JP2001314885A - High load biological treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high load biological treatment method capable of treating a liquid to be treated without filling a high load reaction tank with a carrier to prevent the reduction of an effective volume to enable high load treatment and capable of removing organic matter stably and efficiently, capable of forming sludge good in solid-liquid separability. SOLUTION: The liquid 11 to be treated is introduced into a first aeration tank 1 to be brought into contact with microorganisms under an aerobic condition to decompose organic matter with high BOD load and further introduced into a second aeration tank 2 to decompose organic matter with high BOD load so that a soluble BOD removing ratio becomes 50% or more and a soluble BOD concentration becomes 50-10,000 mg/L. Thereafter, the liquid to be treated is introduced into a third aeration tank 3 filled with a carrier 21 not only to decompose organic matter with low BOD load but also to flucculate sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-load biological treatment method for removing organic substances under aerobic conditions.

[0002]

2. Description of the Related Art In an activated sludge method for biodegrading a BOD component, a liquid to be treated is mixed with activated sludge and aerated to aerobically decompose the BOD component to obtain treated water by solid-liquid separation and to obtain sludge. This method is simple and easy to use, and is the most widely used processing method at present. However, it is difficult to perform treatment under a high load in which the BOD volume load is 1.5 kg / m ³ / d or more, and there is a problem that a large installation space is required for a large reaction tank. If a high-load treatment is simply performed in a reaction vessel having a low solubility BOD concentration represented by a complete mixing reaction vessel, filamentous bacteria will dominate and cause bulking, making solid-liquid separation in the solid-liquid separation process difficult. Then, SS flows out into the processing solution. In order to prevent this, it is effective to install a high-load reaction tank in the preceding stage.

[0003] Therefore, by performing treatment with a high BOD load, it is possible to stably and efficiently remove BOD with a small reaction tank volume, and to form a sludge with good solid-liquid separation properties. A biological treatment method has been proposed (for example, JP-A-2000-42584). FIG.
1 is a system diagram of a high-load biological treatment device described in 000-42584.

In FIG. 3, first and second reaction tanks 3 are provided.
Numerals 1 and 32 are provided with air diffusers 34 and 35, respectively, and are configured to communicate with air supply paths 36 and 37, respectively, to perform aerobic treatment. A liquid passage 41 to be treated and a sludge return line 42 are in communication with the first reaction tank 31. The first and second reaction tanks 31, 32 and the solid-liquid separation tank 33 are connected to lines 43, 4
Contact 4 A treatment liquid passage 45 communicates with the solid-liquid separation tank 33 at the upper part, and a sludge passage 46 communicates with the lower part.
Is branched into a return sludge passage 42 and a waste sludge passage 47.

The first and second reaction tanks 31 and 32 are filled with granular carriers 51 and 52, respectively, and are provided with screens 53 and 54 for separating carriers. Regarding the carrier filling rate, the first reaction tank 31 has a low filling rate, and the second reaction tank 32 has a high filling rate. A second reaction tank 32 is installed in series at a stage subsequent to the first reaction tank 31, and most of the BOD is decomposed in the first reaction tank 31. Thus, the first reaction tank 31 has a high BOD load, and the second reaction tank 32 has a low BOD load.

In the conventional treatment method using the above-described apparatus, first, as a first reaction step, a liquid to be treated and returned sludge are introduced into a first reaction tank 31 from a liquid passage 41 and a return sludge passage 42, respectively. It mixes with the activated sludge, sends air from the air supply passage 36 to aerate from the air diffuser 34, attaches microorganisms to the carrier 51, and decomposes BOD by an aerobic biological reaction.

[0007] By filling the carrier 51 with an addition rate of 5 to 30%, preferably 10 to 20%, various microorganisms are held on the carrier and the treatment is stabilized. Here, the BOD load is 2 to 100 kg / m ³ / d, preferably 1
Microorganisms proliferate under high-concentration BOD loading of 0 to 50 kg / m ³ / d, and BOD is efficiently removed.
Most of the growing microorganisms float without being held by the carrier 51. The carrier 51 is separated by the screen 53 and the mixed solution is sent to the second reaction tank 32 to perform the second reaction step.

