JP7228487B2 - Organic wastewater treatment method and organic wastewater treatment apparatus - Google Patents

Description

The present invention relates to an organic wastewater treatment method and an organic wastewater treatment apparatus.

In recent years, activated sludge treatment is generally used in many cases to treat organic wastewater with a high biochemical oxygen demand (BOD). Activated sludge treatment is easy to maintain and has low running costs. Activated sludge treatment enables stable removal of BOD in influent raw water, and has the advantage of always obtaining good treated water quality. Therefore, activated sludge treatment is widely used for treatment of various organic wastewaters such as domestic wastewater and industrial wastewater.

However, it is known that activated sludge treatment generates excess sludge due to BOD removal. In particular, wastewater with a high BOD concentration generates a large amount of excess sludge, so the ratio of the cost associated with the disposal of excess sludge to the total treatment has increased, and the reduction of excess sludge has become a major issue.

As a method for reducing excess sludge, there is a method of multi-stage treatment that combines high load and low load. For example, dispersed bacteria are generated in the first high-load biological treatment tank, and the second low-load biological treatment tank uses predation of dispersed bacteria by protozoa and metazoans to reduce sludge. A method for reducing the volume of sludge by a food chain is disclosed (Japanese Unexamined Patent Application Publication No. 2010-69482).

JP 2010-69482 A

In the biological treatment method described in Patent Document 1, in order to improve treatment efficiency and reduce the amount of excess sludge generated, the BOD load and pH of the first biological treatment tank and the second biological treatment tank are controlled within a predetermined range. It states that it should be controlled. In this respect, when the properties of 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 first biological treatment tank may become unstable. . As a result, the effect of reducing the volume of sludge in the food chain by feeding on dispersed bacteria cannot be obtained sufficiently. Moreover, if dispersed bacteria are generated excessively in the first biological treatment tank due to changes in the properties of the raw water, and dispersed bacteria remain in the second biological treatment tank, there is a risk of deteriorating the quality of the treated water. Patent Document 1 also describes returning sludge to the first and second biological treatment tanks. However, there is no specific proposal, nor is there any design that takes into account 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 that can always maintain stable treated water quality even when the properties of raw water change and can reduce the amount of excess sludge generated. offer.

As a result of intensive studies by the present inventors in order to solve the above problems, in order to reduce the amount of excess sludge generated while maintaining stable treated water quality at all times without being greatly affected by changes in the properties of raw water, It is important to have bacteria that decompose organic matter in the raw water flowing into the aerobic treatment tank and microorganisms that prey on these bacteria coexist in a well-balanced manner. It has been found that it is effective to control the treatment conditions of the sludge culture tank to be returned to have a certain relationship in relation to the treatment conditions of the aerobic treatment tank.

In one aspect of the organic wastewater treatment method according to the embodiment of the present invention, which has been completed based on the above knowledge, raw water containing organic matter is aerobically treated in an aerobic treatment tank to produce an aerobic treated liquid. a solid-liquid separation process to obtain treated water and separated sludge by solid-liquid separation of the aerobic treated liquid, and a part of the separated sludge is withdrawn as first returned sludge and returned to the aerobic treatment tank. At least part of the separated sludge after the first return treatment and the extraction of the first returned sludge is used as the second returned sludge, and the first returned sludge is placed in a sludge culture tank containing micro-animals capable of decomposing the second returned sludge. The second return sludge is supplied with a flow rate of 2 to 30% of the sludge flow rate, and the hydraulic retention time (HRT) in the sludge culture tank is 0.15 to 6 times that of the aerobic treatment tank. and a second return process of returning the sludge culture solution containing microanimals after the aeration process to the aerobic treatment tank after the aeration process.

In one embodiment of the organic wastewater treatment method according to the embodiment of the present invention, the aerobic treatment includes high-load treatment to obtain a high-load treated liquid by treating raw water in a high-load treatment tank, and high-load treatment. low-load treatment in which the high-load treated liquid obtained in the tank is treated in the low-load treatment tank under load conditions lower than the load conditions of the high-load treatment tank, and the first return treatment reduces the first returned sludge to at least a low load. Including returning to the load treatment tank, the second return treatment returns the second return sludge to the low load treatment tank, and the HRT of the sludge culture tank is 0.15 to 6 with respect to the HRT of the low load treatment tank. It includes aeration treatment at a dissolved oxygen concentration (DO) of 1 mg/L or more and a water temperature of 20°C or more so as to double the amount.

In another embodiment, the organic wastewater treatment method according to the embodiment of the present invention includes arranging two or more sludge culture tanks in series.

In still another embodiment of the organic wastewater treatment method according to the embodiment of the present invention, the flow ratio of the second returned sludge to the first returned sludge is measured, and when the flow ratio exceeds 30% and adjusting to increase the flow rate of the second returned sludge when the flow rate ratio is less than 2% flow rate.

