JP2003245630A - Anaerobic treatment method for organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anaerobic treatment method which enables the efficient anaerobic treatment of organic waste by simple equipment. <P>SOLUTION: For the anaerobic treatment of the organic waste, ammonia nitrogen originating from the organic waste is fixed using a solid acid. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to (1) kitchen waste, (2) livestock manure, (3) sewage sludge, (4) septic tank sludge,
The present invention relates to anaerobic treatment of organic waste such as (5) industrial wastewater sludge, (6) industrial wastewater, and (7) human waste.

[0002]

2. Description of the Related Art An anaerobic digestion method in which an anaerobic bacterium is used to decompose the organic waste is widely used for treating the above various organic wastes. In this anaerobic digestion method, anaerobic bacteria such as methanobacterium decompose organic waste to produce methane gas. The generated methane gas can be recovered and used as a resource.

When the organic waste is digested by the anaerobic bacteria, a part of nitrogen in the organic waste is used for the microbial synthesis of the anaerobic bacteria, but not for the microbial synthesis. Excess nitrogen becomes ammoniacal nitrogen. When the concentration of ammonia nitrogen increases, the concentration of free ammonia increases,
As a result, methane fermentation by anaerobic bacteria is inhibited [“Water and Wastewater” Vol.43, No.3 (2001), pages 12-19].
Therefore, in order to suppress the above fermentation inhibiting factors and maintain the digestion efficiency at a high level, it is necessary to reduce the amount of organic waste fed into the anaerobic treatment tank and reduce the treatment load. In particular, when the organic waste is anaerobically treated by the dry method, the concentration of the organic matter in the treatment tank is higher than that in the wet method, and thus the ammonia concentration is likely to be higher, and the above tendency becomes more remarkable.

As a means for lowering the ammonia concentration in the anaerobic treatment tank, there is a method of neutralizing with a water-soluble acid such as hydrochloric acid or sulfuric acid. However, when ammonia is neutralized with these acids, anions such as chlorine ions and sulfate ions are generated. Then, when the concentration of the anion in the treatment system becomes high, methane fermentation is inhibited. Specifically, 100 ppm for sulfate ions and 15000 for chlorine ions
It is known that when it exceeds ppm, methane fermentation is inhibited.

Further, when anaerobically treating an organic waste having a high nitrogen content, a method of mixing with an organic waste having a low nitrogen content, or diluting with water to reduce the nitrogen concentration is used. Is also adopted by some. However, when the nitrogen concentration of the treatment waste is lowered as described above, the amount of the waste to be treated is increased by the amount of the nitrogen concentration lowered (that is, diluted), so that the treatment efficiency is lowered.

Therefore, as a method for reducing the inhibition of methane fermentation due to the accumulation of ammonia nitrogen in the treatment tank,
For example, Japanese Patent Laid-Open No. 2000-15231 discloses a method in which the fermentation sludge in the anaerobic treatment tank is separated by a membrane separation means, and a part of a liquid content containing a fermentation inhibitor is extracted from the anaerobic treatment tank. ing. However, this method requires not only a membrane separation device and a pressurizing device for operating it, but also a device for treating the membrane-separated methane fermentation inhibitor, which requires equipment cost and operation. The cost increases.

Further, Japanese Patent Laid-Open No. 2001-137888 discloses a method of extracting ammonia contained in organic wastewater to the outside of the system by ammonia stripping and recovering it as a valuable resource. However, in this method, not only an ammonia treatment device is separately required, but also considerable heat energy is required for ammonia stripping, so that it is not possible to meet the demands for simplification of equipment and reduction of operating cost.

