JP2003117597A - Biological treating method for excess sludge by utilizing hydrothermal reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is applicable even when there is no room for the treating capability of an aerator in particular by studying reaction conditions in decomposing organic matter in the sludge produced by a waste water treatment by a hydrothermal reaction, thereby decreasing the amount of the energy to be charged, decreasing the amount of inorganic suspended solids, such as monolithic carbon and finally annihilating or decreasing wastes. SOLUTION: The hydrothermal reaction treatment is performed under reaction conditions of a temperature ranging from >=140 to <200 deg.C and pressure ranging from 0.5 to 1.6 MPa milder than the conventional subcritical conditions and the treated liquid is subjected to an aerobic treatment in a separately installed aerobic bioreaction chamber and thereafter the treated liquid is returned to a biological treating equipment or is discharged as treated water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biological treatment of wastewater utilizing a hydrothermal reaction, which enables the organic matter in sludge generated by wastewater treatment to be completely eliminated or to be greatly reduced.

[0002]

2. Description of the Related Art The most common wastewater treatment method is a biological treatment method, and sewage, domestic wastewater, factory wastewater, livestock excrement wastewater and the like are almost all treated by this method. In biological treatment, the main constituents are microorganisms, so that microorganisms that grow are generated as excess sludge. Therefore, although the amount of sludge has been reduced by anaerobic treatment such as methane fermentation, it cannot be completely eliminated, and most of them are incinerated or landfilled after dehydration.

Therefore, there have conventionally been proposed some methods for treating surplus sludge by utilizing so-called hydrothermal reaction in which water is brought into a state of high temperature and high pressure to react with organic matter of sludge. Here, the high temperature and high pressure state includes a supercritical water state that exceeds the critical point of water (374 ℃, 22MPa) and a subcritical water state that is below the critical point. The former is typically 450 ℃ to 600 ℃, 25MPa. ~ 50M
Pa, the latter is typically 300 ℃ -360 ℃, 9MPa-19
A range of MPa is used.

The conventional methods for treating surplus sludge utilizing the hydrothermal reaction are roughly classified into 1) liquefaction of sludge (utilization as fertilizer and feed), 2) oilification of sludge (utilization of fuel). And 3)
There are three types of decomposition and volume reduction of sludge. Wet oxidation, which is a conventional sludge volume reduction method, is reacted with an oxidizing agent such as oxygen or hydrogen peroxide under the above-mentioned supercritical water conditions in which dehydrated sludge is added as a catalyst to oxidize carbon dioxide or ammonia. So
It requires harsh conditions such as a large amount of catalyst and ultra-high temperature, which is not economically and economically attractive. In addition, supercritical water has a low dielectric constant and significant precipitation of inorganic salts,
It has many problems such as clogging of reactor and pipe system and use of harmful catalyst.

As a method for solving the problems of the method for treating surplus sludge utilizing hydrothermal reaction, Japanese Patent Laid-Open No. 2000-218295 discloses the following method. That is, as shown in FIG. 6, it is a method in which a hydrothermal reaction device 3 is added to a biological treatment device comprising an aeration tank 1 and a solid-liquid separation tank 2, and a subcritical state (320 ° C., 12.1 ° C.) is set in the hydrothermal reaction device. Mpa) and a large amount of water (approximately 90-99%
(About a certain degree), the organic components in the sludge are decomposed so that bacteria can easily treat them, and the treatment liquid is decomposed and eliminated in the existing aeration tank 1. Most of the sludge is microbial cells, and also includes fine plant and animal sludge. Then, due to the hydrothermal reaction, bacteria or bacteria used for biological treatment of wastewater and sludge can be easily treated, so that difficult biodegradable substances in sludge are converted to sugars and amino acids (or some of their molecules are further decomposed), etc. It is decomposed into the easily biodegradable substance, and the resulting treatment liquid is returned to the aeration tank of the biological treatment process, for example, the activated sludge method, where it is decomposed by bacteria.
It is an assimilation.

