JP2001314883A - Biological treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological treatment apparatus capable of stably and efficiently removing an organic substance under a high load and forming sludge having good solid-liquid separation properties. A liquid to be treated 11 and return sludge 12 are introduced into a high-load biological reaction tank 1, and a mixture of air and liquid is ejected from a nozzle 6 toward a downward pipe 3 to be aerated, thereby achieving an oxygen dissolving efficiency. The treatment is carried out at a high BOD load while maintaining a high BOD, and mainly the decomposition of the soluble BOD is carried out. The mixed solution in the high-load biological reaction tank 1 is introduced into the first flocking tank 13 and mixed with the activated sludge in the tank, aerated from the air diffuser 19 to adhere microorganisms to the carrier 23, and to reduce the BOD load. Perform processing and B
Decomposes OD and flocks activated sludge.
The mixed liquid in the first flocking tank 13 flows over the partition plate 15 and flows into the second flocking tank 14 so that the residence time is averaged, and is treated with a low BOD load as in the case of the first flocking tank. To decompose the BOD and floc the activated sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological treatment apparatus 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. Therefore, as a method of reducing the size of the activated sludge reaction tank, a method of connecting a plurality of reaction tanks in series, that is, a method generally called a two-stage activated sludge method has been proposed (for example, Japanese Unexamined Patent Publication No. Sho 55 (1985)).
-28759).

FIG. 2 is a system diagram showing a conventional treatment apparatus using a two-stage activated sludge method. In FIG. 2, reference numeral 41 denotes a first reaction tank, 42 denotes a second reaction tank, and 43 denotes a solid-liquid separation tank. First
And second reaction tanks 41 and 42 are each provided with an air diffuser 44,
45, which are configured to communicate with air passages 46 and 47, respectively, to perform aerobic treatment.

In the treatment method using the above-described apparatus, first, the liquid to be treated and the return sludge are introduced into the first reaction tank 41 from the liquid passage 51 and the return sludge passage 52, respectively, and mixed with the activated sludge in the tank. The air is sent from the air passage 46 and the air diffuser 44
To decompose BOD by aerobic biological reaction. The liquid mixture in the first reaction tank 41 is introduced from the line 53 into the second reaction tank 42 and mixed with the activated sludge in the tank.
And aeration from the air diffuser 45 to decompose BOD by aerobic biological reaction and to flocculate activated sludge. The mixed liquid in the second reaction tank 42 is introduced into the solid-liquid separation tank 43 from a line 54 to be separated into solid and liquid, and the separated liquid is taken out of the processing liquid path 55 as a processing liquid.
And a part is returned from the return sludge passage 52 as return sludge, and the remainder is removed from the waste sludge passage 57 as surplus sludge.

[0005] The two-stage activated sludge method is a method in which the BOD concentration in the first reaction tank is maintained high by setting the load of the first reaction tank 41 of the first step high, thereby obtaining a high decomposition rate. is there. At this time, in the first stage, a decomposition rate 10 times or more as large as the design value of the standard activated sludge method is obtained, so that the volume of the reaction tank can be significantly reduced only by removing the soluble components. However, microorganisms growing in the first reaction tank 41 with a high load are in a dispersed state, and solid-liquid separation is difficult.

[0006] In order to generate flocs that can be separated into solid and liquid, conditions are required in which various microorganisms such as protozoa having a relatively low growth rate can exist. For this reason, in the second reaction tank 42 as the second and subsequent reaction tanks, even if the BOD load is small, the sludge residence time SRT must be sufficient, and the tank volume must be large. Therefore, the total volume of the reaction tank including the second and subsequent stages is usually reduced by only about 30% as compared with the standard activated sludge method. In addition, even when the average sludge retention time in the second reaction tank 42 is sufficiently ensured, a problem that the liquid in a part of the tank flows out of the second reaction tank 42 earlier than the average residence time stays, and that a short pass easily occurs. There is a point. When a short path occurs, the dispersed bacteria flowing from the first reaction tank flow out before contacting and being taken in with the sludge floc of the second reaction tank. May decrease.

On the other hand, as another treatment method for reducing the volume of a reaction tank, a method has been proposed in which a carrier for adhering and holding microorganisms is added to a high-load biological reaction tank and a low-load biological reaction tank (for example, Japanese Unexamined Patent Publication (Kokai) No. 2002-157572). 2000-42584). This method can form a sludge floc with good solid-liquid separation properties, but since the high-load biological reaction tank is filled with the carrier, the effective volume of the high-load biological reaction tank is consumed by the carrier and reduced. I do.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a biological treatment apparatus which can remove organic substances stably and efficiently under a high load and can form sludge having good solid-liquid separation properties. To provide.