On the other hand, in a study investigating the relationship between the inhibitory form and concentration of nitrogen contained in organic waste, ammonium ions become ammonia and methane due to the influence of pH and temperature in the anaerobic treatment tank. It has been reported to inhibit fermentation ["Industrial water", No. 490, (1999.
Mon., pp. 18-32], a method of lowering the dissociation equilibrium concentration of ammonia by lowering the pH of the digestive juice in the anaerobic treatment tank is proposed. That is, in this method,
By adding ferric chloride in the anaerobic treatment tank,
H ₂ S by reducing the sulfur compounds present in the anaerobic treatment tank
Generate. The generated H ₂ S reacts with ferric chloride to generate hydrochloric acid, and the hydrochloric acid reacts with ammonia in the anaerobic treatment tank, whereby the inside of the treatment tank can be controlled to a low pH range. However, with this method, as pointed out in the above-mentioned method, the inhibition of methane fermentation due to an increase in chloride ion concentration is unavoidable. Further, if the chlorine concentration in the treated sludge becomes high, it will cause generation of dioxins when the treated sludge is incinerated, for example.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and an object thereof is to provide an anaerobic method capable of efficiently performing anaerobic treatment of organic waste with a simple facility. It is to provide a processing method.

[0010]

The method for treating organic waste according to the present invention, which has been able to solve the above-mentioned problems, includes an ammonia state derived from organic waste when anaerobicly treating the organic waste. The gist is that nitrogen is fixed using a solid acid.

In the present invention, it is preferable to employ a method of directly introducing the solid acid into the anaerobic treatment site or a method of introducing the solid acid into the returning sludge obtained from the anaerobic treatment site.

The solid acid used in the present invention is preferably bentonite, acid clay, activated clay and silica-alumina, and these may be used alone or in combination of two or more if necessary.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Methane fermentation by anaerobic bacteria is generally carried out at moderate temperature (about 30 to 35 ° C) or high temperature (about 50 to 55 ° C). However, as described above, the presence of ammonia in the treatment system inhibits methane fermentation by anaerobic bacteria. Specifically, medium temperature methane fermentation (35 ° C) inhibits methane fermentation when the ammonia concentration exceeds 5000 to 8000 ppm, and high temperature methane fermentation (55 ° C) inhibits methane fermentation when the ammonia concentration exceeds 2500 to 2800 ppm. It Therefore, as described above, there is also a method of neutralizing ammonia in the anaerobic treatment system with an acid, but this method is not a fundamental solution because the concentration of anions in the treatment system becomes high.

Further, the methane fermentation by anaerobic bacteria is also affected by the pH in the anaerobic treatment tank, and depending on the pH, ammonia nitrogen turns into ammonia and inhibits methane fermentation. Therefore, in order to promote stable methane fermentation from such a viewpoint, it is preferable to keep the pH at about 6.4 to 7.6.

Therefore, when the organic waste itself has a low pH, or when a large amount of organic acid is produced in the process in which the organic waste is decomposed by the anaerobic bacteria, the inside of the anaerobic treatment tank is set to the above preferable range. It is desirable to control the pH to be in the pH range. As a means for controlling the pH in the anaerobic treatment tank, there is a method of using alkali such as ammonia, slaked lime, and potassium hydroxide, but as described above, when the ammonia concentration in the anaerobic treatment tank becomes too high, methane fermentation Therefore, slaked lime or potassium hydroxide is preferably used for pH adjustment. On the other hand, if the ammonia concentration in the organic treatment tank becomes high and the pH exceeds 7.6, methane fermentation is suppressed, so a method of controlling the pH using acid is recommended, but it is generated by neutralization of ammonia. Methane fermentation is inhibited even when the concentration of anions is increased.

Therefore, the inventors of the present invention have examined various ways of improving the anaerobic treatment efficiency by removing ammonia more efficiently when the organic waste is anaerobically treated. It has been found that when the ammonia nitrogen (NH ₄ ⁺ —N) derived from the product is fixed by using a solid acid, the production of ammonia is prevented, and the above-mentioned problems can be solved successfully.

Therefore, the solid acid used in the present invention is required to have a cation exchange ability, and is required to have a function of fixing ammonia nitrogen and stably holding it. Here, "solid acid fixes ammonia nitrogen" means that ammonia nitrogen ionically bonds with solid acid to suppress the amount of ammonia nitrogen in the system.

