JP2021181062A - Method for treating organic waste water and device for treating organic waste water - Google Patents

Abstract

To provide a method and device for treating organic waste water that can maintain stable quality of treated water and can reduce the amount of generation of excess sludge.SOLUTION: A method for treating organic waste water includes: a treatment for aerobically treating raw water containing organic materials in a first aerobic treatment tank 1a to make a first aerobic liquid; a treatment for aerobically treating the first aerobic liquid in a second aerobic treatment tank 1b to make a second aerobic liquid; a treatment for subjecting the second aerobic liquid to solid-liquid separation to make treated water and separated sludge; a first return treatment for pulling out part of the separated sludge as first returned sludge to return it to the first aerobic treatment tank so as to be 5-30% of the inflow of raw water in flow rate; and a second return treatment for returning at least part of the separated sludge that remains after pulling out the first returned sludge, which is termed second returned sludge, to the second aerobic treatment tank.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for treating organic wastewater and an apparatus for treating organic wastewater.

In recent years, activated sludge treatment is generally used as an organic wastewater treatment having a high biochemical oxygen demand (BOD). Activated sludge treatment is easy to maintain and has low running costs. Activated sludge treatment has the advantage that BOD can be stably removed from the inflowing raw water, and good treated water quality can always be obtained. Therefore, activated sludge treatment is often used for various organic wastewater treatments such as domestic wastewater and factory wastewater.

However, it is known that excess sludge is generated by removing BOD in the activated sludge treatment. In particular, wastewater having a high BOD concentration generates a large amount of surplus sludge, so that the ratio of the cost associated with the disposal of surplus sludge to the total treatment is increasing, and the reduction of surplus sludge has become a major issue.

As a method for reducing excess sludge, there is a method of performing multi-stage treatment that combines high load and low load. For example, in JP-A-2010-06482 and JP-A-2005-21179, disperse bacteria are generated in the first biological treatment tank, which is the high-load tank in the first stage, and the second biological treatment, which is the low-load tank in the latter stage. A method for reducing the volume of sludge by a food chain is disclosed, in which the volume of sludge is reduced by utilizing the predation of dispersed bacteria of protozoa and metazoans in a tank.

Japanese Unexamined Patent Publication No. 2010-069482 Japanese Unexamined Patent Publication No. 2005-21179

In the biological treatment methods described in Patent Documents 1 and 2, the BOD load and pH of the first biological treatment tank and the second biological treatment tank are set within a predetermined range in order to improve the treatment efficiency and reduce the amount of excess sludge generated. It is stated that it needs to be controlled within. In this respect, when the properties of the raw water are relatively stable, it is relatively easy to control the BOD load and pH of each biological treatment tank.

However, if a large concentration fluctuation occurs in the raw water for some reason, it becomes difficult to control the BOD load and pH of the biological treatment tank, and the generation of dispersed bacteria in the primary biological treatment tank may become unstable. As a result, the effect of reducing the volume of sludge in the food chain by predating dispersed bacteria cannot be sufficiently obtained. In addition, if the dispersed bacteria are generated too much in the first biological treatment tank due to the change in the properties of the raw water and the dispersed bacteria remain in the second biological treatment tank, there is a risk of deteriorating the quality of the treated water. Patent Documents 1 and 2 also describe the return of sludge to the first and second biological treatment tanks, but the ratio of sludge return and the biological treatment tank to which the sludge is returned are appropriately determined. There is only a statement that it can be set, but there is no concrete proposal, and no design has been made in consideration of changes in the properties of raw water.

In view of the above problems, the present invention provides an organic wastewater treatment method and an organic wastewater treatment apparatus capable of maintaining stable treated water quality at all times and reducing the amount of excess sludge generated.

