JP7633301B2 - Liquid fertilizer manufacturing device and liquid fertilizer manufacturing method - Google Patents

Description

The present invention relates to a liquid fertilizer production device and a liquid fertilizer production method.

Liquid fertilizers are useful for the growth of various types of plants, including grains, vegetables, fruits, flowers, etc. Liquid fertilizers contain inorganic nitrogen, which is broadly classified into (1) ammonia nitrogen, (2) nitrate nitrogen, and nitrite nitrogen.
When the production of liquid fertilizer includes a step of performing electrodialysis to concentrate fertilizer components (nitrogen, phosphate, potassium), particularly when the production of liquid fertilizer uses digested liquid of organic matter as a raw material, precipitation of inorganic components occurs when the fertilizer is concentrated near the ion exchange membrane beyond its solubility product.
For example, if the digestive fluid contains phosphoric acid and calcium, calcium phosphate will precipitate and block the ion exchange membrane.

When an ion exchange membrane becomes clogged, it is common to clean the membrane using an acidic agent. Hydrochloric acid is generally used as the acidic agent due to its cost advantage.

The use of hydrochloric acid for cleaning ion exchange membranes has been practiced in the past.
The cleaning solution generated during the cleaning process contains hydrochloric acid and is acidic, so it cannot be discharged directly into public waters.
In order to release the fertilizer, the pH must be neutralized, and the work and costs involved in the neutralization process are a disadvantage when considering improving the productivity of liquid fertilizer.
Furthermore, if the fertilizer is discharged after neutralization, the phosphoric acid contained in the washing liquid is also discharged, which poses the problem that some of the fertilizer components contained in the raw material are not utilized as liquid fertilizer.

The main objective of the present invention is to provide a liquid fertilizer production device and a liquid fertilizer production method that can utilize the cleaning liquid generated when cleaning the ion exchange membrane of the electrodialysis section as a component of liquid fertilizer.

As a result of extensive research into solving the above problems, the inventors discovered that the above problems could be solved by using nitric acid as an acidic agent to block the ion exchange membrane and using a cleaning solution containing nitric acid as a component of liquid fertilizer, which led to the invention.

That is, the present invention has the following features.
[1] A liquid fertilizer manufacturing apparatus for producing liquid fertilizer containing inorganic nitrogen using digestive liquid of organic matter as a raw material,
an electrodialysis unit for concentrating the liquid to be treated;
and a chemical cleaning mechanism for chemically cleaning the ion exchange membrane of the electrodialysis unit,
When the ion exchange membrane becomes clogged, the chemical cleaning mechanism uses nitric acid to chemically clean the ion exchange membrane.
[2] The liquid fertilizer manufacturing apparatus described in [1], which has a mechanism for returning the cleaning liquid generated during the chemical cleaning to the upstream stage of the electrodialysis section.
[3] A liquid fertilizer manufacturing apparatus as described in [1] or [2], having a mechanism for mixing the cleaning liquid generated by the chemical cleaning with the electrodialysis concentrate of the electrodialysis section.
[4] A liquid fertilizer manufacturing apparatus described in any of [1] to [3], in which the cleaning liquid generated by the chemical cleaning is utilized as a component of liquid fertilizer.
[5] A liquid fertilizer manufacturing apparatus as described in any of [1] to [3], in which the cleaning liquid generated during the chemical cleaning is not discharged to the outside.
[6] A method for producing a liquid fertilizer containing inorganic nitrogen using a digestive liquid of organic matter as a raw material, comprising:
A method for producing a liquid fertilizer, comprising the following steps (1) and (2):
Step (1): An electrodialysis step of concentrating the liquid to be treated;
Step (2): A chemical cleaning step of chemically cleaning the ion exchange membrane with nitric acid when the ion exchange membrane becomes clogged in the electrodialysis step.
[7] The liquid fertilizer production method described in [6], further comprising a step of returning the cleaning liquid generated in the chemical cleaning step to the upstream stage of the electrodialysis step.
[8] A liquid fertilizer production method according to [6] or [7], comprising a step of mixing the cleaning liquid generated in the chemical cleaning step with the electrodialysis concentrate from the electrodialysis step.
[9] A liquid fertilizer production method described in any one of [6] to [8], in which the cleaning liquid generated in the chemical cleaning process is used as a component of liquid fertilizer.
[10] A liquid fertilizer production method described in any of [6] to [8], in which the cleaning liquid generated in the chemical cleaning process is not discharged to the outside.