In still another embodiment of the organic wastewater treatment method according to the embodiment of the present invention, a carrier is added to at least one of the aerobic treatment tank and the sludge culture solution.

In one aspect, an organic wastewater treatment apparatus according to an embodiment of the present invention includes an aerobic treatment tank for aerobically treating raw water containing organic matter to obtain an aerobic treatment liquid, and a solid-liquid a solid-liquid separation tank for obtaining treated water and separated sludge by separation; At least part of the separated sludge containing animals and after extraction of the first returned sludge is used as the second returned sludge, and the second returned sludge having a flow rate of 2 to 30% of the sludge flow rate of the first returned sludge is supplied to the sludge. The sludge culture tank is aerated so that the HRT in the culture tank is 0.15 to 6 times the HRT in the aerobic treatment tank, and the sludge culture solution containing microanimals after the aeration treatment is preferably transferred from the sludge culture tank. and a second return means for returning to the gas treatment tank.

In one embodiment of the organic wastewater treatment apparatus according to the embodiment of the present invention, raw water measuring means for measuring the flow rate of raw water, first returned sludge measuring means for measuring the flow rate of first returned sludge, and second A second returned sludge measuring means for measuring the flow rate of the returned sludge, and measuring the flow rate ratio of the second returned sludge to the first returned sludge at least when the flow rate of the raw water fluctuates, and the flow rate ratio exceeds 30%. a control means for controlling the flow rate of the second returned sludge to be reduced when the flow rate ratio is less than 2%, and the flow rate of the second returned sludge to be increased when the flow rate ratio is less than 2%.

According to the present invention, it is possible to provide an organic wastewater treatment method and an organic wastewater treatment apparatus capable of always maintaining stable treated water quality and reducing the amount of excess sludge generated even when the properties of raw water change.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic showing the treatment flow of the organic wastewater which concerns on 1st Embodiment. It is a schematic diagram showing a treatment flow of organic wastewater according to a second embodiment. It is a schematic diagram showing a treatment flow of organic wastewater according to a third embodiment. 4 is a flow chart showing a processing flow when changing processing conditions of a sludge culture tank. 1 is a schematic diagram showing a conventional organic wastewater treatment flow; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention. not something to do.

(First embodiment)
The organic wastewater treatment apparatus according to the embodiment of the present invention comprises, as shown in FIG. A solid-liquid separation tank 2 for solid-liquid separation to obtain treated water and separated sludge, a first return means 3 for withdrawing a part of the separated sludge as first returned sludge and returning it to the aerobic treatment tank, and a first return At least part of the separated sludge after the sludge is extracted is used as the second return sludge, and the second return sludge is supplied and aerated in a sludge culture tank 4, and the sludge culture solution containing the micro-animals after the aeration treatment is cultured as sludge. A second return means 5 for returning from the tank 4 to the aerobic treatment tank 1 is provided.

As the raw water, various organic wastewaters containing organic matters such as domestic wastewater, sewage, food factories, chemical factories, pulp factories, etc. are used. As the aerobic treatment tank 1, activated sludge containing bacteria that can decompose organic matter (BOD) in the raw water flowing into the aerobic treatment tank, microorganisms that prey on bacteria, etc. is accommodated inside, and the raw water is made suitable by aeration. Although it is not particularly limited as long as it is an apparatus for obtaining an aerobic treatment liquid by treating the water, for example, an aeration tank can be used. In order to improve the treatment efficiency of raw water, a plurality of aerobic treatment tanks 1 may be connected in series or in parallel for multistage treatment.

The aerobic treatment liquid treated in the aerobic treatment tank 1 is supplied to the solid-liquid separation tank 2 and separated into treated water and separated sludge in the solid-liquid separation tank 2 . A part of the separated sludge is returned to the aerobic treatment tank 1 as first returned sludge through the first returning means 3 composed of a pipe or the like. The second return means 5 supplies the sludge amount preset for the first returned sludge to the sludge culture tank as the second returned sludge out of the surplus sludge remaining after the first returned sludge is withdrawn. The remainder of the separated sludge is discharged out of the system as surplus sludge.

The sludge culture tank 4 contains minute animals such as aphids that can decompose the separated sludge separated in the solid-liquid separation tank 2, and supplies the second returned sludge having a flow rate of 2 to 30% of the sludge flow rate of the first returned sludge. Then, the HRT in the sludge culture tank 4 is 0.15 to 6 times the HRT in the aerobic treatment tank 1 for aeration treatment. Micro animals such as aphids stored in the sludge culture tank 4 prey on the second returned sludge, thereby significantly reducing the amount of excess sludge generated.

