method for concentrating the methane fermentation digestate filtrate without impairing its nutritional components. The present invention is completed based on these first-of-its-kind ideas and successful examples made by the inventors.

[0013] In other words, according to each aspect of the present invention, the following embodiments are provided. [1] A circulation treatment system for the screen permeate of methane fermentation digestate, It comprises a liquid storage means, a filtration means, and a circulation means, The liquid storage means is configured to be able to contain the screen permeate liquid, The filtration means is configured to filter the screen permeate in an upward flow, and The circulation means is configured to circulate the screen permeate between the storage means and the filtration means in the system. [2] The system according to item [1], wherein the liquid storage means comprises a solid-liquid separation means for separating the filtrate from the filtration means into solid and liquid. [3] The processing system according to item [2], wherein the solid-liquid separation means is a membrane selected from the group consisting of MF membranes, UF membranes, NF membranes and RO membranes. [4] The system according to item [1], wherein the liquid storage means comprises a partition wall substantially separating the screen permeate and the filtered liquid from the filtration means. [5] A method for producing methane fermentation digestate filtrate, comprising the step of subjecting the screen permeate of methane fermentation digestate to a circulating treatment using the system described in any one of items [1] to [4] to obtain methane fermentation digestate filtrate. [6] A method for producing a concentrated methane fermentation digestate, comprising the step of subjecting the screen permeate of the methane fermentation digestate to a circulating treatment using the system described in any one of items [1] to [4] to obtain a concentrated methane fermentation digestate. [Effects of the Invention]

[0014] According to the present invention, the liquid component of the methanogenic digestate can be efficiently concentrated to obtain a liquid fertilizer. Further, even when the methanogenic digestate is subjected to membrane separation, by providing the system of one aspect of the present invention before that stage, clogging of the membrane can be prevented and a long service life of the membrane can be achieved. Furthermore, according to the present invention, since a concentrated solution of the methanogenic digestate can be obtained without using chemicals such as flocculants without impairing the nutrient components, the obtained concentrated solution can be distributed and used as a liquid fertilizer as it is.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a schematic configuration diagram showing an example of a concentration treatment system for methanogenic digestate. [Figure 2] FIG. 2 is a schematic configuration diagram showing the circulation treatment system of the first embodiment. [Figure 3] FIG. 3 is a flowchart showing the case where concentration treatment is performed by the circulation treatment system 1 of FIG. 2. [Figure 4] FIG. 4 is a schematic configuration diagram showing the circulation treatment system of the second embodiment. [Figure 5] FIG. 5 is a flowchart showing the case where concentration treatment is performed by the circulation treatment system 1 of FIG. 4.

Modes for Carrying Out the Invention

[0016] Hereinafter, the details of each aspect of the present invention will be described, but the present invention can take various aspects as long as its object is achieved.

[0017] Each term in this specification is used in the meaning usually used by those skilled in the art such as in the field of wastewater treatment, unless otherwise specified, and should not be construed as having an unduly limited meaning. Further, the assumptions and theories made in this specification are based on the inventor's knowledge and experience so far, and thus the present invention is not limited only by such assumptions and theories.

[0018] "Comprise", "contain", and "include" mean that elements other than those explicitly stated as being included can be added (synonymous with "at least comprise"), and include "consist of" and "essentially consist of". That is, "comprise" can mean including the explicitly stated elements and any one or two or more elements, consisting of the explicitly stated elements, or essentially consisting of the explicitly stated elements. "Have" is synonymous with "comprise". Examples of elements include limitations such as parts, means, components, steps, conditions, parameters, etc. "And / or" means any one of the plurality of listed related items, or any combination or all combinations of two or more.

[0019] [Summary of the Invention] One aspect of the present invention is a circulation treatment system for the screen permeate of the methanogenic digestion liquid (hereinafter, also simply referred to as "system"). The system of the present invention comprises a liquid storage means, a filtration means, and a circulation means. The liquid storage means is configured to be able to store the screen permeate. The filtration means is configured to filter the screen permeate in an upward flow. The circulation means is configured to circulate the screen permeate between the liquid storage means and the filtration means.