[0009]

The present invention relates to the following biological treatment apparatus. (1) A high-load biological reaction tank that decomposes organic matter by performing aeration at a high BOD load, and is disposed at a stage subsequent to the high-load biological reaction tank, and aerates a mixed solution of the high-load biological reaction tank at a low BOD load. A biological treatment apparatus comprising: a low-load biological reaction tank that decomposes organic matter and flocs sludge; and a solid-liquid separation unit that separates a mixture of the low-load biological reaction tank into treated water and sludge. , The low-load biological reaction tank,
A biological treatment apparatus comprising at least two flocking tanks connected in series. (2) The biological treatment apparatus according to the above (1), wherein at least one of the flocking tanks is filled with a microorganism carrier. (3) In the high-load biological reaction tank, a circulation path for circulating the liquid in the tank, a mixing device for mixing the circulating liquid with an oxygen-containing gas, and a gas-liquid mixture mixed by the mixing device are ejected into the liquid in the tank. The biological treatment apparatus according to the above (1) or (2), comprising: a nozzle that performs the treatment; and a circulation pump.

[0010] In this specification, the term low-load biological reaction tank is used as a collective term for a plurality of flocking tanks connected in series, which are provided at the subsequent stage of the high-load biological reaction tank. The term first flocking tank refers to the first flocking tank provided immediately after the high-load biological reaction tank among a plurality of flocking tanks connected in series, and hereinafter in the direction of the solid-liquid separation means. The second flocking tank and the third flocking tank in this order. . . This is called the final flocking tank.
When the low-load biological reaction tank is composed of two flocking tanks, the second flocking tank is the final flocking tank.

The liquid to be treated in the present invention is an effluent containing an organic substance to be treated by a usual aerobic biological treatment method, but contains an organic or inorganic substance which is hardly biodegradable. And ammonia nitrogen or organic nitrogen or the like may be contained. Such organic effluents include sewage, night soil, food factory effluent, chemical factory effluent, and other industrial effluents. The nitrogen concentration (TN) of the organic effluent is 1/10 of the soluble BOD concentration
Or less, preferably 1/20 or less. If the nitrogen concentration is less than 1/10 of the soluble BOD concentration,
Since the amount of nitrogen gas generated from the nitrification denitrification reaction by the microorganisms is reduced, solid-liquid separation failure caused by sludge floating by nitrogen gas in the solid-liquid separation step is prevented.

In the present invention, the high-load and low-load biological reaction tanks, the aeration means and the solid-liquid separation means can be basically of the same construction as conventional ones. The high-load biological reaction tank is not filled with the microorganism-retaining carrier, and the low-load biological reaction tank is composed of two or more, preferably 2 to 4, flocking tanks. The flocking tank is a conventional low-load biological reaction tank (aeration tank)
Can be used, and one aeration tank can be partitioned by partitioning means such as a partition plate into a plurality of flocking tanks,
Separate aeration tanks may be connected in series to form a plurality of flocking tanks. When a single aeration tank is partitioned, it is partitioned perpendicularly to the direction from the inlet to the outlet of the liquid to be treated or in a direction opposite to the flow. It is preferable that at least one of the flocking tanks is a flocking tank filled with a microorganism-holding carrier.

The high-load biological reaction tank introduces the liquid to be treated, aerates it with aeration means, contacts the microorganisms under aerobic conditions, and decomposes organic matter. In high-load biological reactors, mainly soluble BO
Decompose D at high BOD load. As the high-load biological reaction tank, air, oxygen or oxygen-enriched air may be used, and a normal aeration means such as a diffuser may be used.However, an aeration means capable of increasing oxygen dissolving efficiency as much as possible may be used. It is preferable to use those provided with, for example, those in which a gas-liquid mixture is jetted into a liquid in a tank to generate fine bubbles; those in which bubbles are mechanically shredded and dispersed; it can. Among them, the one that spouts the gas-liquid mixture into the liquid in the tank to generate fine bubbles is preferable. As such a high-load biological reaction tank, a circulation path that circulates the liquid in the tank, a mixing device that mixes the oxygen-containing gas with the circulating liquid in the circulation path, and a gas-liquid mixture that is mixed by the mixing device is placed in a tank. One provided with a nozzle for jetting into the internal liquid and a circulation pump. In such a high-load biological reaction tank,
The mixed solution in the reaction tank is sucked by a circulation pump, and an oxygen-containing gas is mixed into the sucked circulating liquid by a mixing device, and the obtained gas-liquid mixture is supplied from a nozzle provided at the end of the circulation path to the liquid in the tank. By jetting into the air, fine bubbles are generated, thereby increasing the oxygen dissolving efficiency.

