Compost

Abstract

To provide compost and a method for producing the same.SOLUTION: The compost includes carbide, water-soluble phosphate, and at least one of iron(III) oxide, iron(III) carbonate, and iron(III) hydroxide. The compost may contain total phosphoric acid at a concentration of 1 wt.% or more and 21 wt.% or less, and the ratio of water-soluble phosphoric acid to the total phosphoric acid may be 30% or more and 70% or less. A method of producing the compost includes: preparing a mixture by mixing a carbide containing iron(III) phosphate with an organic fertilizer source, treating the mixture under anaerobic conditions, and mixing the anaerobically treated mixture with a base.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One embodiment of the present invention relates to a compost and a method for producing the compost. For example, one embodiment of the present invention relates to a compost rich in water-soluble phosphoric acid and a method for producing the compost. [Background technology]

[0002] Excrement from animals such as livestock can be used as an organic fertilizer source that is the raw material for compost. For example, Patent Document 1 discloses that compost that is effective for plant growth can be produced by mixing animal feces, which is animal excrement, with steel slag that contains calcium oxide, magnesium oxide, silicon oxide, manganese oxide, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-180266 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a compost and a method for producing the same. For example, an object of one embodiment of the present invention is to provide a compost having a novel composition and a method for producing the same. Alternatively, an object of one embodiment of the present invention is to provide a compost rich in fast-acting water-soluble phosphate and a method for producing the same. [Means for solving the problem]

[0005] One embodiment of the invention is a method for producing compost, the method including mixing a char containing iron(III) phosphate with an organic fertilizer source to form a mixture, treating the mixture under anaerobic conditions, and mixing the anaerobic treated mixture with a base.

[0006] One embodiment of the present invention is a compost comprising charcoal, water-soluble phosphate, and at least one of iron(III) oxide, iron(III) carbonate, and iron(III) hydroxide. [Brief description of the drawings]

[0007] [Figure 1] 1 is a flow chart showing a method for producing compost according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a production apparatus for producing compost according to one embodiment of the present invention. [Diagram 3] FIG. 1 is a conceptual diagram showing carbon dioxide storage using a compost production method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, each embodiment of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the gist of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0009] In order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part diagrammatically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention.

[0010] In this specification, the term "phosphate" refers to phosphate in the narrow sense, i.e., H 3 PO 4 It does not only mean the compound represented by the chemical formula: phosphoric acid (H 3 PO 4 ), as well as various phosphates, monohydrogen phosphates, and dihydrogen phosphates. Thus, for example, unless otherwise specified, iron phosphate means not only iron phosphate, but also monohydrogen iron phosphate and dihydrogen iron phosphate, and the iron ion contained therein may be either divalent or trivalent.

[0011] 1. Compost A compost according to one embodiment of the present invention contains carbide (charcoal), water-soluble phosphoric acid, and at least one iron compound selected from iron oxide (III), iron carbonate (III), and iron hydroxide (III). As other components, in addition to water, water-insoluble phosphoric acid (for example, phosphoric acid that is insoluble in water and soluble in a 2% citric acid aqueous solution (citric acid-soluble phosphoric acid)), sulfur-containing compounds, manganese-containing compounds, boron-containing compounds, and fiber contained in the organic fertilizer source that is the raw material for the compost may be contained. Each of these components will be described below.

[0012] 1-1.Carbide Carbide is a porous material that contains carbon as the main component and has pores with cross-sectional diameters ranging from several nanometers to several tens of micrometers. The specific gravity of carbide is 0.05 g / cm 3 More than 0.8g / cm 3 or less than 0.1g / cm 3 More than 0.5g / cm 3 The charcoal may contain zero-valent iron, or may contain iron compounds such as divalent or trivalent iron phosphate, iron chloride, iron sulfate, iron nitrate, iron oxide, and iron bromide. These iron and iron compounds are contained in the charcoal in a state where they are adsorbed or supported on the surface or in the pores of the charcoal. There is no limitation on the proportion of the charcoal contained in the compost, but it is, for example, 2% by weight to 40% by weight or 5% by weight to 35% by weight.