As a result of diligent studies by the present inventors in order to solve the above problems, it was found that it is effective to perform aerobic treatment in multiple stages and to optimize the amount of sludge returned to the first aerobic treatment tank. Got

One aspect of the embodiment of the present invention completed based on the above findings is a treatment in which raw water containing an organic substance is aerobicly treated in a first aerobic treatment tank to obtain a first aerobic treatment liquid. A treatment in which the first aerobic treatment liquid is aerobically treated in a second aerobic treatment tank to obtain a second aerobic treatment liquid, and a treatment in which the second aerobic treatment liquid is solid-liquid separated and separated from the treated water and sludge. The first return process and the first return process, in which a part of the separated sludge is extracted as the first return sludge and returned to the first aerobic treatment tank so that the flow rate is 5 to 30% of the amount of raw water inflow. This is a method for treating organic wastewater, which comprises a second return treatment in which at least a part of the separated sludge after the sludge is extracted is used as a second return sludge, and the second return sludge is returned to a second aerobic treatment tank.

The method for treating organic wastewater according to the embodiment of the present invention further includes, in one embodiment, a third return treatment for extracting the suspended sludge in the second aerobic treatment tank and returning it to the first aerobic treatment tank.

In another embodiment of the method for treating organic wastewater according to the embodiment of the present invention, the first return treatment is performed so that the BOD sludge load of the first aerobic treatment tank is 2 to 10 kg / kg / d. ..

In still another embodiment of the method for treating organic wastewater according to the embodiment of the present invention, alkali is added so that the total alkalinity of the first aerobic treatment tank is 100 to 500 mg / L.

In still another embodiment of the method for treating organic wastewater according to the embodiment of the present invention, the aeration air volume is adjusted so that the dissolved oxygen concentration in the first aerobic treatment tank is 2 to 7 mg / L.

In another aspect of the embodiment of the present invention, a first aerobic treatment tank for aerobicly treating raw water containing an organic substance to obtain a first aerobic treatment liquid and a first aerobic treatment liquid are aerobic. A second aerobic treatment tank for obtaining a second aerobic treatment liquid, a solid-liquid separation tank for solid-liquid separation of the second aerobic treatment liquid to obtain treated water and separated sludge, and a separated sludge. A part of the first return sludge is extracted and returned to the first aerobic treatment tank so that the flow rate is 5 to 30% of the amount of raw water inflow, and the separated sludge after the first return sludge is extracted. It is an organic wastewater treatment apparatus including at least a part of the second return sludge and a second return means for returning the second return sludge to the second aerobic treatment tank.

According to the present invention, it is possible to provide an organic wastewater treatment method and an organic wastewater treatment apparatus capable of maintaining stable treated water quality at all times and reducing the amount of excess sludge generated.

It is a schematic diagram which shows the example of the wastewater treatment apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the example of the wastewater treatment apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the example of the wastewater treatment apparatus which made the solid-liquid separation tank of 1st Embodiment an MBR tank. It is a schematic diagram which shows the example of the wastewater treatment apparatus which made the 2nd solid-liquid separation tank of 1st Embodiment an MBR tank. It is a schematic diagram which shows the example of the conventional wastewater treatment apparatus. It is a schematic diagram which shows another example of the conventional wastewater treatment apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention describes the structure, arrangement, etc. of the components as follows. It is not specific.

As shown in FIG. 1, the organic wastewater treatment apparatus according to the first embodiment of the present invention aerobicly treats raw water containing an organic substance to obtain a first aerobic treatment liquid. The treatment tank 1a, the second aerobic treatment tank 1b that aerobically treats the first aerobic treatment liquid to obtain the second aerobic treatment liquid, and the second aerobic treatment liquid are separated into solid and liquid to treat water. The solid-liquid separation tank 2 for obtaining the separated sludge, and a part of the separated sludge is extracted as the first return sludge and returned to the first aerobic treatment tank 1a so as to have a flow rate of 5 to 30% of the amount of raw water inflow. 1 Return means 3 and a second return means 4 in which at least a part of the separated sludge after the first return sludge is pulled out is used as the second return sludge and the second return sludge is returned to the second aerobic treatment tank 1b. Be prepared.

The raw water is not particularly limited as long as it is wastewater containing organic matter, and for example, various organic wastewater containing organic matter such as domestic wastewater, sewage, food factories, chemical factories, and pulp factories are used. Foods with a small amount of inorganic floating substances (SS) (for example, SS of about 0 to 100 mg / L) and a high concentration of easily decomposable organic substances (for example, BOD value of about 1000 to 2000 mg / L), although not limited to the following. Raw water such as beverage wastewater and domestic wastewater is treated particularly preferably.