[0014] The low-load biological reaction tank is disposed downstream of the high-load biological reaction tank, and the mixed solution of the high-load biological reaction tank is subjected to low BO reaction.
This is a flocking tank that decomposes organic matter by aeration under D load and flocks sludge, and is composed of at least two tanks connected in series. By providing a plurality of flocking tanks connected in series, averaging of the residence time is promoted, and a short path hardly occurs. For this reason, the bacteria in a dispersed state flowing from the high-load biological reaction tank come into sufficient contact with the sludge flocs of the low-load biological reaction tank and are taken up by the flocs. Decrease in separability is prevented, and flocs excellent in solid-liquid separability can be obtained.

The high-load biological reaction tank has a high BOD load, and the low-load biological reaction tank has a low BOD load.
The load is based on the load of the soluble BOD as an index, and the high-load biological reaction tank is 2 to 40 kg-BOD as the soluble BOD sludge load.
/ Kg-VSS / d, preferably 3-10 kg-BOD
/ Kg-VSS / d. With the above load, dominance of filamentous bacteria can be prevented. Low load biological reaction tank is 0.01-0.5kg-BOD
/ Kg-VSS / d, preferably 0.05 to 0.3 kg
-BOD / kg-VSS / d is desirable. In addition, the load of the low-load biological reaction tank is a load as an all-floc tank.

In the low-load biological reaction tank, a low-load reaction is performed by introducing the effluent of the high-load biological reaction tank. Generally, the mixed solution of the high-load biological reaction tank is directly introduced into the first flocking tank, and then the second flocking tank. . . It is introduced in the order of the final flocking tank, and aeration is performed at a low BOD load such that the sludge load as described above as a whole is used to decompose organic substances. In this case, the volume of the low-load biological reaction tank (the entire flocking tank) can be made larger than the volume of the high-load biological reaction tank, and the residence time can be lengthened. The volume ratio of the high-load biological reactor to the low-load biological reactor is such that the volume of the low-load biological reactor is 3 to 100 times, preferably 5 to 50 times, and the residence time HRT is higher than that of the high-load biological reactor. The bioreactor is 0.1-1200 hr, preferably 0.2-24 hr
r, the load of the low-load biological reaction tank can be 0.5 to 24000 hr, preferably 1 to 1200 hr.

It is preferable that at least one of the flocking tanks is filled with a microorganism carrier (hereinafter sometimes simply referred to as a carrier). By filling the carrier, the tank volume can be made smaller. The material, structure, shape, size, and the like of the carrier are not limited as long as it can hold microorganisms on the surface and / or inside, 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 m.
m, 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 spherical,
Any shape such as a cubic shape and an amorphous shape may be used, and the particle size may be within a flowable range, but is 3 to 30 mm, preferably 5 to 20 m.
m, specific gravity of 0.5 to 3.0, preferably 0.8 to 1.2 are suitable.

The packing ratio of the carrier in the flocking tank is 20.
It is desirably about 90%, preferably 30% to 60%. The above packing ratio indicates the ratio of the apparent volume of the carrier before the microorganisms adhere to the volume of the low-load biological reaction tank. In a flocking tank filled with a carrier, microorganisms can be attached to the carrier by aeration with aeration means. When the carrier is filled, it is preferable to provide a carrier separating means such as a screen so that the carrier can be separated and the mixed solution can be taken out.