In the second reaction step, the liquid mixture in the first reaction tank 31 is introduced into the second reaction tank 32 through a line 43 and mixed with the activated sludge in the tank. Aeration is performed from the device 35 to attach microorganisms to the carrier 52, decompose BOD by an aerobic biological reaction, and floc the activated sludge. BOD load 0.1 kg / m ³ / d or more 2 kg / m ³ / under d in the second reaction vessel 32, preferably 0.5~1kg / m ³ / d, the presence of the support 52 adhering microorganisms Aeration of the BO
D is removed and the dispersible sludge introduced from the first reaction tank 31 is flocculated. Excess sludge is separated and becomes sludge floc. The carrier 52 is separated by the screen 54 and the mixed liquid is sent to the solid-liquid separation tank 33 to perform a solid-liquid separation step.

In the solid-liquid separation step, the mixed liquid in the second reaction tank 32 is introduced into the solid-liquid separation tank 33 from the line 44 to be separated into solid and liquid, and the separated liquid is taken out from the processing liquid passage 45 as a processing liquid.
The sludge is taken out from the sludge passage 46, a part is returned from the returned sludge passage 42 as returned sludge, and the remaining portion is taken out from the waste sludge passage 47 as surplus sludge.

In the above conventional processing method, the first reaction tank 3
1 is filled with the carrier 51 at a low filling rate and aerated at a high BOD load, and the second reaction tank 32 is filled with the carrier 52 at a high filling rate and aerated at a low BOD load to perform processing at a high load. In addition, BOD can be stably and efficiently removed with a small reaction tank volume, and sludge having good solid-liquid separation properties can be formed.

[0011] However, since the first reaction vessel for processing under a high BOD load is filled with the carrier, the effective volume of the high-load reaction vessel is consumed by the carrier and decreases. On the other hand, if the treatment is simply performed under a high load without filling the first reaction tank with the carrier, the effect of preventing filamentous bacteria is unstable, and it is difficult to maintain the effect of preventing bulking, especially against fluctuations in water quality.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to enable high-load reaction tanks to be processed without being filled with a carrier, thereby preventing a reduction in effective volume and performing high-load processing. Moreover, an object of the present invention is to propose a high-load biological treatment method capable of stably and efficiently removing organic substances and forming sludge having good solid-liquid separation properties.

[0013]

The present invention is the following high-load biological treatment method. (1) An organic wastewater is introduced into a reaction tank and brought into contact with microorganisms under aerobic conditions, and the organic matter is removed so that the soluble BOD removal rate is 50% or more and the soluble BOD concentration is 50 to 10,000 mg / L. A first reaction step in which decomposition is performed at a high BOD load, and an effluent of the first reaction step is introduced into a reaction tank filled with a microorganism-holding carrier, and microorganisms are attached to the carrier to decompose organic substances under aerobic conditions. A high-load biological treatment method which is performed at a low BOD load and includes a second reaction step of flocking sludge, and a solid-liquid separation step of solid-liquid separation of an effluent of the second reaction step. (2) The BOD load in the first reaction step is 2 to 40 kg-BOD / kg-VSS / d as the sludge load,
BOD load in the reaction step of
The high-load biological treatment method according to the above (1), which is 0.5 kg-BOD / kg-VSS / d. (3) The high-load biological treatment method according to (1) or (2), wherein the first reaction step is performed in two or more reaction vessels connected in series. (4) The method according to any one of (1) to (3) above, wherein the nitrogen concentration of the organic effluent introduced into the first reaction tank is 1/10 or less of the soluble BOD concentration of the organic effluent. High load biological treatment method.

In the present invention, the organic effluent to be treated (hereinafter sometimes referred to as a liquid to be treated) is an effluent containing an organic substance to be treated by a usual aerobic biological treatment method, but is difficult. A biodegradable organic or inorganic substance may be contained, and ammonia nitrogen or organic nitrogen may be contained. Such organic effluents include sewage, night soil, food factory effluent, chemical factory effluent, and other industrial effluents.