[0013] 1-2. Water-soluble phosphate Examples of water-soluble phosphoric acid include phosphates such as lithium phosphate, sodium phosphate, potassium phosphate, and ammonium phosphate, monohydrogen phosphates such as lithium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, and ammonium monohydrogen phosphate, and dihydrogen phosphates such as lithium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, and ammonium dihydrogen phosphate. Representative examples include alkali metal phosphates such as sodium phosphate and potassium phosphate, and alkali metal monohydrogen phosphates such as sodium monohydrogen phosphate and potassium monohydrogen phosphate. These water-soluble phosphoric acids are contained in the present compost at relatively high concentrations. Specifically, they may be contained at a concentration of 30% to 70%, 40% to 60%, or 40% to 50% of the total phosphoric acid in the present compost. The total phosphoric acid refers to the total of water-soluble phosphoric acid and water-insoluble phosphoric acid, and is contained in the present compost at a concentration of, for example, 1% to 21% by weight or 5% to 15% by weight.

[0014] The concentration of water-soluble phosphate can be determined, for example, by using ammonium vanadomolybdate spectrophotometry. In this method, for example, water is added to the compost, and a specified amount of the water-soluble portion is collected as a sample. Nitric acid (1+1) is added to this sample and heated to hydrolyze non-orthophosphate to orthophosphate ions. Ammonium vanadate (V), hexaammonium heptamolybdate, and nitric acid are then added to produce phosphovanadomolybdate. The water-soluble phosphate is quantified by measuring the absorption of phosphovanadomolybdate (for example, at 420 nm) using a UV-Vis spectrophotometer.

[0015] The ammonium vanadomolybdate spectrophotometric method can be used to quantify total phosphate. For example, a certain amount of compost is digested with nitric acid or perchloric acid, and then ammonium vanadate(V), hexaammonium heptamolybdate, and nitric acid are added. The total phosphate is quantified by measuring the absorption of the resulting phosphovanadomolybdate (e.g., at 420 nm) using a UV-Vis spectrophotometer.

[0016] 1-3.Iron compounds The iron compound includes at least one of iron oxide (III), iron carbonate (III), and iron hydroxide (III). The iron compound may be composed of a single compound or may be a mixture. In the compost, a part of the iron compound may be adsorbed or supported on the charcoal, and another part may be present in a state free from the charcoal. The iron compound may be contained in the compost at a concentration of 0.1% by weight or more and 10% by weight or less.

[0017] 1-4.Other ingredients The water-insoluble phosphates mentioned above include calcium hydrogen phosphate, calcium dihydrogen phosphate, calcium phosphate, magnesium monohydrogen phosphate, magnesium phosphate, etc. These water-insoluble phosphates are derived, for example, from compounds supported or adsorbed on charcoal used as raw materials in the compost production process described below, and / or from organic fertilizer sources.

[0018] Examples of sulfur-containing compounds include sulfates of alkali metals and alkaline earth metals. Examples of manganese-containing compounds include manganese salts such as manganese sulfate, manganese nitrate, manganese chloride, manganese carbonate, and manganese borate. Examples of boron-containing compounds include the above-mentioned manganese borate and boric acid. The respective concentrations of these sulfur-containing compounds, manganese-containing compounds, and boron-containing compounds in the compost may be, for example, 0.01% by weight or more and 1% by weight or less.

[0019] As mentioned above, this compost contains a relatively high concentration of water-soluble phosphoric acid, so it can function as a fast-acting fertilizer for plant growth. In addition, this compost contains carbonized porous materials. Such carbonized materials not only improve the moisture retention of soil, but also function as bioreactors, supplying nutrients, water, oxygen, and other nutrients to the soil in a balanced manner through the microorganisms and animals that live symbiotically in the pores. This means that this compost can also contribute to soil improvement.

[0020] 2. Compost production method A method for producing this compost according to one embodiment of the present invention will be described below. The flow of this production method is shown in Figure 1.

