JP2000246224A - Method for treating organic waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably decrease amt. of addition of an oxidizing agent for solubilization and to decrease cost for treatment in a method wherein after org. waste is methane-fermented, it is solubilized by adding the oxidizing agent and methane fermentation is furthermore performed to reduce the vol. SOLUTION: After digested sludge prepd. by methane fermentation in an anaerobic treating tank 1 is aerated in an aeration tank 2 to remove reductive substances in the digested sludge, an oxidizing agent such as ozone and hydrogen peroxide is added in an modifying tank 3 to solubilize it and methane fermentation is furthermore performed in the anaerobic treating tank 1. It is possible to decrease amt. of the oxidizing agent consumed by these reductive substances by removing the reductive substances in the digested sludge by aeration before adding the oxidizing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to high-concentration organic wastewater such as human waste, septic tank sludge, food factory wastewater, chemical factory wastewater, organic sludge from biological treatment processes, food waste, livestock manure, garbage, etc. In particular, in the method of methane fermentation of these organic wastes, adding an oxidizing agent to solubilize these organic wastes, and further reducing the volume by methane fermentation, To reduce the processing cost by reducing the amount of oxidizing agent added.

[0002]

2. Description of the Related Art In an aerobic biological treatment in which an organic wastewater is treated by the action of an aerobic microorganism, as in an activated sludge method, a large amount of bacteria that grow with the decomposition of organic matter is discharged as excess sludge. . Such excess sludge is discarded after being subjected to dehydration, incineration, and other treatments, and there is a problem in that sludge treatment costs and securing a disposal site. Also,
In recent years, the amount of high-concentration organic sewage such as night soil, septic tank sludge, food factory effluent, and chemical factory effluent, food waste, livestock manure, garbage, and the like has been increasing more and more. For this reason, a technique for reducing the volume of these organic wastes is desired.

Conventionally, as a means for reducing the volume of organic sludge, organic sludge is subjected to methane fermentation, and oxidizing agents such as ozone and hydrogen peroxide are added to digested sludge from a methane fermentation tank to solubilize the sludge. There is a method for further methane fermentation of solubilized sludge. According to this method, organic sludge is first subjected to methane fermentation to decompose and reduce the amount of anaerobic components easily decomposed in the organic sludge, and then solubilized. Compared with the case where the oxidizing agent is directly added to the sludge for solubilization, the amount of the oxidizing agent required for solubilization can be reduced, and the volume reduction of the organic sludge can be promoted.

[0004]

However, even the above-mentioned conventional volume reduction method has a problem that the amount of oxidizing agent required for solubilizing digested sludge is still large and the cost of oxidizing agent is high.

[0005] That is, digestive sludge extracted from a methane fermentation tank contains a large amount of reducing substances represented by hydrogen sulfide. On the other hand, for the solubilization of organic sludge, a strong oxidizing agent such as ozone or hydrogen peroxide is required, and reducing substances in digested sludge were originally added for solubilizing digested sludge. It is easily oxidized by an oxidizing agent such as ozone or hydrogen peroxide having a strong oxidizing power, and the oxidizing agent is immediately consumed. For this reason, in the step of solubilizing digested sludge, an oxidizing agent having to be added in an amount equal to or more than the amount of oxidizing agent necessary for solubilization has to be added.

The present invention solves the above-mentioned conventional problems and provides a method for solubilizing an organic waste by methane fermentation, adding an oxidizing agent, and then reducing the volume by methane fermentation. It is an object of the present invention to provide a method for treating organic waste, in which the amount of an oxidizing agent for the treatment is greatly reduced and the treatment cost is reduced.

[0007]

According to the present invention, there is provided a method for treating organic waste, comprising: a first anaerobic digestion step for methane fermentation of an organic waste; and a discharge from the first anaerobic digestion step. An aeration step of aerating digested sludge, a solubilization step of solubilizing the sludge that has passed through the aeration step by contacting the sludge with an oxidizing agent, and a second anaerobic digestion step of methane fermenting the solubilized sludge. Features.

[0008] Reducing substances such as hydrogen sulfide in digested sludge are:
Oxidation or degassing can be easily removed by aeration.
In the method of the present invention, the reducing substances in the digested sludge are removed by oxidative decomposition or degassing by aerating the digested sludge prior to solubilizing the digested sludge by adding an oxidizing agent. Therefore, the oxidizing agent added in the solubilization step is prevented from being consumed by these reducing substances, and the organic waste can be efficiently reduced in volume with a small amount of the oxidizing agent. Become.

