Manufacturing method of liquid fertilizer

Abstract

To provide a manufacturing method of a liquid fertilizer of high nitrogen concentration.SOLUTION: A manufacturing method of liquid fertilizer includes the steps of: supplying organic waste to a methane fermentation tank to which anaerobic microbes are provided; agitating and mixing the supplied organic waste and the anaerobic microbes; measuring pH of a methane fermentation liquid including the agitated and mixed organic waste; and adjusting, based on a value of the measured pH, the methane fermentation liquid to be of pH 6.50-7.30 by supplying acid to the methane fermentation tank.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing liquid fertilizer. [Background technology]

[0002] Conventionally, there is known a technology for obtaining methane gas and liquid fertilizer (liquid fertilizer) by methane fermentation from organic waste such as food waste, livestock manure, and sewage sludge. This technology is useful from the viewpoints of waste treatment, effective use of resources, carbon neutrality, etc., and has been extensively studied.

[0003] In methane fermentation, organic waste is broken down by anaerobic microorganisms into a mixed gas (biogas) that mainly contains methane gas and carbon dioxide gas, and a digestive liquid (fermentation residue). The methane fermentation liquid in the fermentation process and the methane fermentation digestive liquid from which the mixed gas has been extracted after the fermentation process contain a lot of nitrogen (ammonia nitrogen) derived from the organic waste, and the digestive liquid in particular is useful as liquid fertilizer.

[0004] Patent Document 1 discloses "a method for producing liquid fertilizer from organic waste, comprising: a methane fermentation step of subjecting waste liquid containing the organic waste to methane fermentation; a nitrification step of nitrifying ammonia nitrogen in the waste liquid after the methane fermentation into nitrite nitrogen or nitrate nitrogen using nitrifying bacteria; and a denitrification step of denitrifying the waste liquid after the nitrification using a denitrifying microorganism." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-23890 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional methane fermentation methods have focused on improving the treatment speed of organic waste, but have run into the problem of rancidity, which is the accumulation of organic acids (acetic acid, butyric acid, propionic acid, etc.) produced in the fermentation process due to excessive input of raw organic waste. When rancidity occurs, methane fermentation stops, so measures have been taken such as diluting the waste with a large amount of water or adding a base.

[0007] On the other hand, even if the raw material is not excessively charged, the concentration of ammonia nitrogen in the fermentation liquid increases with fermentation, causing the methane fermentation to stop. In this case, as with rancidity, it is necessary to take measures such as diluting the liquid with a large amount of water.

[0008] For practical use as a fertilizer, it is desirable for the methane fermentation digestate to have a high nitrogen concentration. However, in reality, the above-mentioned ammonia inhibition problem has been an obstacle to producing a liquid fertilizer with a high nitrogen concentration.

[0009] An object of the present invention is to provide a method for producing liquid fertilizer having a high nitrogen concentration. [Means for solving the problem]

[0010] Means for solving the above problems include the following aspects. <1> A method for producing liquid fertilizer, comprising the steps of: supplying organic waste to a methane fermentation tank in which anaerobic microorganisms are placed; stirring and mixing the supplied organic waste with the anaerobic microorganisms; measuring the pH of a methane fermentation liquid containing the stirred and mixed organic waste; and, based on the measured pH value, supplying an acid to the methane fermentation tank to adjust the pH to 6.50 to 7.30. <2> The method further includes a step of removing a mixed gas containing methane gas from the methane fermenter. <1> A method for producing a liquid fertilizer according to the above. <3> The total ammonia nitrogen (TAN) concentration of the methane fermentation liquid is 3,000 mg / L.-1 ~15,000mgL -1 That is, <1> or <2> A method for producing a liquid fertilizer according to the above. Effect of the Invention

[0011] According to one embodiment of the present invention, a method for producing a liquid fertilizer with a high nitrogen concentration is provided. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of a liquid fertilizer production apparatus using the liquid fertilizer production method of the present invention. [Diagram 2] Fig. 2 is a plot showing the relationship between the total ammonia nitrogen (TAN) concentration of the methane fermentation liquid and time (right vertical axis). Fig. 2 is a plot showing the relationship between the amount of methane gas produced and time in the liquid fertilizer production method of the present invention (left vertical axis). [Diagram 3] FIG. 3 is a plot showing the relationship between pH of the methane fermentation liquid and time in the method for producing a liquid fertilizer of the present invention. [Figure 4] FIG. 4 is a plot showing the relationship between the amount of methane gas produced and the total ammonia nitrogen (TAN) concentration in the method for producing a liquid fertilizer of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present invention will be described. The description is for illustrating the embodiments, and is not intended to limit the scope of the present invention.

