JP2002273490A - Method of starting up operation of anaerobic digestion fermenter for organic sludge and digestion method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anaerobic digestion method for organic sludge which drastically shortens the starting-up time in starting the operation while grasping the propagation state of methane fermentation bacteria at the start of the operation with good accuracy. SOLUTION: The anaerobic digestion method of separating the organic wastes, such as night soil, septic tank sludge, agricultural sludge, sewer sludge, animal wastes and the like into liquid wastes and organic sludge, introducing the organic sludge into an anaerobic digestion fermenter and subjecting the organic sludge to methane fermentation comprises first feeding materials, such as rice bran, bean curd refuse or garbage and the like, which are liable to be decomposed by the anaerobic digestion fermentation bacteria and have fiber contents to a lesser extent into the anaerobic digestion fermenter in launching and starting the operation of the fermenter to enhance the activity of methanation bacteria, thereby speeding up the launching and drastically shortening the time for starting-up at the start of the operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for anaerobic digestion of organic sludge such as sewage, night soil, livestock waste, garbage and food waste, and more particularly to a method for anaerobic digestion and fermentation of said organic sludge. It relates to a high-speed start-up method at the start of operation and an anaerobic digestion system for organic sludge.

[0002]

2. Description of the Related Art Human waste, septic tank sludge, sewage sludge,
Agricultural sludge, livestock manure, garbage, organic waste treatment systems that generate methane gas and compost from organic waste such as food waste, collect useful resources, and turn them into resources are known. Night soil, septic tank sludge, agricultural sludge, sewage sludge, livestock manure
In the solid-liquid separation process, liquid waste and organic sludge are separated, and the liquid waste is subjected to BOD in aeration and other biological treatment processes.
Decompose and denitrify as needed, remove suspended matter in solid-liquid separation process such as screen and membrane separation, and remove heavy metals such as iron and manganese in heavy metal treatment process to discharge water or reused water I have.

On the other hand, the above-mentioned dewatered sludge is introduced into a methane fermentation tank in an anaerobic fermentation step and subjected to methane fermentation. The generated methane gas is collected and used for cogeneration, and digested sludge flowing out of the fermentation tank is dewatered in a dehydration step. The waste is recovered as fertilizer and solid fuel in the composting process.

[0004]

In methane fermentation, carbohydrates of organic matter in organic sludge are decomposed into lower fatty acids and alcohols by anaerobic digestive fermenters, and proteins are decomposed into amines and ammonia via organic acids. (Digestion and fermentation). The low-molecular-weight organic matter produced by digestion fermentation is decomposed into methane and carbon dioxide by methane gasifying fungi (methane fermentation in a narrow sense). These digestive bacteria and methane gasification bacteria are present in the sludge, and grow under anaerobic and temperature conditions (medium temperature methane fermentation treatment (around 35 ° C.), high temperature treatment (around 55 ° C.)). However, as a problem of the methane fermenter, there is a problem that it takes a long time to start up the anaerobic digester (methane fermenter) because the microorganisms that govern anaerobic digestion, particularly the methane gasifiers, grow slowly.

That is, the ordinary methane fermentation method is generally performed by a floating organism method in which methane bacteria are suspended in the liquid of a methane fermentation tank or near the liquid surface. Unless the volume load is increased in accordance with the growth of the methane fermentation bacterium at the time of starting the fermenter, organic acid accumulation occurs in the methane fermenter, and the processing capacity of organic waste decreases. For this reason, especially in the case of dehydrated organic sludge, startup of methane fermentation usually takes 90 days or more due to a large organic load.

For example, referring to FIG. 7, a description will be given of a change in the volume load and a startup period in which only the organic sludge is gradually increased in load while shifting to a rated volume load of 100%. %, And if the load is increased by 10% every two weeks, it takes about three months or more.

On the other hand, as a technique for shortening the startup period of methane fermentation, granules (granules are anaerobic microbial granules having a cone-like shape) are given to the methane fermentation tank by applying gentle stirring conditions in the tank. Body)
(Japanese Patent Application Laid-Open Nos. 62-22594, 62-22595 and 62-22596)
No.), a method in which granular carriers are filled together with activated sludge into a methane fermentation tank to promote the formation of granules, and denitrifying bacteria are grown on the carriers to convert them into denitrifying bacteria granules. There is a method of filling only the bacterial granules and growing the denitrifying bacteria present in the methane fermenting bacterial granules to convert them into denitrifying bacterial granules (JP-A-7-290088). However, in the case of dehydrated organic sludge, the organic load is large, and the conventional technique does not lead to a significant reduction in the start-up period.

