JPH02999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating organic waste such as treated sludge such as sewage and wastewater, municipal waste, and other industrial waste.

Conventional methods for treating organic sludge from sewage and human waste treatment facilities, and the most commonly used representative treatment method, include polymer flocculants and ferric chloride, which are valuable resources for organic sludge. The process involves adding a large amount of dehydration aids such as lime, dehydration using a mechanical dehydrator, drying and incineration as a dehydrated cake, so a large amount of auxiliary fuel such as heavy oil is consumed for drying and incineration. Moreover, since the high-moisture dehydrated cake with a water content of about 70 to 80% is dried using incineration exhaust gas or hot air and then incinerated, a large amount of unbearable odor is generated.To prevent this odor, the odor gas generated is directly ignited. Since deodorization is done through various deodorizing processes such as combustion deodorization, catalytic combustion deodorization, wet chemical cleaning, and adsorption, the process is complicated and there are serious problems in terms of maintenance and maintenance costs.

In particular, as the environment surrounding oil has deteriorated in recent years, there has been a strong demand for resource conservation, energy conservation, and even energy production in forms other than oil. The most aggressive approach is to carry out methane fermentation of sewage/wastewater treatment sludge and municipal waste, and a technology has been proposed that recovers it in the form of methane gas and electricity. However, there are still some problems with these methane fermentation techniques, and further technical progress is desired by solving these problems. For example, with this conventional technology, it is not possible to generate enough methane gas to make it economically viable, or it is difficult to process and dispose of the residue after methane fermentation.
On the contrary, it had the disadvantage of requiring a large amount of money.

The present invention solves a number of unreasonable problems in the conventional organic waste treatment process, greatly improves biodegradability, prevents the generation of foul-smelling gas, and
The object of the present invention is to provide a method for treating organic matter that can be extremely energy-saving, efficiently treated, produces inexpensive energy, and simplifies post-treatment.

The present invention subjects organic waste to acid fermentation treatment,
In addition, when the heating temperature is 175℃ or higher at pH 5 or lower, 10
This is a method for treating organic waste, which is characterized by carrying out a heat treatment for less than a minute, followed by a methane fermentation treatment.

In other words, when methane fermenting organic waste, it is important to functionally separate the acid fermentation process and the methane production process, and to perform a heat treatment process between both processes, and to perform this heat treatment at a pH of 5 or less. This is one of the characteristics.

In this case, it is important not only to increase the amount of methane gas generated, but also to improve the solid-liquid separation of the residue after methane fermentation, treat odor and heat treatment desorbed liquid, effectively utilize waste heat obtained in the heat treatment process, and compost. Significant improvements can be made in this respect. Moreover, the generated energy can be at least mechanically powered, a heat source for the heating section, sludge heating or moisture reduction, high-level drying,
It includes the process of water treatment of organic sludge generation sources and other power, and the process of supplying and utilizing various heat, power, and electrical energy consuming processes using various pumps.

In addition, in the heat treatment step, if heat treatment is performed in a low pH range of PH5 or less, organic matter may be denatured, for example, hydrolyzed and reduced to a There is a high percentage of dissolved substances that become soluble and become easily biodegradable, and even substances that cannot be decomposed in the normal methane fermentation process can be biodegraded. Regarding the denaturation of organic substances, in the case of the method of the present invention, acid fermentation is performed prior to heat treatment, so organic substances that are easily biodegradable in the acid fermentation process are decomposed, and organic substances that are not decomposed in the acid fermentation process are The efficiency of the heat treatment process is improved because the heat treatment process concentrates on converting organic waste into easily biodegradable substances. Furthermore, since the pH is below 5, the fluidity of organic waste increases, and heat treatment is effective in this respect as well. efficiency will be improved. That is, if acid fermentation treatment is performed as in the present invention,
Naturally, at this stage, the pH is around 5, preferably PH4.5.
The viscosity decreases compared to before the acid fermentation process, and during the acid fermentation process, the pH increases to around 5 or
Since the pH is 5 or less, the amount of acid added to adjust the PH to 5 or less in the heat treatment stage can be significantly reduced. In addition, this characteristic is that after the acid fermentation process,
The same advantage can be obtained even if solid-liquid separation is performed, only the concentrated part resulting from the solid-liquid separation is passed through the heat treatment process, and the separated liquid part is led to the methane fermentation process without passing through the heat treatment process.