[0021] 2-1.Carbide (1) Preparation of charcoal by carbonization of biomass First, a carbonized material is prepared. Specifically, organic matter such as biomass is heated at a low oxygen concentration. Here, biomass is a type of organic matter, which is a substance derived from a living organism and its metabolites. Examples of biomass that can be used in the preparation of a carbonized material include materials derived from wood. Specifically, examples include plank-shaped or columnar wood, thinning materials, pruning waste, construction waste wood, powdered sawdust, particle boats, and other wooden molded products. There are no restrictions on the type of wood, and it can be cedar, cypress, or bamboo. Alternatively, examples of biomass include agricultural waste such as rice husks, bagasse, corn cobs and leaves, and agricultural by-products such as straw, wheat straw, and hay. Alternatively, examples of biomass include plants that are the raw material for fibers such as hemp, flax, cotton, sisal, abaca, and palm hair. Alternatively, the biomass can be algae such as seaweed, food waste, or silage obtained from animal manure.

[0022] (2) Supporting iron compounds on carbide Next, an iron compound is adsorbed or supported on the surface or in the pores of the char obtained by carbonizing the biomass. Specifically, the char is immersed in a solution or suspension containing an iron compound under normal or reduced pressure to adsorb or support the iron compound on the char. Typical examples of iron compounds include iron sulfate (II), iron sulfate (III) (including polyiron sulfate), iron nitrate (II), iron nitrate (III), iron chloride (II), iron chloride (III), iron oxide (II), iron oxide (III), iron bromide (II), iron bromide (III), iron carbonate (II), and iron carbonate (III).

[0023] Next, the carbide with the iron compound adsorbed or supported thereon is heated. The heating temperature may be appropriately selected from the range of 100° C. to 900° C., 500° C. to 800° C., or 600° C. to 750° C. Water is removed by heating, and the carbide with the iron compound supported thereon is obtained.

[0024] The carbide after immersion may be heated in a reducing gas atmosphere such as hydrogen or carbon monoxide, whereby some of the iron compounds are reductively decomposed into zero-valent iron metal, while some of the iron compounds are adsorbed or supported on the surface or in the pores of the carbide as divalent or trivalent iron compounds or a mixture thereof.

[0025] The immersion conditions and heating conditions may be adjusted so that the iron content in the iron compound-supported carbide is 1% by mass to 50% by mass, 3% by mass to 30% by mass, 5% by mass to 25% by mass, or 10% by mass to 25% by mass, based on the iron compound-supported carbide. The iron content in the iron compound-supported carbide can be quantified, for example, by inductively coupled plasma mass spectrometry (ICP-MS).

[0026] (3) Preparation of carbide containing iron phosphate The iron compound-supported carbide is then contacted with water containing phosphoric acid (hereinafter, treated water) to prepare iron phosphate-containing carbide. The treated water may be prepared by dissolving a phosphate, such as sodium phosphate or potassium phosphate, in water, or water from a body of water, such as a river, a lake, or the sea. For example, a container filled with iron-supported carbide may be placed in a river, a lake, or the sea, and the iron compound-supported carbide may be contacted with the water from the body of water. As a result, phosphoric acid contained in the water from the river, the lake, or the sea reacts with the iron compound on the iron compound-supported carbide, and is adsorbed or supported on the carbide as iron phosphate (III), which is less soluble in water, while organic compounds containing phosphoric acid or phosphorus in the water are removed. That is, this method not only makes it possible to prepare iron phosphate-containing carbide at low cost, but also makes it possible to purify water from various water bodies and improve the water quality at the same time.

[0027] 2-2. Composting Subsequently, composting is carried out using the iron phosphate-containing carbonized material as one of the raw materials.

[0028] (1) Mixing with organic fertilizer sources First, the iron phosphate-containing carbide obtained by the above-mentioned method is mixed with an organic fertilizer source. There is no restriction on the amount of the iron phosphate-containing carbide relative to the organic fertilizer source, but for example, 10% by weight to 40% by weight or 15% by weight to 25% by weight of the iron phosphate-containing carbide may be added to the organic fertilizer source. If the viscosity of the resulting mixture (primary mixture) is high, water may be added to adjust the viscosity. Examples of organic fertilizer sources include easily decomposable organic matter of biological origin, such as animal feces and urine, such as cow manure, pig manure, and chicken manure, food waste, such as food residue, agricultural waste, food waste, and sludge. To determine whether an organic matter is easily decomposable, for example, the amount of carbon dioxide generated after mixing with soil or the content of acid detergent-soluble organic matter (AD-soluble organic matter) can be used as one of the indicators.