The first aerobic treatment tank 1a and the second aerobic treatment tank 1b include activated sludge containing bacteria capable of decomposing organic substances (BOD) in raw water flowing into the aerobic treatment tank 1, microorganisms that prey on the bacteria, and the like. Is not particularly limited as long as it is an apparatus in which raw water is appropriately treated by aeration to obtain an aerobic treatment liquid, but for example, an aeration tank or a fluid carrier tank can be used.

The first aerobic treatment liquid treated in the first aerobic treatment tank 1a is introduced into the second aerobic treatment tank 1b and further treated. The second aerobic treatment liquid treated in the second aerobic treatment tank 1b is introduced into the solid-liquid separation tank 2 and separated into the treated water and the separated sludge in the solid-liquid separation tank 2. A part of the separated sludge is returned as the first return sludge to the first aerobic treatment tank 1a via the first return means 3 composed of pipes and the like. The second return means 4 returns at least a part of the separated sludge as the second return sludge to the second aerobic treatment tank 1b via the second return means 4 composed of pipes and the like. The rest of the separated sludge is discharged to the outside of the system as excess sludge.

A flow meter (not shown) may be provided in the pipe for flowing the raw water into the first aerobic treatment tank 1a, and the sludge flow rate of the first return sludge and the second return sludge is set with respect to the raw water inflow rate. A control means for controlling the sludge may be provided. Further, a DO meter for measuring the dissolved oxygen concentration (DO) may be provided in the first aerobic treatment tank 1a, and a control means for controlling DO by the aeration air volume of the first aerobic treatment tank 1a may be provided. .. As the solid-liquid separation tank 2, for example, a settling basin and an MBR (membrane separation activated sludge) tank can be used.

In the first aerobic treatment tank 1a, it is extremely important to properly maintain various conditions of BOD-SS load, DO, and pH, which are important for growing micro-animals. In particular, in order to treat organic wastewater in consideration of fluctuations in raw water concentration, flow rate, etc., the first return means so as to satisfy certain conditions in relation to the treatment conditions with the first aerobic treatment tank 1a. It is important to adjust the treatment conditions of 3.

The role of the first aerobic treatment tank 1a is to grow dispersible bacteria and the like in the first aerobic treatment tank 1a, remove BOD, and then sludge by the micro-animals living in the second aerobic treatment tank 1b. The purpose is to reduce the volume of sludge by preying on it. At that time, the micro-animals grown in the second aerobic treatment tank 1b are sent to the first aerobic treatment tank 1a, which is the main reaction tank for decomposing and removing organic matter, and the first aerobic treatment tank 1a to which the animals have been sent is sent. By maintaining the BOD-SS load under certain conditions, it is possible to maintain stable treated water quality at all times and reduce the amount of excess sludge generated.

In the first embodiment, the flow rate ratio of the first return sludge flow rate (first return sludge flow rate / raw water inflow rate) to the amount of raw water inflow to the first aerobic treatment tank 1a is 5 to 30%. It is more effective to adjust the sludge so that the flow rate is 10 to 30% and further 15 to 30%. If the flow rate ratio of the first returned sludge flow rate is too large, the BOS-SS load of the first aerobic treatment tank 1a is drastically reduced due to the fluctuation of the properties of the raw water, the preferential generation of dispersible bacteria is suppressed, and the amount of sludge generated is increased. May be done. If the flow rate ratio of the first return sludge flow rate is too small, the BOD removal performance in the first aerobic treatment tank 1a deteriorates, and the water quality of the first aerobic treatment liquid deteriorates. Processing may not proceed stably.

The BOD-SS load of the first aerobic treatment tank 1a is preferably adjusted to 2 to 10 kg / kg / d. The BOD-SS load in the entire aerobic treatment tank 1 including the first aerobic treatment tank 1a and the second aerobic treatment tank 1b is preferably 0.1 to 0.5 kg / kg / d, more preferably. It is effective to control the content to 0.15 to 0.4 kg / kg / d, more preferably 0.2 to 0.3 kg / kg / d.