Further, when the solid acid is dissolved in water, the ammonia nitrogen fixed to the solid acid is released, so that the solid acid used in the present invention must be insoluble.
When ammonia nitrogen is fixed with this solid acid, anions due to the neutralization of ammonia as described above are not generated, so that methane fermentation is not hindered by byproducts.

In the present invention, the reason why ammonia nitrogen is "derived from organic waste" is not only the case where the organic waste itself contains ammonia nitrogen,
This is because even if the organic waste itself does not contain ammonia nitrogen, anaerobic bacteria may generate ammonia nitrogen from the nitrogen contained in the organic waste. It is a waste.

Hereinafter, the present invention will be described more specifically with reference to the drawings. However, the present invention is not limited by the illustrated examples, and design changes may be made within a range that can be adapted to the gist of the preceding and the following. Both are included in the technical scope of the present invention.

FIG. 1 is a schematic view showing an example of an anaerobic treatment step. In the figure, 1 indicates an anaerobic treatment tank and 2 indicates a solid-liquid separation tank. A is organic waste, B is gas, C is solid acid, and a to f are routes.

The organic waste A is fed into the anaerobic treatment tank 1 through the route a. In the anaerobic treatment tank 1, the organic waste A is decomposed by an anaerobic bacterium (for example, methanobacterium) into an organic acid, and then decomposed into methane gas, carbon dioxide, hydrogen, water (hereinafter, these The residue after decomposition may be collectively referred to as "treated sludge"). At this time, a part of nitrogen contained in the organic waste A is used for microbial synthesis of anaerobic bacteria, but the excess nitrogen becomes ammonia nitrogen. Therefore, in the present invention, the solid acid C is directly charged into the anaerobic treatment tank 1 which is the site of the anaerobic treatment through the route c and the ammonia nitrogen is fixed to stabilize the production of ammonia while suppressing it. Maintain methane fermentation.

The treated sludge that has been subjected to the anaerobic treatment is route d.
Is sent to the solid-liquid separation tank 2 and separated into a liquid component and a solid component. The separated liquid component is discharged from the path f, and the separated solid component is discharged from the path e to the outside of the system. At this time, in the present invention, since the solid acid is used to fix the ammonia nitrogen, unnecessary chlorine ions may be mixed into the treated sludge as in the case of using hydrochloric acid for neutralizing ammonia. There is no. Therefore, the present invention has an effect of facilitating the disposal of the liquid component and the solid component.

On the other hand, the gas component produced in the anaerobic treatment tank 1 is extracted as gas B from the path b, and after separating methane gas, carbon dioxide, etc., the methane gas is used as fuel for a micro gas turbine, a boiler, etc. (Not shown).

In the method of directly charging the solid acid C into the anaerobic treatment tank, it is preferable to operate while stirring the anaerobic treatment tank 1. This is because when the organic waste A and the solid acid C fed into the anaerobic treatment tank 1 are mixed with stirring, ammonia nitrogen is efficiently fixed to the solid acid C. Therefore, from the viewpoint of ease of mixing in the anaerobic treatment tank 1, the above method is preferably adopted when wet-type anaerobic treatment of liquid organic waste such as industrial wastewater or night soil. Here, “wet and anaerobic treatment” means that the dry mass is
This means anaerobic treatment of 10% or less of liquid organic waste, and the organic waste has a high water content and a high viscosity.

FIG. 2 is a schematic view showing another example of the anaerobic treatment step. In the figure, 3 is an anaerobic treatment tank, 4 is a mixing tank, and g and h are paths. The parts corresponding to those in FIG. 1 are designated by the same reference numerals.

The organic waste A is fed into the anaerobic treatment tank 3 via the route a. The organic waste A sent into the anaerobic treatment tank 3 is anaerobically treated while moving by the plug flow. The gas component generated at this time is the gas B from the path b.
Is extracted as.

