Methane fermentation digestate treatment system

Abstract

An object of the present invention is to provide a system for concentrating and treating a methane fermentation digested liquid, which efficiently concentrates the liquid portion of a methane fermentation digested liquid to obtain liquid fertilizer. [Solution] The above-mentioned object is achieved by a circulation treatment system for screen permeate of methane fermentation digestive liquid, the system comprising a liquid storage means, a filtration means, and a circulation means, the liquid storage means being configured to be capable of containing the screen permeate, the filtration means being configured to filter the screen permeate in an upward flow manner, and the circulation means being configured to circulate the screen permeate between the liquid storage means and the filtration means.

Description

[Technical field]

[0001] The present invention relates to a system for treating methane fermentation digestate. [Background technology]

[0002] Organic resources derived from plants and animals are known as biomass, and are attracting attention as a renewable energy source to replace fossil fuels. For example, it is known that waste biomass such as livestock waste and food waste can be biochemically converted to produce biogas.

[0003] Biogas production utilizes methane fermentation technology. In other words, waste resources are subjected to methane fermentation, which is digested by anaerobic microorganisms, to decompose organic matter and produce methane gas (CH4) as biogas.

[0004] In methane fermentation, digestive liquid, which is the fermentation residue, is generated along with biogas. The methane fermentation digestive liquid is separated into solid and liquid fractions by solid-liquid separation processing, and the solid fraction is used as solid fertilizer. On the other hand, the liquid fraction of methane fermentation digestive liquid is 95% to 98% water and has few nutrients to be used as fertilizer. Therefore, there are attempts to concentrate the liquid fraction of methane fermentation digestive liquid in order to make it eutrophic.

[0005] For example, Non-Patent Document 1 describes the method of separating methane fermentation digestate through a screen to obtain a screen permeate, and then separating the screen permeate through an MF membrane to obtain a membrane permeate and a membrane concentrate, which are then used as liquid fertilizer. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] JRA, "Manual for Vegetable Cultivation Using Concentrated and Modified Methane Fermentation Digestive Liquid," [online], February 2013, Livestock Industry Environmental Improvement Organization, [Retrieved November 8, 2024], Internet<URL:https: / / www.chikusan-kankyo.jp / newhomepage / JRAseika / metanhakkou.pdf> Summary of the Invention [Problem to be solved by the invention]

[0007] The liquid portion of methane fermentation digestate is not only poor in nutrients, but also contains a lot of insoluble solids and is highly viscous. Therefore, if the liquid portion of methane fermentation digestate itself is to be used as liquid fertilizer, there is a problem that it causes clogging at the discharge part of the liquid fertilizer spreader.

[0008] Furthermore, according to the inventors' research, as described in Non-Patent Document 1, when the liquid portion of a methane fermentation digestate is subjected to screen separation and then to MF membrane separation, there is a problem that the MF membrane becomes clogged, resulting in a significant decrease in concentration efficiency.

[0009] Furthermore, little is known so far about a method and a system for efficiently concentrating the liquid portion of a methane fermentation digestate to obtain liquid fertilizer.

[0010] Therefore, an object of the present invention is to provide a concentrating treatment system for methane fermentation digestive liquid, which efficiently concentrates the liquid portion of the methane fermentation digestive liquid to obtain liquid fertilizer. [Means for solving the problem]

[0011] As a result of extensive research into solving the above problems, the inventors have discovered that the methane fermentation digestion liquid can be filtered and concentrated more efficiently by circulating the screen-permeated liquid between a storage means for storing the screen-permeated liquid of the methane fermentation digestion liquid and a filtration means for filtering the screen-permeated liquid in an upward flow.

[0012] Based on this idea, the inventors of the present invention have, through repeated trial and error, succeeded in creating a circulation treatment system for screen-permeated liquid of methane fermentation digested liquid and a method for producing filtrate of methane fermentation digested liquid, which solve the problems of the present invention. Furthermore, they have found a method for concentrating the filtrate of methane fermentation digested liquid without damaging the nutritional components. The present invention has been completed based on the idea and successful examples first conceived by the inventors of the present invention.

