JP7797370B2 - Liquid fertilizer manufacturing method and manufacturing device - Google Patents

Description

The present invention relates to a method and an apparatus for producing a liquid fertilizer.

In recent years, there has been a demand for using digested liquids from organic matter such as livestock waste and food waste as fertilizer or raw materials for fertilizer.
For example, Patent Document 1 proposes that digested liquid of organic matter is subjected to ultrafiltration to separate it into a dispersion containing phosphorus components and sludge and a membrane-permeated liquid containing potassium components and nitrogen components, the membrane-permeated liquid is concentrated by electrodialysis, and the concentrated liquid is further distilled to separate it into a first solution with a high concentration of nitrogen components and a second solution with a potassium component and a low concentration of nitrogen components, and these are used as raw materials for fertilizer.

Japanese Patent Application Laid-Open No. 2019-131432

However, the inventors have discovered that while the method proposed in Patent Document 1 can extract components necessary for plant growth from the digestive fluid through ultrafiltration and electrodialysis, nitrogen and phosphorus components remain in the electrodialysis desalted liquid after the components necessary for plant growth have been extracted, and therefore discharging this liquid into public waters poses an increased environmental burden.

An object of the present invention is to solve the above problems.
In other words, the present invention makes it possible to extract components useful for plant growth contained in the digested liquid, and further to prepare liquid fertilizers with various composition ratios depending on the plant growth conditions and plant types. Furthermore, the concentrations of nitrogen and phosphorus components in the treated water after extracting the components necessary for plant growth can be reduced, and the treated water can be released into public water bodies without increasing the environmental load and can be reused as a water resource.

As a result of extensive research into resolving the above-mentioned issues, the inventors discovered that the above issues could be resolved by using a specific method for producing liquid fertilizer, leading to the present invention.

That is, the present invention has the following features.
[1] A method for producing a liquid fertilizer, comprising the following first to third steps:
First step: A step of subjecting an organic digestion liquid to membrane separation treatment to obtain a membrane permeate containing potassium components and nitrogen components and a dispersion containing sludge;
a second step: subjecting the membrane permeate to electrodialysis to obtain an electrodialysis desalted solution having lower concentrations of potassium components and nitrogen components than the membrane permeate, and an electrodialysis concentrate having higher concentrations of potassium components and nitrogen components than the membrane permeate;
The third step is a step of treating the electrodialysis-deionized liquid with a reverse osmosis membrane to obtain a reverse osmosis membrane permeate having lower concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid, and a reverse osmosis membrane concentrate having higher concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid.
[2] The method for producing a liquid fertilizer according to [1], wherein the digested liquid is a digested liquid obtained by anaerobic fermentation or a digested liquid obtained by aerobic fermentation.
[3] The method for producing a liquid fertilizer according to [1] or [2], wherein the sludge-containing dispersion obtained in the first step has a higher phosphorus concentration than the digested liquid.
[4] The method for producing a liquid fertilizer according to any one of [1] to [3], wherein the electrodialysis concentrate obtained in the second step has a higher phosphorus component concentration than the membrane permeate.
[5] The method for producing a liquid fertilizer according to any one of [1] to [4], wherein the reverse osmosis membrane concentrate obtained in the third step has a higher phosphorus component concentration than the electrodialysis desalted liquid.

[6] A liquid fertilizer manufacturing apparatus comprising the following first to third steps:
First step: A step of subjecting an organic digestion liquid to membrane separation treatment to obtain a membrane permeate containing potassium components and nitrogen components and a dispersion containing sludge;
a second step: subjecting the membrane permeate to electrodialysis to obtain an electrodialysis desalted solution having lower concentrations of potassium components and nitrogen components than the membrane permeate, and an electrodialysis concentrate having higher concentrations of potassium components and nitrogen components than the membrane permeate;
The third step is a step of treating the electrodialysis-deionized liquid with a reverse osmosis membrane to obtain a reverse osmosis membrane permeate having lower concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid, and a reverse osmosis membrane concentrate having higher concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid.
[7] The liquid fertilizer manufacturing apparatus according to [6], wherein the digested liquid is a digested liquid from anaerobic fermentation or a digested liquid from aerobic fermentation.
[8] The liquid fertilizer manufacturing apparatus according to [6] or [7], wherein the dispersion liquid containing sludge obtained in the first step has a higher phosphorus component concentration than the digested liquid.
[9] The liquid fertilizer manufacturing apparatus according to any one of [6] to [8], wherein the electrodialysis concentrate obtained in the second step has a higher phosphorus component concentration than the membrane permeate.
[10] The liquid fertilizer manufacturing apparatus according to any one of [6] to [9], wherein the reverse osmosis membrane concentrated liquid obtained in the third step has a higher phosphorus component concentration than the electrodialysis desalted liquid.