The soluble BOD concentration of the organic effluent is 200 to
20000 mg / L, preferably 500 to 10000 m
g / L, more preferably 1000-5000 mg / L
It is desirable that Also, the nitrogen concentration (T-
N) is 1/10 or less of the soluble BOD concentration, preferably 1
/ 20 or less is desirable. Nitrogen concentration is soluble BO
When the concentration is less than 1/10 of the D concentration, the amount of nitrogen gas generated from the nitrification and denitrification reaction by the microorganisms is reduced.
Poor solid-liquid separation caused by sludge floating due to nitrogen gas in the solid-liquid separation step is prevented. That is, the nitrogen contained in the liquid to be treated is taken up by the microorganisms and consumed in the process of decomposing the organic matter. Generally, about 5 nitrogen is taken into BOD100. As a result, the growth of nitrifying bacteria is restricted in the reaction tank of the second reaction step, and the microorganism-carrying carrier added to the reaction tank of the second reaction step is not a nitrifying bacterium but a protozoan or a hardly degradable substance that contributes to flocking. It is effectively used for retaining microorganisms that contribute to the decomposition of organic matter. Conversely, BO
When nitrogen is excessively contained relative to D, for example, when the concentration exceeds 1/10 of the soluble BOD concentration, nitrate and nitrite nitrogen increase due to the growth of nitrifying bacteria, and denitrification occurs in the solid-liquid separation tank. There is a possibility that sludge floating problem may occur due to nitrogen gas generated by the nitrogen reaction. If sludge floating due to nitrogen gas occurs in the solid-liquid separation tank, it is necessary to additionally provide nitrogen removing means.

In the present invention, the reaction tank, the aeration means and the solid-liquid separation means of the first and second reaction steps can be basically of the same construction as the conventional one. In the apparatus, the reaction vessel in the first reaction step is not filled with the microorganism-holding carrier, and the reaction vessel in the second reaction step is filled with the microorganism-holding carrier to perform the treatment.

In the reaction tank of the first reaction step, the liquid to be treated is introduced, aerated by aeration means and brought into contact with microorganisms under aerobic conditions,
Decompose organic matter. In the reaction tank of the first reaction step, soluble BOD is mainly decomposed at a high BOD load. As the aeration means, a normal air diffuser such as an air diffuser may be used.However, it is preferable to increase the oxygen dissolving efficiency as much as possible. It is also possible to use a material that is sent to be refined, a device that sends pure oxygen or air with an increased oxygen concentration, or a material that is dissolved under pressure. It is preferable that the reaction tank in the first reaction step circulates the liquid to increase the oxygen dissolving efficiency.

In the reaction tank of the first reaction step, soluble BOD
Organic substances are decomposed at a high BOD load so that the removal rate is 50% or more, preferably 70 to 95%, and the soluble BOD concentration is 50 to 10000 mg / L, preferably 100 to 1000 mg / L. The soluble BOD removal rate is a load removal rate, and is a value obtained from the following equation [1].

[0019]

[Number 1] Solubility BOD removal rate _{(%) = {(C 1} × Q + C 3 × RQ-C 2 × (Q + RQ)) / (C 1 × Q)} × 100 ... (1) wherein, C ₁ Is the soluble BOD concentration (kg /
m ³ ), C ₂ is the soluble BOD concentration (kg / m ³ ) of the treatment liquid in the first reaction step, C ₃ is the soluble BOD concentration (kg / m ³ ) of the final treatment liquid, and Q is the liquid to be treated. The amount (m ³ / d) and RQ indicate the amount of returned sludge (m ³ / d). The soluble BOD concentration is a BOD concentration measured for a soluble substance specified in a sewage test method (Japan Sewage Works Association, 1997).

When the soluble BOD concentration of the effluent of the first reaction step (the processing solution of the first reaction step) is within the above range,
By reacting at a high load, for example, by reacting at a high load while supplying oxygen using a diffuser with increased oxygen dissolving efficiency such as a multi-stage ejector,
Even without adding a microorganism-carrying carrier to the reaction tank, the growth rate of microorganisms suitable for a high BOD concentration exceeds the growth rate of filamentous bacteria, and high decomposition activity can be obtained.