[0006] This hydrothermal reaction device is usually attached to a biological treatment device that generates sludge, such as an activated sludge device, and the treatment liquid obtained by the hydrothermal reaction device is used as the original activated sludge treatment device. It is sent back to the aeration tank or contact aeration tank of the equipment and used again for biodegradation. Furthermore, when excess sludge generated from a biological treatment device such as an activated sludge treatment device is treated with another biological treatment device such as an anaerobic treatment device, a hydrothermal reaction device is provided as an accessory to the anaerobic treatment device. It is also possible to perform hydrothermal treatment in advance and then put it in the anaerobic treatment apparatus.

[0007]

Under the conventional subcritical conditions, the hydrothermal reaction itself is carried out at high temperature and high pressure.
Therefore, a large amount of energy needs to be input. Further, under conventional reaction conditions, the amount of inorganic suspended solids such as amorphous carbon (which may be abbreviated as inorganic SS below) generated due to excessive progress of the decomposition reaction is an obstacle to biological treatment again. However, the amount of suspended solids (hereinafter sometimes abbreviated as SS) that must be finally dehydrated and discharged out of the system increases. In addition, if the treatment liquid of the hydrothermal reaction is returned to the original aeration tank and biological treatment is performed as in the conventional case, the load of the original aeration tank will increase, and it may be difficult to apply because there is no room for biological treatment capacity. .

In the present invention, by examining the reaction conditions, the amount of energy input is reduced, and the amount of inorganic SS such as amorphous carbon generated is reduced to eliminate or eliminate the final waste. The purpose is to reduce. Further, in the case of a wastewater treatment facility of a factory, etc., it is often the case that the treatment capacity of the aeration tank is already insufficient, and it may be difficult to apply the conventional technology.Therefore, it is an object to provide a method for solving this. To do.

[0009]

According to the present invention, (1) sludge generated in a biological treatment device for wastewater is sent to a hydrothermal reaction device,
In the excess sludge treatment method that decomposes hardly biodegradable organic matter in sludge into easily biodegradable substances by hydrothermal reaction, hydrothermal reaction treatment is performed at a temperature of 140 ° C or more, which is milder than conventional subcritical conditions.
Treated under reaction conditions in the range of less than 200 ° C and pressure of 0.4 MPa or more and 2.0 MPa or less, aerobically treating the treated solution in an aerobic biological reaction tank separately installed, and then treating the treated solution with the biological treatment apparatus. A method for treating excess sludge biological matter utilizing a hydrothermal reaction, which is characterized in that it is returned to or discharged as treated water, (2) a solid-liquid separator is provided as a pre-process of an aerobic biological reaction tank, A liquid having a low solid content is supplied to the biological reaction tank, and a liquid having a high solid content is sent to an existing biological treatment device and / or a hydrothermal reaction device and / or a dehydration treatment device for treatment. (1) An excess sludge biological treatment method utilizing the hydrothermal reaction according to (1) above, (3) a solid-liquid separation device is provided as a post-step of the aerobic biological reaction tank, and the treated liquid is discharged and concentrated sludge Slurry is hydrothermal reactor and / or dehydration treatment A method of treating excess sludge biological reaction utilizing the hydrothermal reaction according to any one of (1) to (2), characterized in that the liquid to be treated is treated with the liquid to be treated in the hydrothermal reaction device. The surplus sludge biological treatment method utilizing the hydrothermal reaction according to the above (1) to (3), characterized in that the treatment liquid is heat-exchanged.

The hydrothermal treatment used in the present invention is premised on the biofilm treatment in the latter stage, and therefore, the treatment capacity of the entire system is not inferior even if milder conditions are applied than in the case of hydrothermal treatment alone. On the contrary, since carbonization, which is a problem in the case of high temperature and high pressure treatment, does not proceed so much, it has an effect that the property of water after treatment is excellent.

The present inventors have found that SS is decomposed to such an extent that it is sufficiently suitable for biological treatment, and carbonization is suppressed.
It was found that the temperature is preferably 40 ° C or higher and lower than 200 ° C, more preferably 145 ° C or higher and 195 ° C or lower, and combined with the biological reaction in the latter stage, it was possible to significantly reduce the amount of environmental pollutants after treatment. Further, since these devices are more compact than the conventional reaction device, it is easy to add them to the subsequent stage of the existing processing device, and it is not necessary to secure a large new installation space.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to the drawings.