[0013] That is, according to each aspect of the present invention, the following embodiments are provided. [1] A circulating treatment system for screen-permeated liquid of methane fermentation digestion liquid, comprising: The apparatus includes a liquid storage means, a filtering means, and a circulating means, The liquid storage means is configured to be capable of storing the screen permeated liquid, The filtering means is configured to filter the screen permeate in an upward flow manner; and The system, wherein the circulation means is configured to circulate the screen permeate between the storage means and the filtering means. [2] The system according to item [1], wherein the liquid storage means is provided with a solid-liquid separation means for separating the filtrate from the filtration means into solid and liquid. [3] The treatment system according to item [2], wherein the solid-liquid separation means is a membrane selected from the group consisting of an MF membrane, an UF membrane, an NF membrane, and an RO membrane. [4] The system described in item [1], wherein the liquid storage means has a partition that substantially separates the screen permeated liquid from the filtrate by the filtration means. [5] A method for producing a filtrate of a methane fermentation digested liquid, comprising the step of subjecting a screen-permeated liquid of a methane fermentation digested liquid to a circulation treatment using the system described in any one of items [1] to [4] to obtain a filtrate of a methane fermentation digested liquid. [6] A method for producing a concentrate of a methane fermentation digestive liquid, comprising the step of subjecting a screen-permeated methane fermentation digestive liquid to a circulation treatment using the system described in any one of items [1] to [4] to obtain a concentrate of the methane fermentation digestive liquid. Effect of the Invention

[0014] According to the present invention, the liquid portion of the methane fermentation digestive liquor can be efficiently concentrated to obtain liquid fertilizer. Even when the methane fermentation digestive liquor is subjected to membrane separation, clogging of the membrane can be prevented and the membrane's life can be extended by providing a system according to one embodiment of the present invention in the upstream stage. Furthermore, according to the present invention, a concentrated liquid of the methane fermentation digestive liquor can be obtained without damaging the nutritional components by avoiding the use of chemicals such as flocculants, so that the obtained concentrated liquid can be distributed and used as liquid fertilizer as it is. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of a system for concentrating a methane fermentation digestate. [Diagram 2] FIG. 2 is a schematic diagram showing the circulation treatment system of the first embodiment. [Diagram 3] FIG. 3 is a flow chart showing the process of concentration performed by the circulation treatment system 1 of FIG. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a circulation treatment system according to the second embodiment. [Diagram 5] FIG. 5 is a flow chart showing the process of concentration performed by the circulation treatment system 1 of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Each aspect of the present invention will be described in detail below, but the present invention can take various forms as long as it achieves its object.

[0017] Unless otherwise specified, each term in this specification is used in the sense commonly used by a person skilled in the art of wastewater treatment and the like, and should not be interpreted as having an unduly limiting meaning. In addition, the speculations and theories made in this specification are based on the inventor's knowledge and experience to date, and therefore the present invention is not limited solely to such speculations and theories.

[0018] "Comprise, contain, include" means that elements other than those explicitly stated to be included can be added (same meaning as "comprise at least"), but also encompasses "consist of" and "essentially consist of." That is, "comprise" can mean including the explicitly stated elements and any one or more elements, consisting of the explicitly stated elements, or essentially consisting of the explicitly stated elements. "Have" is synonymous with "include." Elements include parts, means, ingredients, steps, conditions, parameters, and other limitations. "And / or" means any one or any or all combinations of two or more of the associated listed items.

[0019] [Summary of the Invention] One aspect of the present invention is a circulation treatment system for screen permeate of methane fermentation digestive liquid (hereinafter, also simply referred to as "the 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 capable of storing the screen permeate. The filtration means is configured to filter the screen permeate in an upward flow manner. The circulation means is configured to circulate the screen permeate between the liquid storage means and the filtration means.

[0020] As described above, the methane fermentation digestive liquid is separated into a solid fraction and a liquid fraction by a screen separation process, and the liquid fraction is concentrated to obtain a liquid fertilizer. As a method for concentrating a methane fermentation digested liquid, for example, as shown in FIG. 1, in a concentrating system for a methane fermentation digested liquid, the methane fermentation digested liquid subjected to anaerobic digestion in a fermenter 100 is subjected to screen separation and separated into a liquid and a solid. The solid is used as solid fertilizer, and the liquid (screen permeate) is subjected to simple filtration in a primary storage tank 110 and then stored in the liquid storage means 10 of the present system 1. In a system according to one embodiment of the present invention (system 1 in FIG. 1), the screen permeate is subjected to filtration while being circulated between the liquid storage means 10 and the filtration means 20. In the system 1, the filtrate subjected to the filtration is sent to a primary treatment water tank 120 and then sent to a concentration water tank 130. In the concentration water tank 130, the filtrate is concentrated by removing water by membrane concentration. This concentrated liquid is commercialized as liquid fertilizer. Among such a series of concentrating and treating systems for methane fermentation digested liquid, the present invention is a system for treating the screen-permeated liquid of the methane fermentation digested liquid before it is subjected to membrane concentration treatment.

[0021] The system according to one embodiment of the present invention is equipped with a liquid storage means, a filtering means, and a circulating means, and thus repeatedly performs an upward flow filtration process while circulating the screen permeate in the liquid storage means. This makes it possible to efficiently remove insoluble solids in the screen permeate and efficiently concentrate the methane fermentation digestate (removing solids and leaving nutrients such as nitrogen and potassium). In this specification, the filtration process of the screen permeate before the membrane concentration process is referred to as "rough filtration".