According to the manufacturing apparatus of the present invention, the cleaning liquid generated during cleaning of the ion exchange membrane of the electrodialysis section can be used as a component of the liquid fertilizer.
According to the manufacturing method of the present invention, there is no need to deal with the trouble of disposing of the cleaning liquid generated when cleaning the ion exchange membrane of the electrodialysis section, and the cleaning liquid can be used as a component of liquid fertilizer.

1 is a diagram showing an example of an embodiment of a liquid fertilizer manufacturing apparatus of the present invention. FIG. 2 is a diagram showing an example of operation of the liquid fertilizer manufacturing apparatus of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments.
The present invention can be implemented in various forms without departing from the spirit of the present invention. The drawings are for the purpose of explaining an example of an embodiment, and are not intended to represent the actual size.

<Liquid fertilizer manufacturing equipment>
The liquid fertilizer manufacturing apparatus of the present invention is a liquid fertilizer manufacturing apparatus that produces liquid fertilizer containing inorganic nitrogen using digested liquid of organic matter as a raw material, and has an electrodialysis section that concentrates the treated liquid, and a chemical cleaning mechanism that chemically cleans the ion exchange membrane of the electrodialysis section, and when the ion exchange membrane becomes clogged, the chemical cleaning mechanism chemically cleans the ion exchange membrane using nitric acid.

The liquid fertilizer production apparatus of the present invention preferably has an electrodialysis section and a chemical cleaning mechanism, and has a mechanism for returning the cleaning liquid to the upstream stage of the electrodialysis section, as described below, or a mechanism for mixing the cleaning liquid with the treated water from the electrodialysis section. In addition to these, it may also have equipment that is ancillary to general liquid fertilizer production apparatuses.

In FIG. 1, an electrodialysis section 40, a chemical washing mechanism 43, a first flow path 44 for the washing liquid, a second flow path 45 for the washing liquid, and a third flow path 46 for the washing liquid are shown as the equipment relating to the present invention.
In addition, as general equipment, a digestive liquid tank 10, a membrane separation section 20, a treated water tank 30, a first flow path 11, a second flow path 21, a third flow path 31, etc. are shown.

As described above, inorganic nitrogen is roughly classified into (1) ammonia nitrogen, and (2) nitrate nitrogen and nitrite nitrogen. The liquid fertilizer of the present invention is a liquid fertilizer containing the inorganic nitrogen.
Here, nitrate nitrogen refers to nitric acid or nitrates.

<Digestive fluids>
The digestive fluid used in the present invention is a digestive fluid of organic matter, and is a liquid obtained after fermentation of organic matter such as human waste.
The digestive liquid includes digestive liquid from anaerobic fermentation and digestive liquid from aerobic fermentation. The digestive liquid from anaerobic fermentation is a liquid fermented under oxygen-free conditions with air blocked off. The digestive liquid from aerobic fermentation is a liquid fermented under air aeration conditions.

<Liquid to be treated>
The liquid to be treated in the electrodialysis section may be any liquid whose raw material is digested liquid of organic matter.
Although it is possible to treat the organic digestive liquid directly in the electrodialysis section, it is preferable to carry out pretreatment before electrodialysis in order to avoid clogging of the electrodialysis section.
Examples of pretreatment include sand filtration, sedimentation, membrane separation using a membrane such as a microfiltration membrane or an ultrafiltration membrane, and a membrane bioreactor.
Among these, the membrane bioreactor is preferred because it is possible to adjust the composition ratio of inorganic nitrogen contained in the liquid fertilizer.