In the first reaction step, 50% or more, preferably 70% to 95%, of the soluble BOD is removed while suppressing the dominance of filamentous bacteria by high-load treatment, and the soluble BOD concentration is 50 to 10000 mg / day. L, preferably 100-1
An effluent of 000 mg / L is obtained. Solubility B as described above
By performing the first reaction so as to obtain an effluent having an OD removal rate and a soluble BOD concentration, it is possible to maintain a bacterial flora suitable for high-load treatment in the first reaction step,
In addition, dominance of filamentous bacteria can be prevented in the second reaction step. The organic matter is decomposed by the microorganisms held in the microorganism-carrying carrier added in the reaction tank of the second reaction step, and flocculation proceeds, so that good treated water having a low organic matter concentration and a low SS concentration can be obtained. it can.

In order to carry out the first reaction so as to obtain an effluent having the above-described soluble BOD removal rate and soluble BOD concentration, the loading conditions are changed in advance to reduce the soluble BOD load by 5%.
0% or more can be removed and the soluble BOD concentration is 50-1
It can be performed by obtaining a sludge load condition of 0000 mg / L. The load at which the effluent having the above-described soluble BOD removal rate and soluble BOD concentration is obtained in the first reaction step varies depending on the water temperature of the liquid to be treated, the amount of organic substances, the BOD concentration, and the like. -BO
D / kg-VSS / d, preferably 3 to 10 kg-BO
D / kg−VSS / d is desirable.

The first reaction step may be performed in one reaction tank, but is preferably performed in a plurality of reaction tanks. When a plurality of reaction vessels are provided, the reaction vessels may be provided in parallel or in series (stepwise), but are preferably provided in series. By performing the first reaction step in a plurality of reaction tanks, particularly in a plurality of reaction tanks provided in series, the first reaction step can be easily and stably performed even when the water quality of the liquid to be treated fluctuates. Steps can be performed. When the first reaction step is performed in a plurality of, for example, two reaction tanks provided in series, the soluble BOD removal rate, the soluble BOD concentration, and the sludge load are set so as to be within the above ranges for the entire two reaction tanks. It is preferable to prevent the bulking due to the dominance of filamentous bacteria by increasing the load of the first reaction tank, and to reduce the load of the second reaction tank slightly to remove soluble BOD. It is desirable to carry out the reaction sufficiently to ensure that the rate and the soluble BOD concentration of the effluent from the first reaction step are within the above ranges.

In the reaction tank of the second reaction step, soluble BO
D is removed by 50% or more, and the soluble BOD concentration is 50%.
A second reaction is carried out by introducing an effluent of the first reaction step of 〜１０10000 mg / L. In general, the mixed solution in the reaction tank of the first reaction step is directly used as the second mixture filled with the microorganism holding carrier.
And the reaction is carried out with a low BOD load. The load of the second reaction step is 0.01 to
It is desirably 0.5 kg-BOD / kg-VSS / d, preferably 0.05 to 0.3 kg-BOD / kg-VSS / d. To achieve such a load, the volume of the reaction tank in the second reaction step can be increased, and the residence time can be increased.

The volume ratio of the reaction tank in the first reaction step to the reaction tank in the second reaction step is smaller than the reaction tank in the first reaction step.
The volume of the reaction vessel in the second reaction step is 3 to 100 times, preferably 5 to 50 times, and the residence time HRT is 0.1 to 1200 hours, preferably 0.2 to 24 hours in the reaction vessel in the first reaction step.
hr, the reaction tank in the second reaction step is 0.5 to 24000 h
r, preferably 1 to 1200 hr.

The microorganism holding carrier (hereinafter, may be simply referred to as a carrier) to be filled in the reaction tank in the second reaction step has a material, a structure, a shape, and a size as long as the microorganism can be held on the surface and / or inside. The material is not limited, but a polymer resin, an inorganic material, or the like can be used as the material. In addition, a porous structure is preferable, and the pore size is 0.5 to 20.
mm, preferably 1 to 5 mm. The shape may be a shape that can be fixed in the reaction tank, but a shape that can flow in a granular form is preferable. In this case, the shape of the particles is arbitrary such as spherical, cubic, amorphous, etc., and the particle size may be within a flowable range, but is 3 to 30 mm, preferably 5 to 2 mm.
0 mm, specific gravity 0.5-3.0, preferably 0.8-1.
Two are preferred.

