JP4004766B2 - Excess sludge biological treatment method using hydrothermal reaction - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological treatment method for wastewater using a hydrothermal reaction that enables complete disappearance of organic matter in sludge generated by wastewater treatment or significant reduction in weight.
[0002]
[Prior art]
Biological treatment methods are the most common wastewater treatment methods, and almost all sewage, household wastewater, factory wastewater, livestock manure wastewater and the like are carried out by this method. In the biological treatment, since the main body is microorganisms, the growing microorganisms are generated as excess sludge. For this reason, sludge is reduced by anaerobic treatment such as methane fermentation, but it cannot be completely extinguished, and most of them are incinerated after dehydration or landfilled.
[0003]
In view of this, several surplus sludge treatment methods using a so-called hydrothermal reaction in which water is brought into a high-temperature and high-pressure state to react with sludge organic matter have been proposed. Here, the high temperature and high pressure state includes a supercritical water state exceeding the critical point of water (374 ° C, 22 MPa) and a subcritical water state below the critical point. In the former case, typically 450 ° C to 600 ° C, 25 MPa In the latter case, typically, the range of 300 ° C. to 360 ° C. and 9 MPa to 19 MPa is used.
[0004]
Conventional surplus sludge treatment methods using this hydrothermal reaction can be broadly divided into 1) liquefaction of sludge (use of fertilizer and feed), 2) sludge liquefaction (use of fuel) and 3). There are three types of sludge decomposition and volume reduction. Wet oxidation, which is a conventional method for reducing sludge volume, reacts with oxidants such as oxygen and hydrogen peroxide under the supercritical water conditions where dehydrated sludge is added as a catalyst, and oxidizes to carbon dioxide or ammonia. Therefore, harsh conditions such as a large amount of catalyst and ultra-high temperature are required, and they are not in terms of energy and cost. In addition, supercritical water has a low dielectric constant and significant precipitation of inorganic salts, which has many problems such as reactor and pipe system blockage and the use of harmful catalysts.
[0005]
Japanese Patent Laid-Open No. 2000-218295 discloses the following method as a method for solving the difficulty of the method of treating excess sludge using hydrothermal reaction. That is, as shown in FIG. 6, a hydrothermal reaction apparatus 3 is added to a biological treatment apparatus comprising an aeration tank 1 and a solid-liquid separation tank 2, and a subcritical state (320 ° C., 12.1 MPa) and in the presence of a large amount of water (approximately 90 to 99%), the organic components in the sludge are decomposed so that bacteria can be easily treated, and this treatment liquid is decomposed and extinguished in the existing aeration tank 1 is there. Most of the sludge is microbial cells, and other plant and animal fines are also included. And, in order to make it easier for bacteria used for biological treatment of wastewater and sludge to be treated by hydrothermal reaction, sugar and amino acids (or a part of the molecule is further decomposed) The treatment liquid obtained by decomposing into an easily biodegradable substance is returned to a biological treatment process, for example, an aeration tank of an activated sludge method, where it is decomposed and assimilated by bacteria.
[0006]
This hydrothermal reactor is usually installed attached to a biological treatment device that generates sludge like an activated sludge device, and the treatment liquid obtained by the hydrothermal reactor is aerated by the original activated sludge treatment device. It is returned to the tank or the contact aeration tank and used again for biodegradation. Furthermore, when surplus 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 attached to the anaerobic treatment device. It can also be put into an anaerobic treatment apparatus after hydrothermal treatment in advance.
[0007]
[Problems to be solved by the invention]
Under conventional subcritical conditions, the hydrothermal reaction itself takes place at a high temperature and pressure, which requires a large amount of energy. In addition, under conventional reaction conditions, the amount of inorganic suspended solids such as amorphous carbon (hereinafter sometimes abbreviated as “inorganic SS”) generated due to excessive progress of the decomposition reaction is large, which is an obstacle to biological treatment again. As a result, the amount of suspended solids (hereinafter sometimes abbreviated as SS) that must be finally dehydrated and removed from the system increases. In addition, when the treatment liquid of the hydrothermal reaction is returned to the original aeration tank as in the past and biological treatment is performed, the load on the original aeration tank increases, so there is no room for biological treatment capacity, which may be difficult to apply. .
[0008]
The present invention aims to reduce the amount of energy input by examining the reaction conditions, and to eliminate or reduce the final waste by reducing the amount of inorganic SS such as amorphous carbon generated. With the goal. In addition, in the case of factory wastewater treatment facilities, 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 prior art, so the purpose is to provide a method for solving this. To do.