[0014] In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present embodiment, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in the present embodiment. In addition, in the numerical ranges described in the present embodiment, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

[0015] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0016] In this specification, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

[0017] In the present specification, each component may contain a plurality of corresponding substances. In the present embodiment, when the amount of each component in the composition is mentioned, in the case where a plurality of substances corresponding to each component are present in the composition, the amount means the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0018] As used herein, the term "methane fermentation liquor" encompasses methane fermentation liquor containing organic waste undergoing a methane fermentation process, and liquid fertilizer.

[0019] As used herein, the term "pH" refers to the pH at a temperature of 37°C.

[0020] In this specification, the term "high nitrogen concentration" refers to a total ammonia nitrogen (TAN) concentration of 3,000 mg L -1 ~15,000mgL -1 This means that.

[0021] <How to make liquid fertilizer> The method for producing a liquid fertilizer of the present invention comprises: The method includes a step of supplying organic waste to a methane fermentation tank containing anaerobic microorganisms (hereinafter also referred to as the "organic waste supplying step"); a step of stirring and mixing the supplied organic waste with the anaerobic microorganisms (hereinafter also referred to as the "stirring and mixing step"); a step of measuring the pH of the methane fermentation liquid containing the stirred and mixed organic waste (hereinafter also referred to as the "pH measuring step"); and a step of supplying an acid to the methane fermentation tank based on the measured pH value to adjust the pH to 6.50 to 7.30 (hereinafter also referred to as the "pH adjusting step"). By including the above steps, a liquid fertilizer with a high nitrogen concentration can be obtained. The reason for this is presumed to be as follows.

[0022] In the method for producing liquid fertilizer of the present invention, the pH of the methane fermentation liquid containing organic waste is adjusted to 6.50 to 7.30. At pH 6.50 to 7.30, rancidity is unlikely to occur. On the other hand, since pH 6.50 to 7.30 is a weakly acidic to neutral to weakly basic condition, the concentration of free ammonia nitrogen (FAN), which is considered to have stronger inhibitory toxicity among ammonia inhibition, is lower than that in the case of conventional basic conditions. Therefore, in the method for producing liquid fertilizer of the present invention, since the resistance to ammonia inhibition is improved, the methane fermentation process is likely to proceed smoothly even at high nitrogen concentrations, and it is presumed that a methane fermentation liquid (i.e., liquid fertilizer) with a high nitrogen concentration can be obtained. In addition, under the weakly acidic to neutral to weakly basic conditions of pH 6.50 to 7.30, free ammonia nitrogen (FAN) is likely to remain in the methane fermentation liquid as a non-volatile salt without volatilization, and this is also presumed to improve the nitrogen concentration in the methane fermentation liquid.

[0023] Here, FIG. 1 is a schematic diagram showing an example of a liquid fertilizer manufacturing apparatus using the liquid fertilizer manufacturing method of the present invention. The liquid fertilizer manufacturing apparatus shown in FIG. 1 includes a methane fermentation tank 4, which includes an organic waste supplying means 2, an agitation means 5, a pH measuring means 6, and an acid supplying means 7. The organic waste supplying means 2 is connected to an organic waste storage container 1, and supplies organic waste from the organic waste storage container 1 to the methane fermentation tank 4. The acid supplying means 7 is connected to an acid storage container 9, and is configured to supply acid from the acid storage container 9 to the methane fermentation tank 4 upon receiving a command from a control unit 8 electrically connected to the pH measuring means 6. The methane fermentation tank 4 is connected to the outside and a liquid fertilizer storage container 10 via a line, and after the completion of methane fermentation, the mixed gas and liquid fertilizer are taken out, respectively.

[0024] The production method of the present invention will be described in detail below.

[0025] (Organic waste supply process) In the organic waste supply step, the organic waste is supplied to a methane fermentation tank in which anaerobic microorganisms are placed.

[0026] The organic waste may be supplied by an organic waste supply means from an organic waste storage container to a methane fermentation tank in which anaerobic microorganisms are placed (see FIG. 1).

[0027] -Organic waste- Examples of organic waste include food waste, food residues, livestock manure, sewage sludge, and the like.