In this way, a very large amount of biodegradable organic matter is produced, and since this is in a low pH range, the amount of methane gas generated from the methane fermentation process is greater than the amount generated from a normal methane fermentation process in order to undergo methane fermentation efficiently. This also increases the amount of energy that can be recovered. Generally, the pH in a methane fermenter is 7.0 to 8.0, whereas the introduction of easily biodegradable organic matter in the PH range of 5 or lower into the methane fermenter is extremely helpful in promoting methane fermentation.

Furthermore, in the present invention, most of the fermentation residues are in the form of slurry, and solid-liquid separation of the methane fermentation residues is included in the treatment and disposal of the fermentation residues. However, solid-liquid separation of this fermentation residue is very difficult, and in order to avoid expending more energy than that recovered in the methane fermentation process, it is necessary to - By heat-treating wastewater treatment sludge, the solid-liquid separability is significantly improved, and the improvement in solid-liquid separability due to this heat treatment is not impaired by methane fermentation after the heat treatment. In other words, heat treatment is performed under acidic conditions with a pH of 5 or lower, and methane fermentation is carried out without taking measures to return the pH value to around neutrality, so organic waste is simply heat treated and methane fermented without adjusting the pH. It exhibits solid-liquid separation performance that is more advanced than the technology, which further improves the solid-liquid separation of methane fermentation residues compared to the prior art, and significantly reduces the energy required for the solid-liquid separation operation.

Furthermore, when organic waste is heat-treated, scale tends to adhere to the heat treatment equipment and the piping system used to utilize heat effectively through the heat exchanger and the heat treatment equipment, resulting in a decline in the heat treatment and heat exchange function. To prevent this, the pH is
It is effective to adjust the pH of organic waste to 5 or less, and in particular, a large amount of acid is required to adjust the pH of organic waste to 5 or less. However, in the present invention, acid fermentation is performed before the heat treatment process. Because of this, the pH value is lower than waste that does not undergo acid fermentation, and the amount of acid consumed is small.
Only a small amount of acid is needed to adjust the pH to 5 or less. In this case, depending on the waste, it may have already been processed through the acid fermentation process.
A pH of 5 or less is often achieved, and there are cases where acid is not required and it is possible that the process can be carried out without the use of acid. If the pH does not reach 5 or less in the acid fermentation process, the acid used for pH adjustment is preferably an organic acid, but if a mineral acid is used, hydrochloric acid is most preferred. In this way, heat treatment is performed at a pH of 5 or below, which not only increases fluidity but also solves the problem of scale adhesion to the heat treatment equipment body, heat exchanger, and the inside of the piping via these, allowing heat treatment and heat exchange to be carried out efficiently. It will be done. The waste heat generated from this heat treatment process can also be effectively used, for example, to heat the acid fermentation process and the methane fermentation process. As a result, in the acid fermentation step, heating may be performed in either a medium temperature range or a high temperature range, but a high temperature range is possible and desirable. Acid fermentation in a high temperature range can improve the acid fermentation speed, reduce the volume of the acid fermenter, and reduce the amount of waste after acid fermentation, and can also reduce the size of these heat treatment equipment. The effect of reducing the amount of heat required for heating is further increased by performing solid-liquid separation after the acid fermentation step and applying heat treatment only to the concentration section.

In addition, in the method of the present invention, the heating temperature in the heat treatment is set to 175°C or higher, as compared to 175°C or lower, the dehydration overrate is greatly improved, and the dehydration property is improved.
This is also because the rate of organic matter decomposition during methane fermentation increases significantly.

In addition, heat treatment at temperatures above 175°C not only showed no inhibition of digestion, but also markedly improved the solid-liquid separation performance of the methane fermentation liquid at around 175°C. Significant improvements can be made in terms of improved solid-liquid separation of the residue after fermentation, and treatment of odors and heat-treated liquid.
Furthermore, the heating time of the heat treatment has a large effect on the temperature at 175℃.
If heat treatment is performed for more than 30 minutes, not only will digestion be inhibited in the subsequent methane fermentation process, but the solid-liquid separation performance will also deteriorate, the decomposition rate of VS will deteriorate, the amount of gas generated will decrease, and the dehydrated cake will contain water. If the heating temperature is 175℃ or higher, the heating time will be
It should be kept within 10 minutes.