[0009]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a system diagram showing a processing apparatus suitable for carrying out the organic waste processing method of the present invention. In the figure, 1 is a methane fermentation tank (anaerobic treatment tank), 2 is an aeration tank, 3 is a reforming tank, 4 is an ozone generator, and 5 is a sludge concentrator.

First, the organic waste is introduced into the treatment object introduction path 1.
1 and introduced into the anaerobic treatment tank 1 for methane fermentation treatment. In the anaerobic treatment tank 1, the organic waste is mixed with the concentrated sludge returned from the sludge concentration device 5 described later and the solubilized sludge returned from the reforming tank 3, and the methane fermentation is performed under stirring by a stirrer or the like. Processing is performed. Organic matter in the mixed sludge is decomposed by acid-producing bacteria and methane-producing bacteria in this methane fermentation. The digestion gas containing methane gas generated by this methane fermentation is discharged from the gas extraction path 12 to the outside of the system.

From the anaerobic treatment tank 1, a sludge transfer passage 13
After a part of the mixed sludge is taken out and sent to the sludge concentrating device 5 to be concentrated, the mixed sludge is returned to the anaerobic treatment tank 1 through the sludge return path 14. A part of the concentrated sludge is discharged as extra sludge from the surplus sludge passage 15 outside the system as necessary. The separated water from the sludge concentrator 5 is discharged from the treatment water channel 16 to the outside of the system.

As the sludge concentrator 5, a sedimentation tank, a membrane separator, a centrifugal concentrator, or the like can be employed.

A part of the mixed sludge in the anaerobic treatment tank 1 is
It is sent to the aeration tank 2 via the sludge extraction path 17 and is subjected to aeration treatment. The type of the aeration tank 2 is not particularly limited, as long as the sludge is exposed to air, and any type can be used. For example, as shown in FIG. 1, a diffuser method in which sludge is introduced into the aeration tank 2 and air is blown from the diffuser pipe 2A may be used, or a mechanical aeration method in which the sludge is brought into contact with air may be used. Alternatively, an aeration method in which sludge is sprayed from above may be used.
By the aeration in the aeration tank 2, reducing substances such as hydrogen sulfide in the digested sludge are oxidized or diffused into the air to be removed. Here, since the reducing substance is removed according to the amount of aeration and the aeration time, aeration conditions can be experimentally set according to the amount of the reducing substance in the digested sludge. This aeration condition cannot be said unconditionally depending on the anaerobic condition of the methane fermentation sludge, but in general, the aeration time may be about 0.5 to 5 hours.

The sludge aerated in the aeration tank 2 is sent from the sludge transfer passage 18 to the reforming tank 3 for solubilization.
In the apparatus of FIG. 1, an ozone treatment tank is employed as the reforming tank 3, and an ozone injection path 19 for injecting ozone from the ozone generator 4 is provided below the reforming tank 3. In the reforming tank 3, the solid component in the sludge is oxidized and decomposed by blowing ozone from the ozone injection passage 19 into contact with the sludge, thereby enhancing biodegradability. The sludge solubilized by the ozone treatment is returned to the anaerobic treatment tank 1 from the sludge return path 20, and the organic component modified to be easily biodegradable by the ozone treatment is digested and decomposed.

As described above, by solubilizing digested sludge subjected to methane fermentation and performing methane fermentation again, the amount of excess sludge discharged to the outside of the system can be significantly reduced.

According to the present invention, in the solubilization treatment of the digested sludge, the digested sludge is subjected to aeration treatment in advance to remove the reducing substances in the sludge. The oxidizing agent is effectively used for solubilizing the sludge without being wasted. For this reason, the amount of oxidizing agent used to achieve the desired amount of generated excess sludge can be significantly reduced as compared with the conventional case. Also,
The amount of surplus sludge generated can be significantly reduced with the same amount of oxidizing agent as before.

The apparatus shown in FIG. 1 is an example of an embodiment of the present invention, and the method of the present invention is not limited to the method shown in FIG.

For example, in FIG. 1, an ozone treatment tank to which ozone is added is adopted as a solubilizing means, but a solubilizing means using an oxidizing agent having a strong oxidizing power such as hydrogen peroxide may be used.

In FIG. 1, the digested sludge withdrawn from the anaerobic treatment tank 1 is subjected to aeration treatment and solubilization treatment, and then circulated again to the anaerobic treatment tank 1, whereby the first anaerobic digestion step and the second anaerobic digestion step are performed. Although the anaerobic digestion step is performed in the same anaerobic digestion tank, a separate anaerobic digestion tank is provided, and the first anaerobic digestion step and the second anaerobic digestion step are performed in separate anaerobic digestion tanks. Is also good. In this case, the digested sludge of the second anaerobic digestion step is separated into a solid and a liquid to separate the excess sludge and the liquid component.