[0028] The total solids (TS) concentration of the organic waste is preferably 6% to 10% by mass relative to 100% by mass of the organic waste. With a TS concentration of 6% to 10% by mass, the fluidity and stirrability of the methane fermentation liquid containing the organic waste are improved, which makes the methane fermentation process easier. TS is a value obtained by drying the organic waste at 105°C for 24 hours using a dryer (for example, a constant temperature dryer ONW-600S, manufactured by AS ONE Corporation), and then measuring the mass difference before and after drying.

[0029] The moisture content of the organic waste is preferably 90% to 94% by mass relative to 100% by mass of the organic waste. With a moisture content of 90% to 94% by mass, the fluidity and stirrability of the methane fermentation liquid containing the organic waste are improved, which makes it easier to carry out the methane fermentation process smoothly. The moisture content is a value calculated by 100-TS (% by mass).

[0030] The C / N ratio of the organic waste is preferably 6 to 20. When the C / N ratio of the organic waste is within the above range, the total ammonia nitrogen (TAN) concentration in the methane fermentation liquid does not become too high, and the influence of ammonia inhibition is easily reduced. On the other hand, the total ammonia nitrogen (TAN) concentration does not become too low, and the nitrogen concentration of the methane fermentation liquid (liquid fertilizer) is easily improved. The C / N ratio can be determined by analyzing the organic waste that has been left to stand for 48 hours or more in an environment of 60°C, and then finely pulverized and homogenized with an elemental analyzer (e.g., vario EL cube, manufactured by elementar).

[0031] -Organic waste storage container- When organic waste is supplied from an organic waste storage container to a methane fermentation tank in which anaerobic microorganisms are placed by an organic waste supplying means, the shape, size, etc. of the organic waste storage container are not particularly limited as long as it is capable of storing organic waste. The organic waste storage container may be equipped with a stirring means for stirring the organic waste. The organic waste storage container may be equipped with a temperature control means for eliminating the influence of decay of the stored organic waste on the methane fermentation process. The organic waste storage container may be kept at a low temperature, for example, 4°C to 5°C.

[0032] -Means of supplying organic waste- When organic waste is supplied from an organic waste storage container to a methane fermentation tank in which anaerobic microorganisms are placed by an organic waste supplying means, the shape, size, etc. of the organic waste supplying means are not particularly limited as long as it can supply organic waste. It is preferable that the organic waste supplying means is linked to a control unit for controlling the supply amount of organic waste. Examples of the organic waste supplying means include a metering pump.

[0033] The amount of organic waste to be fed is the organic load based on the ignition loss VS (VS: Volatile Solid) standard for the methane fermentation tank. For example, 20.0 g-VSL -1 d -1 The VS is a value that can be determined by drying organic waste at 105°C for 24 hours, heating it in a muffle furnace (e.g., FO300, manufactured by Yamato Scientific Co., Ltd.) at 600°C for 2 hours, and then measuring the difference in mass before and after heating.

[0034] The amount of organic waste fed to the methane fermentation tank is also cr At a standard organic load, for example, 20g-COD cr L -1 d -1 The following is the result.

[0035] -Methane fermentation tank- The shape, size, etc. of the methane fermentation tank are not particularly limited. The material is preferably one with excellent chemical resistance because the liquid properties of the methane fermentation liquid containing organic waste change. For example, it may be a tank-type reactor made of polyvinyl chloride. The methane fermentation tank is preferably equipped with a temperature control means from the viewpoint of controlling the methane fermentation process. An example of the temperature control means is a heat exchanger. In addition, anaerobic microorganisms are placed in the methane fermentation tank in the liquid fertilizer manufacturing method of the present invention. The methane fermentation tank may be placed with small amounts of elements such as iron, selenium, cobalt, and molybdenum for the metabolism of the anaerobic microorganisms.

[0036] -Anaerobic microorganisms- The anaerobic microorganism is preferably an anaerobic bacterium, and the anaerobic bacterium is preferably a hydrolytic / acid-fermenting bacterium, a symbiotic acetogen, or a methanogen.

[0037] (Stirring and mixing process) In the stirring and mixing step, the supplied organic waste and anaerobic microorganisms are stirred and mixed.