The membrane bioreactor is also called a "membrane separation activated sludge process."
A membrane bioreactor uses a treatment tank containing treated water and activated sludge, and a membrane such as a microfiltration membrane or an ultrafiltration membrane.
In the membrane bioreactor, the digestive liquid is treated with activated sludge, whereby nitrification by aerobic bacteria progresses and ammonia nitrogen is converted into nitrate nitrogen and nitrite nitrogen. The treated digestive liquid is filtered through the membrane, and the separated liquid that permeates the membrane is sent to the electrodialysis section.
Hereinafter, "membrane bioreactor" may be referred to as "MBR."

<Electrodialysis section>
The electrodialysis unit of the present invention concentrates the separated liquid filtered in the membrane separation unit. As the electrodialysis unit, a known electrodialysis device may be used.
An example of the electrodialysis device is DW-1 manufactured by AGC Engineering Co., Ltd.

An electrodialysis device is a device in which multiple sets of cation exchange membranes and anion exchange membranes are alternately stacked with spacers between them, with a pair of electrodes disposed at both ends, and deionization chambers (chambers D), which are spaces partitioned by the anion exchange membrane on the anode side and the cation exchange membrane on the cathode side, and concentration chambers (chambers C), which are spaces partitioned by the cation exchange membrane on the anode side and the anion exchange membrane on the cathode side, are arranged alternately.
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. At that time, the cathode side of compartment C is separated by an anion exchange membrane, so the cations 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 desalted in compartment D and concentrated in compartment C.

In the electrodialysis section, the separated liquid to be treated is separated into an electrodialysis concentrate and an electrodialysis desalted liquid. The electrodialysis concentrate has a higher salt concentration than the separated liquid before treatment, and the electrodialysis desalted liquid has a lower salt concentration than the separated liquid before treatment.

When the liquid to be treated contains phosphoric acid and calcium components, these components react with each other in the electrodialysis process to form calcium phosphate.
For example, when the liquid to be treated contains a water-soluble phosphate salt and a water-soluble calcium salt, the phosphate ions react with the calcium ions in the electrodialysis process to form water-insoluble calcium phosphate, which may adhere to the ion exchange membrane and cause clogging of the ion exchange membrane.
In order to remove calcium phosphate adhering to the ion exchange membrane, the ion exchange membrane is generally washed with an acidic agent, and hydrochloric acid has traditionally been used due to its cost advantage.

<Chemical cleaning mechanism>
The chemical cleaning mechanism of the present invention is a mechanism for chemically cleaning the ion exchange membrane of the electrodialysis section, and is a mechanism for chemically cleaning the ion exchange membrane by using nitric acid when the ion exchange membrane is clogged.
The chemical cleaning mechanism may be any mechanism capable of detecting clogging of the ion exchange membrane and supplying a required amount of nitric acid when the ion exchange membrane is clogged, and may be an automatic cleaning mechanism or a manual cleaning mechanism.
The chemical cleaning mechanism must be resistant to nitric acid, but in other respects, any known mechanism may be used.

<Nitric acid>
The nitric acid used in the chemical cleaning mechanism is not particularly limited, and any commercially available nitric acid may be used.
The purity of the nitric acid is not particularly limited.
The concentration of nitric acid is not particularly limited, but is preferably 0.5 to 5 mass % from the viewpoints of the chemical resistance of the members used in the electrodialysis unit, including the ion exchange membrane, and the cleaning effect of the liquid-contacting parts of the electrodialysis unit.

<Cleaning solution>
The cleaning solution obtained in the present invention is obtained by cleaning the ion exchange membrane of the electrodialysis unit with nitric acid, and contains as its components phosphate ions and calcium ions produced by dissolving calcium phosphate, which was a blockage in the ion exchange membrane, and nitrate ions. Because nitric acid is used, the cleaning solution is acidic.
In this example, the blocking material in the ion exchange membrane is calcium phosphate, but the blocking material is not limited to calcium phosphate. Depending on the components contained in the digestive fluid, magnesium phosphate, calcium carbonate, etc. may become blocking material, and the components contained in the cleaning fluid are various.