[0009]
[Means for Solving the Problems]
The present invention includes (1) surplus sludge treatment method in which sludge generated in a biological wastewater treatment device is sent to a hydrothermal reactor, and the hardly biodegradable organic matter in the sludge is decomposed into easily biodegradable substances by hydrothermal reaction. , Hydrothermal reaction treatment is milder than conventional subcritical conditions, at a temperature in the range of 140 ° C to less than 200 ° C, and at a pressure in the range of 0.4 MPa to 2.0 MPa. Surplus sludge biological treatment method utilizing hydrothermal reaction, characterized in that after the aerobic treatment in the aerobic biological reaction tank, the treatment liquid is returned to the biological treatment apparatus or discharged as treated water, (2) A solid-liquid separator is provided as a pre-process of the aerobic biological reaction tank, and among the processing liquids, a liquid with a low solid content is supplied to the biological reaction tank, and a liquid with a high solid content is supplied to the existing biological processing apparatus and / or Or send to hydrothermal reactor and / or dehydration equipment The surplus sludge biological treatment method using the hydrothermal reaction as described in (1) above, wherein (3) a solid-liquid separation device is provided as a subsequent step of the aerobic biological reaction tank, The excess sludge using the hydrothermal reaction according to any one of (1) to (2), wherein the sludge slurry that has been discharged is sent to a hydrothermal reaction device and / or a dehydration device. Biological reaction treatment method, (4) Excess sludge using hydrothermal reaction as described in (1) to (3) above, wherein in the hydrothermal reactor, heat exchange is performed between the liquid to be treated and the treatment liquid. Biological treatment method.
[0010]
The hydrothermal treatment used in the present invention is based on the premise that the biofilm treatment is performed in the subsequent stage. Therefore, even if milder conditions are applied than in the case of hydrothermal treatment alone, not only the treatment capacity of the whole system is inferior, but also the high temperature. Since the carbonization which has been a problem in the case of high-pressure treatment does not progress so much, it has an effect that the properties of water after treatment are excellent.
[0011]
The present inventors have found that SS is preferably decomposed to a degree suitable for biological treatment and carbonization is suppressed at 140 ° C. or more and less than 200 ° C., more preferably 145 ° C. or more and 195 ° C. or less. Combined with biological reactions, the amount of environmental pollutants after treatment can be significantly reduced. In addition, since these apparatuses are more compact than conventional reaction apparatuses, they can be easily added to the subsequent stage of existing processing apparatuses, and it is not necessary to secure a large installation space.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, it demonstrates still in detail using the figure of this invention.
[0013]
As shown in FIG. 1, the basic configuration of the present invention includes an aeration tank 1, a solid-liquid separation tank 2, a hydrothermal reactor 3, and a biological reaction tank 4. The sludge separated and concentrated in the solid-liquid separation tank 2 is extracted from the line L4 to obtain a drawn sludge. A part of the sludge is sent to the hydrothermal reactor 3 via the line L7 as the treated sludge, where the hardly biodegradable substances in the sludge are converted into easily biodegradable low-molecular substance groups and obtained. The treated liquid is sent to the biological reaction tank 4 via the line L8, is metabolized by the microbial function, and is returned to the aeration tank 1 from the line L9.
[0014]
A part of the drawn sludge is returned to the aeration tank via the line L5 as return sludge. Furthermore, if the amount of extracted sludge is large, it is discharged out of the system as excess sludge. However, in the case of the present invention, surplus sludge is generated if the capacity of the hydrothermal reactor is insufficient, but normally, so-called surplus sludge is not generated if the hydrothermal reactor has sufficient capacity. . In addition, minerals such as minerals in sludge and traces of carbon particles generated by dehydrogenation and deoxygenation are finally removed from the system as trace components in the treated water or from solid-liquid separation tanks. There is a need.
[0015]
In the method of the present invention, a stirred tank and / or a tubular reactor is used as the type of the hydrothermal reactor, but a tubular reactor having a small residence time distribution is more preferable in view of the quality of treated water.
[0016]
In the method of the present invention, the heating / temperature raising method can be appropriately selected from direct heating by steam, indirect heating, heating by electric heating, and the like.
[0017]
In the method of the present invention, the hydrothermal reaction conditions are preferably conditions in which SS is sufficiently decomposed to a degree suitable for biological treatment and carbonization is suppressed, specifically 140 ° C. or more and less than 200 ° C., Furthermore, it is preferably 145 ° C or higher and 195 ° C or lower.