By the way, since the treated sludge obtained from the anaerobic treatment tank 3 which is the place for anaerobic treatment may contain untreated organic waste, a part of the treated sludge is anaerobically used as return sludge. May be returned to processing tank 3. Further, since the treated sludge obtained from the anaerobic treatment tank 3 contains anaerobic bacteria, in order to keep the amount of anaerobic bacteria in the anaerobic treatment tank 3 constant, part of the treated sludge is seed sludge. May be returned to the anaerobic treatment tank 3. However, when anaerobic treatment is performed while moving the organic waste in the anaerobic treatment tank 3 by the plug flow, the concentration of ammonia nitrogen in the anaerobic treatment tank 3 increases as the anaerobic treatment progresses, and by extension The production causes inhibition of methane fermentation. Therefore, in this illustrated example, by introducing solid acid C into the treated sludge obtained from the anaerobic treatment site, the concentration of ammonia nitrogen in the treated sludge is reduced, and this is changed to the anaerobic treatment tank 3
By returning it to, it is possible to continue stable anaerobic treatment without inhibiting methane fermentation.

That is, in this example, the treated sludge obtained from the anaerobic treatment tank 3 is fed into the mixing tank 4 through the route g, and in the mixing tank 4, the solid acid C is introduced into the treated sludge through the route c. And mix. Treated sludge mixed with solid acid C (hereinafter,
The sludge in which the treated sludge and the solid acid C are mixed is sometimes referred to as "mixed sludge") is an anaerobic treatment tank as return sludge.
Return to.

The above-mentioned method of introducing the solid acid C into the returned sludge obtained from the anaerobic treatment tank can be suitably used when the inside of the anaerobic treatment tank 1 is not stirred. That is, when solid-state organic waste such as kitchen waste, livestock manure, sewage sludge, septic tank sludge and industrial wastewater sludge is dry-anaerobically treated, the organic waste is stirred and mixed in the anaerobic treatment tank. However, even if a solid acid is added to the solid organic waste in the anaerobic treatment tank, ammonia nitrogen cannot be sufficiently fixed. However, in the above method, since the solid acid is mixed with the sludge returned after the anaerobic treatment, it is possible to obtain a sufficient reduction effect for ammonia nitrogen without stirring in the anaerobic treatment tank. be able to.

Here, "dry-type anaerobic treatment" means anaerobic treatment of solid organic waste having a dry mass of more than 10%, and the organic waste has a low water content. High viscosity.

In the above, the case where a part of the sludge subjected to the anaerobic treatment is returned to the anaerobic treatment tank 3 is shown, but if necessary, the whole sludge is temporarily returned to the anaerobic treatment tank 3. It is also within the scope of the present invention to carry out the digestion sufficiently and then to withdraw a part thereof in the direction of the solid-liquid separation tank.

When the organic waste is anaerobically treated, two or more anaerobic treatment tanks may be provided and the acid fermentation and the methane fermentation may be performed separately. In such a case, ammonia nitrogen is more likely to be produced in the methane fermentation process than in the acid fermentation process.Therefore, the solid acid is added to the organic waste that has undergone the acid fermentation and mixed, and this is subjected to the anaerobic treatment in the subsequent stage. Tank (methane fermentation tank)
It is preferable to feed the solid acid directly to the methane fermentation tank provided at a later stage than the acid fermentation tank.

The type of solid acid used in the present invention is not particularly limited, but preferred examples include natural solid acids such as bentonite and acid clay, semi-natural solid acids such as activated clay and silica-alumina. These may be used alone, or two or more of them may be mixed and used at an arbitrary ratio. The silica-alumina refers to a composite oxide of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ), and does not include silica alone or alumina alone.

Among these, bentonite is practical in view of ion exchange capacity and price. Further, bentonite is a sodium silicate salt, and as it is apparently used as a granulating agent for fertilizers, it is considered that there is almost no effect on the living body, and therefore it also has almost no effect on anaerobic bacteria. Don't give.