[0029] The amount of carbon dioxide generated from an organic fertilizer source can be quantified by adding water to a mixture of a given amount of sample and soil, initiating incubation, and quantifying the amount of carbon dioxide generated during incubation. The generated carbon dioxide can be captured with an aqueous solution of sodium hydroxide, and barium chloride can be added to the mixture to precipitate it as barium carbonate, which can then be titrated with hydrochloric acid to quantify the amount of carbon dioxide. For example, if the amount of carbon dioxide generated within 10 days from the start of incubation is 200 mg or more, 300 mg or more, or 400 mg or more per gram of dried sample, the sample can be determined to be an easily decomposable organic matter and usable as an organic fertilizer source for producing the present compost.

[0030] The amount of AD soluble organic matter is determined, for example, by boiling a sample in an acid detergent solution (e.g., a solution of 20 g of cetyltrimethylammonium bromide dissolved in 1 L of 0.5 mol / L sulfuric acid) for 1 hour and filtering. The residue is washed, dried, and weighed. The residue is then incinerated and weighed, and the weight difference before and after incineration is calculated as the amount of acid detergent fiber (ADF). Since AD ​​soluble organic matter is organic matter other than ADF, the weight of the ADF and the residue after incineration is subtracted from the weight of the sample to calculate the amount of AD soluble organic matter. If the amount of AD soluble organic matter thus obtained is 500 mg or more, 600 mg or more, or 700 mg or more per 1 g of dried sample, it can be determined that the sample is easily decomposable organic matter and can be used as an organic fertilizer source for producing this compost.

[0031] However, in an embodiment of the present invention, the organic fertilizer source is not limited to the above-mentioned indicators and their numerical values, and any organic matter that can be decomposed by anaerobic microorganisms can be used as the organic fertilizer source.

[0032] The iron phosphate-containing carbide and the organic fertilizer source may be mixed in a chamber that can be sealed or that can maintain anaerobic conditions, and there are no restrictions on the configuration or shape of the chamber. For example, as shown in FIG. 2, the iron phosphate-containing carbide and the organic fertilizer source are put into a chamber 100 equipped with a hopper 104. A screw feeder 106 for conveying the iron phosphate-containing carbide and the organic fertilizer source to the chamber 100 may be provided between the hopper 104 and the chamber 100. In order to promote decomposition by anaerobic microorganisms, the chamber 100 may be configured to be rotatable, or an agitator 102 may be provided in the chamber. The chamber 100 may be configured to be sealed so as to block outside air. In addition, although not shown, the chamber 100 may be provided with one or more openings for adding water to the inside of the chamber 100 or for replacing the gas in the chamber 100. In addition, if the environment is anaerobic, it is not necessary to mix the iron phosphate-containing carbide and the organic fertilizer source in the chamber. For example, iron phosphate-containing charcoal and an organic fertilizer source may be piled up and fermented to create an anaerobic environment therein.

[0033] (2) Anaerobic treatment Subsequently, the primary mixture obtained by mixing the iron phosphate-containing carbide and the organic fertilizer source is treated under anaerobic conditions to decompose the organic matter contained in the organic fertilizer source. This anaerobic treatment may be performed in the chamber 100 or in a chamber different from the chamber 100. The anaerobic treatment may be performed by the action of anaerobic microorganisms contained in the organic fertilizer source, but in order to promote the decomposition of the organic matter, anaerobic microorganisms may be added separately. Examples of anaerobic microorganisms include nitrate-reducing bacteria, iron-reducing bacteria, sulfate-reducing bacteria, acid-producing bacteria, acetogenic bacteria, and methanogenic archaea, and preferably iron-reducing bacteria and methanogenic archaea. The anaerobic treatment may be performed at the temperature of the external environment in which the chamber 100 is placed, or may be performed while heating using a heater (not shown). When heating, the temperature may be, for example, 30° C. or higher and 60° C. or lower. The time of the anaerobic treatment may also be set arbitrarily, and may be appropriately selected from the range of, for example, 1 day to 120 days, 10 days to 60 days, or 15 days to 30 days.