[0018]
In the method of the present invention, as the type of the aerobic bioreactor, a normal biological treatment method such as an activated sludge method or a biofilm method is possible, but the biofilm method is particularly preferred from the viewpoint of the treatment capacity. In particular, the merit of the biofilm method is utilized more when there is no space.
[0019]
In the present invention, when a fixed bed type reaction tank is used as a biological reaction tank, a settling tank 5 is provided as a pretreatment step of the biological reaction tank 4 as shown in FIG. After separation, the biological reaction tank 4 can be supplied. On the other hand, the separated sludge slurry can be returned to an existing biological treatment apparatus and / or hydrothermal reaction apparatus, and dehydrated if necessary.
[0020]
As another embodiment, an example of using a biofilm filtration method in a biological treatment apparatus will be described with reference to FIG. The wastewater is treated from L1, for example, in a biofilm filtration tank 7 using foamed plastic as a filter medium. After a certain time has elapsed since the treatment was started, so-called backwashing is performed to remove sludge accumulated in the filter medium layer. The backwash wastewater is collected in the backwash wastewater sludge concentration tank 8. Usually, since a plurality of 7 are installed, the time of backwashing of each tank is shifted little by little so that the amount of generated wastewater is leveled. The sludge concentrated in 8 is sent to the hydrothermal reactor 3 from the line L7. The subsequent steps are the same as those in FIG.
[0021]
This configuration is characterized in that, in performing biological treatment of wastewater, instead of a normal aeration tank, biological treatment is performed in the same manner as the hydrothermal treatment liquid, and the supernatant after biological treatment is discharged as it is. Is possible.
[0022]
In the present invention, depending on the regulation value of the waste water quality (BOD (biochemical oxygen demand), SS, etc.), as shown in FIG. Can be treated in the biological reaction tank 4, and this treatment solution can be discharged from L14. If only SS exceeds the regulation value in the water quality of L14 and cannot be returned to the existing biological treatment equipment, it can be sent to the settling tank 5 from L15 and discharged after the SS is settled and separated. In this case, the separated SS is taken out from 5, and returned to 3 again through L12 and processed. SS that cannot be biologically treated is contained in 5 upper discharge water at a dilute concentration and released. If it still accumulates due to the balance of the system, a dehydrator 6 can be installed and processed.
[0023]
FIG. 5 shows an example of a detailed configuration of the hydrothermal reactor 3, that is, the water to be treated and the treated water are heat-exchanged by the heat exchanger 10 and recovered.
[0024]
【Example】
Specific examples of the present invention will be described below.
[0025]
[Example 1]
(Raw water: Artificial drainage)
In this example, in order to reproduce wastewater containing a large amount of organic matter, an aqueous solution of glucose and peptone was prepared and used as artificial wastewater. The BOD was prepared at the following concentration so as to be 500 mg / L.
[0026]
Ingredient glucose 380mg / L
Peptone (protein hydrolyzate) 130mg / L
In the following, the concentrations of pollutants are all indicated by BOD (biodegradable) and SS (non-biodegradable).
[0027]
(apparatus)
In this embodiment, the basic apparatus configuration shown in FIG. 1 is adopted.
[0028]
Aeration tank 1: Volume 5m ³
Solid-liquid separation tank 2: Volume 0.5 m ³
Hydrothermal reactor 3: Volume 10 L
Biological reactor 4: Volume 75 L
(Results)
The raw water (artificial wastewater) was BOD 500 mg / L, and this was supplied to the aeration tank 1 at 10,000 kg / day. The excess sludge separated in the solid-liquid separation tank 2 was 200 kg / day and SS 10,000 mg / L. 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, resulting in BOD 1500 mg / L and SS 1500 mg / L. When the obtained processing solution was further sent to the biological reaction tank 4 via the line L8 and processed, the BOD was 150 mg / L and the SS was 2000 mg / L.
[0029]
When the treated liquid is returned to the aeration tank 1, the load on the aeration tank is only 0.6% increase compared to the case where the sludge is not returned to the outside of the system and is left as it is with the conventional apparatus capacity. It shows that it can continue to be used.
[0030]
[Comparative Example 1]
The 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. When the liquid treated in the same manner as in Example 1 is returned to the aeration tank 1, the load on the aeration tank is increased by 6% compared to the case where the sludge is not returned and separated from the system as it is. It will lead to diminished ability.
[0031]
[Example 2]
(apparatus)
In the present embodiment, a settling tank 5 was added and an apparatus configuration shown in FIG. 2 was adopted.