[11] A liquid fertilizer comprising at least one selected from the membrane permeate obtained in the first step, the dispersion containing sludge obtained in the first step, the electrodialysis concentrate obtained in the second step, and the reverse osmosis membrane concentrate obtained in the third step, in the method for producing a liquid fertilizer according to any one of [1] to [5].
[12] A liquid fertilizer comprising at least one selected from the membrane permeate obtained in the first step, the dispersion containing sludge obtained in the first step, the electrodialysis concentrate obtained in the second step, and the reverse osmosis membrane concentrate obtained in the third step, of the liquid fertilizer manufacturing apparatus according to any one of [6] to [10].

The method for producing a liquid fertilizer of the present invention can extract components useful for plant growth contained in the digested liquid, and can also prepare liquid fertilizers with various composition ratios depending on the plant growth conditions and plant species. Furthermore, since the reverse osmosis membrane permeate after extraction of the components necessary for plant growth has low concentrations of nitrogen and phosphorus components, even if it is released into public water bodies such as rivers, it does not increase the environmental load and can be reused as a water resource.
The liquid fertilizer manufacturing device of the present invention can extract components useful for plant growth contained in the digested liquid, and can prepare liquid fertilizers with various composition ratios depending on the plant growth conditions and plant types. Furthermore, it can obtain reverse osmosis membrane permeate that can be reused as a water resource without increasing the environmental load even if it is released into public water bodies such as rivers.
The liquid fertilizer of the present invention contains components contained in the digested fluid that are useful for plant growth, and can have various composition ratios depending on the plant growth conditions and type of plant.

The following describes in detail the embodiments of the present invention. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following content as long as it does not exceed the gist of the present invention.
Furthermore, when the expression "to" is used in this specification, it is intended to include the numerical values or physical values written before and after it. Furthermore, numerical values or physical values written as upper and lower limits are intended to include those values.

[Method for producing liquid fertilizer]
The method for producing a liquid fertilizer of the present invention includes the following first to third steps.

[First step]
The first step of the present invention is a step of subjecting an organic digested liquid to membrane separation treatment to obtain a membrane permeate containing potassium components and nitrogen components and a dispersion containing sludge.
The digestive fluid of organic matter is the liquid obtained after fermenting organic matter such as human waste.
Examples of the digestive fluid include digestive fluid from anaerobic fermentation and digestive fluid from aerobic fermentation.

The digested liquid from anaerobic fermentation is a liquid that has been fermented under oxygen-free conditions, with air being blocked off.
The digested liquid of aerobic fermentation is the fermented liquid under aeration conditions.
Of the digested liquid obtained by anaerobic fermentation and the digested liquid obtained by aerobic fermentation, the digested liquid obtained by anaerobic fermentation is preferred because it allows the recovery of biogas such as methane gas.

The membrane separation process is a solid-liquid separation process in which solids contained in a liquid are separated by utilizing the pore size of holes opened on the surface of a membrane.
Examples of membranes used in membrane separation treatment include microfiltration membranes and ultrafiltration membranes.
Among these, an ultrafiltration membrane capable of separating finer solids is preferred in terms of preventing clogging of the flow path of the electrodialysis device installed in the second step.

The potassium component is a component useful for plant growth, and specifically refers to potassium ions. There are no particular limitations on the counter ions of potassium ions.

The nitrogen component is also useful for plant growth and exists in the form of organic nitrogen, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, and the like.
Among these, ammonium nitrogen and nitrate nitrogen are preferred because they are useful as liquid fertilizers, and nitrate nitrogen is more preferred because it can also be applied to crops grown hydroponically.

The concentration of phosphorus components in the digestive fluid is preferably 1 mg/L or more, and more preferably 100 mg/L or more.

The membrane permeate contains a potassium component and a nitrogen component, and may also contain other components.
The higher the concentration of potassium in the membrane permeate, the more preferable it is.
The higher the concentration of the nitrogen component in the membrane permeate, the more preferable it is.