The packing ratio of the carrier in the reaction tank in the second reaction step is desirably 20 to 90%, preferably 30 to 60%. The above-mentioned filling rate indicates the ratio of the apparent volume of the carrier before microorganism attachment to the volume of the reaction tank in the second reaction step. The reaction vessel in the second reaction step is filled with the above-mentioned carrier, and aerated by aeration means to adhere microorganisms to the carrier. As aeration means, blockage by the carrier is unlikely to occur,
A material suitable for flowing the carrier is preferable, and for example, an air diffuser having a hole diameter smaller than the particle size of the carrier can be employed.

The second reaction step may be performed in one reaction tank, or may be performed in a plurality of reaction tanks. When a plurality of reaction tanks are provided, it is preferable that the carrier is filled in all the reaction tanks, but there may be a reaction tank that is not filled. When a plurality of reaction vessels are provided, the reaction vessels may be provided in parallel or in series (stepwise), but are preferably provided in series. When performing the second reaction step in a plurality of reaction vessels,
The short path of the dispersible sludge contained in the processing solution of the first reaction step is prevented, and the sludge is surely flocculated.
This has the effect of obtaining good treated water having a low concentration, and is thus preferable.
The second reaction tank is preferably provided with a carrier separation means such as a screen so that the carrier can be separated and the mixed solution can be taken out. An intermediate step or another step may be interposed between the first and second steps.

As the solid-liquid separation means in the solid-liquid separation step, known solid-liquid separation means such as a sedimentation separation tank, a pressurized flotation tank, and a membrane separation device can be used. Alternatively, the whole amount is returned to the reaction tank. Usually, it is returned to the reaction tank in the first reaction step, but it may be returned to the reaction tank in the second reaction step or to both tanks. When the BOD concentration of the liquid to be treated is extremely high, the return may not be required in some cases.

In the treatment by the above treatment apparatus, the liquid to be treated is introduced into the reaction tank as the first reaction step and aerated at a high BOD load so that the soluble BOD removal rate and the soluble BOD concentration fall within the above ranges. To decompose organic matter. Since no carrier is added to the reaction tank in the first reaction step, no effective volume is consumed by the carrier, and therefore, the sludge load is 2 kg-B.
OD / kg-VSS / d or more, 3kg-BOD
/ Kg-VSS / d or more.

In the second reaction step, the mixed solution in the reaction tank in the first reaction step is introduced into the reaction tank and aerated at a low BOD load, and the BO is aerobically aerated under the presence of a carrier with microorganisms attached thereto.
D is removed and sludge is flocculated. The reaction tank of the second reaction step is opposite to the reaction tank of the first reaction step, B
By lowering the OD load to some extent and adding a carrier, it is possible to flocculate microorganisms in a small reactor volume. The process of flocking involves many types of microorganisms, and there are many parts that are not clear.However, it is necessary that protozoa that prey on the cells and bacteria with a low growth rate coexist, and that various species be maintained. It is said that the sludge retention time SRT required for that is about 4 to 10 days. By adding a carrier, it becomes possible to maintain a sufficient amount of these microorganisms requiring the above-mentioned SRT in the system, and flocking can be achieved with a small reactor volume.

Here, the reason for setting the BOD load low is as follows.
This is because oxygen can be supplied to microorganisms inside the carrier by keeping the BOD concentration in the reaction tank in the second reaction step low. It is preferable that oxygen can be supplied to the microorganisms inside the carrier, because a large amount of the microorganisms can be retained in the reaction tank by adding a large amount of the carrier. The appropriate sludge load for keeping the oxygen supply inside the carrier suitable is within the above range, and the carrier is preferably granular in order to facilitate the supply of oxygen to the inside of a large amount of the carrier.