[0032]
Aeration tank 1: Volume 5m ³
Solid-liquid separation tank 2: Volume 0.15m ³
Hydrothermal reactor 3: Volume 10 L
Biological reactor 4: Volume 75 L
Settling tank 5: Volume 15 L
(Results)
The raw water (artificial wastewater) had the same properties as those of Example 1, that is, BOD 500 mg / L, and was supplied to the aeration tank 1 at 10,000 kg / day. The excess sludge separated in the solid-liquid separation tank 2 was 200 kg / day and SS 10,000 mg / L. 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 1500 mg / L and SS 1500 mg / L were obtained. The obtained treatment liquid was further sent to the sedimentation tank 5 via line L8, and SS was separated. As a result, SS 10,000 mg / L and BOD 1500 mg / L sludge were separated at 30 kg / day and passed to the biological reaction tank 4. The BOD 1500mg / L, SS 30mg / L treatment liquid was sent only 170kg / day. After biological treatment, this liquid became BOD 150 mg / L and SS 500 mg / L.
[0033]
The effect when the treated liquid is returned to the aeration tank 1 is almost the same as that of the first embodiment, but since the SS is separated in the settling tank 5, the advantage that a fixed bed can be used as the biological reaction tank 4. There is. The SS sludge separated in the sedimentation tank 5 is usually returned directly to the aeration tank 1, but may be sent directly to the solid-liquid separation tank 2 or the hydrothermal reactor 3.
[0034]
[Example 3]
(apparatus)
In this embodiment, a biofilm filtration tank 7 having the same mechanism as that of the biological reaction tank 4 is employed instead of the aeration tank 1 to obtain the apparatus configuration shown in FIG.
[0035]
Biofilm filtration tank 7: Volume 0.25m ³ × 5 Backwash wastewater sludge concentration tank 8: Volume 0.15m ³
Hydrothermal reactor 3: Volume 40 L
Biological reaction tank 4: 60 L capacity
(Results)
The raw water (artificial wastewater) had the same properties as in Example 1, that is, BOD 500 mg / L, and this was supplied to the biofilm filtration tank 7 in total 10,000 kg / day. The supernatant treated in the biofilm filtration tank 7 had a BOD lowered to 50 mg / L and could be discharged as it was.
[0036]
The individual biofilm filtration tank 7 was operated for 23 hours, and the supply of raw water was stopped and backwashing was performed. In addition, since the timing of backwashing was made uniform for each biofilm filtration tank 7, it was performed every 4 to 5 hours.
[0037]
The backwash drainage containing the sludge removed from the filter media layer by one backwash was 150 kg, BOD 50 mg / L, and SS 2,000 mg / L.
[0038]
The excess sludge separated in the backwash wastewater sludge concentration tank 8 was 2,000 kg / L 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 300 mg / L and SS 300 mg / L were obtained. When the obtained processing solution was further sent to the biological reaction tank 4 via the line L8 and processed, BOD was 30 mg / L and SS was 380 mg / L. The treated liquid was returned to the biofilm filtration tank 7.
[0039]
In the configuration of the present embodiment, a vast space for providing an aeration tank is not required as in Embodiments 1 and 2, and a compact biofilm filtration tank 7 is used instead. It can also be installed to treat food wastewater.
[0040]
[Example 4]
In this example, BOD 100 mg / L raw water (artificial drainage) prepared by the same method as in Example 1 was used.
[0041]
When this raw water was treated with an apparatus having the same configuration as in Example 3, the BOD was 10 mg / L and SS was 75 mg / L in the waste water from the biological reaction tank 4. When the liquid processed in this way satisfies the discharge standard of the sewer, it may be discharged as it is and may be left to the public final sewage treatment.
[0042]
[Example 5]
In the property of treated water as in Example 3, it may be impossible to discharge the waste water from the biological reaction tank 4 to the sewer as it is because of the problem of SS regulation values. Therefore, as shown in FIG. 4, a sedimentation tank 5 (40 L) was provided, and wastewater (750 kg / day) from the biological reaction tank 4 was sent to the sedimentation tank 5 to separate and separate SS.
[0043]
The supernatant after sedimentation separation was BOD 30 mg / L and SS 30 mg / L, which were below the discharge standard value.
[0044]
The separated sludge was 13 kg / day and had an SS content of 20,000 mg / L, so it was returned to the hydrothermal treatment tank 3 as it was.
[0045]
[Example 6]
A similar experiment was performed with the same apparatus configuration as in Example 5 except that the properties of the raw water (artificial drainage) were changed to BOD 1,000 mg / L.
[0046]
The supernatant after sedimentation separation was BOD 60 mg / L and SS 30 mg / L, which were below the discharge standard value.