Further, anaerobic bacteria involved in methane fermentation are:
The growth rate is significantly lower than that of the heterotrophic bacterium involved in BOD oxidation, and when the methane fermentation tank is started up, as described above, the methane fermentation rate must be increased in accordance with the growth of the methane fermentation bacterium. Although organic acid accumulation occurs in the tank, the processing capacity of organic waste decreases,
Since methane fermentation is performed in a closed tank because of anaerobic conditions, the growth state of methane fermentation bacteria cannot be determined, and therefore the rated load must be increased with a margin. Especially, in the past, there was no method to quickly evaluate the performance of methane fermentation, so the load that could be input could not be calculated clearly, and the load was determined empirically. .

In view of the prior art, the present invention provides an anaerobic digestion method of organic sludge which can greatly reduce the start-up time at the start of operation while accurately grasping the growth state of methane fermentation bacteria at the start of operation. The purpose is to provide.

[0010]

In order to solve the above-mentioned problems, the present invention converts organic wastes such as night soil, septic tank sludge, agricultural sludge, sewage sludge, livestock manure, etc. into liquid waste and organic sludge. In the anaerobic digestion method of organic sludge, which is separated and introduced into the anaerobic digestion fermenter by introducing the organic sludge into the anaerobic digestion and fermentation by anaerobic digestion, at the time of starting the operation of the anaerobic digester and fermenter for organic sludge. After increasing the activity of methane gasifying bacteria by adding a substance with a low fiber content that is easily decomposed by anaerobic digestive fermentation bacteria such as rice bran, okara or garbage, or in parallel with this, Feeding the dehydrated organic sludge to the fermenter, gradually increasing the volume load of the sludge, and shifting to a rated load, and after shifting to the rated load, the anaerobic digestion fermenter Fermented in The digested sludge is dewatered separated, the dehydrating sludge composting process, while the certain dehydration separated so the separated liquid to the anaerobic digestion system of the organic sludge, characterized in that the biological treatment.

[0011] According to the invention, when the activity of the methane gasifier at the start of operation is low, the methane gasifier is easily decomposed by an anaerobic digestive fermentation bacterium such as rice bran, okara or garbage. Increase the activity of. After increasing the activity of the methane gasifier, dehydrated organic sludge is introduced into the digestion fermenter to shift the sludge to a rated load while gradually increasing the volume load.

According to this invention, the period during which the fermentation is stabilized at the start-up of the methane fermentation treatment can be substantially reduced, for example, to about 5 to 6 weeks, which is about 12 weeks in the conventional method.

[0013] In this case, the organic sludge is not periodically increased in a stepwise manner, but is performed in an irregular cycle based on the result of measuring the degree of increase in the activity of the methane gasifying bacteria. The start-up can be speeded up and the start-up time at the start of operation can be significantly reduced without reducing the processing capacity of the object.

That is, when the amount of organic sludge introduced into the digestion fermenter at the start of operation is too large, the load of organic matter becomes excessive, and in that case, the reaction rate of acid-producing bacteria is faster than that of methane bacteria. Therefore, accumulation of volatile fatty acids such as acetic acid and propionic acid is observed. Then, when the volatile fatty acid concentration increases and the free volatile fatty acid concentration increases, methane fermentation becomes inhibited, and if the volatile fatty acid concentration is not immediately reduced, the methane bacteria loses activity, and In such cases, it was necessary to reduce or stop the input of organic waste, or to suppress the increase in free volatile fatty acids by adding an alkali agent and wait for the reduction of volatile fatty acids, but the methane gasification bacteria The above effects can be obtained without lowering the processing capacity of organic waste by stepwise charging based on the result of measuring the degree of activity increase.

In the measurement method described above, an appropriate amount of sludge during methane fermentation is withdrawn from the digestion fermentation tank during the start-up of the anaerobic digestion fermentation tank, and the sludge is quantitatively charged into a container, and the gas phase is replaced with nitrogen gas. After that, add an appropriate amount of a solution of Na acetate,
It is preferable to use a measurement method of maintaining the temperature at a predetermined temperature, measuring the amount of gas generated from this container over time, and calculating the load that can be processed in the entire methane fermentation tank.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings. However, unless otherwise specified, dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the invention, but are merely illustrative examples. FIG. 1 is an overall block diagram showing the basic configuration of the present invention, in which methane gas and compost are produced from organic waste such as night soil, septic tank sludge, sewage sludge, agricultural sludge, livestock manure, garbage, and food waste. 1 shows an organic waste treatment system for recycling.