By performing aeration in the presence of such a carrier to which microorganisms are attached, BOD is removed and dispersible sludge introduced from the reaction tank in the first reaction step is flocculated. The sludge that has excessively adhered is separated into floating flocs and sent to the solid-liquid separation step as a mixed solution. In addition, since the soluble BOD that has not been decomposed in the reaction tank of the first reaction step, that is, the relatively hardly decomposable soluble BOD component is always supplied to the reaction tank of the second reaction step, Microorganisms that decompose organic substances that are hard to decompose are accumulated, and the COD of treated water can be reduced.

In the solid-liquid separation step, the mixed liquid in the reaction tank in the second reaction step is separated into solid and liquid, the separated liquid is taken out as a processing liquid, and part or all of the separated sludge is optionally subjected to the first and / or second separation. The excess sludge is returned to the reaction tank in the above reaction step, and is sent to a dehydration system if excess sludge is generated.

In the method of the present invention, by treating as described above, a volume load of 1.5 kg
-BOD / m ³ / d or more, specifically 1.5 to 4 kg-
BOD / m ³ / d, 0.5 to 1 kg-BOD with sludge load
Aerobic biological treatment of organic wastewater at a high load of about / kg-VSS / d, and can efficiently and stably remove organic substances, and also has good solid-liquid separation sludge. Can be formed.

[0036]

According to the present invention, the decomposition of organic substances is carried out under a high BOD load so that the soluble BOD removal rate and the soluble BOD concentration are in specific ranges in the reaction tank in the former stage, and the microorganism holding carrier in the latter stage is used. Organic substances are decomposed at a low BOD load in the filled reaction tank and sludge is flocculated. Therefore, even if the reaction tank at the preceding stage, which is treated at a high BOD load, is not filled with a carrier, excellent excretion of filamentous fungi can be achieved. Occupation can be reliably prevented, and a bacterial flora suitable for high-load processing can be maintained. Therefore, a reduction in the effective volume of the high-load reaction tank can be prevented and high-load processing can be performed. Organic substances can be efficiently removed, and sludge having good solid-liquid separation properties can be formed.

[0037]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of the processing apparatus according to the embodiment, and shows an example in which two aeration tanks are provided as reaction tanks in a first reaction step.

In FIG. 1, the first, second, and third aeration tanks 1, 2, and 3 are provided with air diffusers 5, 6, and 7, respectively, and communicate with air supply paths 8, 9, and 10, respectively, to be aerobic. It is configured to perform processing. The first aeration tank 1 has a liquid passage 1 to be treated.
1 and the return sludge passage 12 are in communication. The first, second and third aeration tanks 1, 2, 3 and the solid-liquid separation tank 4 are connected by lines 15, 16, 17. The upper part of the solid-liquid separation tank 4 is connected to a processing liquid passage 18, the lower part is connected to a sludge passage 19, and the sludge passage 19 is branched into a return sludge passage 12 and a waste sludge passage 20.

The third aeration tank 3 is filled with a granular carrier 21 and a carrier separating screen 22 is provided.
The first and second aeration tanks 1 and 2 are not filled with a carrier.
The first and second aeration tanks 1 and 2 are arranged in series, and these constitute a reaction tank in the first reaction step. A third aeration tank 3 is installed in series at a stage subsequent to the second aeration tank 2, and most of the BOD is decomposed in the first and second aeration tanks 1 and 2. Thereby, the first and second aeration tanks 1 have a high BOD load, and the third aeration tank 3 has a low BOD load.

In the treatment method using the above-described apparatus, first, as the first reaction step, the liquid to be treated and the returned sludge are introduced into the first aeration tank 1 from the liquid passage 11 and the return sludge passage 12, respectively. It mixes with sludge, sends air from the air supply path 8 and aerates from the air diffuser 5, and decomposes organic matter by an aerobic biological reaction. The mixed liquid (liquid in the tank) of the first aeration tank 1 is sent to the second aeration tank 2 and mixed with the activated sludge in the tank, and the air is supplied to the air supply passage 9.
From the air diffuser 6 to decompose organic substances by an aerobic biological reaction.