In the sludge culture tank 4, it is extremely important to appropriately maintain various conditions such as water temperature, DO, and HRT, which are important for growing minute animals such as aphids. In particular, in order to treat organic wastewater in consideration of fluctuations in raw water concentration, water temperature, flow rate, etc., certain It is important to adjust the processing conditions of the sludge culture tank 4 so as to satisfy the conditions.

The role of the sludge culture tank 4 is to prey on the sludge in the sludge culture tank 4 by micro-animals grown in the sludge culture tank 4, thereby reducing the volume of the sludge. However, more than that, the micro-animals grown in the sludge culture tank 4 are sent to the aerobic treatment tank 1, which is the main reaction tank for decomposing and removing organic matter, and the sludge is eaten by the aerobic treatment tank 1 to which they are sent. It is also particularly important to suppress the growth of excess sludge by using the septic system in order to constantly maintain stable treated water quality and to reduce the amount of excess sludge generated.

At that time, when the HRT of the sludge culture tank 4 is too small with respect to the HRT of the aerobic treatment tank 1, especially when the ratio is less than 0.15, the treatment in the sludge culture tank 4 is too insufficient, Micro-animals may not grow sufficiently in the sludge culture tank 4 . Moreover, even if the HRT of the sludge culture tank 4 alone is sufficient, if the HRT of the aerobic treatment tank 1 is too long, the micro-animals sent from the sludge culture tank 4 will be mixed with other microorganisms in the aerobic treatment tank 1. Therefore, it becomes difficult to maintain a constant amount of microorganisms in the system as a whole.

On the other hand, if the HRT of the sludge culture tank 4 is too large relative to the HRT of the aerobic treatment tank 1, especially if the ratio exceeds 6, the volume of the sludge culture tank 4 will increase, leading to an increase in equipment costs. Furthermore, in this case, the ratio of the amount of microorganisms in the treatment system increases, which causes the quality of the treated water to become unstable.

Even if the tank capacity and HRT of the sludge culture tank 4 alone are appropriate, if the HRT of the aerobic treatment tank 1 is too short, the micro-animals sent from the sludge culture tank 4 are excessive even in the aerobic treatment tank 1. is maintained at At first glance, it seems that sludge volume reduction is good if there are many micro-animals. The microbial balance of the water is lost, and the quality of the treated water deteriorates. That is, it is extremely important to appropriately determine the treatment conditions of the sludge culture tank 4 in balance with the treatment conditions of the aerobic treatment tank 1 .

It is also possible to consider the balance between the sludge amount (sludge flow rate) of the second returned sludge supplied to the sludge culture tank 4 and the sludge amount (sludge flow rate) of the first returned sludge after considering such a balance of HRT. is important. When the sludge flow rate of the second returned sludge is too small relative to the first returned sludge, especially when it falls below 2% of the sludge flow rate of the first sludge, the ratio of the sludge in the entire system passing through the sludge culture tank 4 is too low, it may not be possible to maintain sufficient micro-animals in the sludge culture tank 4 to obtain the effect of reducing excess sludge.

On the other hand, if the sludge flow rate of the second returned sludge is too large relative to the sludge flow rate of the first returned sludge, especially if it exceeds 30%, the proportion of micro-animals in the entire system will be too high, resulting in Bacteria and microorganisms necessary for water treatment are reduced, and the treated water quality may not be maintained well. Moreover, if the sludge flow rate of the second returned sludge is too high, the volume of the sludge culture tank 4 must be increased in order to maintain the HRT appropriately, which leads to an increase in the cost of the apparatus.

In this embodiment, the ratio of the HRT in the sludge culture tank 4 to the HRT in the aerobic treatment tank 1 (sludge culture tank HRT/aerobic treatment tank HRT) can be adjusted to be 0.3 to 6 times. More preferably, it is still more preferably 0.3 to 3 times. When the sludge culture tank HRT/aerobic treatment tank HRT is 0.15 to 3 times, the second returned sludge has a flow rate of about 3 to 30%, more preferably 4 to It is preferable to return about 15 flow rate to the sludge culture tank 4 . When the sludge culture tank HRT/aerobic treatment tank HRT is more than 3 times and 6 times or less, the sludge flow rate of the first returned sludge should be returned to the sludge culture tank 4 at a flow rate of about 2 to 10%. is preferred. By adjusting the treatment conditions of the sludge culture tank 4 and the aerobic treatment tank 1 in this way, it is possible to stably grow micro-animals such as aphids contained in the sludge culture tank 4 .

The higher the suspended solids (MLSS) concentration of the second returned sludge supplied to the sludge culture tank 4, the smaller the volume of sludge to be supplied, and the necessary HRT can be secured while making the capacity of the sludge culture tank 4 compact. It is possible to obtain a high sludge volume reduction effect. The MLSS of the second returned sludge is preferably 6000 mg/L or more, more preferably 8000 to 15000 mg/L or more.