Nitrate ions are nitrate nitrogen, which is one of the inorganic nitrogens contained in liquid fertilizers, and phosphate ions are phosphorus components that are useful as fertilizer components, so the cleaning solution obtained in the present invention contains components that are useful as liquid fertilizers, and therefore this cleaning solution can also be used as liquid fertilizer.
Conventional cleaning solutions using hydrochloric acid contain chloride ions, making them unsuitable as fertilizers, and it has been difficult to use them as liquid fertilizers.
To utilize the cleaning solution of the present invention as a liquid fertilizer, the cleaning solution may be returned to the upstream stage of the electrodialysis section, or may be mixed with the concentrated electrodialysis solution in the electrodialysis section.

The cleaning liquid may be returned to the upstream stage of the electrodialysis section, for example, to the digestive liquid tank 10 shown in FIG. 1, to the membrane separation section 20, or to the treated water tank 30.
The place where the cleaning liquid is returned is not limited, and may be any place upstream of the electrodialysis section.

When returning the cleaning liquid to the membrane separation section 20, a mechanism for returning the cleaning liquid to the membrane separation section 20, such as the first flow path 44 for the cleaning liquid shown in FIG.
When the cleaning liquid is returned to the membrane separation section 20, the cleaning liquid is acidic and may affect the treatment in the membrane separation section.
For example, when the membrane separation unit is an MBR, returning the acidic washing liquid may cause the pH of the digestive liquid in the MBR to fluctuate, which may affect the progress of nitrification in the MBR. Conversely, when the pH of the digestive liquid in the MBR is high (alkaline), the acidic washing liquid can be used as a pH adjuster.

In the case where the cleaning liquid is returned to the treated water tank 30, a mechanism for returning the cleaning liquid to the treated water tank 30, as represented by the second cleaning liquid flow path 45 shown in FIG.
When returning the cleaning liquid to the treated water tank 30, it is preferable to design the tank so that it is not affected by the fact that the cleaning liquid is acidic. For example, this can be achieved by increasing the capacity of the treated water tank and by monitoring the pH in the treated water tank to control the timing of returning the cleaning liquid.
After the cleaning solution is returned to the treated water tank, no special treatment is required, and it may be sent directly to the electrodialysis section for electrodialysis treatment.

When the cleaning liquid is mixed with the electrodialysis concentrate in the electrodialysis section, a mechanism for mixing the cleaning liquid with the electrodialysis concentrate, as represented by the third cleaning liquid flow path 46 shown in FIG. 1, may be provided.
When the cleaning solution is mixed with the electrodialysis concentrate, the pH of the resulting liquid fertilizer may fluctuate because the cleaning solution is acidic. However, since the effect of the pH fluctuation of the electrodialysis concentrate is small, there is no need to adjust the pH of the electrodialysis concentrate.

In order to utilize the cleaning solution of the present invention as liquid fertilizer, it is preferable to return the cleaning solution to the treated water tank 30 since the cleaning solution is not affected by its acidity and does not require any special treatment.
As described above, the liquid fertilizer manufacturing apparatus of the present invention is characterized in that the cleaning liquid generated during chemical cleaning is utilized as a component of liquid fertilizer.
The liquid fertilizer manufacturing apparatus of the present invention is also characterized in that the cleaning liquid generated during the chemical cleaning is not discharged to the outside.

<Liquid fertilizer manufacturing method>
The liquid fertilizer production method of the present invention is a liquid fertilizer production method for producing a liquid fertilizer containing inorganic nitrogen using a digestive liquid of organic matter as a raw material, and includes the following steps (1) and (2):
Step (1): An electrodialysis step of concentrating the liquid to be treated;
Step (2): A chemical cleaning step of chemically cleaning the ion exchange membrane with nitric acid when the ion exchange membrane becomes clogged in the electrodialysis step.