In the first and second aeration tanks 1 and 2, high BOD
The treatment is performed under load, and the decomposition of the soluble BOD is mainly performed, and the effluent of the second aeration tank 2 has a soluble BOD removal rate of 5%.
0% or more, preferably 70-95%, and soluble BOD
The concentration is 50 to 10000 mg / L, preferably 100 to
Organic substances are decomposed so as to have a concentration of 1000 mg / L. The BOD removal rate and the BOD concentration in the first aeration tank 1 may or may not fall within the above ranges, but are preferably contained. Even when the load is relatively high and the BOD removal rate in the first aeration tank 1 falls and does not fall within the above range, if it falls within the above range together with the second aeration tank 2, the process proceeds to the second reaction step. Will be sufficiently low. Conversely, when the load is low and the BOD concentration in the second aeration tank 2 is too low to fall within the above range, the BOD concentration in the first aeration tank 1 is easily maintained to be within the above range,
Since the BOD removal rate increases, it is easy to satisfy the above range only with the first aeration tank 1. Therefore, the dominance of filamentous bacteria in the first aeration tank 1 can be reliably prevented, and a bacterial flora suitable for high-load treatment can be maintained. By performing the first reaction step in the two aeration tanks of the first and second aeration tanks 1 and 2, the first reaction can be easily and stably performed even when the water quality of the liquid to be treated fluctuates. Can be.

The BOD load of the first and second aeration tanks 1 and 2 is 2 to 40 kg-BOD / kg as a total sludge load.
-VSS / d, preferably 3 to 10 kg-BOD / kg
-VSS / d is desirable. The microorganisms grow by the high concentration BOD loading, and the BOD is efficiently removed. The mixed solution in the second aeration tank 2 is sent to the third aeration tank 3, and the second reaction step is performed.

In the second reaction step, the mixed solution in the second aeration tank 2 is introduced into the third aeration tank 3 from the line 16 and mixed with the activated sludge in the tank, and is dispersed by sending air from the air supply passage 10. Air device 7
Then, microorganisms are attached to the carrier 21 to decompose the BOD by an aerobic biological reaction and to flocculate the activated sludge. The BOD load in the third aeration tank 3 is 0.01 to 0.5 kg-BOD / kg-V as sludge load.
SS / d, preferably 0.05-0.3 kg-BOD /
It is desirable to be kg-VSS / d. By performing aeration in the presence of the carrier 21 to which the microorganisms are attached, the BOD is removed, and the dispersible sludge introduced from the second aeration tank 2 is flocculated. Excess sludge is separated and becomes sludge floc. Carrier 2 by screen 22
1 and the mixed solution is sent to the solid-liquid separation tank 4 to perform a solid-liquid separation step.

In the solid-liquid separation step, the mixed liquid in the third aeration tank 3 is introduced into the solid-liquid separation tank 4 from the line 17 to be separated into solid and liquid, and the separated liquid is taken out from the treatment liquid passage 18 as a treatment liquid. The sludge is taken out from the sludge passage 19, a part of the sludge is returned as return sludge from the return sludge passage 12, and the rest is returned as sludge.
Take from 0.

In the above-described treatment method, the first and second aeration tanks 1 and 2 are aerated at a high BOD load so as to obtain a specific soluble BOD removal rate and a specific BOD concentration.
By filling the carrier 21 at a high filling rate and aerating with a low BOD load, the entire apparatus can be processed with a high load, and the BOD can be removed stably and efficiently with a small aeration tank volume. It is possible to form sludge having good solid-liquid separation properties. In this case, the first and second
Since no carrier is added to the aeration tanks 1 and 2, the effective volume is not consumed by the carrier, so that the treatment can be performed with a higher load than when the carrier is added.

[0046]

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

Example 1 A soluble BOD concentration of 2150 mg /
L, a chemical factory effluent having a nitrogen concentration of about 100 mg / L was treated. The returned sludge was returned to the first aeration tank in the same amount as the raw water. Table 1 shows the test conditions, Table 2 shows the sludge concentration and sludge load, and Table 3 shows the soluble BOD concentration and the BOD removal rate at the beginning of water passage. FIG. 2 shows the daily change of SVI. Table 4 shows the average water quality during the test period.