The total alkalinity of the first aerobic treatment tank 1a is preferably 100 to 500 mg / L, more preferably 200 to 400 mg / L, and further 200 to 300 mg / L. Is effective. When the pH of the first aerobic treatment tank 1a fluctuates, the bacterial flora in the tank changes, which causes destabilization of the treated water quality and deterioration of the sludge volume reduction effect. That is, it is important to maintain the pH buffering action so that the pH fluctuation in the first aerobic treatment tank 1a does not occur. The pH of the first aerobic treatment tank 1a is preferably 6.0 to 8.5, more preferably 7.0 to 8.0. The suspended solids (MLSS) concentration in the first aerobic treatment tank 1a can be 1000 to 4000 mg / L, and more typically 1000 to 2000 mg / L.

The dissolved oxygen concentration (DO) of the first aerobic treatment tank 1a is preferably adjusted so that the aerated air volume is 2 to 7 mg / L, and more preferably 4 to 6 mg / L. It is more effective. The DO of the second aerobic treatment tank 1b is preferably adjusted to 1 to 7 mg / L, and more preferably to about 2 to 4 mg / L. DO affects the flora in the aerobic treatment tank, and DO control makes it possible to maintain the flora effectively for reducing excess sludge and maintain stable treated water quality.

Although the activated sludge method can be adopted for the second aerobic treatment tank 1b, the same sludge volume reduction effect can be obtained by the fluid carrier method in which the microbial carrier is added. As the second aerobic treatment tank 1b, an MBR tank can also be used. By using the MBR tank, a settling basin becomes unnecessary, and the device can be made compact. Further, since the MLSS of the second aerobic treatment tank 1b is not easily affected by the sedimentation property of the sludge and can be stably maintained at a predetermined concentration, the amount of sludge returned to the first aerobic treatment tank 1a can be set to a predetermined amount. , The BOD-SS load of the first aerobic treatment tank 1a can be set stably.

As a microbial carrier, from synthetic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide, and photocurable resin, gel carriers using polymers such as carrageenan and sodium alginate, polyethylene, polyurethane, polypropylene, etc. A fluid carrier such as As the shape of the carrier, any of spherical, rectangular, and cylindrical shapes can be used, and the effective diameter thereof is preferably a diameter that can be separated more stably than the screen provided at the outlet of the second aerobic treatment tank 1b.

The BOD-SS load of the second aerobic treatment tank 1b is such that the BOD-SS load of the entire aerobic treatment tank 1 including the first aerobic treatment tank 1a and the second aerobic treatment tank 1b is 0.1 to 0. It is adjusted to be 5 kg / kg / d, for example, 0.2 to 0.4 kg / kg / d, preferably 0.2 to 0.3 kg / kg / d. The hydraulic residence time (HRT) of the second aerobic treatment tank 1b can be 8 to 24 hours, more preferably 12 to 24 hours, further 22 to 24 hours, and the MLSS is 3000 to 5000 mg / L. Further, it is preferable to treat it so as to be 4000 to 5000 mg / L.

The flow rate ratio of the second return sludge flow rate (second return sludge flow rate / raw water inflow water amount) to the amount of raw water inflow to the second aerobic treatment tank 1b is 80 to 100 flow rate%, more preferably 85 to 90 flow rate%. It is more preferable to adjust so as to be. This has the effect of maintaining the BOD-SS load and maintaining the micro-animals that prey on activated sludge.

As the solid-liquid separation tank 2, a membrane separation tank (MBR tank) as shown in FIG. 3 can also be used. By using the membrane separation tank 2 as the solid-liquid separation tank 2, it is possible to set the MLSS concentration of the separated sludge higher than when the sedimentation basin is used. At that time, the flow rate ratio of the first return sludge flow rate (first return sludge flow rate / raw water inflow water amount) to the amount of raw water inflow to the first aerobic treatment tank 1a may be adjusted to be 5 to 15%. More preferred. Further, in this case, the flow rate ratio of the second returned sludge flow rate (second returned sludge flow rate / raw water inflow water amount) to the raw water inflow amount to the second aerobic treatment tank 1b is adjusted to be 60 to 70 flow rate%. ..