In order to more stably and reliably grow minute animals such as aphids in the sludge culture tank 4 when returning the aerobic treatment tank 1, it is preferable to set the dissolved oxygen concentration (DO) to 1 mg / L or more. Preferably it is 2-5 mg/L. The higher the DO, the easier it is for micro-animals such as aphids to proliferate, fully prey on activated sludge, and achieve a high sludge volume reduction effect.

The DO value may be adjusted as an operating condition of the aerobic treatment tank 1, but in the sludge culture tank 4, by controlling the DO more strictly than in the aerobic treatment tank 1, more preferable microanimal proliferation effect and A high sludge volume reduction effect can be obtained. Therefore, regardless of whether or not the DO is adjusted in the aerobic treatment tank 1, it is preferable to adjust the DO in the sludge culture tank 4 using a DO control device or the like.

The water temperature of the sludge culture tank 4 is preferably 20°C or higher, more preferably 20 to 35°C. The higher the water temperature of the sludge culture tank 4, the easier it is for micro-animals such as aphids to proliferate, and the micro-animals can sufficiently consume the activated sludge, resulting in a higher sludge volume reduction effect. The treatment water temperature range may be adjusted as an operating condition of the aerobic treatment tank 1, but adjusting the water temperature range of the sludge culture tank 4 provides higher microanimal proliferation and sludge volume reduction effects. For example, it is preferable to install a water temperature control device in the sludge culture tank 4 and control the water temperature to 20° C. or higher.

A small amount of raw water may be allowed to flow into the sludge culture tank 4. However, if undecomposed organic matter in the raw water remains in the sludge culture tank 4, it may affect the growth of micro-animals. When flowing into the tank 4, it is necessary to strictly control the amount of inflow raw water. Even if the DO, water temperature, and HRT of the sludge culture tank 4 and the aerobic treatment tank 1 are controlled within appropriate ranges, the sludge culture tank 4 into which raw water flows does not allow raw water to flow into the sludge culture tank 4. This is because it becomes difficult to balance both the microanimal proliferation effect and the sludge volume reduction effect compared to the case.

It is preferable to arrange the sludge culture tanks 4 in two or more stages in series. When the sludge culture tanks 4 are arranged in series in two or more stages, even if undecomposed organic matter remains in the second returned sludge, it is decomposed in the sludge culture tank 4 in the previous stage. is a favorable breeding environment for minute animals such as aphids. As a result, the micro-animals can grow more stably, and as a result, more efficient treatment can be performed while reducing the amount of excess sludge discharged out of the system.

It is advantageous for the growth and activation of micro-animals to place the sludge in the sludge culture tank 4 in an environment where organic matter does not remain as much as possible. It is preferable to flow into the downstream portion where less residual BOD is present. That is, the second return sludge supplied from the sludge culture tank 4 to the aerobic treatment tank 1 is preferably returned to a position downstream of the return position of the first return sludge. When the number of aerobic treatment tanks 1 is one, the second return sludge is preferably allowed to flow into the latter half of the treatment of the aerobic treatment tank 1 . When the aerobic treatment tank 1 has multiple stages, it is preferable to allow at least part of the second returned sludge from the sludge culture tank 4 to flow into the aerobic treatment tank 1 in the second and subsequent stages.

The aerobic treatment tank 1 can employ an activated sludge system, but a similar sludge volume reduction effect can be obtained by adopting a fluidized carrier system in which a microbial carrier is added.

Examples of microbial carriers include synthetic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide, and photocurable resins, gel carriers using polymers such as carrageenan and sodium alginate, polyethylene, polyurethane, and polypropylene. and a fluid carrier.

The shape of the carrier may be spherical, square or cylindrical, and its effective diameter is preferably 3 to 10 mm so that the particles can be stably separated from the screen provided at the outlet of the aerobic treatment tank 1 . The specific gravity of the carrier is preferably 1.01 to 1.05 so that it can flow uniformly in an aerated state. In addition, it is effective to set the carrier filling amount to 5 to 30 V/V %, preferably 10 to 20 V/V %, which enables uniform mixing and flow in the bioreactor.

(Processing method)
In the method for treating organic wastewater according to the first embodiment, first, raw water is supplied into the aerobic treatment tank 1 and is aerobically treated in the aerobic treatment tank 1 . In the aerobic treatment tank 1, raw water is aerobically treated with, but not limited to, HRT of 0.5 to 1.5 days, DO of 1.0 to 4.0 mg/L, and MLSS of 2500 to 5000. to obtain an aerobic treatment liquid. The aerobic treated liquid is separated into treated water and separated sludge by solid-liquid separation.

Part of the surplus sludge is returned to the aerobic treatment tank 1 as first returned sludge. The sludge culture tank 4 is supplied with the second returned sludge having a flow rate of 2 to 30% of the sludge flow rate of the first returned sludge. The sludge culture tank 4 is typically aerated so that DO is 1 mg/L or more and HRT is 0.15 to 6 times the HRT of the aerobic treatment tank 1. A sludge culture solution containing animals is sent from the sludge culture tank 4 to the aerobic treatment tank 1 .