[0020] As described above, the methanogenic digestion liquid is separated into a solid component and a liquid component by a screen separation process, and the liquid component is concentrated to obtain a liquid fertilizer. As a method for concentrating methane fermentation digestate, as shown in Figure 1, for example, in a methane fermentation digestate concentration system, the methane fermentation digestate subjected to anaerobic digestion in the fermentation tank 100 is subjected to screen separation to separate it into liquid and solid components. The solid component is used as solid fertilizer, and the liquid component (screen permeate) is subjected to simple filtration in the primary storage tank 110 and then stored in the liquid storage means 10 of this system 1. In one embodiment of the present invention (system 1 in Figure 1), the screen permeate is subjected to filtration while circulating between the liquid storage means 10 and the filtration means 20. In system 1, the filtered liquid is sent to the primary treatment tank 120 and then to the concentration tank 130. In the concentration tank 130, the filtered liquid is concentrated by membrane concentration to remove water. This concentrated liquid is then commercialized as liquid fertilizer. The present invention relates to a series of methane fermentation digestate concentration treatment systems, specifically a system that treats the screen permeate of the methane fermentation digestate before subjecting it to membrane concentration treatment.

[0021] A system according to one aspect of the present invention comprises a liquid storage means, a filtration means, and a circulation means, thereby repeatedly performing an upward flow filtration process while circulating the screen permeate in the liquid storage means. This efficiently removes insoluble solids from the screen permeate and efficiently concentrates the methane fermentation digestate (removing solids while retaining nutrients such as nitrogen and potassium). In this specification, filtering the screen permeate before membrane concentration is referred to as "coarse filtration".

[0022] [System of the first aspect] The system of the first embodiment will be explained below with reference to Figure 2. System 1 includes a liquid storage means 10, a filtration means 20, and a circulation means 30. System 1 has a structure in which the screen permeate L, which has been subjected to screen separation outside the system, is circulated between the storage means 10 and the filtration means 20, and upward flow filtration is repeatedly performed by the filtration means 20.

[0023] The liquid storage means 10 is capable of accommodating the screen permeate L used for screen separation, which is supplied from outside the system via the water supply pipe T1.

[0024] Screen permeate L is a screen-treated liquid obtained by subjecting the fermentation residue (methane fermentation digestate) produced by methane fermentation of waste resources to solid-liquid separation (screen separation). Waste resources include, but are not limited to, livestock excrement and food waste. Methane fermentation digestate generally contains about 95% to 98% water, and nutrients such as nitrogen and potassium make up about 3%. In addition, methane fermentation digestate contains a large amount of insoluble solids and has high viscosity.

[0025] The filtration means 20 has the function of removing insoluble solids from the screen permeate L and has the function of performing coarse filtration. The filtration means 20 is configured to filter the screen permeate L (or a mixture of the screen permeate L and the crude filtrate LF filtered by the filtration means 20) in an upward flow from the bottom to the top. The filtration means 20 is not particularly limited as long as it is configured to filter the filter media by passing water through it in an upward flow.

[0026] The filtration means 20 preferably has a filtration performance that removes solid particles of 0.05 mm or larger. The filter media preferably removes solid particles of 0.05 mm or larger, and the thickness of the filter media layer is preferably about 30 cm to 50 cm. The filtration rate can be appropriately selected depending on the viscosity of the filter media and the screen permeate, for example, 5 m / day to 30 m / day.

[0027] In System 1, the upward flow filtration process using the filtration means 20 allows for quick and easy removal and cleaning of the filter media layer by passing water through it in a downward flow from the top to the bottom of the filtration means 20, even if the filter media layer becomes clogged with solids in the screen permeate L. As a result, filtration efficiency is increased, and concentration can be achieved efficiently. Furthermore, since the solids obtained after removal and cleaning contain nutrients, it is preferable to use them as solid fertilizer.

[0028] In System 1, it is preferable to provide a partition wall 11 within the liquid storage means 10 that substantially separates the screen permeate L and the crude filtrate LF filtered by the filtration means 20. Here, "substantially separating partition wall" means that the partition wall does not have to completely separate the screen permeate L and the crude filtrate LF filtered by the filtration means 20. That is, within the liquid storage means 10, the screen permeate L and / or the crude filtrate LF may overflow over the partition wall 11 and be mixed. For example, the partition wall 11 can be configured to form a two-compartment structure that substantially separates the screen permeate L and the crude filtrate LF. The partition wall 11 may be, for example, plate-shaped or cylindrical.