As shown in FIG. 1, the basic structure of the present invention comprises an aeration tank 1, a solid-liquid separation tank 2, a hydrothermal reaction device 3 and a biological reaction tank 4. The sludge that has been separated and concentrated in the solid-liquid separation tank 2 is drawn from the line L4 to obtain drawn sludge.
A part of the sludge is sent to the hydrothermal reaction device 3 as a sludge to be treated through a line L7, where the hardly biodegradable substance in the sludge is converted into a readily biodegradable low-molecular substance group, and obtained. The treated liquid thus obtained is sent to the biological reaction tank 4 via a line L8,
Metabolically decomposes due to microbial function, and aeration tank 1 from line L9
Will be returned to.

A part of the drawn sludge is returned to the aeration tank via the line L5 as return sludge. If the amount of drawn sludge is large, it is discharged as excess sludge out of the system.
However, in the case of the present invention, surplus sludge is generated if the capacity of the hydrothermal reaction device is insufficient, but if the hydrothermal reaction device has sufficient capacity, normally so-called surplus sludge is not generated. . In addition, inorganic substances such as mineral substances in sludge and traces of carbon particles generated by dehydrogenation and deoxygenation are finally removed as trace components in treated water or outside the system from solid-liquid separation tanks. There is a need.

In the method of the present invention, a stirred tank and / or a tubular reactor is used as the type of hydrothermal reactor, but a tubular reactor having a small residence time distribution is more preferable in consideration of treated water quality and the like. preferable.

In the method of the present invention, the method of heating / heating may be appropriately selected from direct heating with steam, indirect heating, heating with electric heating and the like.

In the method of the present invention, the hydrothermal reaction conditions are preferably such that SS is decomposed to a degree suitable for biological treatment and carbonization is suppressed. It is preferably lower than ℃, more preferably 145 ℃ or more and 195 ℃ or less.

In the method of the present invention, the aerobic bioreactor may be of any type such as an activated sludge method and a biofilm method, but the biofilm method is particularly preferred from the viewpoint of treatment capacity. . In particular, the advantage of the biofilm method is brought to full advantage when there is not enough space.

In the present invention, when a fixed bed type reaction tank is used as the biological reaction tank, a sedimentation tank 5 is provided as a pretreatment step for the biological reaction tank 4 as shown in FIG.
The undecomposed sludge can be separated into and then supplied to the biological reaction tank 4. On the other hand, the separated sludge slurry can be returned to the existing biological treatment apparatus and / or hydrothermal reaction apparatus, and can be dehydrated if necessary.

As another embodiment, an example in which a biofilm filtration method is used in a biotreatment device will be described with reference to FIG.
The waste water is treated from L1 in a biofilm filtration tank 7 using, for example, foamed plastic as a filter medium. After a lapse of a certain time after starting the treatment, so-called backwashing is performed to remove sludge accumulated in the filter medium layer. Backwash drainage is backwash drainage sludge concentrator 8
Collected in. Usually, a plurality of 7 are installed, so the backwash time of each tank is slightly shifted so that the amount of wastewater generated is leveled. The sludge concentrated in 8 is sent to the hydrothermal reaction device 3 through the line L7. The subsequent steps are the same as in FIG.

This structure is characterized in that, when biological treatment of waste water is carried out, biological treatment is carried out in the same manner as in the case of hydrothermal treatment liquid, in place of an ordinary aeration tank. Can be released as is.

In the present invention, as shown in FIG. 4, the liquid to be treated may be treated by the hydrothermal reactor 3 from L7 depending on the regulated values of the water quality of wastewater (BOD (biochemical oxygen demand), SS, etc.). , The treatment liquid is treated in the biological reaction tank 4, and the treatment liquid is treated with L14.
It can be released more. Of the water quality of L14, SS
If only the amount exceeds the regulation value and cannot be returned to the existing biological treatment equipment, it can be sent from L15 to the settling tank 5 to separate SS for sedimentation and then discharged. In this case, the separated SS is taken out from 5, and again passed through L12 to 3
Will be returned and processed. The biologically unprocessable SS component is contained in the upper discharge water of 5 at a dilute concentration and is released. If it still accumulates on the balance of the system, install a dehydrator 6
Can be processed.