The high-load biological reaction tank performs the high-load reaction step. This step may be constituted by a single aeration tank, or may be constituted by a plurality of aeration tanks. A plurality of aeration tanks may be provided in parallel, or may be provided in series (stepwise).
By providing a plurality of aeration tanks as the high-load biological reaction tank, a high-load biological reaction can be easily and stably performed even when the water quality of the liquid to be treated fluctuates. Especially when installed in series, the effect of preventing filamentous bacteria is great. In addition, intermediate or other steps may be interposed between the high and low load reaction 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 high-load biological reaction tank, but it may be returned to the low-load biological reaction tank, or may be returned 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 biological treatment apparatus of the present invention, a liquid to be treated is introduced into a high-load biological reaction tank as a high-load reaction step, and aerated at a high BOD load to decompose organic substances. In a high-load biological reactor, the BO in the reactor is
It is necessary to keep the D concentration high, and the sludge load is
The load is preferably set to 40 kg-BOD / kg-VSS / d, particularly in the above range. Since no carrier is added to the high-load biological reaction tank, no effective volume is consumed by the carrier, so that the treatment can be performed at a higher load.

In the low-load reaction step, the mixed solution in the high-load biological reaction tank is sequentially introduced from the first flocking tank to the final flocking tank, aerated at a low BOD load, and BOD is removed under aerobic conditions. Floc sludge. The low-load biological reaction tank can reduce the BOD load to some extent, contrary to the high-load biological reaction tank, and can flocculate microorganisms with a small reaction tank volume. When the carrier is filled, it is desirable to add 20 to 90%, preferably 30 to 60% of the carrier. 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. The sludge retention time SRT required for that is 4
It is said to be about 10 days. By providing a plurality of flocking tanks, averaging of the residence time can be promoted to make it difficult for a short path to occur, and thus flocs having excellent solid-liquid separation properties can be formed. When a carrier is filled, it is possible to maintain a sufficient amount of these microorganisms that require the above-mentioned SRT in the system, and it is possible to stably form flocs with a smaller reactor volume.

Here, the reason for setting the BOD load low is as follows.
This is because the bacteria in the dispersed state generated by the high-load treatment in the first stage are preyed on the protozoa, and the production of a viscous substance for the cells to floc is promoted. When the carrier is filled, if the BOD load is low, it is possible to supply oxygen to the microorganisms inside the carrier, so that a large amount of microorganisms having a long required SRT can be held in the reaction tank. Therefore, the tank volume can be made smaller. 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 this way, B
As the OD is removed, the dispersible sludge introduced from the high-load biological reaction tank flocks. 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 low-load biological reaction tank is always supplied with a soluble BOD that has not been decomposed in the high-load biological reaction tank, that is, a relatively hard-to-decompose soluble BOD component, a relatively hard-to-decompose organic substance is added to the carrier. Microorganisms that decompose water are accumulated, and an increase in the COD of the treated water can also be prevented.

In the solid-liquid separation step, the mixed liquid in the final flocking tank is subjected to solid-liquid separation, the separated liquid is taken out as a treatment liquid, and part or all of the separated sludge is returned to the high-load biological reaction tank as necessary, and excess sludge is removed. If this occurs, send it to the dehydration system.

[0026]

According to the biological treatment apparatus of the present invention, a high-load biological reaction tank that decomposes organic matter by performing aeration at a high BOD load;
A low-load biological reaction tank that decomposes the organic matter by aerating the mixed solution of the high-load biological reaction tank at a low BOD load and flocs sludge, wherein the low-load biological reaction tank is connected at least in series. Since it is composed of two tanks, it is possible to remove organic substances stably and efficiently under a high load, and to form sludge having good solid-liquid separation properties.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of the processing apparatus of the embodiment, and shows an example in which two flocking tanks are provided in series as a low-load biological reaction tank, and both flocking tanks are filled with a carrier.

In FIG. 1, the high-load biological reaction tank 1 includes a circulation path 2 for circulating the liquid in the tank, and a downward pipe 3 having both ends opened and supported vertically in the liquid in the tank. A circulating pump 4 and an air mixing device 5 are provided in the passage 2. At the end of the circulation path 2, a nozzle 6 is provided in a state where the nozzle 6 is accommodated in an upper end opening portion of the downward pipe 3. An air supply path 7 communicates with the air mixing device 5, and the air and the circulating liquid are mixed by the air mixing device 5, and this gas-liquid mixture is ejected from the nozzle 6 into the liquid in the tank to perform aerobic treatment. Is configured. A liquid path 11 to be treated and a return sludge path 12 communicate with the high-load biological reaction tank 1. The high-load biological reaction tank 1 is not filled with a carrier.