[0022] [First embodiment of the system] The system according to the first embodiment will be described below with reference to FIG. The system 1 includes a liquid storage means 10 , a filtering means 20 , and a circulation means 30 . The system 1 has a structure in which the screen-permeated liquid L, which has been subjected to screen separation outside the system, is circulated between a liquid storage means 10 and a filtration means 20, while the filtration means 20 repeatedly performs an upward flow filtration process.

[0023] The liquid storage means 10 is capable of storing the screen-permeated liquid L that has been subjected to screen separation from the outside of the system via a water supply pipe T1.

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

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

[0026] The filtering means 20 preferably has a filtering performance of removing solids of 0.05 mm or more. The filter medium preferably removes solids of 0.05 mm or more, and the thickness of the filter medium layer is preferably, for example, about 30 cm to 50 cm. The filtering speed can be appropriately selected depending on the filter medium and the viscosity of the screen-permeated liquid, and is, for example, 5 m / day to 30 m / day.

[0027] In the system 1, the upward flow filtration process by the filtration means 20 allows rapid and easy peeling and cleaning even when the filter layer is clogged with solids in the screen-permeated liquid L by passing water downward from the top side to the bottom side of the filtration means 20. As a result, the filtration efficiency is increased and the concentration process can be efficiently achieved. In addition, since the solids obtained by the peeling and cleaning contain nutrients, they are preferably used as solid fertilizer.

[0028] In the system 1, it is preferable to provide a partition wall 11 in the liquid storage means 10 that substantially separates the screen permeated liquid L from the coarse filtrate LF filtered by the filtration means 20. Here, the term "partition wall that substantially separates" means that the configuration does not necessarily completely separate the screen permeated liquid L from the coarse filtrate LF filtered by the filtration means 20. In other words, in the liquid storage means 10, the screen permeated liquid L and / or the coarse filtrate LF may overflow over the partition wall 11 and be mixed. For example, the partition wall 11 may be configured to substantially separate the screen permeated liquid L and the coarse filtrate LF to form a two-tank structure. The partition wall 11 may be, for example, plate-shaped or cylindrical.

[0029] The circulation means 30 is configured to circulate the screen permeated liquid L (or a mixture of the screen permeated liquid 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 an outward water supply pipe T2 that supplies the screen permeated liquid L stored in the liquid storage means 10 to the filtration means 20, a return water supply pipe T3 that returns the crude filtrate LF that has been subjected to the upward flow filtration process by the filtration means 20 to the liquid storage means 10, and a pump P that enables these water supply and return. The circulation means 30 can circulate the screen permeated liquid L between the liquid storage means 10 and the filtration means 20 via the outward water supply pipe T2 and the return water supply pipe T3.

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

[0031] In addition to the liquid storage means 10, the filtering means 20 and the circulation means 30, the system 1 may include other components.

[0032] Other configurations include, for example, simple filtering means 12 (see FIG. 1) disposed upstream of the water supply pipe T1. This simple filtering means subjects the screen permeated liquid L stored in the liquid storage means 10 to simple filtering processing, improving the filtering efficiency in the system 1. For example, the simple filtering means preferably has filtering performance for removing solids of 1 mm or more. The filter medium of the simple filtering means is not particularly limited as long as it can remove solids of 1 mm or more, and examples thereof include metal membranes.

[0033] The method for circulating the screen-permeated liquid of the methane fermentation digestate by the system 1 of the first embodiment will be described with reference to the flow chart shown in FIG.

[0034] As illustrated in FIG. 3, the screen permeate L subjected to screen separation outside the system is stored in the liquid storage means 10 by the water supply pipe T1 (S101). Next, the screen permeate L stored in the liquid storage means 10 is sent to the filtration means 20 by the forward water supply pipe T2 (S102). The sent screen permeate L is subjected to upward flow filtration by the filtration means 20 (S103). The rough filtrate LF subjected to filtration by the filtration means 20 is returned to the liquid storage means 10 by the return water supply pipe T3 (S104). Then, S102 to S104 are repeated. The filtrate LC that has been sufficiently subjected to rough filtration is sent to the outside of the system by the water supply pipe T4 (S105). The filtrate LC sent to the outside of the system is concentrated by removing water (see FIG. 1).

[0035] Here, the system 1 of the first embodiment may be of a continuous type or a batch type. That is, in the system 1 of the first embodiment, the feed of the screen permeated liquid L from outside the system in the liquid storage means 10 and the feed of the coarse filtrate LF to the outside of the system may be continuously performed, or the feed of the screen permeated liquid L from outside the system in the liquid storage means 10 and the feed of the coarse filtrate LF to the outside of the system may be temporarily stopped, and the screen permeated liquid may be circulated and subjected to filtration treatment. In either case, the ratio of solids in the liquid subjected to filtration treatment is reduced by mixing the screen permeated liquid L with the coarse filtrate LF in the liquid storage means 10, thereby improving the efficiency of the filtration treatment. In addition, clogging of the filter layer of the filtration treatment means 20 can be prevented.