In the present invention, since the solid acid is used to fix ammonia nitrogen, it is possible to control the treatment system within a suitable pH range without increasing the anion concentration in the anaerobic treatment system. it can. That is, for example, when bentonite is used as the solid acid, Na ions are released from the bentonite, and ammonia nitrogen is fixed to the bentonite. At this time, since the concentration of ammonia nitrogen decreases, the pH in the anaerobic treatment tank also decreases. The present inventors have confirmed that Na ions released from bentonite have a smaller inhibitory effect on methane fermentation than ammonia.

The adsorption amount of the cation (ammonia nitrogen) of the solid acid is about 80 milliequivalents of ammonia nitrogen to 100 g of bentonite and about 50 milliequivalents of ammonia nitrogen to 100 g of acid clay. .

In the present invention, the amount of the solid acid used in the anaerobic treatment of the organic waste is not particularly limited as long as it can fix the ammonia nitrogen existing in the anaerobic treatment tank, but the treatment target is not limited. 0.1 to 10 for organic waste
A mass% range is preferred. The reason for this is that when solid acid is added to the organic waste in an amount of 0.1% by mass, about 5000 ppm of ammonia nitrogen can be fixed, but the organic waste also contains Na ions and Ca ions in addition to ammonia nitrogen. This is because these cations may be fixed to the solid acid.

On the other hand, the effect of fixing the ammonia nitrogen by the solid acid described above is saturated at 10% by mass with respect to the organic waste, and even if it is added in excess of this amount, the effect does not change. Since the amount is increased, the upper limit was made 10 mass%. More preferably, it is 1.0 to 5.0 mass%.

The shape of the solid acid used in the present invention is not particularly limited, but a large surface area is desirable from the viewpoint of facilitating adsorption of ammonia nitrogen. Therefore, it is preferable that the solid acid has a powder form (for example, a particle size of about 100 μm or less).

The organic wastes to be treated by the anaerobic treatment method of the present invention include solid organic wastes such as kitchen waste, livestock manure, sewage sludge, septic tank sludge, industrial wastewater sludge, and industrial wastewater. It includes both liquid organic waste such as human waste.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following Examples are not intended to limit the scope of the present invention, and any modification of the design of the present invention can be made without departing from the gist of the preceding and the following. Within the technical scope of.

[0043]

Example 1 According to the anaerobic treatment process shown in FIG. 1, the organic waste was wet-anaerobically treated.

The kitchen waste having the composition shown in Table 1 was deionized water.
Diluted to prepare organic waste A. Organic waste A
Is a garbage load (kg ・ T
S / m ³/ D) was changed. That is, the organic waste A
If the concentration is low, the garbage load is low, and if the concentration is high, the kitchen waste is
The garbage load is high. Here, TS is the total amount of substance.

[0045]

[Table 1]

The organic waste A was fed into the anaerobic treatment tank 1 through the route a at a flow rate of 50 L (0.05 m ³ ) per day, and anaerobically treated with a hydraulic retention time (HRT) of 20 days. . The effective volume of the anaerobic treatment tank 1 is 1 m ³ (1000 L), and the temperature in the anaerobic treatment tank 1 is 36 ° C. The experimental conditions are as follows. [Inventive Example] Bentonite (solid acid) was added once a day through route c. The input amount is 1% by mass (500 g) with respect to the input amount of the organic waste A. [Comparative Example 1] Hydrochloric acid was used to control the pH of the anaerobic treatment tank 1 so that the pH was 7. [Comparative Example 2] The operation was performed without adding bentonite (solid acid) or hydrochloric acid.

Anaerobic treatment tank when the garbage load is changed
The ammonia concentration (ppm) and pH in 1 were measured. Ammonia concentration was measured by water quality analysis according to the sewer test method, and pH was measured by a pH meter. The measurement results are shown in FIGS. 3 and 4, respectively. In addition, the amount of methane gas produced per day (Ltr./
d) is shown in FIG.