First and second flocking tanks 13 and 14
Are provided in series by being partitioned by a partition plate 15 in a direction perpendicular to the direction from the inlet to the outlet of the liquid to be treated, and these constitute a low-load biological reaction tank. The partition plate 15 is provided such that the liquid mixture in the first flocking tank 13 flows over the partition plate 15 and flows into the second flocking tank 14. A flow hole can be formed in the partition plate 15, but a shape that does not cause back mixing is preferable. The first and second flocking tanks 13 and 14 are each provided with an air diffuser 1
9 and 20, and communicate with the air passages 21 and 22, respectively.
It is configured to perform aerobic treatment.

The first and second flocking tanks 13 and 14 are filled with granular carriers 23 and 24, respectively. The first and second flocking tanks 13 and 14 are provided with carrier separation screens 25a and 25b, respectively.
The first and second flocking tanks 13 and 14 are installed at the subsequent stage of the high-load biological reaction tank 1, and the high-load biological reaction tank 1 and the first flocking tank 13 communicate with each other via a line 27, and B in the liquid to be treated is removed.
Most of the OD is decomposed in the high-load biological reactor 1. Thus, the high-load biological reaction tank 1 has a high BOD load, and the first and second flocking tanks 13 and 14 have a low BOD load.

The second flocking tank 14 and the solid-liquid separation tank 31 are connected by a line 28. The upper part of the solid-liquid separation tank 31 is connected to a treatment channel 32, and the lower part is connected to a sludge channel 33.
The sludge passage 33 branches into the return sludge passage 12 and the waste sludge passage 34.

In the treatment method using the above-described apparatus, first, as a high-load reaction step, the liquid passage 11 to be treated is placed in the high-load biological reaction tank 1.
The liquid to be treated and the return sludge are introduced from the return sludge passage 12, respectively, mixed with the activated sludge in the tank, and the organic matter is decomposed by an aerobic biological reaction. In this case, the circulation pump 4
The liquid in the tank is suctioned by the
And the air supplied from the air supply path 7 is mixed in
The obtained gas-liquid mixture is jetted downward from the nozzle 6 into the liquid in the tank of the downward pipe 3. By performing aeration in this manner, fine bubbles are generated, and aerobic treatment can be performed while maintaining high oxygen dissolution efficiency.

In the high-load biological reaction tank 1, the treatment is performed at a high BOD load, and mainly the decomposition of soluble BOD is performed. The BOD load of the high-load biological reaction tank 1 is 2 to 40 as a sludge load.
kg-BOD / kg-VSS / d, preferably 3 to 10
It is desirable to set kg-BOD / kg-VSS / d.
Microorganisms proliferate due to high concentration BOD loading, and BO
D is removed. The mixed solution in the high-load biological reaction tank 1 is sent from the line 27 to the first flocking tank 13 to perform a low-load reaction process.

In the low-load reaction step, the liquid mixture in the high-load biological reaction tank 1 is introduced into the first flocking tank 13 through the line 27, mixed with the activated sludge in the tank, and air is sent from the air supply passage 21. Aeration is performed from the air diffuser 19 to attach microorganisms to the carrier 23, decompose the BOD by an aerobic biological reaction, and flocculate the activated sludge. The mixed solution in the first flocking tank 13 flows over the partition plate 15 and flows into the second flocking tank 14. The carrier 23 is separated by the screen 25a. The influent is mixed with the activated sludge in the tank in the second flocking tank 14, and air is sent from the air supply passage 22 to the air diffuser 2.
Aeration is performed from 0 to attach microorganisms to the carrier 24, decompose BOD by an aerobic biological reaction, and flocculate the activated sludge.

The BOD load in the first and second flocking tanks 13 and 14 is 0.01 to 0.5 k as a sludge load.
g-BOD / kg-VSS / d, preferably 0.05 to
It is desirable to set it to 0.3 kg-BOD / kg-VSS / d. By performing aeration in the presence of the carriers 23 and 24 to which the microorganisms are attached, the BOD is removed and the dispersible sludge introduced from the high-load biological reaction tank 1 is flocculated. Excess sludge is separated and becomes sludge floc. The carrier 24 is separated by the screen 25b and the second
The mixed solution in the flocking tank 14 is sent to the solid-liquid separation tank 31 to perform a solid-liquid separation step.

In the solid-liquid separation step, the mixed solution in the second flocking tank 14 is introduced from a line 28 into a solid-liquid separation tank 31 to be separated into treated water and sludge, and the separated liquid is treated as treated water. 32, the sludge is taken out of the sludge path 33,
A part is returned from the return sludge passage 12 as return sludge, and the remainder is taken out from the waste sludge passage 34 as excess sludge.