FIG. 5 shows an example of a detailed configuration of the hydrothermal reaction apparatus 3, that is, the water to be treated and the treated water are heat-exchanged by the heat exchanger 10 to recover heat.

[0024]

EXAMPLES Specific examples of the present invention will be described below.

[Example 1] (Treatment raw water: artificial drainage) In this example, in order to reproduce the drainage containing a large amount of organic substances, an aqueous solution of glucose and peptone was prepared and used as artificial drainage. It was prepared at the following concentrations so as to have a BOD of 500 mg / L.

Component glucose 380 mg / L peptone (protein hydrolyzate) 130 mg / L In addition, the following concentrations of pollutants are all BOD (biodegradable),
Shown as SS (non-biodegradable).

(Device) In this embodiment, the basic device configuration shown in FIG. 1 was adopted.

Aeration tank 1: Volume 5 m ³ Solid-liquid separation tank 2: Volume 0.5 m ³ Hydrothermal reactor 3: Volume 10 L Biological reaction tank 4: Volume 75 L (implementation result) Raw water (artificial drainage) is BOD 500 mg / L,
This was supplied to the aeration tank 1 at 10,000 kg / day. The surplus sludge separated in the solid-liquid separation tank 2 is SS 10,000 at 200 kg / day.
It was mg / L. This is sent to the hydrothermal reactor 3 and the temperature
When hydrothermally treated at 0 ° C., pressure of 0.6 MPa and residence time of 1 hour, BOD was 1500 mg / L and SS was 1500 mg / L. When the obtained treatment liquid was further sent to the biological reaction tank 4 via a line L8 for treatment, BOD 150 mg / L, SS
It became 2000 mg / L.

When the treated liquid is returned to the aeration tank 1, the load on the aeration tank is increased by only 0.6% as compared with the case where the sludge is directly returned to the outside without returning it. The ability indicates that it can continue to be used.

Comparative Example 1 Raw water (artificial wastewater) was treated under the same conditions as in Example 1 except that the biological reaction tank 4 was omitted and the conventional apparatus configuration shown in FIG. 6 was used. When the liquid treated in the same manner as in Example 1 was returned to the aeration tank 1, the load on the aeration tank was increased by 6% as compared with the case where the sludge was separated from the system without returning it, and the actual treatment It will lead to the loss of ability.

[Embodiment 2] (Apparatus) In this embodiment, an apparatus configuration shown in FIG. 2 is adopted by adding a sedimentation tank 5.

Aeration tank 1: Volume 5 m ³ Solid-liquid separation tank 2: Volume 0.15 m ³ Hydrothermal reactor 3: Volume 10 L Biological reaction tank 4: Volume 75 L Sedimentation tank 5: Volume 15 L (implementation results) Raw water ( (Artificial drainage) has the same properties as in Example 1, that is, BOD 500 mg / L.
To 10,000 kg / day. The excess sludge separated in the solid-liquid separation tank 2 was SS 10,000 mg / L at 200 kg / day.
This is sent to the hydrothermal reactor 3, temperature 150 ℃, pressure 0.6M
When hydrothermally treated with Pa and residence time of 1 hour, BOD150
It became 0 mg / L and SS 1500 mg / L. The obtained treatment liquid is
Furthermore, when SS was sent to the settling tank 5 via line L8, SS 10,000 mg / L, BOD 150 was obtained at 30 kg / day.
Sludge of 0 mg / L is separated and BOD 150 is fed to the biological reaction tank 4.
The processing solution of 0 mg / L and SS 30 mg / L was sent only 170 kg / day. After biological treatment, this solution is BOD 150 mg / L, SS 50
It became 0 mg / L.

The effect of returning the treated liquid to the aeration tank 1 is almost the same as that of the first embodiment, but S in the sedimentation tank 5 is changed.
Since S is separated, there is an advantage that a fixed-bed biological reaction tank 4 can be used. In addition, S separated in the settling tank 5
The S sludge is usually returned directly to the aeration tank 1, but it may be sent directly to the solid-liquid separation tank 2 or the hydrothermal reaction device 3.