[0038] Stirring and mixing may be performed by a known stirring means (see FIG. 1). Stirring and mixing brings the organic waste into contact with anaerobic microorganisms, accelerating the methane fermentation process. Stirring and mixing is also preferable from the viewpoint of controlling the fermentation process, since it can homogenize the liquid properties and temperature distribution of the methane fermentation liquid containing the organic waste. Stirring and mixing is preferably performed under anaerobic conditions in order to promote the activity of anaerobic microorganisms.

[0039] The stirring speed of the methane fermentation liquid containing organic waste and the anaerobic microorganisms is, for example, 100 rpm to 150 rpm. When the stirring speed of the organic waste and the anaerobic microorganisms is within the above range, the generation of scum (sludge) is easily suppressed.

[0040] From the viewpoint of progressing the methane fermentation process and promoting the activity of methanogens, the temperature when stirring the methane fermentation liquid containing organic waste with the anaerobic microorganisms is preferably in the mid-temperature range of 35° C. to 37° C. or in the high-temperature range of 55° C. to 57° C. In particular, a temperature of 35° C. to 37° C. in the mid-temperature range is more preferable because it reduces the concentration of free ammonia nitrogen (FAN), which is considered to have the strongest inhibitory toxicity among ammonia inhibition.

[0041] (pH measurement process) In the pH measurement step, the pH of the methane fermentation liquid containing the organic waste that has been stirred and mixed is measured.

[0042] The pH may be measured using a pH measuring means (see FIG. 1). Examples of the pH measuring means include a known pH meter. It is preferable that the pH measuring means is linked to a control unit that issues an acid supply command to the acid supply means according to the measured pH value.

[0043] From the viewpoint of controlling the liquid properties of the methane fermentation liquid containing organic waste, it is preferable to measure pH frequently. -1 , preferably once every 5 hours -1 , and more preferably once every 0.5 hours -1 is the frequency.

[0044] (pH adjustment process) In the pH adjustment step, an acid is supplied to the methane fermentation tank based on the measured pH value to adjust the pH to 6.50 to 7.30. The pH is preferably adjusted to 6.60 to 7.20, more preferably 6.70 to 7.10, and even more preferably 6.80 to 7.00.

[0045] In the pH adjustment step, an acid supplying means may be used (see FIG. 1).

[0046] -acid- The acid may be an inorganic acid or an organic acid. Among them, inorganic acids are preferred from the viewpoint of avoiding influence on the methane fermentation process. Examples of inorganic acids include hydrochloric acid, phosphoric acid, and sulfuric acid. These acids may be used alone or in combination of two or more kinds, as long as the effects of the present invention are not impaired.

[0047] -Acid supply means- When an acid supplying means is used in the pH adjustment step, the shape, size, etc. of the acid supplying means are not particularly limited as long as it can supply acid. Examples of the acid supplying means include a metering pump. It is preferable that the acid supplying means is controlled to supply acid based on the measured pH value to adjust the pH to 6.50 to 7.30, preferably 6.60 to 7.20, more preferably 6.70 to 7.10, and even more preferably 6.80 to 7.00. It is preferable that the acid supplying means is linked to the pH measuring means and linked to a control unit that issues commands according to the measured pH value. The control unit may be linked to a recording unit, etc.

[0048] In the liquid fertilizer manufacturing method of the present invention, after the organic waste supplying step, the stirring and mixing step, the pH measuring step, and the pH adjusting step may be performed in parallel. In addition, the liquid fertilizer manufacturing method of the present invention may be completed as appropriate while observing the progress of the methane fermentation process. Upon completion, the hydraulic retention time (HRT: Hydraulic Retention Time) of the methane fermentation liquid is not particularly limited, but is preferably 10 to 60 days, more preferably 15 to 40 days, and even more preferably 20 to 30 days under the conditions of a medium temperature range of 35°C to 37°C and a pH of 6.50 to 7.30. The liquid fertilizer may be completed as appropriate with reference to the total ammonia nitrogen (TAN: Total Ammonium Nitrogen) concentration, the free ammonia nitrogen (FAN: Free Ammonia Nitrogen) concentration, or the amount of mixed gas produced.

[0049] -Methane fermentation liquid (liquid fertilizer)- The total ammonia nitrogen (TAN) concentration of the methane fermentation liquid is preferably 3,000 mg / L from the viewpoint of producing a liquid fertilizer with a high nitrogen concentration. -1 ~15,000mgL -1 , more preferably 5,000 mgL -1 ~12,500mgL -1 , and more preferably 7,000 mgL -1 ~11,000mgL -1The total ammonia nitrogen (TAN) concentration of the methane fermentation liquid can be measured, for example, by ion chromatography.