In this system, human waste, septic tank sludge, agricultural sludge, sewage sludge, and livestock manure are removed in a removing step 1 and separated into liquid waste and organic dewatered sludge 11 in a solid-liquid separation step 2. , The liquid waste is subjected to BOD decomposition and denitrification as necessary in the aeration and other biological treatment step 3,
Suspended matter is removed in a solid-liquid separation step (not shown) such as a screen or a membrane separation, and heavy metals such as iron and manganese are removed in a heavy metal treatment step 10 to be discharged water or reused water. On the other hand, the organic dewatered sludge 11 is introduced into a methane fermentation tank (anaerobic digestion fermentation tank 5) in an anaerobic fermentation step and is subjected to methane fermentation. The generated methane gas is collected, supplied to cogeneration, and discharged from the fermentation tank. The digested sludge to be dewatered in the dewatering step 6 is collected in the composting step 7 as fertilizer or solid fuel. On the other hand, the separated liquid subjected to the dehydration separation is returned to the biological treatment step 3, BOD decomposition and, if necessary, denitrification, and heavy metals such as iron and manganese are removed in the heavy metal treatment step 10 to discharge water or reused water. And

When the methane fermentation tank (anaerobic digestion fermentation tank 5) is started up using only organic sludge, a target volume load (here, 4 kg VTS / m ³ ) is used as shown in FIG.
/ Day) at a load of 50% and 10
It took 14 weeks (more than 3 months) for 90 to 100 days to start stable operation when the load was increased by%.

(Example 1) First, as shown in FIG. 2, a substance having a low fiber content that is easily decomposed by anaerobic digestive fermentation bacteria such as rice bran, okara or garbage 4 is first introduced to determine the activity of methane gasification bacteria. A first embodiment in which dehydrated organic sludge is charged into the digestion fermenter after the increase and the volume load of the sludge is gradually increased while shifting to a rated load is shown. Numerals 8 and 9 in the figure denote valves for controlling the introduction of rice bran, okara or garbage 4 and the dehydrated organic sludge 11.

In this embodiment, at the start of operation of the methane fermentation tank (anaerobic digestion and fermentation tank 5), garbage 4 is charged at 20% of the volume load, and then increased by 10% to 30% in the first week. Second
After further increasing the amount by 10% to 40% in the week, the garbage is extracted by 10% to 30% in the third week, and the organic sludge 11 is supplied 40% for the first time. In the fourth week, garbage is further extracted by 10% to 20%, and organic sludge 11 is further added by 40% to 80%. Finally, in the fifth week, 20% of organic garbage is added to keep the garbage at 20%, and 100% is added to shift to the rated load. As a result, it was greatly reduced to 5 to 6 weeks (1.5 months) before shifting to the stable operation state. The garbage 4 has the ability to improve the activity of the methane bacteria group about twice as much as the organic matter in comparison with the organic sludge 11, so that the activity can be increased with a small input amount of 20%.

Example 2 Next, according to FIG. 3, a substance having a low fiber content that is easily decomposed by an anaerobic digestive fermentation bacterium such as rice bran, okara or garbage 4 is first charged to determine the activity of the methane gasification bacterium. A second embodiment in which dehydrated organic sludge is gradually fed into the digestion fermenter in parallel with increasing the load to shift to the rated load is shown.

In this embodiment, at the start of operation of the methane fermentation tank (anaerobic digestion fermentation tank 5), garbage 4 is charged at 20% of the volume load, and at the same time, organic sludge 11 is charged at 35%. Next, the organic sludge 11 was increased by 15% in the first week to 50%, further increased in the second week by 20% and fed to 70%, and then increased by 20% in the third week to 90%. To In the fourth week, the organic sludge 11 was extracted 15% and reduced to 75% to reduce the load. Finally, in the fifth week, an additional 25% of the organic sludge 11 is added to 100% to shift to the rated load. Also in this example, it was greatly reduced to 5 to 6 weeks (1.5 months) before shifting to the stable operation state. The ratio of the garbage 4 to the organic sludge 11 and the value of the volume load are merely reference values, and are not limited to the values shown here. Is also variable.