Example 2 The second aeration tank was omitted, the first reaction step was performed only in the first aeration tank, and the sludge load was 6.5 kg-BOD / kg.
Processing was performed in the same manner as in Example 1 except that the voltage was changed to -VSS / d. As a result, the soluble BOD concentration of the effluent of the first aeration tank was 220 mg / L.

Comparative Example 1 The sludge load of the first aeration tank was 3.2 kg-BOD / kg-V
Processing was carried out in the same manner as in Example 2 except that SS / d was changed. As a result, the soluble BOD concentration of the effluent of the first aeration tank was 42.5 mg / L (BOD removal rate 97%). In this comparative example, the soluble BOD concentration did not satisfy the conditions of the present invention.

Comparative Example 2 The sludge load of the first aeration tank was 43.0 kg-BOD / kg-
Processing was carried out in the same manner as in Example 2 except that VSS / d was changed. As a result, the soluble BOD concentration of the effluent of the first aeration tank was 832 mg / L (BOD removal rate 24%). In this comparative example, the soluble BOD removal rate did not satisfy the conditions of the present invention.

[0051]

[Table 1] * 1 Reaction tank of the first reaction step * 2 Reaction tank of the second reaction step

[0052]

[Table 2] * 1 Unit is kg-BOD / kg-VSS / d

[0053]

[Table 3] * 1 First aeration tank effluent * 2 Second aeration tank effluent * 3 Third aeration tank effluent

[0054]

[Table 4]

As can be seen from the results shown in FIG. 2, in Examples 1 and 2, the SVI was about 100 or less throughout the test period, and stable sedimentation could be maintained. on the other hand,
In Comparative Examples 1 and 2, bulking by filamentous bacteria occurred, and the treatment was substantially impossible. As can be seen from Table 4, in Examples 1 and 2, good treated water quality was obtained. Most of the nitrogen in the raw water was also removed, and no problems such as floating occurred.

[Brief description of the drawings]

FIG. 1 is a system diagram of a high-load biological treatment device according to an embodiment.

FIG. 2 is a graph showing the results of Examples.

FIG. 3 is a system diagram of a conventional high-load biological treatment device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st aeration tank 2 2nd aeration tank 3 3rd aeration tank 4,33 Solid-liquid separation tank 5,6,7,34,35 Aeration device 8,9,10,36,37 Air supply path 11,41 Cover Treatment liquid passage 12, 42 Return sludge passage 15, 16, 17, 43, 44 Line 18, 45 Treatment liquid passage 19, 46 Sludge passage 20, 47 Waste sludge passage 31 First reaction tank 32 Second reaction tank 21, 51, 52 carrier 22, 53, 54 screen

Claims (4)

[Claims] An organic effluent is introduced into a reaction tank, and is brought into contact with microorganisms under aerobic conditions. The soluble BOD removal rate is 50% or more, and the soluble BOD concentration is 50 to 10,000 mg / L.
A first reaction step in which organic substances are decomposed at a high BOD load so that the effluent of the first reaction step is introduced into a reaction tank filled with a microorganism-retaining carrier, and the microorganisms are attached to the carrier to be aerobic. A high-load biological treatment method including a second reaction step for decomposing organic matter with a low BOD load and flocculating sludge, and a solid-liquid separation step for solid-liquid separation of the effluent of the second reaction step . 2. The BOD load in the first reaction step is 2 to 40 kg-BOD / kg-VSS / d as a sludge load, and the BOD load in the second reaction step is 0.1 to 2 kg as a sludge load.
The high-load biological treatment method according to claim 1, wherein the amount is from 0.01 to 0.5 kg-BOD / kg-VSS / d. 3. The high-load biological treatment method according to claim 1, wherein the first reaction step is performed in two or more reaction vessels connected in series. 4. The method according to claim 1, wherein the nitrogen concentration of the organic effluent introduced into the first reaction tank is 1/10 or less of the soluble BOD concentration of the organic effluent. Load biological treatment method.