(Processing method)
In the method for treating organic wastewater according to the first embodiment, first, raw water is supplied into the first aerobic treatment tank 1a, and the raw water is aerobically treated in the first aerobic treatment tank 1a. In the first aerobic treatment tank 1a, for example, HRT is 5 hours, DO is 2 to 7 mg / L, total alkalinity is 200 mg / L, and MLSS is 1000 mg / L, and the raw water is aerobic. The treatment is performed to obtain a first aerobic treatment liquid.

Subsequently, the first aerobic treatment liquid obtained in the first aerobic treatment tank 1a is supplied into the second aerobic treatment tank 1b, and the first aerobic treatment liquid is further aerobic in the second aerobic treatment tank 1b. Process. In the second aerobic treatment tank 1b, for example, the treatment liquid is aerobicly treated with HRT for 22 hours, DO for 1 to 7 mg / L, and MLSS for 4000 mg / L, and the second aerobic treatment tank 1b is used. Obtain a treatment solution. The second aerobic treatment liquid is separated into treated water and separated sludge by the solid-liquid separation tank 2.

A part of the separated sludge containing micro-animals obtained in the solid-liquid separation tank 2 is returned to the first aerobic treatment tank 1a as the first return sludge. In the first aerobic treatment tank 1a, the first return sludge having a flow rate of 5 to 30% with respect to the inflow of raw water is introduced. At least a part of the remaining separated sludge containing micro-animals is further returned to the second aerobic treatment tank 1b as the second return sludge.

According to the organic wastewater treatment apparatus and treatment method according to the first embodiment of the present invention, the first returned sludge having a flow rate% of 5 to 30% with respect to the amount of raw water inflow is placed in the first aerobic treatment tank 1a. By introducing the sludge, the activated sludge that removes BOD and the micro-animals that prey on the activated sludge can be maintained in the first aerobic treatment tank 1a in a fixed amount and in a state in which each is highly active.

The amount of excess sludge generated varies slightly depending on the amount of BOD removed. According to the organic wastewater treatment apparatus and treatment method according to the first embodiment of the present invention, a certain amount of micro-animals that prey on activated sludge are also maintained in the first aerobic treatment tank 1a with high activity. Therefore, even if the amount of excess sludge generated fluctuates due to fluctuations in the amount and concentration of raw water, stable sludge volume reduction is possible at all times. As a result, even if the properties of the raw water fluctuate, the treatment in the first aerobic treatment tank 1a can be stabilized, and the amount of excess sludge generated can be reduced while maintaining stable treatment water quality at all times.

If the return flow rate ratio is too small, the amount of highly active return sludge retained in the first aerobic treatment tank 1a will decrease. Highly active returned sludge acts as a driving force in the initial process of BOD removal and accelerates BOD removal. Therefore, if the amount of accumulated returned sludge is too small, BOD removal does not proceed quickly and the treated water quality deteriorates. .. In addition, when the BOD load fluctuates due to fluctuations in the amount and concentration of raw water, it cannot be dealt with, and the aerobic treatment becomes unstable. On the other hand, when the return flow rate ratio is excessive, the BOD-SS load in the first aerobic treatment tank 1a becomes small, the preferential generation of dispersible bacteria is suppressed, the food chain is out of balance, and the amount of excess sludge generated. Leads to an increase in.

Even in such a case, according to the organic wastewater treatment apparatus and treatment method according to the first embodiment, a part of the separated sludge is extracted as the first return sludge and the raw water is sent to the first aerobic treatment tank 1a. By performing the first return process of returning the water so that the flow rate is 5 to 30% of the inflow rate, it is possible to maintain stable treated water quality at all times regardless of changes in the properties of the raw water, and the amount of excess sludge generated. Reduction is possible. The volume of the first aerobic treatment tank 1a is set by the BOD-SS load, but according to the organic wastewater treatment apparatus and the treatment method according to the first embodiment, the first aerobic treatment tank 1a. Since the volume of 1a is about 1/3 to 1/10 of the volume of the second aerobic treatment tank 1b, it is possible to suppress the increase in size of the entire apparatus simply by arranging the small first aerobic treatment tank 1a. At the same time, wastewater treatment can be treated stably and efficiently.