Therefore, according to these embodiments, the effective load is increased although the amount of input is small by inputting the biologically easily decomposable substance at the start. This has the effect of increasing the residence time, making it possible to grow methane bacteria efficiently without letting out methane gasification bacteria,
As a result, the methane bacterium can be grown more quickly than when a large amount of the hardly decomposable substance is introduced. <Example 3> In Example 3, the stepwise increase in the volume load of the organic sludge 11 and the raw garbage in the methane fermentation tank (anaerobic digestion fermentation tank 5) was not performed at regular intervals of one week. This is performed at irregular intervals based on the result of measuring the degree of increase in the activity of methane gasifying bacteria. This measurement is preferably made in the process of starting up the dehydrated organic sludge 11 by extracting an appropriate amount of the methane fermentation sludge and placing it in a vial bottle (68 ml capacity).
ml, and replace the gas phase with nitrogen gas.
Is added and kept at a predetermined temperature. The amount of gas generated over time from the vial bottle was measured, and sludge 1
From the amount of gas generated per ml, the load that can be processed in the entire sludge digestion fermenter (methane fermenter) is calculated. This measurement takes several hours and is increased to the determined load the next day.

This embodiment will be described with reference to the flowchart of FIG. FIG. 5 shows an increase in the volume load when the activity of the methane gasification bacteria in the methane fermentation tank (anaerobic digestion and fermentation tank 5) was measured, and FIG. 5 shows the measured methane fermentation tank (anaerobic digestion and fermentation tank 5). It is a graph which shows the state of increase of methane gasification activity.

Gasification activity means the amount of fermentation gas generated per unit time of methane fermentation tank volume. Here, it is assumed that 1 Nm ³ of fermentation gas is generated per kg of organic matter VTS. First, as shown in FIG. 4, at the start of operation, garbage is charged at 20% of the volume load, and the activity is measured by the above-described measuring method.
(S1) The gas generation capacity from acetic acid of 1 ml of methane fermentation sludge is calculated, and then the gas generation capacity per fermenter is calculated. (S
2) For example, the gas generation capacity from acetic acid is 0.1 ml gas / m
In the case of 1 sludge / hr, 0.1 m ³ × 2 per day
4 = 2.4 m ³ / m ³ sludge / day. Generally, since 70% of the methane fermentation gas passes through acetic acid, the inherent gas generation capacity of the sludge is 2.4 ÷ 0.7 = 3.42 m ³
/ ^M is ³ sludge / day. However, since the activity is measured under the optimal conditions, the actual capacity of the fermentation is 70% under the actual fermentation conditions.
It is considered that only about% can be demonstrated. Therefore, the value of the activity measurement is directly used for the gas generation ability of the sludge.

Next, the volume load of the organic substance that can be charged is calculated from the gas generating capacity. (S3) The amount of gas generated per decomposed organic substance is 1 Nm ³ gas /
Decomposed kg VTS. For example, in the case of sludge, 30% of organic matter is decomposed. Assuming that the gasification capacity is 2.4 m ³ / m ³ sludge / day, the amount of sludge that can be input is 2.4 ÷ 0.3
= 8 is calculated to be kgVTS / ^{m 3} sludge / day.

Next, in the evaluation step (S4), if the volume load exceeds the current value, the input amount is maintained. If the volume load is the same as the current value, the input amount of garbage is first increased by 5% to reduce the amount of garbage. When the input amount exceeds 40%, the organic sludge is first reduced to 40%.
%throw into. Next, in response to the increase in the input of organic sludge,
Pull out the garbage step by step. In the third to fourth weeks, the organic sludge is further added by 20%, and the sludge is set to 100%, and the load shifts to the rated load. As a result, it took 4 to 5 weeks (more than one month) to shift to the stable operation state, which was significantly shorter than that of the above-described embodiment.

[0028]

As described above, according to the present invention as set forth in claims 1 and 4, garbage such as easily decomposable rice bran, okara or garbage is not used at the time of start-up of the operation. Promotes the growth of methane bacteria and increases the number and activity of the bacteria quickly. Thereafter, the anaerobic digestion and fermentation tank can be quickly set up by gradually adding a hardly decomposable substance such as sludge. According to the second and third aspects of the present invention, it is possible to easily and quickly obtain the result of measuring the gas generation capacity of digested sludge. Therefore, it has an effect of determining an appropriate load and quickly reflecting the input amount, so that the anaerobic digestion and fermentation tank can be started up without causing rancidity.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing a basic configuration of the present invention.