[0029] The circulation means 30 is configured to circulate the screen permeate L (or a mixture of the screen permeate L and the crude filtrate LF filtered by the filtration means 20) between the liquid storage means 10 and the filtration means 20. The circulation means 30 includes a forward water supply pipe T2 that supplies the screen permeate L contained in the liquid storage means 10 to the filtration means 20, a return water supply pipe T3 that returns the crude filtrate LF, which has been subjected to upward flow filtration by the filtration means 20, back to the liquid storage means 10, and a pump P that enables this supply and return. The circulation means 30 allows the screen permeate L to circulate between the liquid storage means 10 and the filtration means 20 via the forward water supply pipe T2 and the return water supply pipe T3.

[0030] The supply water pipe T2 is located upstream of the circulation means 30, and the return water pipe T3 is located downstream of the circulation means 30. In this example, a pump P is provided in the supply water pipe T2.

[0031] System 1 may include other components in addition to the liquid storage means 10, filtration means 20, and circulation means 30.

[0032] Other configurations include, for example, a simple filtration means 12 (see Figure 1) located upstream of the water supply pipe T1. This simple filtration means subjects the screen permeate L contained in the liquid storage means 10 to a simple filtration process, improving the filtration efficiency in system 1. For example, the simple filtration means preferably has a filtration performance that removes solid particles of 1 mm or larger. The filter material of the simple filtration means is not particularly limited as long as it can remove solid particles of 1 mm or larger, but examples include metal membranes.

[0033] A method for circulating the screen permeate of methane fermentation digestate using System 1 of the first embodiment will be explained using the flowchart shown in Figure 3.

[0034] As illustrated in Figure 3, the screen permeate L, which has been subjected to screen separation outside the system, is collected in the storage means 10 via the water supply pipe T1 (S101). Next, the screen permeate L contained in the storage means 10 is sent to the filtration means 20 via the forward water supply pipe T2 (S102). The screen permeate L that has been sent is subjected to upward flow filtration treatment by the filtration means 20 (S103). The crude filtrate LF that has been subjected to filtration treatment by the filtration means 20 is returned to the storage means 10 via the return water supply pipe T3 (S104). After that, steps S102 to S104 are repeated. The filtrate LC that has been sufficiently subjected to crude filtration is sent outside the system via the water supply pipe T4 (S105). The filtrate LC sent outside the system is concentrated by processes such as water extraction (see Figure 1).

[0035] Here, the system 1 of the first embodiment may be continuous or batch type. That is, in the system 1 of the first embodiment, the supply of screen permeate L from outside the system to the liquid storage means 10 and the supply of coarse filtrate LF to outside the system may be carried out continuously, or the supply of screen permeate L from outside the system to the liquid storage means 10 and the supply of coarse filtrate LF to outside the system may be temporarily stopped, and the screen permeate may be circulated and used for filtration. In either case, the proportion of solids in the liquid used for filtration is reduced by mixing the screen permeate L with the coarse filtrate LF in the liquid storage means 10, thereby improving the filtration efficiency. In addition, clogging of the filter media layer of the filtration processing means 20 can be prevented.

[0036] [System of the second aspect] The system of the second embodiment includes a liquid storage means 10, a filtration means 20 and a circulation means 30, in addition to a membrane separation means 40.

[0037] The system of the second embodiment will be explained in detail with reference to Figure 4. In Figure 4, components common to System 1 in Figure 2 are denoted by the same reference numerals. Furthermore, in the following, as a general rule, the differences between the system of the second embodiment and the system of the first embodiment will be explained, and the parts that overlap with the system of the first embodiment will not be explained.

[0038] System 2 has a configuration in which a membrane separation means 40 is provided before the crude filtrate LF, which has undergone sufficient upward flow filtration by the filtration means 20, is sent out of the system while the screen permeate L is circulated between the storage means 10 and the filtration means 20.

[0039] The membrane separation means 40 has the function of performing solid-liquid separation on the crude filtrate LF filtered by the filtration means 20 within the liquid storage means 10. Examples of membrane separation means include, but are not limited to, MF membranes, UF membranes, NF membranes, and RO membranes.

[0040] In System 2, by having a membrane separation means 40, a filtrate LC containing concentrated nutrients such as nitrogen and potassium can be obtained from the crude filtrate LF obtained by the filtration means 20. Furthermore, even with a structure having such a membrane separation means 40, in System 1, the screen permeate L is subjected to the membrane separation process in a clarified state, thus preventing clogging of the membrane separation means 40 and achieving a longer membrane lifespan.