(Second embodiment)
As shown in FIG. 2, the organic wastewater treatment apparatus according to the second embodiment of the present invention draws out the suspended sludge in the second aerobic treatment tank 1b and returns it to the first aerobic treatment tank 1a. It is different from the organic wastewater treatment apparatus according to the first embodiment in that it further has a third return means 5.

The flow rate ratio of the third return sludge flow rate (third return sludge flow rate / raw water inflow water amount) to the amount of raw water inflow to the first aerobic treatment tank 1a shall be 1 to 10 flow rate%, further 5 to 10 flow rate%. It is preferable to adjust to. Others are substantially the same as the organic wastewater treatment apparatus according to the first embodiment, and thus the description thereof will be omitted.

Since the third return sludge is the floating sludge in the second aerobic treatment tank 1b, it is characterized by having a higher DO than the sludge separated from the solid-liquid separation tank 2. Therefore, according to the organic wastewater treatment apparatus and the treatment method using the organic wastewater treatment apparatus according to the second embodiment, the suspended sludge in the second aerobic treatment tank 1b is extracted via the third return means 5. By performing the third return process of returning to the first aerobic treatment tank 1a, the DO in the first aerobic treatment tank 1a is more suitable when the third return sludge is returned to the first aerobic treatment tank 1a. It becomes possible to maintain the state, and it is possible to maintain stable treated water quality and maintain an effective flora for reducing excess sludge.

Although the present invention has been described by the first and second embodiments, it should not be understood that the statements and drawings that form part of this disclosure are limiting the invention. From this disclosure, various alternative embodiments can be derived to those skilled in the art, and at the implementation stage, they can be deformed and embodied within a range that does not deviate from the gist.

Examples of the present invention are shown below together with comparative examples, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

(Example 1)
Using organic wastewater having an organic matter (BOD) concentration of 1000 mg / L as raw water, wastewater treatment was performed under the basic treatment conditions shown in Table 1 using the organic wastewater treatment apparatus shown in FIG. In Example 1, the supply flow rate of raw water is 2.5 L / d, and in the first aerobic treatment tank, the BOD-SS load is 5 kg / kg / d, the MLSS concentration is 1000 mg / L, and the DO is 2 to 7 mg / L. After aerobic treatment in, solid-liquid separation was performed in a solid-liquid separation tank, and a part of the obtained separated sludge was used as the first return sludge to the first aerobic treatment tank at 0.4 L / d. I sent it back. In the second aerobic treatment tank, after aerobic treatment under the conditions of MLSS concentration 4000 mg / L and DO2-7 mg / L, solid-liquid separation was performed in the solid-liquid separation tank, and the obtained separated sludge was performed. Was returned to the second aerobic treatment tank at 2.2 L / d as the second return sludge. At this time, the BOD-SS load in all the aerobic treatment tanks was 0.3 kg / kg / d. Alkali was added so that the total alkalinity in the first aerobic treatment tank was 200 mg / L.

In Example 1, as shown in Table 1, the flow rate of the first returned sludge to the first aerobic treatment tank was adjusted to be 15 flow rate% as the flow rate ratio to the amount of inflow of raw water, and the BOD-SS load was 5 kg / It was set to kg / d.

Comparative Example 1 uses an aerobic treatment tank having a volume of 2.5 L based on the conventional standard activated sludge treatment flow of FIG. 5 in which the first aerobic treatment tank is not installed, and under the conditions shown in Tables 1 and 2. Wastewater treatment was performed. In Comparative Example 1, the flow rate ratio of the sludge returned to the aerobic treatment tank to the amount of inflow of raw water was set to 100 flow rate% (2.5 L / d). The analysis of each item was performed in accordance with the sewage test method (Japan Sewerage Association 2012 version).