In this way, in the present invention, biodegradability is increased by acid fermenting organic waste, heat-treating it at 175°C or higher and then methane fermentation at a pH of 5 or less, and thereby reducing the amount of methane gas generated. Not only is the solid-liquid separation of the methane fermentation residue improved. Since the heat treatment is carried out at a pH of 5 or less, the fluidity of the waste increases, the heat treatment is performed efficiently, the heat treatment time is shortened, and there is no possibility of scale build-up on the heat treatment equipment body, heat exchanger, or the inside of the piping that passes through them. The problem is solved, heat exchange is performed efficiently, and the pH after acid fermentation is
Since it is an adjustment and a heat treatment, the amount of chemicals required for pH adjustment is small, and the amount of waste is reduced by acid fermentation, so the heat treatment equipment can be made smaller.

Incidentally, heat treatment of organic waste often produces a considerable odor, which is particularly noticeable in the heat treatment of sewage treatment sludge, but by performing methane fermentation after heat treatment, a considerable amount of the odor components can be removed. In addition to eliminating the risk of secondary pollution,
The chromatic component of the heat treatment desorbed liquid is very dark, and it is very difficult to remove the chromatic component using only biological treatment.However, at least ferric chloride is used as a flocculation aid during solid-liquid separation of the methane fermentation residue. By employing the solid-liquid separation method used as a method, it was possible to remove a considerable amount of chromatic components.

Here, the amount of ferric chloride added is such that the pH after addition is at least 5.5 or less, and the amount is preferably 10 to 30% based on the solid content of the methane fermentation residue. If solid-liquid separation is difficult with only this ferric chloride, calcium or magnesium-based alkali such as slaked lime or magnesium hydroxide may be further added as a coagulation aid. In this way, when solid-liquid separation is performed by adding at least ferric chloride as a flocculation aid to the methane fermentation residue, there is also the advantage that coloring components generated during the heat treatment process can be removed at the same time as the solid-liquid separation.

To explain an embodiment of the present invention with reference to the drawings, organic waste 1 is put into an acid fermenter 2 and heated to a high temperature or medium temperature range by a heat treatment device 4 and a heat exchanger 6. The material is allowed to remain in the acid fermenter 2 for a residence time sufficient to carry out acid fermentation, and is stirred throughout or as appropriate. Organic waste after acid fermentation or concentrate separated by solid-liquid separator 7 is left as is if its pH is 5 or less, otherwise organic acid 3 or hydrochloric acid is added to it to make the pH 5 or less. Heat treatment equipment 4 with a treatment temperature of 175℃ or less
heat-treated. The waste that has been heat-treated for a predetermined period of time is put into a methane fermentation tank 5 that exchanges heat with the heat treatment device 4, and is allowed to remain there for a residence time sufficient for methane fermentation, and is stirred throughout or as needed. At least ferric chloride is added as a flocculation aid 9 to the treated material 13 coming out of the methane fermentation tank 5, and then solid-liquid separation is performed in a solid-liquid separator 10, and the desorbed liquid 11 is returned to the water treatment system. . Note that when solid-liquid separation is performed after the acid fermentation is completed, it is preferable that the separated liquid 8 is flowed into the methane fermentation tank 5 for treatment.

As described above, the present invention not only increases the biodegradability of organic waste and increases the amount of methane gas generated, but also improves the solid-liquid separation of methane fermentation residue, and improves various aspects related to heat treatment and heat exchange. In addition to its advantages, it also solves the problems of malodor components and color components of the desorbed liquid, which have traditionally been considered major problems in heat treatment, and has the benefit of being able to comprehensively recover energy from organic waste. There is.

Next, an example of the present invention will be shown in comparison with a conventional method. When 78.4% (hereinafter referred to as VS/TS) sewage sludge with a pH of 5.6 is allowed to stay for one day in an acid fermenter that is controlled at 52±1°C and continuously stirred for three days, the pH of the sludge is 78.4%, pH5.0,
Acid-fermented sludge with TS: 3.0%, VS: 2.2%, and VS/TS: 74.5% was obtained. When this was placed in an autoclave with a capacity of 5 and heat treated at 175℃ for 10 minutes, the pH
5.1, TS: 3.0%, VS: 2.2%, VS/TS: 73.2%
A heat-treated sludge with an odor concentration of:
1,040,000, and the chromaticity of the desorbed liquid was 580. When this heat-treated sludge is kept in a methane fermentation tank maintained at 35±1℃ and continuously stirred for 15 days (the capacity of the methane fermentation tank is 45), 61% of the VS is decomposed and the gas is released per day. 56.9 occurred, PH7.6, TS: 1.7%,
Methane fermentation sludge with VS: 0.85% and VS/TS: 51.5% was obtained. Add ferric chloride to this at 20% per TS,
Water content was 65.4% when 50% slaked lime was added, filtration pressure: 4Kg/cm ² , filtration time: 30 minutes, compression pressure: 9Kg/cm ² , and compression time: 20 minutes.
A dehydrated cake was obtained. The dehydration solution has a chromaticity of 22,
Odor concentration of dehydrated cake: 380.