[Embodiment 3] (Apparatus) In this embodiment, a biofilm filtration tank 7 having the same mechanism as the bioreaction tank 4 was adopted in place of the aeration tank 1 to form the apparatus configuration shown in FIG.

Biofilm filtration tank 7: Volume 0.25 m ³ × 5 units Backwash drainage sludge concentrator 8: Volume 0.15 m ³ Hydrothermal reactor 3: Volume 40 L Bioreaction tank 4: Volume 60 L (implementation result) Raw water (Artificial drainage) had the same properties as in Example 1, that is, BOD 500 mg / L, and was supplied to the biofilm filtration tank 7 in total at 10,000 kg / day. The BOD of the supernatant treated in the biofilm filtration tank 7 was lowered to 50 mg / L, and the supernatant could be discharged as it was.

The operation of each biofilm filtration tank 7 is 2
After continuing for 3 hours, supply of raw water was stopped and backwashing was performed. The backwashing was performed every 4 to 5 hours because the biofilm filtration tanks 7 were made uniform in timing.

The backwash drainage containing sludge removed from the filter medium layer by one backwash is 150 kg, BOD 50 mg / L, SS 2,000
It was mg / L.

The surplus sludge separated in the backwash drainage sludge thickener 8 was 2,000 mg / L SS at 750 kg / day. When this was sent to the hydrothermal reactor 3 and hydrothermally treated at a temperature of 150 ° C., a pressure of 0.6 MPa and a residence time of 1 hour, BOD of 300 mg / L,
SS became 300 mg / L. When the obtained treatment liquid was further sent to the biological reaction tank 4 via a line L8 for treatment, the BOD was 30 mg / L and the SS was 380 mg / L. The treated liquid was returned to the biofilm filtration tank 7.

The configuration of this embodiment does not require a vast space for providing an aeration tank as in the first and second embodiments,
Instead of using the compact biofilm filtration tank 7,
It is also possible to install it in a restaurant or the like in the building to treat food wastewater.

Example 4 In this example, BOD 100 mg / L raw water (artificial drainage) prepared by the same method as in Example 1 was used.

When this raw water was treated with an apparatus having the same structure as in Example 3, B was discharged from the biological reaction tank 4
OD was 10 mg / L and SS was 75 mg / L. When the liquid thus treated meets the discharge standard of sewerage, it may be discharged as it is and entrusted to the final public sewerage treatment.

[Embodiment 5] With the nature of the treated water as in Embodiment 3, it may not be possible to discharge the waste water from the biological reaction tank 4 to the sewer as it is because of the SS regulation value problem.
Therefore, as shown in FIG. 4, a settling tank 5 (40 L) is provided, and wastewater (750 kg / day) from the biological reaction tank 4 is sent to the settling tank 5 and S
S was separated by sedimentation.

The supernatant after sedimentation is BOD 30 mg / L, S
It became S 30 mg / L, which was below the discharge standard value.

The separated sludge is 13 kg / day, and SS
Since the content was 20,000 mg / L, the hydrothermal treatment tank 3 as it is
Sent back to.

[Example 6] With the same apparatus configuration as in Example 5, the same experiment was conducted by changing the property of raw water (artificial drainage) to BOD 1,000 mg / L.

The supernatant after sedimentation was BOD 60 mg / L,
SS became 30 mg / L, which was below the discharge standard value.

The separated sludge was 27 kg / day, and SS
The content was 20,000 mg / L, and when returned to the hydrothermal treatment tank 3, it exceeded the capacity of the apparatus. Therefore, a dehydrator 6 was installed to perform dehydration treatment, and separation was performed outside the system. 2.7 sludge finally separated
The water content was 80% at kg / day.

[Embodiment 7] In the configuration of Embodiment 1, the heat exchanger 10 is installed in the line of the water to be treated which goes to the hydrothermal treatment apparatus 3, and heat is exchanged with the high temperature treated water after the decomposition treatment.

The temperature change before and after heat exchange is 30
℃ → 125 ℃, treated water is 150 ℃ → 55 ℃, the flow rate is 200
The heat exchange DUTY at kg / day was 3,300 kJ / hr.

[Embodiment 8] In the configuration of Embodiment 3, the heat exchanger 10 is installed in the line of the water to be treated which goes to the hydrothermal treatment apparatus 3, and heat is exchanged with the high temperature treated water after the decomposition treatment.