In the above treatment method, the high-load biological reaction tank 1
Since no carrier is added to, effective volume consumption by the carrier does not occur, so that processing can be performed with a higher load. In addition, since the circulation path 2 is provided, and the aerobic treatment is performed by ejecting a gas-liquid mixture to generate fine bubbles, the oxygen dissolving efficiency can be increased and the treatment can be performed with a higher load. In addition, since the first and second flocking tanks 13 and 14 are provided to perform the low-load reaction step, the averaging of the residence time is promoted, and a short path hardly occurs. Bacteria in a dispersed state flowing from the biological reaction tank 1 come into sufficient contact with the sludge flocs of the first and second flocking tanks 13 and 14 to be taken into the flocs, thereby forming sludge having good solid-liquid separation properties. can do. Further, since the carriers 23 and 24 are filled, the tank volume can be further reduced.

[0038]

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

Test Example Using the apparatus shown in FIG. 1, the BOD concentration was 3560 mg / L and the SS
Wastewater from a chemical manufacturing plant having a concentration of 13.5 mg / L was treated. However, in the case of the comparative example, one partition was not provided and one tank was provided. In the example, the first, second, and third flocking tanks were provided using two partition plates. Change the conditions to RUN1 to RU
N6 was tested. RUN1 to RUN4 are comparative examples, R
UN5 and UN6 are examples. Table 1 shows the test conditions. The MLSS of the reaction tank was set at about 5000 mg / L. The total capacity of the high-load biological reactor and the low-load biological reactor is the same for all RUNs, and the volume ratio of the high-load biological reactor and the low-load biological reactor is changed to adjust the sludge load on the high-load biological reactor. did.

RUN1 to RUN3 were tested by changing the sludge load of the low-load biological reactor. For RUN4, the carrier was added to the low-load biological reactor. In RUN5, the first to third flocking tanks were provided, but the carrier was not added to any tanks. In RUN 6, the carrier was added to all of the first to third flocking tanks. The carrier is a cube with a side of 10 mm,
A polyurethane sponge having a pore diameter of 1.0 mm was used. The filling rate was 60% in all tanks. The results are shown in Tables 2 and 3.

[0041]

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

[0042]

[Table 2]

[0043]

[Table 3]

As a result of the test, RUN1 caused bulking by filamentous bacteria. RUN 2 and 3 did not bulk. As can be seen from the results in Table 3, when the low-load biological reaction tank is a plurality of tanks connected in series, it is effective in reducing the SS concentration of the treated water, and RUN6 <RUN5 ≒ R
UN4 <RUN3. It is also found that the addition of the carrier is effective.

[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 system diagram of a conventional high-load biological treatment device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High load biological reaction tank 2 Circulation path 3 Down pipe 4 Circulation pump 5 Air mixing device 6 Nozzle 7 Air supply path 11, 51 Liquid path to be processed 12, 52 Returned sludge path 13 First flocking tank 14 Second flocking Tanks 19, 20, 44, 45 Air diffusers 21, 22, 46, 47 Air supply paths 23, 24 Carriers 25a, 26b Screens 27, 28, 53, 54 Lines 31, 43 Solid-liquid separation tanks 32 Processing water paths 33, 56 Sludge passage 34, 57 Waste sludge passage 41 First reaction tank 42 Second reaction tank 55 Treatment liquid passage

Claims (3)

[Claims] 1. A high-load biological reaction tank that decomposes organic matter by performing aeration at a high BOD load, and a mixed liquid in the high-load biological reaction tank that is disposed at a subsequent stage of the high-load biological reaction tank and aerated at a low BOD load. Biodegradation tank that decomposes organic matter and flocs sludge, and solid-liquid separation means that separates the liquid mixture in the low-load biological reaction tank into treated water and sludge. In the apparatus, the low-load biological reaction tank includes at least two flocking tanks connected in series. 2. The biological treatment apparatus according to claim 1, wherein at least one of the flocking tanks is filled with a microorganism carrier. 3. The high-load biological reaction tank has a circulation path for circulating the liquid in the tank, a mixing device for mixing the circulating liquid with an oxygen-containing gas, and a gas-liquid mixture mixed by the mixing device. And a circulating pump.
Or the biological treatment device according to 2.