According to the organic wastewater treatment apparatus and treatment method according to the first embodiment of the present invention, the sludge flow rate of the first returned sludge is placed in the sludge culture tank 4 containing micro-animals capable of decomposing the second returned sludge. After supplying the second return sludge with a flow rate of 2 to 30% of the aerobic treatment tank 4, the HRT in the sludge culture tank 4 is aerated so that it is 0.15 to 6 times the HRT in the aerobic treatment tank 1. A second return process is performed to return the treated sludge culture medium containing micro-animals to the aerobic treatment tank 1 . As a result, the activated sludge that removes BOD and the micro-animals that prey on the activated sludge can be maintained in the aerobic treatment tank 1 in a constant amount and in a highly active state. In addition, since the activated sludge that removes BOD is always kept in the aerobic treatment tank 1 at a constant amount and highly active, stable aerobic treatment is possible even if the BOD load fluctuates due to fluctuations in the flow rate and concentration of raw water. be. The amount of excess sludge generated varies depending on the amount of BOD removed, but 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 preying on activated sludge, Since the sludge is maintained at a high level of activity, stable sludge volume reduction is possible even if the amount of excess sludge generated fluctuates due to fluctuations in raw water flow rate and concentration. As a result, the treatment in the aerobic treatment tank 1 can be stabilized even if the properties of the raw water change, and the amount of excess sludge generated can be reduced while always maintaining stable treated water quality.

(Second embodiment)
The organic wastewater treatment apparatus according to the second embodiment of the present invention, as shown in FIG. and a low load treatment tank 1b for treating the high load treatment liquid obtained in the high load treatment tank 1a under load conditions lower than those of the high load treatment tank 1a.

The first returning means 3 returns the first returned sludge to at least the low-load treatment tank 1b. The first returning means 3 may further return the first returned sludge to the high-load treatment tank 1a as necessary. The second returning means 5 returns the second returned sludge to the low load treatment tank 1b. The HRT in the sludge culture tank 4 is adjusted to be 0.15 to 6 times the HRT in the low-load treatment tank 1b. It is aerated above 20°C. Others are the same as those of the organic wastewater treatment apparatus according to the first embodiment, so the description is omitted.

In the high-load treatment tank 1a, treatment is performed to oxidatively decompose about 50% or more of the BOD (organic components) in the raw water, and a high-load treated liquid is obtained. For example, the BOD load condition of the high load treatment tank 1a is 1 to 10 kg-BOD/m ³ /d, more specifically 3.0 to 8.0 kg-BOD/m ³ /d, more specifically 3.0 to 5.0 kg-BOD/m ³ /d. In the high-load treatment tank 1a, BOD in raw water is oxidized and removed by aeration treatment with a DO of 1.0 mg/L or more in the coexistence of activated sludge. The microorganism carrier described in the first embodiment may be accommodated in the high-load treatment tank 1a.

The high-load treatment liquid treated in the high-load treatment tank 1a is supplied to the low-load treatment tank 1b, and the sludge in the high-load treatment liquid is reduced in volume by predation by minute animals such as aphids, and the high-load treatment is performed. A treatment aimed at removing TN (total nitrogen) in the liquid is performed. For example, the BOD load condition of the low load treatment tank 1b is 0.05 to 1.5 kg-BOD/m ³ /d, more specifically 0.1 to 1.2 kg-BOD/m ³ /d, Specifically, it is 0.1 to 1.0 kg-BOD/m ³ /d. The microbial carrier described in the first embodiment may also be accommodated in the low-load treatment tank 1b.

(Processing method)
In the organic wastewater treatment method according to the second embodiment, first, raw water is supplied to the high-load treatment tank 1a, and in the high-load treatment tank 1a, for example, BOD load conditions are 2 to 20 kg-BOD/m ³ /d , HRT 0.1-1.0 days, MLSS 500-2000 mg/L to obtain a high-load treatment solution. This high-load treatment solution is treated in the low-load treatment tank 1b under conditions such as a BOD load of 1 to 5 kg-BOD/m ³ /d, an HRT of 0.2 to 2.0 days, and an MLSS of 2000 to 10000 mg/L. Obtain a processing solution. The low-load treated liquid is solid-liquid separated in the solid-liquid separation tank 2 to obtain treated water and separated sludge.

A part of the separated sludge is supplied to the low load treatment tank 1b and/or the high load treatment tank 1a as first return sludge. The sludge culture tank 4 is supplied with the second returned sludge having a flow rate of 2 to 30% of the sludge flow rate of the first returned sludge. In the sludge culture tank 4, the DO is typically 1 mg/L or more, and the aeration treatment is performed so that the HRT is 0.15 to 6 times that of the low-load treatment tank 1b. can get. The sludge culture solution is returned to the low load treatment tank 1b.