[0050] After the process is completed, the methane fermentation liquid can be removed from the methane fermenter as liquid fertilizer. The liquid fertilizer may be stored, for example, in a liquid fertilizer storage container (see FIG. 1).

[0051] According to the method described above, the present invention can provide a method for producing liquid fertilizer with a high nitrogen concentration.

[0052] (Mixed gas extraction process) In addition, the method for producing a liquid fertilizer of the present invention may further include a step of extracting a mixed gas containing methane gas from the methane fermentation tank.

[0053] The method of extracting the mixed gas is not particularly limited. For example, the mixed gas may be extracted through a line (see FIG. 1). By including the mixed gas extraction step, the extracted mixed gas can be used in a combustion facility, gas power generation, etc. The extracted mixed gas may be temporarily stored in a mixed gas storage container, for example, and then may be used in a combustion facility, gas power generation, etc. after desulfurization measures, etc. are taken. EXAMPLES

[0054] Hereinafter, the embodiments of the present invention will be further described with reference to examples, but the embodiments of the present invention are not limited to these.

[0055] - Preparation of organic waste - We used simulated food waste as organic waste. The simulated food waste was made by mixing 200g of cabbage, 42.4g of ground beef and pork, 60.6g of udon noodles, and 200mL of pure water in a blender (HGB2WTS3 Blender, FMI) for 20 seconds, then put into a 500mL i-boy and frozen. The composition was 66% cabbage, 14% ground beef and pork, and 20% udon noodles. After thawing, the organic load was 2g-VSL -1 d -1In order to promote the growth of methanogens, the metal element (Fe: 100 mg / L -1 , Co: 1 mg L -1 , Mo: 5 mg L -1 , Ni: 5 mg L -1 ) was added. Because a preliminary study had confirmed that the long fibers of cabbage would cause clogging of the tubing pump, the thawed simulated food waste was crushed in a homogenizer (Hiscotron NS-52K, Microtech Nithion) until no long cabbage fibers were detected. The composition values ​​of the simulated food waste are shown in Table 1. The total solids concentration TS of the simulated food waste was measured by drying it at 105°C for 24 hours in a dryer (constant temperature dryer ONW-600S, AS ONE) and measuring the mass difference. The VS value was measured by drying it at 105°C for 24 hours, then introducing it into a muffle furnace (FO300, Yamato Scientific) at 600°C for 2 hours and measuring the mass difference. The moisture content of the simulated food waste was also measured with a moisture meter (MX50, AS ONE). TS, VS and moisture content were all measured after mixing in a blender and before freezing and storing.

[0056] [Table 1]

[0057] - Preparation of anaerobic microorganisms - To contain anaerobic microorganisms, a mixture of 3 L each of methane fermentation digested liquid made from cow manure (Yamaga Biomass Center, Kumamoto Prefecture) and digested liquid made from food waste (Tokyo Gas, Tokyo) was prepared. Before starting the measurements, the mixture was pre-fermented for 3 months to allow the methanogens to acclimate.

[0058] -Preparing the fermentation tank- A fermentation tank with a total volume of 9.6 L and an effective reaction volume of 6 L was made from a polyvinyl chloride pipe of VU200 (inner diameter 194 mm and inner diameter 97 mm). The fermentation tank was installed so that the ports connected to the outside (stirrer, pH meter installation part and gas-liquid separation tube) were below the liquid level to maintain an anaerobic state. The fermentation tank was kept at a temperature of 37°C, which is the temperature range for mesophilic methane fermentation, by using a heater (silicon belt heater V-5-100V-150W, Yagami) wrapped directly around the fermentation tank and a heater (ribbon heater R1111, Sansho) installed on the outside of the fermentation tank, set at 40°C and 30°C, respectively. The fermentation tank was covered with polyurethane insulation, and an acrylic box was placed over the entire fermentation apparatus. Furthermore, the parts in contact with the outside were sealed with piping putty to maintain a constant temperature.