Comparative Example 1 shows the analysis results of the sludge generation amount and the soluble BOD in the treated water when the organic wastewater is treated by the conventional activated sludge treatment method in which only one aerobic treatment tank is used. On the other hand, in Example 1, the first return sludge flow rate ratio to the amount of raw water inflow was 15%, the BOD-SS load of the first aerobic treatment tank was 5 kg / kg / d, and the total alkalinity of the first aerobic treatment tank was. The results of the analysis of the sludge generation amount and the soluble BOD in the treated water when the DO of the first aerobic treatment tank is adjusted to a suitable range of 200 mg / L and 2 to 7 mg / L are shown. In Example 1, stable treated water quality comparable to that of Comparative Example 1 was obtained, and the sludge generation amount was reduced by 40% as compared with the sludge generation amount in Comparative Example 1, and a good sludge volume reduction effect was obtained. Was done.

In Comparative Example 2, in the treatment apparatus shown in FIG. 1, sludge generation is generated when the first return sludge flow rate ratio to the raw water inflow amount is 2 flow rate% and the second return sludge amount to the raw water inflow amount is 2.2 L / d. The amount and the result of the soluble BOD in the treated water are shown. In Comparative Example 2, the amount of sludge returned to the first aerobic treatment tank is small, the BOD-SS load of the first aerobic treatment tank temporarily increases rapidly, and the amount of sludge generated increases. In addition, since the amount of highly active separated sludge returned is small, the BOD removal performance in the first aerobic treatment tank deteriorates, and the quality of the treated water deteriorates.

In Comparative Example 3, in the treatment apparatus shown in FIG. 1, sludge generation is generated when the first return sludge flow rate ratio to the raw water inflow amount is 50 flow rate% and the second return sludge amount to the raw water inflow amount is 2.2 L / d. The amount and the result of the soluble BOD in the treated water are shown. In Comparative Example 3, since a large amount of sludge is returned to the first aerobic treatment tank, the BOD-SS load of the first aerobic treatment tank is temporarily lowered, and the preferential growth of dispersible bacteria is suppressed. As a result, the food chain does not proceed well in the second aerobic treatment tank in the subsequent stage, the amount of sludge generated increases, and it becomes equivalent to the standard activated sludge method, and no reduction effect is observed.

As described above, according to the present disclosure, in the first aerobic treatment tank for aerobicly treating organic wastewater, the BOD-SS load is 5 kg / kg / d, DO is 2 to 7 mg / L, and the total alkalinity is 100 to 500 mg. By performing aeration treatment under the condition of / L, dispersive bacteria and the like are predominantly grown in the first aerobic treatment tank, and these are preyed on by micro animals in the second aerobic treatment tank to generate excess sludge. Can be seen to be reduced. Further, as shown in FIG. 6, not only is the separated sludge solid-liquid separated from the second aerobic treatment tank returned to the second aerobic treatment tank, but also the amount of raw water inflow is as shown in FIG. By introducing the activated sludge into the first aerobic treatment tank at a flow rate of 5 to 30%, the amount of activated sludge retained in the first aerobic treatment tank is maintained in a well-balanced manner. Further BOD removal and predation of activated sludge proceed, and it becomes possible to further suppress the generation of excess sludge.

(Example 2)
In Example 2, the same organic wastewater as in Example 1 is used as raw water, and the organic wastewater treatment apparatus shown in FIG. 2 is used so that the third return sludge flow rate ratio to the amount of raw water inflow is 5%. In addition, the third return sludge was introduced into the first aerobic treatment tank, and the conditions were adjusted so as to be as shown in Table 3. In Comparative Example 4, wastewater treatment was performed under the conditions shown in Tables 1 and 2 based on the conventional standard activated sludge treatment flow of FIG. 5 in which the first aerobic treatment tank was not installed.

In Example 2, the first return sludge flow rate ratio to the raw water inflow rate is 10 flow rate%, the second return sludge flow rate ratio to the raw water inflow water amount is 70 flow rate%, the third return sludge flow rate ratio to the raw water inflow water amount is 5 flow rate%, and the second. Suitable range of 1 aerobic treatment tank BOD-SS load 5 kg / kg / d, 1st aerobic treatment tank total alkalinity 200 mg / L, 1st aerobic treatment tank DO 2-7 mg / L The results of the analysis of the sludge generation amount and the soluble BOD in the treated water when adjusted to are shown. It can be seen that in Example 2, more stable treated water quality can be obtained as compared with Comparative Example 4, and the sludge generation amount is reduced by about 50% as compared with the sludge generation amount in Comparative Example 2.