[0034] In this anaerobic treatment, the chamber 100 becomes a reducing environment as the organic matter is decomposed, and the oxidation-reduction potential (ORP) of the primary mixture becomes more negative. As a result, trivalent iron phosphate is reduced to divalent iron phosphate. Therefore, when iron-reducing bacteria that use trivalent iron compounds as electron acceptors are included, the trivalent iron phosphate included in the iron compound-containing carbide is reduced to divalent iron phosphate by the action of the iron-reducing bacteria. Since divalent iron phosphate has a higher solubility in water than trivalent iron phosphate, at least a portion of the iron phosphate dissolves in the water included in the primary mixture and dissociates into divalent iron ions and phosphate ions. For example, when trivalent iron phosphate included in the iron compound-containing carbide is FePO 4 In the case of divalent iron phosphate Fe 3 (PO 4 ) 2 is generated.

[0035] (3) Addition of base The anaerobically treated primary mixture is then mixed with a base. The base may be one in which an anion that combines with ferrous ions to give an iron compound with low solubility in water and a cation that combines with phosphate ions to give soluble phosphate are ionic-bonded. Specifically, alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates are included. The base may be added as an aqueous solution or in a solid state. The addition of the base causes an ion exchange, and the divalent iron ions and phosphate ions dissociated by the anaerobic treatment ionically bond with the anions and cations of the base, respectively. For example, when an alkali metal hydroxide is used as the base, an alkali metal salt of phosphoric acid is produced, and divalent iron hydroxide is produced. When an alkali metal carbonate or bicarbonate is used as the base, an alkali metal salt of phosphoric acid is produced, and divalent iron carbonate and iron bicarbonate are produced, respectively.

[0036] The base may be added in the chamber 100 where the organic fertilizer source and the iron compound-containing carbide are mixed, or in a chamber different from the chamber 100. For example, as shown in FIG. 2, the primary mixture may be conveyed to a chamber 110 connected to the chamber 100 via a valve 108 such as a rotary valve, and the base may be added to the chamber 110. Although not shown, the chambers 100 and 110 do not have to be connected to each other. As with the chamber 100, the chamber 110 may also be provided with a hopper 112 and an agitator 114, and may further be provided with a screw feeder (not shown). The mixture (secondary mixture) obtained after the mixing with the base is completed may be taken out of the chamber 110 using a valve 116 such as a rotary valve.

[0037] The above (2) anaerobic treatment and (3) addition of a base may be carried out simultaneously. For example, a base may be added to a primary mixture obtained by mixing an iron phosphate-containing carbide with an organic fertilizer source, and then the mixture may be treated under anaerobic conditions to decompose the organic matter contained in the organic fertilizer source. Alternatively, an iron phosphate-containing carbide, an organic fertilizer source, and a base may be mixed, and then the mixture may be treated under anaerobic conditions to decompose the organic matter contained in the organic fertilizer source.

[0038] (4) Sterilization The above steps allow the production of a compost according to one embodiment of the present invention, but a sterilization treatment may be carried out subsequently. The sterilization treatment is preferably carried out by treating the compost in an oxidizing atmosphere. The treatment in an oxidizing atmosphere may be carried out, for example, by contacting the compost with a gas containing oxygen (oxygen gas, air) (aeration). At this time, the compost may also be irradiated with ultraviolet light. This sterilization treatment can remove or reduce bacteria, microorganisms, etc. contained in the organic fertilizer source. Furthermore, the water content can be appropriately controlled by evaporating the water contained in the organic fertilizer source or water added separately, and as a result, a compost that is easy to handle can be obtained.

[0039] As described above, the phosphate ions liberated from the divalent iron phosphate produced by anaerobic treatment react with the cations of the added base to give alkali metal phosphates, monohydrogen phosphates, and dihydrogen phosphates. Since these salts are water-soluble, the compost according to one embodiment of the present invention functions as an excellent source of water-soluble phosphate and can contribute to plant growth as a fast-acting fertilizer.