In FIG. 3 to FIG. 5, ● indicates the results of the present invention, × indicates the results of Comparative Example 1, and ∘ indicates the results of Comparative Example 2. The present inventors have confirmed that when the temperature of the anaerobic treatment is 36 ° C., the methane fermentation is inhibited when the ammonia concentration in the anaerobic treatment tank exceeds 5000 ppm.

The following can be considered from FIGS. 3 to 5. In the example of the present invention, bentonite (solid acid) is directly charged into the anaerobic treatment tank 1 which is a place for anaerobic treatment to fix ammonia nitrogen, so that a garbage load of 5.2 kg · TS / m ³ /
Even if d, the concentration of ammonia in the anaerobic treatment tank 1 is 5000
It never exceeded ppm (Fig. 3). Further, in the example of the present invention, the pH in the anaerobic treatment tank 1 does not exceed 7.6 even when the garbage load is 5.2 kg · TS / m ³ / d (Fig. 4). Therefore, when the method of the present invention is adopted, methane fermentation is not hindered by ammonia even if the garbage load is increased, anaerobic treatment can be stably advanced, and methane gas can be efficiently generated (FIG. 5). ).

On the other hand, in Comparative Example 1, p in the anaerobic treatment tank
Although H is controlled to around 7 with hydrochloric acid (Fig. 4), when the garbage load exceeds 3 kg · TS / m ³ / d, the ammonia concentration in the anaerobic treatment tank exceeds 5000 ppm (Fig. 3). . That is, when the garbage load exceeds 3 kg · TS / m ³ / d, ammonia inhibits methane fermentation, anaerobic treatment does not proceed stably, and methane gas is hardly produced (FIG. 5).

In Comparative Example 2, the garbage load is 3 kg.
At TS / m ³ / d or higher, the ammonia concentration in the anaerobic treatment tank 1 exceeds 5000 ppm (Fig. 3). Further, when the garbage load is set to 3 kg · TS / m ³ / d or more, the pH in the anaerobic treatment tank exceeds 7.6 (Fig. 4). from this result,
When the kitchen load is increased to 3 kg · TS / m ³ / d or more, ammonia inhibits methane fermentation, so stable anaerobic treatment cannot be maintained and methane gas is hardly generated (Fig. 5).

Here, the garbage load is 2.8 kg · TS / m ³ /
The concentration of ammonia in the liquid component when the treated sludge after anaerobic treatment was subjected to solid-liquid separation in the solid-liquid separation tank was measured to be 4000 ppm, whereas in Comparative Example 1 it was 4650 ppm. In Comparative Example 2, it was 4800 ppm. Therefore, according to the method of the present invention, it can be seen that ammonia remaining in the sludge after the anaerobic treatment can be reduced.

Example 2 According to the anaerobic treatment process shown in FIG. 2, the organic waste was anaerobically treated by a dry method.

The kitchen waste having the composition shown in Table 2 was designated as organic waste A.

[0055]

[Table 2]

A mixture of 500 g of the organic waste A and 500 g of seed sludge described below was put into the anaerobic treatment tank 3 of 1 kg per time, and anaerobically treated by a batch system for 15 days. In the anaerobic treatment tank 3, organic waste is moving by plug flow. A part (500 g) of the treated sludge after the anaerobic treatment was used as the seed sludge.

The effective volume of the anaerobic treatment tank 3 is 0.002 m ³ (2
L), and the temperature in the anaerobic treatment tank 3 is 55 ° C. The experimental conditions are shown below. [Example of the present invention] Part of treated sludge after anaerobic treatment (500 g)
Was fed into the mixing tank 4 through the route g, and 5 g of bentonite (solid acid) was introduced through the route c and mixed. The mixed sludge was used as seed sludge. The amount of bentonite added was 1% by mass with respect to the treated sludge. [Comparative Example 1] Part of treated sludge after anaerobic treatment (500 g)
Was fed into the mixing tank 4 through the route g, and the pH was adjusted to 7 using hydrochloric acid. The treated sludge after pH adjustment was used as seed sludge. [Comparative Example 2] Part of treated sludge after anaerobic treatment (500 g)
Was directly used as seed sludge.