Example 2 The acid fermentation sludge, which was the same as in Example 1 up to the acid fermentation process, was centrifugally concentrated at 1360G for 10 minutes without chemical injection.
TS: 5.1%, VS: 3.8%, VS/TS: 74.5% thickened sludge is 1.7, TS: approx. 2300mg/, VS: approx.
1.3 of 1700 mg/separate solution was obtained. This thickened sludge was put into an autoclave with a capacity of 5 and heated to 175°C.
When heat treated for 10 minutes at PH5.2, TS: 5.1%, VS:
3.8%, VS/TS: 74.3% heat treated sludge was obtained,
The odor concentration was 1,230,000, and the chromaticity of the desorbed liquid was 730. This heat-treated sludge and the centrifuged liquid were mixed for 35±
Remain in a methane fermenter maintained at 1℃ and continuously stirred for 15 days (methane fermenter capacity 45
) and 95% of VS decomposes and gas is released per day.
57.0 occurred, PH7.7, TS: 1.7%, VS: 0.9%,
VS/TS: 53.6% methane fermentation sludge was obtained.
Add 15% ferric chloride per TS and 50% slaked lime to this.
% added, filtration pressure: 4Kg/cm ² , filtration time: 30 minutes,
When pressurized dehydration was performed under the conditions of pressing pressure: 9 Kg/cm ² and pressing time: 20 minutes, a dehydrated cake with a moisture content of 63.8% was obtained. The color of the dehydrated solution was 25, and the odor concentration of the dehydrated cake was 350.

Comparative example: When the same sewage sludge as in Examples 1 and 2 is placed in an autoclave with a capacity of 5 and heat-treated at 175°C for 30 minutes,
PH5.8, TS: 3.5%, VS: 2.8%, VS/TS: 78.2
% heat treated sludge was obtained. The odor concentration of this heat-treated sludge is 930,000, and the chromaticity of the desorbed liquid is 520, which is 35±
Remain in a methane fermenter maintained at 1℃ and continuously stirred for 15 days (methane fermenter capacity 45
) and 51% of VS decomposes to produce gas per day.
53.2 occurred, PH7.6, TS: 2.1%, VS: 1.4%,
VS/TS: 64.2% methane fermentation sludge was obtained.
If this is left to stand for one day, it will settle and concentrate, and the volume occupied by the thickened sludge will be 23%, TS: 7.4%, VS: 4.8
% thickened sludge is obtained. The precipitated and separated water at this time had a chromaticity of 550 and an odor concentration of 760. To the obtained thickened sludge, 20% ferric chloride and 50% slaked lime were added per TS, filtration pressure: 4Kg/cm ² , filtration time:
When pressurized dehydration was performed for 30 minutes, compression pressure: 9Kg/cm ² , and compression time: 20 minutes, the water content was 67.1%.
A dehydrated cake was obtained. This dehydrated solution had a chromaticity of 17 and an odor concentration of 330.

[Brief explanation of drawings]

The drawing is a flow sheet of one embodiment of the method of the present invention. 1...Organic waste, 2...Acid fermenter, 3...
Hydrochloric acid or organic acid, 4... Heat treatment device, 5... Methane fermentation tank, 6... Heat exchange, 7... Solid-liquid separation section,
9... Coagulation aid, 10... Solid-liquid separator, 11...
...Liquid removed by solid-liquid separation, 12...Generated gas.

Claims (1)

[Claims] 1. Organic waste is subjected to acid fermentation treatment, and further PH
A method for treating organic waste, which comprises subjecting the waste to heat treatment at a heating temperature of 175°C or higher for less than 10 minutes at a temperature of 5°C or lower, followed by methane fermentation treatment. 2. Claim 1, wherein the acid fermentation step involves solid-liquid separation after acid fermentation, in which only the concentrate is heat-treated, and the separated liquids are introduced into the methane fermentation step without being heat-treated. Treatment method described in section. 3. The treatment method according to claim 1 or 2, wherein the methane fermentation step includes a solid-liquid separation step of methane fermentation residue after methane fermentation. 4. Claim 3, wherein the methane fermentation step is a solid-liquid separation treatment after methane fermentation, and at least ferric chloride is added as a coagulation aid to this solid-liquid separation treatment. Processing method described.