According to the organic wastewater treatment apparatus according to the second embodiment, organic wastewater can be treated more stably by multi-stage aerobic treatment in the high-load treatment tank 1a and the low-load treatment tank 1b. can be done systematically.

(Third Embodiment)
The organic wastewater treatment apparatus according to the third embodiment of the present invention, as shown in FIG. 2 in that it comprises a first returned sludge measuring means 53 for measuring, a second returned sludge measuring means 54 for measuring the flow rate of the second returned sludge, and a control means 6 . Others are the same as those of the organic wastewater treatment apparatus according to the second embodiment, so the description is omitted.

As the raw water measuring means 51, a generally available flowmeter, MLSS meter, or the like can be used. The raw water measuring means 51 can measure the flow rate of the raw water and the fluctuations in the concentration of organic matter in the raw water. The raw water measuring means 51 is electrically connected to the control means 6 so that measurement results are sent to the control means 6 .

As the first returned sludge measuring means 53 and the second returned sludge measuring means 54, a flowmeter or the like for measuring the sludge flow rate can be used. The first returned sludge measuring means 53 and the second returned sludge measuring means 54 are electrically connected to the control means 6 so that measurement results are sent to the control means 6 . A measuring means 52 such as an MLSS meter for measuring the MLSS concentration in the tank may be arranged in the low-load treatment tank 1b. Based on the MLSS concentration in the low-load treatment tank 1b measured by the measuring means 52, the sludge flow rate of the first returned sludge may be optimized.

Based on the measurement result of the raw water measuring means 51, the control means 6 measures the flow rate ratio of the second returned sludge to the first returned sludge at least when the raw water flow rate fluctuates, and measures the second returned sludge to the first returned sludge. The sludge flow rate of the second returned sludge is controlled so that the flow rate ratio of the second returned sludge is in the range of 2 to 30 flow rate %.

For example, when the measurement result of the raw water flow rate exceeds a preset threshold value, the control means 6 determines that the raw water flow rate "fluctuation" has occurred, and measures the flow rate ratio of the second returned sludge to the first returned sludge. You may make it As a result, when the flow rate ratio exceeds 30%, the control means 6 reduces the flow rate of the second return sludge, and when the flow rate ratio is below 2%, the control means 6 increases the flow rate of the second return sludge. It is preferable to control the sludge flow rate of the second return sludge so as to As a result, stable treated water quality can be maintained at all times even if the properties of raw water fluctuate, and the volume of surplus sludge generated can be reduced.

A processing flow in a method for treating organic wastewater according to the third embodiment of the present invention will be described with reference to the flow chart of FIG. While the raw water is supplied to the high-load treatment tank 1a, the low-load treatment tank 1b, and the solid-liquid separation tank 2 in FIG. The measurement result measured by 51 and the sludge flow rate of the first returned sludge measured by the first returned sludge measuring means 53 are measured.

In step S2, the control means 6 calculates the HRT of the aerobic treatment tank 1 (the low-load treatment tank 1b in the case of FIG. 3). In step S<b>3 , the control means 6 calculates the sludge flow rate of the second returned sludge with respect to the first returned sludge supplied to the sludge culture tank 4 . The flow rate of the first returned sludge can be made constant here. In step S4, the control means 6 calculates the flow rate ratio R1 represented by the second return sludge flow rate/first return sludge flow rate. In step S5, the control means 6 determines whether or not the flow ratio R1 falls within the range of 2 to 30%. In step S6, if the flow rate ratio R1 is outside the range of 2 to 30%, the process returns to step S3, resets the sludge flow rate of the second returned sludge, and repeats steps S4 to S6. In step S6, if the flow rate ratio R1 is within the range of 2 to 30%, the setting is completed.

After the sludge flow rate of the second returned sludge is set in step S3, the process also proceeds to step S8, where the control means 6 controls the sludge culture tank HRT/aerobic treatment tank HRT (in the case of FIG. 3, the sludge culture tank HRT /low load treatment tank HRT) is calculated. In step S9, it is determined whether or not the ratio R2 is within the range of 0.15 to 6.0 times. If R2 is not within the range of 0.15 to 6.0 times in step S9, the process returns to step S3 to reset the sludge flow rate of the second returned sludge. In step S9, if the ratio R2 is within the range of 0.15 to 6.0 times, the process proceeds to step S10 and the setting is completed.

According to the organic wastewater treatment apparatus and treatment method according to the third embodiment, the control means 6 can adjust more suitable treatment conditions according to the property fluctuations of the raw water. is relatively large, it is possible to quickly follow the optimal treatment conditions according to the properties of the raw water.