The ammonia concentration (ppm) and pH in the anaerobic treatment tank 3 when the anaerobic treatment was performed under the above conditions were measured daily by the same method as described above. These results are shown in FIGS. 6 and 7, respectively. Moreover, the result of having measured the methane gas production amount (mL / d) per day is shown in FIG. However, FIG.
In FIG. 8, ● indicates the results of the present invention, × indicates the results of Comparative Example 1, and ∘ indicates the results of Comparative Example 2. When the temperature of the anaerobic treatment is 55 ° C, the ammonia concentration in the anaerobic treatment tank is 2500ppm.
The present inventors have confirmed that the methane fermentation is inhibited when the ratio exceeds.

The following can be considered from FIGS. 6 to 8. In the example of the present invention, bentonite (solid acid) was added to the treated sludge obtained from the anaerobic treatment site to fix ammonia nitrogen, and the sludge was returned to the anaerobic treatment tank 3 to perform the anaerobic treatment. The ammonia concentration in tank 3 is kept below 2500 ppm (Fig. 6). Further, the pH in the anaerobic treatment tank 3 did not exceed 7.6 even after operating for 15 days (Fig. 7). Therefore, methane fermentation is not hindered by ammonia, and on average it is about 3000 mL per day.
Methane gas is stably generated (Fig. 8). That is,
When the amount of methane gas produced for 15 days is integrated, it can be seen that 100 m ³ or more of methane gas can be produced per ton of kitchen waste by using the method of the present invention.

On the other hand, in Comparative Example 1, since the pH of the seed sludge is controlled to around 7 with hydrochloric acid, the pH in the anaerobic treatment tank 3 is
It did not exceed 7.6 by the 12th day (Fig. 7). But 13
The pH in the anaerobic treatment tank 3 after the first day exceeded 7.6. Also, the ammonia concentration in the anaerobic treatment tank was 2500p on the 7th day.
pm is exceeded (Fig. 6). Therefore, from the 7th day onward, methane fermentation was inhibited by ammonia, and the amount of methane gas produced decreased sharply (Fig. 8). In other words, when adding up the amount of methane gas produced for 15 days, 46 m ³ per 1 ton of kitchen waste
Can only produce methane gas.

Further, in Comparative Example 2, the ammonia concentration in the anaerobic treatment tank 3 exceeds 2500 ppm after the third day (FIG. 6). Also, the pH in the anaerobic treatment tank should be 6th day or later.
It exceeds 7.6 (Fig. 7). Therefore, from the third day onward, methane fermentation was inhibited by ammonia, and the amount of methane gas produced decreased sharply (Fig. 8). That is, if the amount of methane produced for 15 days is integrated, only 57.6 m ³ of methane gas can be produced per ton of kitchen waste.

Example 3 In accordance with the anaerobic treatment process shown in FIG. 9, the effect of adding a solid acid when the organic waste was anaerobically treated was examined.

FIG. 9 is a schematic diagram showing the anaerobic treatment process used in the experiment, in which 5 is an acid fermentation tank, 6 methane fermentation tank, and i.
Indicate the routes respectively. The parts corresponding to those in FIG. 1 are designated by the same reference numerals.

FIG. 9 shows a case where the anaerobic treatment is carried out by two-stage fermentation, in which the organic waste A is fed into the acid fermentation tank 5 through the route a. The capacity of this acid fermentation tank 5 is 200 L. Wastewater that has undergone acid fermentation is processed from route i in the methane fermentation tank.
It is sent to 6. The effective volume of this methane fermentation tank 6 is 1m.
³ (1000L).

As the organic waste A, waste water from a food factory was used. The organic matter in the wastewater is mainly starch, and the biochemical oxygen demand (BOD) is 8,000 to 12,000 pp.
m. The wastewater after the acid fermentation of the organic waste A is sent to the methane fermentation tank 6 at a rate of 1000 L (1 m ³ ) per day, and the anaerobic treatment (hydromethane retention time (HRT) is set to 24 hours). Fermented). The temperature in the methane fermentation tank 6 is 36 ℃
Is.