[0041] A method for circulating the screen permeate of methane fermentation digestate using System 2 of the second embodiment will be explained using the flowchart shown in Figure 5.

[0042] As illustrated in Figure 5, the screen permeate L, which has been subjected to screen separation outside the system, is collected in the liquid storage means 10 via the water supply pipe T1 (S201). Next, the screen permeate L collected in the liquid storage means 10 is sent to the filtration means 20 via the outbound water supply pipe T2 (S202). The collected screen permeate L is subjected to upward flow filtration by the filtration means 20 (S203). The crude filtrate LF, which has been subjected to filtration by the filtration means 20, is returned to the liquid storage means 10 via the return water supply pipe T3 (S204). After that, steps S102 to S204 are repeated. The crude filtrate LF, which has been sufficiently subjected to coarse filtration, is subjected to solid-liquid separation by the membrane separation means 40 (S205). The solid-liquid separated filtrate LC is sent outside the system via the water supply pipe T4 (S206). The filtrate LC, which is sent outside the system, is concentrated by processes such as water extraction (see Figure 1).

[0043] Here, the system 2 in the second embodiment may be continuous or batch type. In addition, in system 2, the screen permeate L is subjected to coarse filtration by the filtration means 20, which improves the efficiency of the subsequent solid-liquid separation process in the membrane separation means 40. Furthermore, clogging of the membrane separation means 40 can be prevented, and its lifespan can be extended. Moreover, the coarse filtration process by the filtration means 20 removes solids, yielding a pre-membrane filtration solution containing nutrients, and a subsequent concentration process yields a nutrient-rich solution.

[0044] [Another aspect of the present invention] Another aspect of the present invention is a method for producing a methane fermentation digestate filtrate using a system according to one aspect of the present invention. The method for producing a methane fermentation digestate filtrate includes the step of subjecting the screen permeate of the methane fermentation digestate to a circulation treatment using a system according to one aspect of the present invention to obtain a methane fermentation digestate filtrate.

[0045] [Another aspect of the present invention] A further embodiment of the present invention is a method for producing a concentrated methane fermentation digestate using a system according to one embodiment of the present invention. The method for producing a concentrated methane fermentation digestate includes the step of subjecting the screen permeate of the methane fermentation digestate to a circulating treatment using a system according to one embodiment of the present invention to obtain a concentrated methane fermentation digestate. [Industrial applicability]

[0046] A system according to one aspect of the present invention can efficiently obtain a concentrated methane fermentation digestate without damaging the nutritional components and avoiding the use of chemicals such as flocculants, and can therefore be distributed and used directly as liquid fertilizer. [Explanation of Symbols]

[0047] 1,2 System 10 Liquid storage means 11 Bulkhead 12 Simple filtration method 20 Filtration means 30 Circulation means 40 Membrane separation means 100 fermentation tanks 110 Primary storage tank 120 Primary treatment tanks 130 Concentration water tank T1 water pipe T2 Outbound water supply pipe T3 Return water supply pipe T4 water pipe P Pump

Claims

1. A circulation treatment system for the screen permeate of methane fermentation digestate, It comprises a liquid storage means, a filtration means, and a circulation means, The liquid storage means is configured to be able to contain the screen permeate liquid, The filtration means is configured to filter the screen permeate in an upward flow, and The circulation means is configured to circulate the screen permeate between the storage means and the filtration means in the system.

2. The system according to claim 1, wherein the liquid storage means comprises a solid-liquid separation means for separating the filtrate from the filtration means into solid and liquid.

3. The processing system according to claim 2, wherein the solid-liquid separation means is a membrane selected from the group consisting of MF membranes, UF membranes, NF membranes, and RO membranes.

4. The system according to claim 1, wherein the liquid storage means comprises a partition wall that substantially separates the liquid permeated by the screen from the liquid filtered by the filtration means.

5. A method for producing a methane fermentation digestate filtrate, comprising the step of subjecting the screen permeate of the methane fermentation digestate to a circulating treatment using the system described in any one of claims 1 to 4 to obtain a methane fermentation digestate filtrate.

6. A method for producing a concentrated methane fermentation digestate, comprising the step of subjecting the screen permeate of the methane fermentation digestate to a circulating treatment using the system described in any one of claims 1 to 4 to obtain a concentrated methane fermentation digestate.

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