The sludge is a solid material containing water derived from the digestive fluid.
In addition to the potassium and nitrogen components, phosphorus is also useful for plant growth, so the sludge preferably contains phosphorus. Phosphorus components include insoluble and soluble phosphorus components, and the insoluble phosphorus components are in the form of suspended phosphorus.

The dispersion containing sludge is the sludge in the membrane separation tank in the first step.
The concentration of the sludge in the dispersion is preferably 5,000 to 20,000 mg/L, more preferably 8,000 to 12,000 mg/L.

The concentration of insoluble phosphorus components in the sludge dispersion is higher than the concentration of insoluble phosphorus components in the digested liquid.

[Second process]
The second step of the present invention is a step of subjecting the membrane permeate to electrodialysis to obtain an electrodialysis desalted solution having lower concentrations of potassium components and nitrogen components than the membrane permeate, and an electrodialysis concentrated solution having higher concentrations of potassium components and nitrogen components than the membrane permeate.

The electrodialysis treatment is carried out by alternately stacking a large number of cation exchange membranes and anion exchange membranes with spacers interposed between them, placing a pair of electrodes on both ends of the stack, and alternately arranging deionization chambers (chambers D), which are spaces partitioned by anion exchange membranes on the anode side and cation exchange membranes on the cathode side, and conversely, concentrating chambers (chambers C), which are spaces partitioned by cation exchange membranes on the anode side and anion exchange membranes on the cathode side.
When the stock solution is supplied to compartment D, the cations pass through the cation exchange membrane toward the cathode and move to compartment C, which is closer to the cathode. However, because the cathode side of compartment C is separated by an anion exchange membrane, they cannot move further to the adjacent compartment D.
Similarly, anions move from compartment D to compartment C on the anode side. As a result, they are desalinated in compartment D and concentrated in compartment C.

An example of an apparatus used for electrodialysis treatment is the DW-1 manufactured by AGC Engineering Co., Ltd.

The electrodialysis desalted liquid is desalted water desalted in chamber D of the electrodialysis treatment.
The electrodialysis desalted liquid contains a potassium component and a nitrogen component, and may also contain other components.
The concentration of potassium components in the electrodialysis desalted liquid is preferably lower than the concentration of potassium components in the membrane permeate liquid.
The concentration of nitrogen components in the electrodialysis desalted liquid is preferably lower than the concentration of nitrogen components in the membrane permeate liquid.

The electrodialysis concentrate is a concentrate concentrated in chamber C of the electrodialysis treatment.
The electrodialysis concentrate contains a potassium component and a nitrogen component.
The concentration of potassium components in the electrodialysis concentrate is preferably higher than the concentration of potassium components in the membrane permeate.
The concentration of nitrogen components in the electrodialysis concentrate is preferably higher than the concentration of nitrogen components in the membrane permeate.

The electrodialysis concentrate preferably contains a phosphorus component.
The concentration of phosphorus components in the electrodialysis concentrate is higher than the concentration of phosphorus components in the membrane permeate.

[Third step]
The third step of the present invention is a step of treating the electrodialysis-deionized liquid with a reverse osmosis membrane to obtain a reverse osmosis membrane permeate having lower concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid, and a reverse osmosis membrane concentrate having higher concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid.

The reverse osmosis membrane treatment is a treatment that utilizes the principle of membrane separation, in which a solvent is transferred from the concentrated solution side to the dilute solution side through a semipermeable membrane by applying a pressure greater than the osmotic pressure to the concentrated solution side.
An example of a reverse osmosis membrane used in the reverse osmosis membrane treatment is CPA5 manufactured by Nitto Denko Corporation.

The reverse osmosis membrane permeate is a liquid that has passed through a reverse osmosis membrane.
The reverse osmosis membrane permeate contains at least potassium and nitrogen components, the concentrations of which are lower than the concentrations of potassium and nitrogen components in the electrodialysis desalted liquid.
The concentration of potassium components in the reverse osmosis membrane permeate is preferably lower than the concentration of potassium components in the electrodialysis desalted liquid.
The concentration of nitrogen components in the reverse osmosis membrane permeate is preferably lower than the concentration of nitrogen components in the electrodialysis desalted liquid.