As described above, according to the second embodiment, in the first aerobic treatment tank for aerobically treating organic wastewater, the BOD-SS load is 2 to 10 kg / kg / d, DO2 to 7 mg / L, and total alkali. By performing aeration treatment under the condition of a degree of 100 to 500 mg / L, dispersive bacteria and the like are predominantly grown in the first aerobic treatment tank, and these are preyed on by micro animals in the second aerobic treatment tank. It can be seen that the generation of excess sludge can be reduced. Further, by introducing the separated sludge solid-liquid separated from the second aerobic treatment tank into the first aerobic treatment tank at a flow rate of 5 to 30% of the amount of raw water inflow, the activated sludge in the first aerobic treatment tank is introduced. Since the retention amount is maintained in a well-balanced manner, further BOD removal and predation of activated sludge proceed in the first aerobic treatment tank, and it becomes possible to further suppress the generation of excess sludge.

In addition, since the third return sludge is the floating sludge in the second aerobic treatment tank, it is characterized by having a higher DO than the sludge separated from the solid-liquid separation tank. Therefore, when the third returned sludge is returned to the first aerobic treatment tank, the DO in the first aerobic treatment tank can be maintained in a more appropriate state, and stable treatment water quality can be maintained and excess sludge can be reduced. It is possible to maintain an effective flora.

1 ... Aerobic treatment tank 1a ... 1st aerobic treatment tank 1b ... 2nd aerobic treatment tank 2 ... Solid-liquid separation tank 3 ... 1st return means 4 ... 2nd return means 5 ... 3rd return means

Claims (6)

A treatment in which raw water containing organic substances is aerobicly treated in a first aerobic treatment tank to obtain a first aerobic treatment liquid, and
A treatment in which the first aerobic treatment liquid is aerobically treated in the second aerobic treatment tank to obtain a second aerobic treatment liquid, and
A treatment in which the second aerobic treatment liquid is solid-liquid separated to obtain treated water and separated sludge, and
The first return treatment, in which a part of the separated sludge is extracted as the first return sludge and returned to the first aerobic treatment tank so as to have a flow rate of 5 to 30% of the amount of raw water inflow.
It is characterized by having a second return treatment in which at least a part of the separated sludge after the first return sludge is pulled out is used as a second return sludge, and the second return sludge is returned to the second aerobic treatment tank. How to treat organic wastewater. The method for treating organic wastewater according to claim 1, further comprising a third return treatment for drawing out the floating sludge in the second aerobic treatment tank and returning it to the first aerobic treatment tank. The method for treating organic wastewater according to claim 1 or 2, wherein the first return treatment is performed so that the BOD sludge load of the first aerobic treatment tank is 2 to 10 kg / kg / d. The method for treating organic wastewater according to any one of claims 1 to 3, wherein an alkali is added so that the total alkalinity of the first aerobic treatment tank is 100 to 500 mg / L. The method for treating organic wastewater according to any one of claims 1 to 4, wherein the amount of aerated air is adjusted so that the dissolved oxygen concentration in the first aerobic treatment tank is 2 to 7 mg / L. .. A first aerobic treatment tank that aerobicly treats raw water containing organic substances to obtain a first aerobic treatment liquid,
A second aerobic treatment tank for aerobically treating the first aerobic treatment liquid to obtain a second aerobic treatment liquid, and a second aerobic treatment tank.
A solid-liquid separation tank for solid-liquid separation of the second aerobic treatment liquid to obtain treated water and separated sludge.
A first return means for drawing out a part of the separated sludge as the first return sludge and returning it to the first aerobic treatment tank so as to have a flow rate of 5 to 30% of the amount of raw water inflow.
It is characterized by comprising a second return means in which at least a part of the separated sludge after the first return sludge is pulled out is used as a second return sludge and the second return sludge is returned to the second aerobic treatment tank. Organic wastewater treatment equipment.

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