<Step (1)>
Step (1) is an electrodialysis step for concentrating the liquid to be treated, and its gist is the same as that of the "electrodialysis section" explained in the section on the liquid fertilizer production apparatus.
On the other hand, as is clear from the fact that it is referred to as an electrodialysis step rather than an electrodialysis unit in step (1), the electrodialysis step does not refer to a specific facility called an electrodialysis unit, but includes the operation and act of electrodialysis.

<Step (2)>
Step (2) is a chemical cleaning step in which nitric acid is used to chemically clean the ion exchange membrane when it becomes clogged during the electrodialysis step. The gist of this step is the same as the "chemical cleaning mechanism" described in the section on the liquid fertilizer production equipment.
On the other hand, as is clear from the fact that it is referred to as a chemical cleaning process rather than a chemical cleaning mechanism in process (2), the chemical cleaning process does not refer to a specific piece of equipment called a chemical cleaning mechanism, but rather includes the operation and act of chemical cleaning.

<Step of returning the cleaning solution to the front stage of the electrodialysis step>
The purpose of the process of returning the cleaning liquid to the upstream stage of the electrodialysis process is the same as that explained in the section on the liquid fertilizer manufacturing apparatus.
On the other hand, in the invention of the liquid fertilizer manufacturing method, as is clear from the term "process," the process of returning the cleaning liquid to the upstream stage of the electrodialysis section does not refer to a specific facility for returning the cleaning liquid to the upstream stage of the electrodialysis process, but includes the operation of returning the cleaning liquid to the upstream stage of the electrodialysis process and the act of returning the cleaning liquid to the upstream stage of the electrodialysis process.

<Step of blending the cleaning solution with the electrodialysis concentrate from the electrodialysis step>
The purpose of the process of mixing the cleaning liquid with the electrodialysis concentrate is the same as that described in the section on the liquid fertilizer production apparatus.
On the other hand, in the invention of the liquid fertilizer production method, as is clear from the term "step," the step does not refer to a specific facility for mixing the cleaning liquid with the electrodialysis concentrate, but includes the operation of mixing the cleaning liquid with the electrodialysis concentrate and the act of mixing the cleaning liquid with the electrodialysis concentrate.

As described above, the liquid fertilizer production method of the present invention is characterized in that the cleaning liquid generated during chemical cleaning is utilized as a component of the liquid fertilizer.
Furthermore, the liquid fertilizer manufacturing method of the present invention is characterized in that the cleaning liquid generated during the chemical cleaning is not discharged to the outside.

<Liquid fertilizer>
The liquid fertilizer of the present invention is obtained by the liquid fertilizer production apparatus or the liquid fertilizer production method of the present invention, and contains inorganic nitrogen.
In addition to the inorganic nitrogen, the liquid fertilizer may contain other additives that are generally used as fertilizers.

<Applications>
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 culture or hydroponic culture depending on the growing conditions and type of plant.

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

[Evaluation method]
(1) Electrical Conductivity Electrical conductivity was measured using "HE-480H" manufactured by Horiba, Ltd.

[Example]
The raw water used was a digestive liquid of organic matter, which was a digestive liquid derived from aerobic fermentation of human waste.
As the membrane separation section, a water tank having a volume of 2 ^m3 and equipped with an ultrafiltration membrane manufactured by Mitsubishi Chemical Corporation (membrane material: polyvinylidene fluoride, nominal pore size: 0.05 μm, membrane shape: hollow fiber) was used.
The digestive liquid was poured into a water tank and the ultrafiltration membrane was immersed in the digestive liquid. In this state, continuous suction filtration was performed to separate the separated liquid filtered through the ultrafiltration membrane from a dispersion containing sludge that was not filtered.
The electrical conductivity of the separated liquid was 7 mS/cm. The electrical conductivity of the separated liquid is proportional to the concentration of dissolved components such as nitrogen, phosphoric acid, and potassium, which are useful components of the liquid fertilizer.
The separated liquid obtained was stored in a treated water tank.