[0040] On the other hand, the iron ions (II) liberated from the divalent iron phosphate produced by anaerobic treatment react with the anions of the base to produce divalent iron compounds (iron hydroxide (II), iron carbonate (II), iron bicarbonate (II), etc.). These divalent iron compounds are quickly oxidized by oxygen contained in the primary or secondary mixture, or by oxygen in the oxidative atmosphere during sterilization treatment, to produce trivalent iron compounds (iron hydroxide (III), iron carbonate (III), iron oxide (III), etc.). For example, iron bicarbonate (II) present in water is also oxidatively decomposed to give iron hydroxide (III). These trivalent iron compounds have low solubility in water and are precipitated in the compost. Therefore, the frequency factor of the reaction (ion exchange) between the precipitated trivalent iron compounds and water-soluble phosphoric acid is extremely small, and these reactions are very slow. As a result, water-soluble phosphoric acid is hardly lost due to the precipitated trivalent iron compounds, and this compost can maintain its function as a fast-acting fertilizer.

[0041] (5) Other processes The obtained compost may be used alone as a fertilizer, or may be used after mixing with a fertilizer aid containing the above-mentioned sulfur-containing compound, manganese-containing compound, or boron-containing compound. In this case, the fertilizer aid may be added so that the concentration of the sulfur-containing compound, manganese-containing compound, or boron-containing compound in the compost is, for example, 0.01% by weight to 1% by weight. Mixing may be performed using a mixer, which may be selected from a free-fall mixer, a forced mixer, a Y-branch mixer, an agitator mixer, a paddle mixer, or the like.

[0042] Furthermore, the obtained compost may be dried, molded, etc. In the molding, the compost may be processed into any shape such as pellets, rods, granules, powder, etc. If necessary, crushing and classification may be performed to adjust the particle size of the compost. For example, the compost may be crushed and classified so that the average particle size is 10 mm or less, or 0.1 mm to 10 mm. Crushing may be performed using a crusher, and for example, a crusher such as a vibration mill, jet mill, ball mill, roller mill, rod mill, hammer mill, impact mill, rotary mill, pin mill, pin-disk mill, or planetary mill can be used. Crushing the compost using a crusher increases the surface area, and as a result, the elution of water-soluble phosphoric acid into the soil is promoted. Classification is performed using a classifier, and either a dry classifier or a wet classifier may be used as the classifier. For example, an air classifier, a gravity field classifier, an inertial field classifier, a centrifugal field classifier, etc. are exemplified as the classifier.

[0043] The compost according to one embodiment of the present invention produced by the above-mentioned method is rich in water-soluble phosphoric acid, and therefore exhibits immediate effects comparable to chemical fertilizers and can function as a fertilizer suitable for top dressing. In addition, since the main components, carbonized matter and organic fertilizer sources, are derived from natural resources, farming methods using this compost can be recognized as a type of organic farming.

[0044] Furthermore, the main component, charcoal, can be obtained by carbonizing biomass. In other words, charcoal is prepared by effectively utilizing biomass derived from plants that is produced by fixing carbon dioxide through photosynthesis. Furthermore, the water quality of various water systems can be improved in the process of producing compost using this charcoal, and the carbon dioxide fixed by plants can be stored underground as charcoal by spreading this compost on soil.

[0045] More specifically, as shown in Fig. 3, according to each embodiment of the present invention, biomass is carbonized to prepare a charcoal (1), and then a charcoal carrying an iron compound is prepared from the charcoal (2). This charcoal carrying an iron compound contributes to water purification when it is converted into a charcoal containing iron phosphate (3), and is converted into compost containing charcoal originating from biomass through a series of processes including mixing with an organic fertilizer source, anaerobic treatment, and mixing with a base (4). This compost is spread on soil as a fast-acting fertilizer and used to grow plants (5). Plants fix carbon dioxide from the atmosphere through photosynthesis to provide food and structural materials, and also produce biomass as a by-product, which is the raw material for charcoal (6).