[0047]
The separated sludge is 27 kg / day and has an SS content of 20,000 mg / L. If it is returned to the hydrothermal treatment tank 3, it will exceed the capacity of the equipment. did. The finally separated sludge was 2.7 kg / day and the water content was 80%.
[0048]
[Example 7]
In the structure of Example 1, the heat exchanger 10 was installed in the to-be-processed water line which goes to the hydrothermal-treatment apparatus 3, and heat exchange with the high temperature treated water after a decomposition process was performed.
[0049]
The temperature changes before and after heat exchange were 30 ° C → 125 ° C for treated water and 150 ° C → 55 ° C for treated water, the flow rate was 200 kg / day, and the heat exchange DUTY was 3,300 kJ / hr.
[0050]
[Example 8]
In the structure of Example 3, the heat exchanger 10 was installed in the to-be-processed water line which goes to the hydrothermal treatment apparatus 3, and heat exchange with the high temperature treated water after a decomposition process was performed.
[0051]
The temperature changes before and after heat exchange were 30 ° C → 125 ° C for treated water and 150 ° C → 55 ° C for treated water, the flow rate was 750 kg / day, and the heat exchange DUTY was 12,500 kJ / hr.
[0052]
【The invention's effect】
The combination of the hydrothermal reaction apparatus and the biological reaction tank of the present invention has the following advantages.
(1) The characteristics of the hydrothermal reaction are many operating factors such as the ratio of water and solids, and the temperature, pressure, and time of the reaction, and there are various combinations of reaction conditions between the hydrothermal reactor and the biological reaction tank. There is certainty in processing results.
(2) In particular, the temperature and pressure conditions are kept lower than the conventional one, thereby reducing the input energy and finally removing by suppressing the generation of amorphous SS such as amorphous carbon generated at high temperatures. The required solid waste can be greatly reduced or even eliminated.
(3) The bioreactor of the hydrothermal treatment liquid can be miniaturized by adopting a highly efficient biofilm reactor or the like.
(4) Since the biological reaction tank uses microorganisms acclimatized with the hydrothermal treatment liquid, the decomposition efficiency is high, the biological reaction tank becomes small, and the influence on the existing aeration tank is small.
(5) The treatment liquid in the biological reaction tank is discharged as it is or after the sludge mixed therein is removed and then discharged, the existing aeration tank can be prevented from being affected.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of a simple configuration including a biological reaction tank that characterizes the present invention.
FIG. 2 is a diagram showing an embodiment of a configuration in which a sedimentation tank is added in front of 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 in the present invention.
FIG. 4 is a diagram showing an embodiment of a configuration for discharging the wastewater after treatment in the biological reaction tank in the present invention when the regulation is cleared.
FIG. 5 is a diagram showing a heat recovery configuration in an embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Aeration tank 2 Solid-liquid separation tank 3 Hydrothermal reactor 4 Biological reaction tank 5 Sedimentation tank 6 Dehydration apparatus 7 Biological treatment tank 8 Backwash drainage sludge concentration tank 9 High pressure pump
10 Heat exchanger
11 Heater
12 Hydrothermal reactor
13 Cooler
14 Pressure control valve L1 to L20 Piping

Claims (4)

Surplus sludge biological treatment method comprising a step of sending surplus activated sludge generated in a biological wastewater treatment device to a hydrothermal reactor and decomposing the hardly biodegradable organic matter in the sludge into an easily biodegradable substance by a hydrothermal reaction. In
Performing the hydrothermal reaction treatment 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;
After the water heat treatment step, and further comprising the step of aerobic treatment in the aerobic biological reactor with biofilm methods separately installing the treatment liquid,
A surplus sludge biological treatment method using hydrothermal reaction, comprising a step of returning the aerobically treated treatment liquid to the biological treatment apparatus or discharging it as treated water. A solid-liquid separation device is provided as a pre-process of the aerobic biological reaction tank, and among the processing liquids, a liquid with a low solid content is supplied to the biological reaction tank, and a liquid with a high solid content is installed in an existing biological processing apparatus and 2. The surplus sludge biological treatment method using hydrothermal reaction according to claim 1, wherein the treatment is carried out by sending to a hydrothermal reaction device and / or a dehydration treatment device. 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. The surplus sludge biological treatment method using the hydrothermal reaction in any one of claim | item 1-2. The surplus sludge biological treatment method using hydrothermal reaction according to any one of claims 1 to 3, wherein in the hydrothermal reaction device, heat exchange is performed between the liquid to be treated and the treatment liquid.

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