The separated liquid was treated as water to be treated with an electrodialysis device "DW-1 type" (cation ion exchange membrane: CMVN, anion ion exchange membrane: AMVN) manufactured by AGC Engineering Co., Ltd. The electrodialysis voltage was set to 13 to 15 V, and the separated liquid was separated into an electrodialysis concentrate and an electrodialysis desalted liquid.
The electrodialysis desalted liquid was returned to the treated water tank at a flow rate of 1.1 m ³ /h for circulating operation.

As shown in Figure 2, continuous operation of electrodialysis was started on June 8, 2022. The electrodialysis voltage at this time was 15V.
As the operation continued, the concentration ratio calculated from the electrical conductivity (EC concentration ratio) tended to decrease. This decrease in concentration ratio was due to the clogging of the ion exchange membrane of the electrodialysis device. When the ion exchange membrane was clogged, no liquid flowed out to the electrodialysis concentrate side, and the concentration ratio decreased.

When the electrical conductivity of the electrodialysis concentrate had decreased to 46.1 mS/cm and the EC concentration rate had reached 6.6 times, the operation of the electrodialysis apparatus was stopped.
50 L of an aqueous solution of nitric acid having a concentration of 1.5% by mass was prepared, and the solution was circulated between the outlet of the concentrated liquid side of the electrodialysis device and the inlet of the electrodialysis device, thereby chemically cleaning the ion exchange membrane.
Thereafter, the electrodialysis was washed with water, washed with a 1% by mass aqueous NaOH solution, and washed with water again, and then the continuous operation of electrodialysis was resumed at a voltage of 13 V. When the electrodialysis concentrate was resumed, the electrical conductivity was 81.6 mS/cm, and the EC concentration rate had recovered to 11.7 times, confirming that the clogging of the ion exchange membrane was eliminated by the nitric acid washing. Details are shown in Table 1 and FIG. 2.

Continuing the operation, the ion exchange membrane was chemically cleaned using a 2% by mass aqueous solution of nitric acid on August 24th. On September 26th, the ion exchange membrane was chemically cleaned using a 1% by mass aqueous solution of nitric acid. In both cases, the EC concentration ratio was restored when operation was resumed after the chemical cleaning, and it was confirmed that the blockage of the ion exchange membrane was eliminated by cleaning with nitric acid at various concentrations.

The operation was continued, and on November 14, the ion exchange membrane was chemically washed using a 3% by mass aqueous hydrochloric acid solution. The EC concentration ratio recovered when operation was resumed after the chemical washing. Since there was no difference in the degree of recovery between washing with nitric acid and washing with hydrochloric acid, it was confirmed that the blockage of the ion exchange membrane could be eliminated even when nitric acid was used, just as in the case of using conventional hydrochloric acid.
In addition, it was confirmed that when an ion exchange membrane is cleaned with nitric acid, the cleaning solution contains components that are useful as liquid fertilizer, and therefore the cleaning solution can be used as liquid fertilizer.

REFERENCE SIGNS LIST 10 Digested liquid tank, 11 First flow path 20 Membrane separation section (MBR), 21 Second flow path, 22 Sludge extraction flow path 30 Treated water tank, 31 Third flow path 40 Electrodialysis section, 41 Electrodialysis desalted liquid flow path, 42 Electrodialysis concentrated liquid flow path, 43 Chemical washing mechanism, 44 First flow path for washing liquid, 45 Second flow path for washing liquid, 46 Third flow path for washing liquid

Claims (14)