The ammonia concentration in the methane fermentation tank 6 was measured by the same method as above, and when the ammonia concentration in the methane fermentation tank 6 exceeded 4000 ppm, solid acid C was added from the route c to the wastewater after the acid fermentation. I put it in. Bentonite is used as the solid acid C, and the input amount is 10 kg per time. still,
The input amount corresponds to 1% by mass of the capacity of the methane fermentation tank 6.

Ammonia concentration in methane fermentation tank 6 (pp
The results of measuring m) and pH are shown in FIGS. 10 and 11, respectively. The arrows shown in FIGS. 10 and 11 are
The time when the solid acid is charged is shown. Further, FIG. 12 shows the fluctuation of the methane gas production amount (m ³ / d) per day.

FIG. 13 shows changes in BOD before and after methane fermentation. ● in the figure is BOD before methane fermentation
Concentration, ◯ indicates the BOD concentration after methane fermentation, respectively.

As is clear from FIGS. 10 and 11, the ammonia concentration in the methane fermentation tank 6 exceeded 4000 ppm.
When bentonite was added on the 5th, 105th, and 165th days, a decrease in ammonia concentration and pH in the methane fermentation tank was observed 10 days after the addition. Therefore, the ammonia concentration in the methane fermentation tank 6 is 5000 pp even after operating for 225 days.
It did not exceed m.

As is clear from FIG. 12, the production amount of methane gas is stable at 140 to 190 m ³ / d. Further, as is clear from FIG. 13, 95% or more of BOD can be stably removed.

[0071]

According to the present invention, the anaerobic treatment of organic waste can be efficiently carried out by a simple method such as fixing ammonia nitrogen with a solid acid, so that equipment cost and operating cost can be reduced. It was possible to provide a possible anaerobic treatment method.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an anaerobic treatment process.

FIG. 2 is a schematic view showing another example of the anaerobic treatment step.

FIG. 3 is a graph showing the relationship between the garbage load and the ammonia concentration in the anaerobic treatment tank.

FIG. 4 is a graph showing the relationship between kitchen load and pH in the anaerobic treatment tank.

FIG. 5 is a graph showing a relationship between garbage load and methane gas production amount.

FIG. 6 is a graph showing changes in the concentration of ammonia in the anaerobic treatment tank.

FIG. 7 is a graph showing changes in pH in the anaerobic treatment tank.

FIG. 8 is a graph showing fluctuations in the amount of methane gas produced per day.

FIG. 9 is a schematic view showing an example of an anaerobic treatment process.

FIG. 10 is a graph showing changes in the concentration of ammonia in the methane fermentation tank.

FIG. 11 is a graph showing changes in pH in a methane fermentation tank.

FIG. 12 is a graph showing fluctuations in the amount of methane gas produced per day.

FIG. 13 is a graph showing changes in BOD before and after methane fermentation.

[Explanation of symbols]

1: Anaerobic treatment tank 2: Solid-liquid separation tank 3: Anaerobic treatment tank 5: Acid fermentation tank 6: Methane fermentation tank 4: Mixing tank A: Organic waste B: Gas C: Solid acid a to i: route

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Claims (4)

[Claims] 1. A method for anaerobic treatment of organic waste, which comprises fixing ammonia nitrogen derived from the organic waste with a solid acid in the anaerobic treatment of the organic waste. 2. The method for anaerobic treatment of organic waste according to claim 1, wherein the solid acid is directly put into a place for anaerobic treatment. 3. The method for anaerobic treatment of organic waste according to claim 1 or 2, wherein the solid acid is put into returning sludge obtained from a site of anaerobic treatment. 4. The method for anaerobic treatment of organic waste according to claim 1, wherein the solid acid is at least one selected from bentonite, acid clay, activated clay and silica-alumina.