The reverse osmosis membrane concentrate is a liquid that did not pass through the reverse osmosis membrane.
The reverse osmosis membrane concentrated liquid contains at least potassium and nitrogen components, the concentrations of which are higher than the concentrations of potassium and nitrogen components in the electrodialysis desalted liquid.
The concentration of potassium components in the reverse osmosis membrane concentrate is preferably higher than the concentration of potassium components in the electrodialysis desalted liquid.
The concentration of nitrogen components in the reverse osmosis membrane concentrate is preferably higher than the concentration of nitrogen components in the electrodialysis desalted liquid.

The reverse osmosis membrane concentrate preferably contains a phosphorus component.
The concentration of phosphorus components in the reverse osmosis membrane concentrate is higher than the concentration of phosphorus components in the electrodialysis desalted liquid.

[Liquid fertilizer manufacturing equipment]
The liquid fertilizer manufacturing apparatus of the present invention includes the following first to third steps.

[First step]
This is the same as the first step described in the section on the manufacturing method of liquid fertilizer.

[Second process]
This is the same as the second step described in the section on the manufacturing method of liquid fertilizer.

[Third step]
This is the same as the third step described in the section on the manufacturing method of liquid fertilizer.

[Liquid fertilizer]
The liquid fertilizer of the present invention comprises at least one selected from the membrane permeate obtained in the first step, the sludge-containing dispersion obtained in the first step, the electrodialysis concentrate obtained in the second step, and the reverse osmosis membrane concentrate obtained in the third step of the liquid fertilizer manufacturing method of the present invention or the liquid fertilizer manufacturing apparatus of the present invention.
The liquid fertilizer may be used alone or in combination of two or more of these.

The liquid fertilizer of the present invention uses at least one selected from the membrane permeate obtained in the first step, the sludge-containing dispersion obtained in the first step, the electrodialysis concentrate obtained in the second step, and the reverse osmosis membrane concentrate obtained in the third step, and may further contain additives commonly used in fertilizers.
Examples of additives include organic fertilizers and chemical fertilizers that are already used as fertilizers. From the viewpoint of efficacy for plants and ease of use, water-soluble fertilizers are preferred.

The liquid fertilizer preferably contains nitrogen, potassium, and phosphorus, and more preferably contains calcium, magnesium, sulfur, manganese, and boron as other components.
The other components may be originally contained in the membrane permeate obtained in the first step, the sludge-containing dispersion obtained in the first step, the electrodialysis concentrate obtained in the second step, or the reverse osmosis membrane concentrate obtained in the third step, or may be added thereto later.

[Application]
The liquid fertilizer of the present invention can be used as a general fertilizer, but is particularly suitable for use as a base fertilizer or top dressing in soil and hydroponic cultivation of plants.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded.
In the following examples and comparative examples, various physical properties were measured by the following methods.

[Evaluation method]
(1) TOC (total organic carbon concentration)
The total organic carbon concentration was measured using a total organic carbon analyzer ("TOC-310V" manufactured by Nitto Seiko Analytech Co., Ltd.) which uses a combustion method.

(2) TN (total nitrogen concentration)
The total nitrogen concentration was measured using a nitrogen detector (Nitto Seiko Analytech Co., Ltd., "ND-210 Model") connected to the rear of a total organic carbon analyzer (Nitto Seiko Analytech Co., Ltd., "TOC-310V"). The measurement method used with this analyzer is the oxidative decomposition-chemiluminescence method (decompression method).

(3) PO ₄ -P (phosphate phosphorus concentration)
The phosphoric acid phosphorus concentration was measured by ion chromatography using "IC-2100" manufactured by Tosoh Corporation.
A column of "TSKgel SuperIC-A HS" manufactured by Tosoh Corporation was used, and a mixture of NaHCO ₃ and NaCO ₃ was used as the mobile phase, and detection was carried out by electrical conductivity.

(4) K (potassium concentration)
The potassium concentration was measured by flame photometry.

[Example 1]
The digestate used was aerobic fermentation digestate derived from human waste.
In the first step, this digested liquid was subjected to suction filtration using an ultrafiltration membrane manufactured by Mitsubishi Chemical Corporation (membrane material: polyvinylidene fluoride, nominal pore size: 0.05 μm, membrane shape: hollow fiber), to obtain a liquid that passed through the ultrafiltration membrane and a dispersion containing sludge.
In the second step, the obtained ultrafiltration membrane permeate was treated with an electrodialysis apparatus manufactured by AGC Engineering Co., Ltd. (cation ion exchange membrane: CMVN, anion ion exchange membrane: AMVN) to obtain an electrodialysis desalted liquid and an electrodialysis concentrated liquid.
The electrodialysis-deionized liquid was used as raw water to carry out reverse osmosis membrane evaluation.