A liquid fertilizer manufacturing apparatus that produces liquid fertilizer containing inorganic nitrogen using digestive liquid of organic matter as a raw material,
an electrodialysis unit for concentrating the liquid to be treated;
a chemical cleaning mechanism for chemically cleaning the ion exchange membrane of the electrodialysis unit;
A mechanism for returning the cleaning liquid generated in the chemical cleaning to a stage upstream of the electrodialysis unit ,
When the ion exchange membrane becomes clogged, the chemical cleaning mechanism uses nitric acid to chemically clean the ion exchange membrane. A liquid fertilizer manufacturing apparatus that produces liquid fertilizer containing inorganic nitrogen using digestive liquid of organic matter as a raw material,
an electrodialysis unit for concentrating the liquid to be treated;
a chemical cleaning mechanism for chemically cleaning the ion exchange membrane of the electrodialysis unit;
a mechanism for mixing the cleaning solution generated by the chemical cleaning with the electrodialysis concentrate discharged from the electrodialysis unit,
When the ion exchange membrane becomes clogged, the chemical cleaning mechanism uses nitric acid to chemically clean the ion exchange membrane . 3. The liquid fertilizer manufacturing apparatus according to claim 1, wherein the liquid to be treated is concentrated in the electrodialysis section and separated into an electrodialysis concentrated liquid containing the inorganic nitrogen and an electrodialysis desalted liquid containing the inorganic nitrogen. A membrane separation unit capable of adjusting the composition ratio of the inorganic nitrogen contained in the liquid fertilizer is further provided in the upstream of the electrodialysis unit,
The liquid fertilizer manufacturing apparatus according to claim 1 , wherein the mechanism for returning the cleaning solution to the upstream stage of the electrodialysis unit is a mechanism for returning the cleaning solution to the membrane separation unit. Further provided is a membrane separation unit capable of adjusting the composition ratio of the inorganic nitrogen contained in the liquid fertilizer in the upstream of the electrodialysis unit, and a treated water tank for storing the separated liquid obtained in the membrane separation unit between the electrodialysis unit and the membrane separation unit,
The liquid fertilizer manufacturing apparatus according to claim 1 , wherein the mechanism for returning the cleaning solution to the upstream stage of the electrodialysis unit is a mechanism for returning the cleaning solution to the treated water tank. The liquid fertilizer manufacturing apparatus according to claim 1 , further comprising a mechanism for mixing the cleaning liquid generated in the chemical cleaning with the electrodialysis concentrate discharged from the electrodialysis section. The liquid fertilizer manufacturing apparatus according to claim 1 or 2 , wherein the cleaning liquid generated in the chemical cleaning is utilized as a component of liquid fertilizer. The liquid fertilizer manufacturing apparatus according to claim 1 or 2 , wherein the cleaning liquid generated during the chemical cleaning is not discharged to the outside. A liquid fertilizer production method for producing liquid fertilizer containing inorganic nitrogen using digestive liquid of organic matter as a raw material,
an electrodialysis step of concentrating the liquid to be treated;
and a chemical cleaning step of chemically cleaning the ion exchange membrane with nitric acid when the ion exchange membrane is clogged in the electrodialysis step .
A liquid fertilizer manufacturing method, in which the cleaning liquid generated in the chemical cleaning step is utilized as a component of liquid fertilizer. The method for producing a liquid fertilizer according to claim 9, wherein in the electrodialysis step, the liquid to be treated is concentrated and separated into an electrodialysis concentrated liquid containing the inorganic nitrogen and an electrodialysis desalted liquid containing the inorganic nitrogen. The liquid fertilizer manufacturing method according to claim 9 or 10 , further comprising a step of returning the cleaning liquid generated in the chemical cleaning step to a stage preceding the electrodialysis step. The liquid fertilizer manufacturing method according to claim 11, wherein in the step of returning the cleaning liquid to an upstream stage of the electrodialysis step, the pH of the liquid to be treated is monitored to control the timing of returning the cleaning liquid. The method for producing a liquid fertilizer according to claim 9 or 10 , further comprising a step of mixing the cleaning liquid generated in the chemical cleaning step with the electrodialysis concentrate in the electrodialysis step. The liquid fertilizer manufacturing method according to claim 9 or 10 , wherein the cleaning liquid generated in the chemical cleaning step is not discharged to the outside.

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