In FIG. 1, the sludge from the anaerobic treatment tank 1 is extracted, concentrated by the sludge concentration device 5, and the concentrated sludge is returned to the anaerobic treatment tank 1. In this manner, the sludge is concentrated. The sludge volume is reduced, the reaction efficiency of the aeration and solubilization treatment, and the operation efficiency of the apparatus are improved, which is effective in improving the treatment efficiency. When the digested sludge is concentrated in this way, as shown in FIG. 1, in addition to extracting the sludge from the anaerobic treatment tank 1 and returning it after concentration, the extracted sludge from the anaerobic treatment tank 1 to be subjected to aeration and solubilization treatment is directly used. The solid sludge may be separated and concentrated, and the concentrated sludge may be aerated and solubilized.

The liquid separated by such a sludge concentration treatment is discharged out of the system and treated by an arbitrary method such as an activated sludge treatment.

[0023]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 and 2 Organic sludge was treated using the apparatus shown in FIG.

A jar fermenter having an effective capacity of 2 L was used as an anaerobic treatment tank 1 having a liquid volume of 1.5 L, and a temperature of 53 L.
C. was controlled. High-temperature anaerobic sludge from a sewage treatment plant was used as the seed sludge. In this anaerobic treatment tank 1, raw sludge obtained by concentrating excess sludge from a urine treatment plant to about 5% by weight as TS was supplied as an object to be treated in an amount of 130 mL per day. Sludge thickener 5
, An excess sludge was appropriately extracted so as to maintain the sludge concentration in the anaerobic treatment tank 1 at 50,000 mg-TS / L. 1 digestion sludge in anaerobic treatment tank 1
130 mL was withdrawn, introduced into the reforming tank 3 via the aeration tank 2, subjected to solubilization treatment by aeration treatment and ozone treatment, and then returned to the anaerobic treatment tank 1.

The amount and time of aeration in the aeration tank 2;
Table 1 shows the amount of ozone reaction and the amount of ozone used in the reforming tank 3.
As shown in FIG.

When such processing is performed for 40 days,
The amount of surplus sludge generated (cumulative) was as shown in FIG.

Comparative Examples 1 and 2 In Examples 1 and 2, aeration was not performed in the aeration tank.
The digested sludge extracted from the anaerobic treatment tank 1 was treated in the same manner except that only the solubilization treatment was performed under the conditions shown in Table 1 and the digested sludge was returned to the anaerobic treatment tank 1. 40 at this time
The generation amount (cumulative) of the excess sludge after the day treatment was as shown in FIG.

[0029]

[Table 1]

The following is clear from the results.

That is, by comparing the results of Example 1 and Comparative Example 1 and the results of Example 2 and Comparative Example 2 with each other, by performing aeration treatment, the amount of excess sludge generated is greatly reduced with the same amount of ozone used. You can see that Further, by comparing the results of Comparative Example 1 and Example 2, it can be seen that by performing aeration treatment, the amount of ozone used, which results in the same amount of excess sludge generation, can be significantly reduced.

[0032]

As described in detail above, according to the organic waste of the present invention, the organic waste is subjected to methane fermentation, solubilized by adding an oxidizing agent, and further reduced in volume by further methane fermentation. In this method, the amount of an oxidizing agent added for solubilization can be greatly reduced, and the processing cost can be reduced. Therefore, according to the present invention, the volume of organic waste can be reduced efficiently at low cost.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a processing apparatus suitable for implementing an organic waste processing method of the present invention.

FIG. 2 is a graph showing the amount of excess sludge generated in Examples 1 and 2 and Comparative Examples 1 and 2.

[Explanation of symbols]

 Reference Signs List 1 Anaerobic treatment tank 2 Aeration tank 3 Reforming tank 4 Ozone generator 5 Sludge concentrator

Continued on front page F term (reference) 4D004 AA01 AA02 AA03 AA04 BA03 BA10 CA13 CA18 CA36 CA41 CA50 CB04 CC01 CC02 CC11 4D040 AA02 AA27 4D059 AA01 AA02 AA03 AA05 AA07 AA08 BA12 BA13 BA31 BA34 BA60 BC44 BK16 DA43

Claims (1)

[Claims] 1. A first anaerobic digestion step for methane fermentation of an organic waste, an aeration step for aerating digested sludge discharged from the first anaerobic digestion step, and a sludge that has passed through the aeration step. A method for treating organic waste, comprising: a solubilization step of solubilizing by contacting with an oxidizing agent; and a second anaerobic digestion step of methane fermenting the solubilized sludge.