The temperature change before and after the heat exchange is 30
℃ → 125 ℃, treated water is 150 ℃ → 55 ℃, flow rate is 750
The heat exchange DUTY was 12,500 kJ / hr at kg / day.

[0052]

The combination of the hydrothermal reaction apparatus and the biological reaction tank of the present invention has the following advantages. (1) The characteristics of hydrothermal reaction are many operating factors such as the ratio of water to solids, temperature, pressure, and time of reaction, and there are various combinations of reaction conditions between the hydrothermal reaction device and the biological reaction tank. Therefore, there is certainty in the processing results. (2) In particular, by controlling the temperature and pressure conditions to be lower than those of the conventional ones, the input energy is reduced, and inorganic SS such as amorphous carbon generated at high temperature is suppressed from being finally removed. The required solid waste can be significantly reduced and even eliminated. (3) As a bioreaction tank for the hydrothermal treatment liquid, a highly efficient biofilm reaction tank or the like can be used to reduce the size. (4) Since the biological reaction tank uses the microorganisms acclimatized with the hydrothermal treatment liquid, the decomposition efficiency is high, the biological reaction tank becomes small, and the existing aeration tank is less affected. (5) It is possible to prevent the existing aeration tank from being affected by discharging the treatment liquid of the biological reaction tank as it is or by removing the mixed sludge and then discharging it.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a simple structure including a biological reaction tank, which characterizes the present invention.

FIG. 2 is a diagram showing an example of a configuration in which a sedimentation tank is added before a biological reaction tank in the present invention.

FIG. 3 is a diagram showing an example of a configuration in which a biofilm filtration method is used in a biological treatment apparatus according to the present invention.

FIG. 4 is a diagram showing an embodiment of the present invention in which the waste water after treatment in the biological reaction tank is discharged when it clears the regulation.

FIG. 5 is a diagram showing a heat recovery configuration according to an embodiment of the present invention.

FIG. 6 is a diagram showing an example of a conventional technique.

[Explanation of symbols]

1 aeration tank 2 Solid-liquid separation tank 3 Hydrothermal reactor 4 Biological reaction tank 5 settling tank 6 dehydrator 7 biological treatment tank 8 Backwash drainage sludge thickener 9 High pressure pump 10 heat exchanger 11 heater 12 Hydrothermal reactor 13 Cooler 14 Pressure control valve L1 to L20 piping

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Claims (4)

[Claims] 1. A step of feeding surplus activated sludge generated in a wastewater biological treatment device to a hydrothermal reaction device and decomposing the hardly biodegradable organic matter in the sludge into an easily biodegradable substance by hydrothermal reaction, In the excess sludge biological treatment method, the hydrothermal reaction treatment is performed under reaction conditions of a temperature of 140 ° C. or higher and lower than 200 ° C. and a pressure of 0.4 MPa or higher and 2.0 MPa or lower, and after the hydrothermal treatment step, It is characterized by having a step of aerobically treating the treatment liquid in an aerobic biological reaction tank separately installed, and returning the treatment liquid subjected to the aerobic treatment to the biological treatment device or discharging it as treated water. ,
Surplus sludge biological treatment method utilizing hydrothermal reaction. 2. A solid-liquid separator is provided as a pre-process of the aerobic biological reaction tank, a liquid having a low solid content in the treatment liquid is supplied to the biological reaction tank, and a liquid having a high solid content is already installed. 2. The biological treatment device and / or the hydrothermal reaction device and / or the dehydration treatment device according to claim 1 for processing.
The method for treating excess sludge biological matter, which utilizes the hydrothermal reaction according to 1. 3. A solid-liquid separation device is provided as a post-process of the aerobic biological reaction tank, the treatment liquid is discharged, and the concentrated sludge slurry is sent to a hydrothermal reaction device and / or a dehydration treatment device for treatment. The method for treating excess sludge biological matter utilizing the hydrothermal reaction according to any one of claims 1 to 2. 4. The surplus sludge biological treatment method using the hydrothermal reaction according to claim 1, wherein the liquid to be treated and the treatment liquid are heat-exchanged in the hydrothermal reaction device. .