Examples of the present invention are presented below along with comparative examples, which are provided for a better understanding of the invention and its advantages and are not intended to be limiting of the invention.

Organic wastewater having an organic substance (BOD) concentration of 500 mg/L was used as raw water, and the wastewater was treated under the basic treatment conditions shown in Table 1 using the organic wastewater treatment apparatus shown in FIG. That is, in Example 1, the raw water supply flow rate is 50 L / d, the BOD-SS load in the aerobic treatment tank is 0.30 kg / kg / d, the MLSS concentration is 4000 mg / L, and the DO is 3.0 mg / L. After aerobic treatment, solid-liquid separation was performed in a solid-liquid separation tank, and part of the obtained separated sludge was returned to the aerobic treatment tank at 50 L/d as first returned sludge. In Example 1, as shown in Table 1, the HRT ratio of the sludge culture tank was 0.15 times that of the aerobic treatment tank, and the flow ratio of the second returned sludge to the first returned sludge (the second 2 return sludge flow rate / first return sludge flow rate) is 10%, the sludge flow rate of the second returned sludge is adjusted, the second returned sludge is supplied to the sludge culture tank, and the sludge culture solution after treatment is It was returned to the aerobic treatment tank 1. The MLSS of the first returned sludge and the second returned sludge was 8000 mg/L.

In Example 2, in the treatment apparatus of FIG. In Example 3, the HRT ratio of the sludge culture tank in the treatment apparatus of FIG. The sludge flow rate of the second returned sludge is adjusted so that the flow rate ratio (second returned sludge flow rate/first returned sludge flow rate) is 30%, and the second returned sludge is supplied to the sludge culture tank, and the sludge after treatment The treatment was the same as in Example 1, except that the culture solution was returned to the aerobic treatment tank 1.

In Example 4, using the treatment apparatus of FIG. 2, a high-load treatment tank with a capacity of 5 L and a low-load treatment tank with a capacity of 16 L were used, and the BOD-SS load in the high-load treatment tank was 5.0 kg/kg. / d, and the BOD-SS load of the low load treatment tank is adjusted so that the overall BOD-SS load is 0.30 kg / kg / d, and the HRT ratio of the sludge culture tank and the second return sludge The flow rate ratio was set to the conditions shown in Table 2, and 5 L/d of returned sludge was returned to the high-load treatment tank.

Comparative Example 1 was processed based on the conventional processing flow of FIG. 5 without installing a sludge culture tank. In Comparative Examples 2 to 5, wastewater was treated under the conditions shown in Tables 1 and 2 using the treatment apparatus shown in FIG.

"Frequency of appearance of micro-animals" in Table 2 is obtained by sampling a certain amount of sludge supplied from the inlet side of the aerobic treatment tank or low-load treatment tank and observing it under a microscope. O and x indicate the results graded. Regarding treated water quality, BOD and COD _Mn are measured, and the results are shown in descending order from the best with ⊙, ◯, and ×. As a result of evaluating the sludge flow rate (L/d) discharged outside the system and the sludge amount (g/d) calculated from the sludge concentration, the sludge reduction effect was evaluated in order from the lowest amount of excess sludge generated ◎, 〇, The results marked with x are shown. Comprehensive evaluation is the result of comprehensively taking into account the appearance frequency of minute animals, treated water quality, and sludge volume reduction effect.

Since Comparative Example 1 was a conventional activated sludge treatment system without a sludge culture tank, almost no micro-animals contributing to the reduction of excess sludge were observed, and the sludge reduction effect was almost non-existent. Although Comparative Examples 2 to 4 have a sludge culture tank, the ratio of the sludge flow rate of the second returned sludge to the first returned sludge is 2 to 30%, and the HRT ratio of the sludge culture tank to the aerobic treatment tank is 0.5%. As a result of deviating from 15 to 6 times, it was not possible to maintain well-balanced micro-animals in the activated sludge system, and it was not possible to obtain a good sludge volume reduction effect or stable treated water quality.

In Examples 1 to 4, the flow rate ratio of the second returned sludge to the first returned sludge is 2 to 30%, and the HRT ratio of the sludge culture tank to the aerobic treatment tank is within a suitable range of 0.15 to 6 times. Adjusted results are shown. In Examples 1 to 4, since an appropriate amount was maintained in micro-animals in the system, especially in the low-load treatment tank, treated water quality with good sludge volume reduction effect was stably obtained. Especially in Example 4, by further returning part of the first return sludge (5 L / d) to the high load treatment tank, the BOD-SS load of the high load treatment tank is reduced, and it flows into the low load treatment tank. It was found that the soluble BOD (S-BOD) was greatly reduced and better treated water quality was obtained.