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

[0037] The system of the second embodiment will be specifically described with reference to Fig. 4. In Fig. 4, the same components as those of the system 1 of Fig. 2 are denoted by the same reference numerals. In the following, the system of the second embodiment will be described in principle with respect to the parts that are different from the system of the first embodiment, and the parts that overlap with the system of the first embodiment will not be described.

[0038] The system 2 is configured to circulate the screen permeate L between the liquid storage means 10 and the filtration means 20, while including a membrane separation means 40 at a stage preceding the sending out of the system of the crude filtrate LF that has been sufficiently filtered by the filtration means 20 in an upward flow manner.

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

[0040] In the system 2, by adopting a structure having a membrane separation means 40, a filtrate LC in which nutrients such as nitrogen and potassium are concentrated can be obtained from the crude filtrate LF by the filtration means 20. Furthermore, even if the system 1 has a structure having such a membrane separation means 40, the screen permeated liquid L is subjected to membrane separation treatment in a clarified state, so that clogging of the membrane separation means 40 can be prevented and a long life of the membrane can be achieved.

[0041] The method for circulating the screen-permeated liquid of the methane fermentation digestate by the system 2 of the second embodiment will be described with reference to the flow chart shown in FIG.

[0042] As illustrated in FIG. 5, the screen permeate L subjected to screen separation outside the system is stored in the liquid storage means 10 via the water supply pipe T1 (S201). Next, the screen permeate L stored in the liquid storage means 10 is sent to the filtration means 20 via the forward water supply pipe T2 (S202). The sent screen permeate L is subjected to upward flow filtration by the filtration means 20 (S203). The rough filtrate LF subjected to filtration by the filtration means 20 is returned to the liquid storage means 10 via the return water supply pipe T3 (S204). Thereafter, S102 to S204 are repeated. The rough filtrate LF that has been sufficiently subjected to rough filtration is subjected to solid-liquid separation by the membrane separation means 40 (S205). The filtrate LC that has been subjected to solid-liquid separation is sent to the outside of the system via the water supply pipe T4 (S206). The filtrate LC sent outside the system is concentrated after the water is removed (see Figure 1).

[0043] Here, the system 2 of the second embodiment may be of a continuous type or a batch type. In the system 2, the screen-permeated liquid L is roughly filtered by the filtration means 20, improving the efficiency of the solid-liquid separation process in the subsequent membrane separation means 40. Also, clogging of the membrane separation means 40 can be prevented, and a longer life can be achieved. Furthermore, solids are removed by the rough filtration process by the filtration means 20, and a pre-membrane filtration liquid containing nutrients is obtained, and a nutrient-enriched liquid is obtained by a subsequent concentration process.

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

[0045] [Another aspect of the present invention] Yet another aspect of the present invention is a method for producing a concentrated liquid of a methane fermentation digested liquid using the system of one aspect of the present invention. The method for producing a concentrated liquid of a methane fermentation digested liquid includes a step of subjecting a screen-permeated liquid of the methane fermentation digested liquid to a circulation treatment using the system of one aspect of the present invention to obtain a concentrated liquid of the methane fermentation digested liquid. [Industrial Applicability]

[0046] The system of one embodiment of the present invention can efficiently obtain a concentrated liquid from methane fermentation digestive liquid without damaging the nutritional components and avoiding the use of chemicals such as flocculants, so that the liquid can be distributed and used as liquid fertilizer as is. [Explanation of symbols]

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

Claims

1. A circulating treatment system for a screen permeate of a methane fermentation digestion liquid, comprising: The apparatus includes a liquid storage means, a filtering means, and a circulating means, The liquid storage means is configured to be capable of storing the screen permeated liquid, The filtering means is configured to filter the screen permeate in an upward flow manner; and The system, wherein the circulation means is configured to circulate the screen permeate between the storage means and the filtering means.

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

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

4. The system of claim 1 , wherein the liquid storage means comprises a partition wall that substantially separates the screen permeate from the filtrate from the filtration means.

5. A method for producing a filtrate of a methane fermentation digestive liquid, comprising a step of subjecting a screen-permeated liquid of a methane fermentation digestive liquid to a circulation treatment using the system according to any one of claims 1 to 4 to obtain a filtrate of the methane fermentation digestive liquid.

6. A method for producing a concentrated liquid of a methane fermentation digestive liquid, comprising a step of subjecting a screen-permeated liquid of a methane fermentation digestive liquid to a circulation treatment using the system according to any one of claims 1 to 4 to obtain a concentrated liquid of the methane fermentation digestive liquid.

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