FIG. 2 is a graph showing a first embodiment according to the present invention.

FIG. 3 is a graph showing a second embodiment according to the present invention. (When the amount of garbage is fixed)

FIG. 4 is a measurement flow chart of performing the stepwise increase of the volume load of the organic sludge and the garbage at irregular intervals based on the result of measuring the degree of activity increase of the methane gasifier.

FIG. 5 is a graph showing a second example in which the volume load is increased when the activity is measured based on FIG.

FIG. 6 is a graph showing the measured methane gasification activity.

FIG. 7 is a graph showing a change in the volume load and a period at the time of startup in which only the organic sludge is shifted to a rated volume load of 100% while the load is gradually increased.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Debris removal process 2 Solid-liquid separation process 3 Biological treatment process 4 Garbage such as rice bran and okara 5 Methane fermentation tank (anaerobic digestion fermentation tank) 6 Dehydration step 7 Composting step 8, 9 Valve 10 Heavy metal treatment step 11 Organic Sludge

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Nakamura 12 Nishikicho, Naka-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. Yokohama Works (72) Inventor Kiyoshi Suga 1-8-1, Koura, Kanazawa-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. 4D004 AA02 AA03 AA04 BA03 BA04 CA17 4D059 AA01 AA02 AA03 AA07 BA12 BE00 BE49 CC01 4H061 AA02 CC36 CC39 CC42 CC51 CC55 FF06 GG10 GG19 GG50 GG54 GG69 GG70

Claims (4)

[Claims] (1) night soil, septic tank sludge, agricultural sludge, sewage sludge,
An anaerobic digestion method for organic sludge, in which organic waste such as livestock manure is separated into liquid waste and organic sludge, and the organic sludge is introduced into an anaerobic digestion fermenter and methane fermented by anaerobic digestion. At the start of the operation of the anaerobic digestion and fermentation tank for organic sludge, a substance having a low fiber content that is easily decomposed by the anaerobic digestion and fermentation bacteria such as rice bran, okara or garbage is first charged, and methane gasification is performed. After or in parallel with increasing the activity of the fungus, organic sludge is charged into the digestive fermenter,
A method for starting operation of an anaerobic digestion and fermentation tank for organic sludge, wherein the sludge is shifted to a rated load while the volume load is gradually increased. 2. The organic method according to claim 1, wherein the stepwise increase in the volume load of the organic sludge is performed at irregular intervals based on the result of measuring the degree of increase in the activity of the methane gasifier. How to start up the anaerobic digestion and fermentation tank for sludge. 3. The method according to claim 2, wherein the sludge undergoing methane fermentation is withdrawn from the digestion fermentation tank in an appropriate amount during the start-up of the anaerobic digestion fermentation tank, and a certain amount of the sludge is charged into a vessel. After replacing with gas, an appropriate amount of a solution of Na acetate is added, the temperature is maintained at a predetermined temperature, the amount of gas generated over time from this container is measured, and a load that can be processed in the entire methane fermentation tank is measured by a measuring method. 3. The method according to claim 2, further comprising the steps of: 4. Night soil, septic tank sludge, agricultural sludge, sewage sludge,
An anaerobic digestion system for organic sludge, in which organic waste such as livestock manure is separated into liquid waste and organic sludge, and the organic sludge is introduced into an anaerobic digestion and fermentation tank and methane fermented by anaerobic digestion. At the start of the operation of the anaerobic digestion and fermentation tank for the organic sludge, a substance having a low fiber content that is easily decomposed by the anaerobic digestion and fermentation bacteria such as rice bran, okara or garbage is first introduced and methane gas is supplied. After or in parallel with increasing the activity of the bacterium, the dehydrated organic sludge is put into the digestion fermentation tank, and while the volume load of the sludge is increased stepwise, the sludge is shifted to the rated load. Anaerobic digestion of organic sludge, wherein the digested sludge fermented in the anaerobic digestion fermenter is dewatered and separated, and the dewatered sludge is subjected to compost treatment, while the separated liquid subjected to dehydration separation is subjected to biological treatment. System M