Thus, according to the organic wastewater treatment apparatus and treatment method according to the embodiment of the present invention, the aerobic treatment tank for aerobically treating the organic wastewater, or the high-load treatment tank and the low-load tank treatment In a two-tank bioreactor consisting of When the water temperature is 20 to 35° C., the DO is 1 mg/L or more, and the HRT ratio is 0.15 to 6.0 times, minute animals such as aphids grow stably in the sludge culture tank. By supplying micro-animals such as aphid worms to the low-load treatment tank, it is possible to prey on the activated sludge in the low-load treatment tank and suppress the generation of excess sludge.

Furthermore, by making the HRT of the sludge culture tank 0.15 to 6 times that of the aerobic treatment tank (low-load treatment tank), Since the amount of excess sludge consumed by animals and the amount of activated sludge retained in the aeration tank are maintained in a well-balanced manner, it is possible to stably control the amount of excess sludge and obtain good treated water quality at the same time throughout the system. .

DESCRIPTION OF SYMBOLS 1... Aerobic treatment tank 1a... High-load treatment tank 1b... Low-load treatment tank 2... Solid-liquid separation tank 3... First return means 4... Sludge culture tank 5... Second return means 6... Control means 51... Raw water measurement means 52... Measuring means 53... First returned sludge measuring means 54... Second returned sludge measuring means

Claims (7)

aerobic treatment in which raw water containing organic matter is aerobically treated in an aerobic treatment tank to obtain an aerobic treated liquid;
Solid-liquid separation treatment to obtain treated water and separated sludge by solid-liquid separation of the aerobic treated liquid;
A first return process of withdrawing a part of the separated sludge as a first return sludge and returning it to the aerobic treatment tank;
At least part of the separated sludge after the extraction of the first returned sludge is used as second returned sludge, and sludge of the first returned sludge is placed in a sludge culture tank containing micro-animals capable of decomposing the second returned sludge. The dissolved oxygen concentration is 1 mg/L or more so that the HRT in the sludge culture tank is 0.15 to 6 times the HRT in the aerobic treatment tank. A method for treating organic wastewater, comprising, after aeration treatment, a second return treatment of returning the aerated sludge culture solution containing the microanimals to the aerobic treatment tank. The aerobic treatment is
a high-load treatment for obtaining a high-load treated liquid by treating the raw water in a high-load treatment tank;
a low load treatment in which the high load treatment liquid obtained in the high load treatment tank is treated in the low load treatment tank under load conditions lower than those of the high load treatment tank,
The first return processing is
Returning the first return sludge to at least the low-load treatment tank;
The second return processing is
The second return sludge is returned to the low-load treatment tank, and the dissolved oxygen concentration (DO) is adjusted so that the HRT of the sludge culture tank is 0.15 to 6 times the HRT of the low-load treatment tank. 2. The method for treating organic wastewater according to claim 1, comprising aeration treatment at a temperature of 1 mg/L or higher and a water temperature of 20° C. or higher. 3. The method for treating organic wastewater according to claim 1 or 2, comprising arranging said sludge culture tanks in two or more stages in series. measuring the flow ratio of the second return sludge to the first return sludge;
Adjusting to reduce the flow rate of the second return sludge when the flow rate ratio exceeds 30 flow rate % and to increase the flow rate of the second return sludge when the flow rate ratio is less than 2 flow rate % The method for treating organic wastewater according to any one of claims 1 to 3. The method for treating organic wastewater according to any one of claims 1 to 4, comprising adding a carrier to at least one of the aerobic treatment tank and the sludge culture solution. an aerobic treatment tank for aerobically treating raw water containing organic matter to obtain an aerobic treatment liquid;
a solid-liquid separation tank for solid-liquid separation of the aerobic treated liquid to obtain treated water and separated sludge;
a first returning means for withdrawing part of the separated sludge as first returned sludge and returning it to the aerobic treatment tank;
At least part of the separated sludge after extracting the first returned sludge containing micro-animals capable of decomposing the separated sludge is used as the second returned sludge, and 2 to 30% of the sludge flow rate of the first returned sludge a sludge culture tank in which the HRT in the sludge culture tank is aerated at a dissolved oxygen concentration of 1 mg/L or more so that the HRT in the sludge culture tank is 0.15 to 6 times the HRT in the aerobic treatment tank;
and second returning means for returning the sludge culture solution containing the microanimals after the aeration treatment from the sludge culture tank to the aerobic treatment tank. Raw water measuring means for measuring the flow rate of the raw water;
a first return sludge measuring means for measuring the flow rate of the first return sludge;
a second return sludge measuring means for measuring the flow rate of the second return sludge;
At least when the flow rate of the raw water fluctuates, the flow rate ratio of the second return sludge to the first return sludge is measured, and when the flow rate ratio exceeds 30 flow rate%, the flow rate of the second return sludge is reduced. and control means for increasing the flow rate of the second return sludge when the flow rate ratio is below 2 flow rate %.

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