[0046] Through the cycle constructed by the series of processes (1) to (6), atmospheric carbon dioxide is fixed as organic matter through photosynthesis, and this organic matter is used as food or materials while biomass is produced as a by-product. The biomass is converted into charcoal through carbonization, and is finally spread into the ground as compost. Thus, atmospheric carbon dioxide is stored in the ground as carbon, thereby contributing to the reduction of atmospheric carbon dioxide. In addition, by using carbonate as a base when producing this compost, carbon dioxide can be further fixed as ferric carbonate, making it possible to make an even greater contribution to the reduction of atmospheric carbon dioxide. EXAMPLES

[0047] 1. Preparation of iron phosphate-containing carbide 400 g of charcoal obtained by carbonizing cedar wood was immersed in 10 L of an aqueous solution of polyferric sulfate (iron content 11%) at room temperature for 10 minutes at a gauge pressure of -0.09 MPa, with the normal atmospheric pressure being zero. The charcoal was then dried at 105°C for 24 hours, and further heated at 900°C for 1 hour in the presence of nitrogen and carbon monoxide gas to obtain an iron compound-supported charcoal. The iron content in the iron compound-containing charcoal was determined by extracting iron by treating the crushed iron compound-supported charcoal according to JIS K 1474, and measuring the extracted iron content with an inductively coupled plasma optical emission spectrometer (PerkinElmer, Optima 5300 DV). As a result, it was confirmed that the iron compound-supported charcoal contained 21% by weight of iron based on the total amount of the iron compound-supported charcoal.

[0048] A column packed with 2 kg of iron compound-loaded carbide was passed through with 2 L / day of sewage sludge dewatering separated liquid for 4 days. The sewage sludge dewatering separated liquid used here was the filtrate obtained by centrifuging sludge at a sewage treatment plant in Kanagawa Prefecture. The iron phosphate-containing carbide obtained was then dried at 105°C for 8 hours. 2. Example 1 In this example, the results of treating iron phosphate-containing charcoal under anaerobic conditions are described. 2-1. Experiment In a 200 mL polypropylene container, 40 mL of water, 5 g of iron phosphate-containing carbide, and 2 g of paddy field soil were added. Furthermore, 1 g of dog food (Pedigree (registered trademark) manufactured by MARS) was added as an organic fertilizer source, and the obtained primary mixture was stirred. Thereafter, 1 g of the organic fertilizer source was added every day, and stirring was continued for 13 days. The total amount of the organic fertilizer source was 13 g. As Comparative Example 1, a similar experiment was performed using 2 g of charcoal by-produced in a gasification power generation device and 1.5 g of iron phosphate (III) (iron phosphate (III) n-hydrate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) instead of the iron phosphate-containing carbide.

[0049] The pH of the obtained primary mixture was measured using a pH meter (HORIBA Measurement Method Model JF25), and the oxidation-reduction potential ORP was measured using a HORIBA glass electrode type hydrogen ion concentration indicator D-52. The total iron amount and the amount of water-soluble iron were measured in the same manner as for measuring the iron content of the iron compound-supported carbonized material. For the measurement of the total iron amount, a sample was used that was sampled from the primary mixture after being uniformly stirred. On the other hand, for the measurement of the amount of water-soluble iron, the mixture was filtered, and the obtained filtrate was used as the sample.

[0050] 2-2. Results and Discussion The measurement results of the primary mixture are shown in Table 1. As shown in Table 1, there is no significant difference in pH and ORP between Example 1 and Comparative Example 1. The initial pH of the primary mixture in Example 1 and Comparative Example 1 was 9.1 and 9.2, respectively, and compared to these initial pHs, the pH after 13 days had dropped significantly. This result means that a reducing environment was obtained by the action of anaerobic microorganisms contained in the paddy field soil used in Example 1 and Comparative Example 1. Here, the weight ratio of iron in the water-soluble portion to the total iron (W Fe / T Fe ), it can be seen that Example 1 is extremely high compared to Comparative Example 1. Fe / T Fe This is thought to be because the iron ions and phosphate ions in the reagent-derived iron phosphate (III) have a strong bond and are hardly dissolved in the primary mixture. Fe / T Fe This is thought to be because the iron phosphate (III) supported on the carbide was produced by bonding at room temperature, and therefore the bonding strength between the iron ions and phosphate ions was weak, resulting in high solubility. [Table 1]

[0051] These results suggest that the reduction of iron phosphate(III) by anaerobic microorganisms in the primary mixture of iron phosphate-containing charcoal and organic fertilizer source proceeds rapidly, resulting in efficient production of water-soluble iron phosphate(II).