The reverse osmosis membrane evaluation used a spin flow cell manufactured by Iwai Pharmatech Co., Ltd. The membrane used was a CPA5 manufactured by Nitto Denko Corporation.
A reverse osmosis membrane was installed in the evaluation device cell, and raw water was supplied to the cell using a pressure pump. The concentrated solution was returned to the raw water using a circulating filtration method. Treated water at each recovery rate was sampled and water quality analysis was performed.
Here, the recovery rate is a calculated value of reverse osmosis membrane permeate/reverse osmosis membrane feed liquid.
The results are shown in Table 1.

It was found that if the recovery rate of the reverse osmosis membrane permeate is within the above range, i.e., if the recovery rate is 70% or less, the wastewater standard values of N < 100 mg/L and P < 8 mg/L can be uniformly met, and the environmental load can be reduced even if the liquid is discharged into public waters.
The reverse osmosis concentrate contains potassium, nitrogen, and phosphorus, which are effective as liquid fertilizer, and can be used as liquid fertilizer as is. It can also be used as dilution water to adjust the concentration of the electrodialysis concentrate, or it can be returned to the ultrafiltration and electrodialysis processes for reconcentration, among other effective uses.

Claims (10)

A method for producing a liquid fertilizer, comprising the following first to third steps:
First step: A step of subjecting an organic digestion liquid to membrane separation treatment to obtain a membrane permeate containing potassium components and nitrogen components and a dispersion containing sludge;
a second step: subjecting the membrane permeate to electrodialysis to obtain an electrodialysis desalted solution having lower concentrations of potassium components and nitrogen components than the membrane permeate, and an electrodialysis concentrate having higher concentrations of potassium components and nitrogen components than the membrane permeate;
The third step is a step of treating the electrodialysis-deionized liquid with a reverse osmosis membrane to obtain a reverse osmosis membrane permeate having lower concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid, and a reverse osmosis membrane concentrate having higher concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid. The method for producing liquid fertilizer according to claim 1, wherein the digested liquid is a digested liquid from anaerobic fermentation or a digested liquid from aerobic fermentation. The method for producing liquid fertilizer described in claim 1 or 2, wherein the sludge-containing dispersion obtained in the first step has a higher phosphorus concentration than the digested liquid. The method for producing a liquid fertilizer described in claim 1 or 2, wherein the electrodialysis concentrate obtained in the second step has a higher phosphorus concentration than the membrane permeate. The method for producing a liquid fertilizer according to claim 1 or 2, wherein the reverse osmosis membrane concentrated liquid obtained in the third step has a higher phosphorus concentration than the electrodialysis desalted liquid. A liquid fertilizer manufacturing device including the following first to third means :
First means : A means for subjecting a digested liquid of organic matter to membrane separation treatment to obtain a membrane permeate containing potassium components and nitrogen components and a dispersion containing sludge;
second means : means for subjecting the membrane permeate to electrodialysis to obtain an electrodialysis desalted solution having lower concentrations of potassium components and nitrogen components than the membrane permeate and an electrodialysis concentrated solution having higher concentrations of potassium components and nitrogen components than the membrane permeate;
Third means : A means for treating the electrodialysis-deionized liquid with a reverse osmosis membrane to obtain a reverse osmosis membrane permeate having lower concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid, and a reverse osmosis membrane concentrate having higher concentrations of potassium components and nitrogen components than the electrodialysis-deionized liquid. The liquid fertilizer manufacturing apparatus according to claim 6, wherein the digested liquid is a digested liquid from anaerobic fermentation or a digested liquid from aerobic fermentation. 8. The apparatus for producing a liquid fertilizer according to claim 6, wherein the sludge-containing dispersion obtained by the first means has a higher phosphorus concentration than the digested liquid. 8. The apparatus for producing a liquid fertilizer according to claim 6, wherein the electrodialysis concentrate obtained by the second means has a higher phosphorus concentration than the membrane permeate. 8. The apparatus for producing a liquid fertilizer according to claim 6, wherein the reverse osmosis membrane concentrated liquid obtained by the third means has a higher phosphorus concentration than the electrodialysis desalted liquid.