[0059] <Example 1> The amount of simulated food waste fed to a methane fermentation tank containing anaerobic microorganisms is the organic matter load on the methane fermentation tank, and is 2g-VSL based on the ignition loss VS (Volatile Solids) standard. -1 d -1 The simulated food waste was supplied by controlling the flow rate so that the simulated food waste was fed 10 times per day and setting the pump timer (Digital Daily Time Switch H5F, Omron). A tubing pump (Tubing Pump TP-20SA, AS ONE) was used to supply the simulated food waste. To prevent the effects of decay, the container containing the simulated food waste was placed in a refrigerator and the temperature was maintained at 4°C. To prevent the generation of scum, the container containing the simulated food waste was constantly stirred with an agitator at a rotation speed of 200 rpm, and the fermentation tank was also constantly stirred with an agitator (TORNADO, AS ONE) at a rotation speed of 100 rpm. The pH in the methane fermentation tank was maintained in the range of 6.63 to 7.00 by supplying 2M (mol / L) hydrochloric acid with a tubing pump (fixed-volume pump MP2000, Tokyo Rikakikai). The amount of hydrochloric acid supplied was controlled with a field controller (mk-750pH, Automatic Systems Research). The pH in the fermentation tank was measured with a pH meter (InPro 3030 combined pH electrode, Mettler Toledo) (see Figure 3). To simulate organic waste with a high nitrogen content, ammonium chloride was added to the simulated food waste at a concentration of 17.2 g / L on the 36th day and 28.7 g / L on the 97th day from the start of the experiment.

[0060] <Comparative Example 1> The procedure was the same as in Example 1, except that the pH in the methane fermentation tank was not controlled (see FIG. 3).

[0061] <Measurement> The total ammonia nitrogen (TAN) concentration in the methane fermentation liquid of the examples and comparative examples was measured using a high-performance liquid chromatograph (Prominence, Shimadzu Corporation). Sampling was performed periodically. The analysis conditions for the high-performance liquid chromatograph were: data collection time 30 min, pump flow rate 1.0 mL min -1 The column oven was set to 40° C., the amount of rinse solution was 2500 μL, and a column for cation analysis (YS-50, Shodex) and a column for anion analysis (Shim-pack IC-A1, Shimadzu Corporation) were used.

[0062] The gas flow rate of the generated mixed gas was measured, and the amount of methane gas generated was calculated from the gas composition. A volumetric gas flow meter (Milligas Counter MGC-1 V3.4 PMMA, Japan Flow Control) was used to measure the gas flow rate. A gas chromatograph (GC-2014S AT 100V, Shimadzu Corporation) was used to analyze the gas composition. A TCD (Thermal Conductivity Detector) was used as the detector, argon was used as the carrier gas, and a Shincarbon-ST 50 / 80 (Shinwa Kako) column was used, with a column flow rate of 30 mL min -1 It was decided.

[0063] The results are shown in Table 2 and Figures 2 and 4.

[0064] [Table 2]

[0065] From the results of Table 2 and FIG. 2, in Example 1 where pH control was performed, the total ammonia nitrogen (TAN) concentration reached 3,000 mg / L on about the 50th day. -1 It can be seen that a liquid fertilizer (methane fermentation liquid) with a high nitrogen concentration is obtained. It can also be seen that methane fermentation does not stop thereafter, and the total ammonia nitrogen (TAN) concentration increases. On the other hand, in Comparative Example 1 in which pH control was not performed, the amount of mixed gas produced decreased after about the 150th day, and then methane fermentation stopped (see Figures 2 and 4). [Explanation of symbols]

[0066] 1. Organic waste storage container 2. Organic waste supply means 3,8 Control section 4. Methane fermentation tank 5. Mixing means 6 pH measuring means 7 Acid supply means 9. Acid Storage Container 10 Liquid Fertilizer Storage Container 100 Liquid fertilizer manufacturing equipment

Claims

1. Supplying organic waste to a methane fermentation tank containing anaerobic microorganisms; A step of stirring and mixing the supplied organic waste and anaerobic microorganisms; Measuring the pH of the methane fermentation liquid containing the stirred and mixed organic waste; A step of supplying an acid to the methane fermentation tank based on the measured pH value to adjust the pH to 6.50 to 7.30; A method for producing a liquid fertilizer, comprising:

2. The method for producing a liquid fertilizer according to claim 1, further comprising the step of extracting a mixed gas containing methane gas from the methane fermentation tank.

3. The total ammonia nitrogen (TAN) concentration of the methane fermentation liquid is 3,000 mg L －１ ~15,000mgL －１ The method for producing a liquid fertilizer according to claim 1 or 2,

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