[0052] 3. Example 2 This example describes the results of treating a primary mixture of iron phosphate-containing charcoal and an organic fertilizer source under anaerobic conditions followed by mixing with a base.

[0053] 3-1. Experiment The primary mixture was treated under anaerobic conditions for 13 days in the same manner as in Example 1. After this, sodium carbonate was added to the primary mixture, which was then stirred for 24 hours. The amount of sodium carbonate added was changed to 4.5 g, 9.0 g, and 22.5 g to obtain the secondary mixtures of Examples 2 to 4, respectively.

[0054] The pH, ORP, total iron content, and water-soluble iron content were measured in the same manner as in Example 1. The total phosphate concentration and the water-soluble phosphate concentration were both measured by ammonium vanadomolybdate absorptiometry. The UV-Vis spectrophotometer used was a Shimadzu UV-2600.

[0055] 3-2. Results and Discussion The analysis results are shown in Table 2. As shown in Examples 2 to 4 in Table 2, the weight ratio of iron in the water-soluble portion to the total iron amount (W Fe / T Fe ) tends to increase. This is thought to be because the addition of sodium carbonate generates carbon dioxide gas in the secondary mixture, promoting the anaerobic reaction, which in turn advances the reduction reaction of iron, increasing the amount of iron (II) ions in the water-soluble portion.

[0056] Weight ratio W of water-soluble phosphoric acid to total phosphoric acid in the secondary mixture p / T p increases with increasing amount of base added. In Comparative Example 2, where no base was added, W p / T p is extremely low. This indicates that the phosphate ions derived from the water-soluble iron(II) phosphate produced by the treatment under anaerobic conditions are ionically bonded to the alkali metal ions contained in the base and exist as water-soluble sodium phosphate in the secondary mixture. [Table 2]

[0057] The above results show that by treating a mixture of iron phosphate-containing carbonized material and an organic fertilizer source under anaerobic conditions and then mixing with a base containing an alkali metal as a cation, ion exchange between the iron phosphate (II) produced under anaerobic conditions and the base proceeds, resulting in the production of water-soluble phosphoric acid (phosphate of an alkali metal). From this, it can be understood that by applying the production method according to one embodiment of the present invention, compost rich in water-soluble phosphoric acid can be produced.

[0058] The above-described embodiments of the present invention may be combined as appropriate as long as they are not mutually inconsistent. Any embodiment in which a person skilled in the art appropriately adds or deletes components or modifies the design based on each embodiment is also included in the scope of the present invention as long as it includes the gist of the present invention.

[0059] Even if there are other effects and advantages different from those brought about by the respective embodiments described above, those which are clear from the description in this specification or which can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0060] 100: chamber, 102: agitator, 104: hopper, 106: screw feeder, 108: valve, 110: chamber, 112: hopper, 114: agitator, 116: valve

Claims

1. carbide, Water-soluble phosphoric acid, and A compost comprising at least one of iron(III) oxide, iron(III) carbonate, and iron(III) hydroxide.

2. 2. The compost according to claim 1, containing total phosphoric acid at a concentration of 1% by weight or more and 21% by weight or less.

3. 3. The compost according to claim 2, wherein the ratio of said water-soluble phosphoric acid to said total phosphoric acid is 30% or more and 70% or less.

4. 2. The compost according to claim 1, comprising the carbonized material in an amount of 2% by weight or more and 20% by weight or less.

5. 2. The compost of claim 1, further comprising at least one of a sulfur-containing compound, a manganese-containing compound, and a boron-containing compound.

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