JP2000334490A - Biological denitrification and dephosphorization apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the capacity of a cleaning blower for air cleaning of microorganism carrier in an aerobic vessel. SOLUTION: Phosphorus is eluted from sludge in an anaerobic vessel 10. Nitric acid in circulating liquid is removed in a denitrification vessel 12. In the aerobic vessel 14, nitrification treatment is performed, at the same time, phosphorus is taken into the sludge and, in a sedimentation vessel 16, the sludge is sedimented, thereby, the treated water which is subjected to denitrification and dephosphorization is obtained. Therein, the microorganism carrier 40 is arranged in the aerobic vessel 14 and, underneath the carrier, a cleaning air injecting member 42 is arranged. Further, the cleaning air injecting member 42 is divided into plural blocks and, at the time of cleaning, the respective blocks inject the cleaning air and clean the microorganism carrier 40 every block in order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for circulating raw water in the order of an anaerobic tank, a denitrification tank, an aerobic tank, and a sedimentation tank, returning sludge from the sedimentation tank to the anaerobic tank, and mixing the aerobic tank. The present invention relates to a biological denitrification and dephosphorization apparatus for performing a denitrification and a dephosphorization treatment by circulating a liquid through a denitrification tank, and particularly relates to an apparatus in which a microorganism carrier is disposed in an aerobic tank.

[0002]

2. Description of the Related Art Hitherto, there has been known a biological denitrification dephosphorization apparatus in which raw water is circulated in the order of an anaerobic tank, a denitrification tank, an aerobic tank, and a sedimentation tank to perform denitrification and dephosphorization treatment. . In this apparatus, the raw water first flows into the anaerobic tank, where it is mixed anaerobically with the sludge returned from the settling tank. By the anaerobic treatment in the anaerobic tank, the elution of phosphorus from the sludge is promoted.
Next, the mixed liquid from the anaerobic tank flows into the denitrification tank, where it is mixed with the circulating liquid from the aerobic tank. As a result, a denitrification process for reducing and removing nitric acid in the circulating fluid from the aerobic tank using the organic matter (BOD (biochemical oxygen demand) component) in the raw water as a hydrogen donor is performed. Next, the mixed solution from the denitrification tank flows into the aerobic tank that has been aerated, where nitration of ammoniacal nitrogen and the like contained in the raw water is performed. At this time, the sludge that has undergone anaerobic treatment in the anaerobic tank excessively ingests phosphoric acid in the liquid. Then, the mixed solution from the aerobic tank flows into the sedimentation tank and is subjected to precipitation treatment, whereby treated water from which nitrogen and phosphorus have been removed is obtained in the supernatant. The organic matter in the raw water is removed in the denitrification tank and the nitrification tank.

In such a biological denitrification / dephosphorization apparatus, nitrifying bacteria responsible for nitrification in an aerobic tank have a slow growth rate, which causes a long residence time in the aerobic tank. . Therefore, the entrapment immobilization method in which a nitric acid bacterium is taken into gel beads and fixed and a few millimeter square cube is flowed in an aerobic tank, or a resinous sphere with a diameter of several millimeters is flowed in an aerobic tank and nitrified into this sphere Methods for attaching bacteria have been proposed.

[0004] In each of these methods, the nitrifying activity of the entire treatment system is maintained at a high level by keeping nitrifying bacteria that grow slowly at a high concentration in the aerobic tank, and as a result, the processing time in the aerobic tank is reduced. What you want to do.

However, in these methods, since the microbial carrier is made to flow in the aerobic tank, the flowability of the microbial carrier must be maintained and the outflow of the microbial carrier out of the aerobic tank must be prevented. There is a problem in operation management, such as no longer.

[0006] To solve such problems,
Japanese Patent Application Laid-Open No. 9-10793 proposes a method of disposing a fixed-bed type microorganism carrier in an aerobic tank.
In this method, a net-like microbial carrier having a predetermined gap is installed in an aerobic tank, so that ordinary suspended sludge, water to be treated, and aerated air can pass through the gap, and sludge containing nitrifying bacteria. Is attached to the surface of the microorganism carrier. As a result, the nitrifying bacteria can be held in the aerobic tank at a high density, and the nitrification activity of the entire processing system can be increased. As a result, the processing time in the aerobic tank can be reduced. Also, in this method, it is not necessary to fluidize the microorganism carrier in the aerobic tank,
There are few problems in operation management.

[0007]

However, in this method, BOD oxidizing bacteria excessively adhere to the microorganism carrier depending on the installation place of the microorganism carrier and operating conditions, and protozoa that prey on the BOD oxidizer colonize. When excessive BOD oxidizing bacteria adhere to the microorganism carrier, the activity of the nitrifying bacteria adhered to the microorganism carrier cannot be maintained at a sufficient level.

In order to solve this problem, it is conceivable to periodically introduce air below the microorganism carrier to perform air cleaning of the microorganism carrier. By this air washing, excess microorganisms can be peeled off, and the surface of the microorganism carrier can be maintained in a state suitable for adhesion and growth of nitrifying bacteria.

[0009] However, when such cleaning air is supplied to the microorganism carrier, a considerably large capacity blower is required as a cleaning blower, and the equipment cost and operation management cost of the whole apparatus increase. There was a point.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a biological denitrification / dephosphorization apparatus capable of performing sufficient cleaning with a relatively small cleaning blower.

[0011]

According to the present invention, raw water is circulated in the order of an anaerobic tank, a denitrification tank, an aerobic tank, and a sedimentation tank.
In the biological denitrification dephosphorization device for performing denitrification and dephosphorization by returning the settled sludge from the settling tank to the anaerobic tank and circulating the mixture in the aerobic tank to the denitrification tank, the aerobic tank A microbial carrier disposed in the aerobic tank; an aerated air pipe provided in the aerobic tank for ejecting aerated air; and an intermittent provided below the microbial carrier in the aerobic tank. Cleaning air piping for jetting the cleaning air to clean the microorganism carrier, and switching means for partially supplying the cleaning air to the cleaning air piping and sequentially switching the supply portion. Features.

As described above, according to the present invention, it is possible to prevent the sludge from adhering excessively to the microorganism carrier in the aerobic tank to a level that inhibits the nitrification activity by air cleaning, and to reduce the environment near the microorganism carrier by nitrifying bacteria. It is possible to maintain a state suitable for attachment and habitat.

[0013] Since the air for washing is partially and sequentially supplied to the microorganism carrier at the time of the air washing, the amount of the air for washing at the time of washing can be relatively reduced, and the equipment becomes expensive. Can be prevented. Further, as the microorganism carrier, one obtained by laminating and laminating a large number of plastic net pipes, or one having a large number of standing erect pipes is preferable.

It is preferable that the aeration air supplied to the aeration air pipe and the cleaning air supplied to the cleaning air pipe be used by branching air from a single air supply source. If there is room in the air supply source, the air for cleaning can be supplied by increasing the amount of air during cleaning. If there is no room, the air for cleaning can be supplied by reducing or partially stopping the air for aeration.

[0015]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a denitrification / dephosphorization apparatus according to an embodiment. As described above, this apparatus has, as its basic components, an anaerobic tank 10, a denitrification tank 12, and an aerobic tank 1
4, a sedimentation tank 16 is provided. Raw water, which is treated water,
First, it flows into the anaerobic tank 10. The sludge returned from the settling tank 16 is also supplied to the anaerobic tank 10. The inside of the anaerobic tank 10 is stirred by the stirrer 22. Therefore, in the anaerobic tank 10, the returned sludge and the raw water are mixed and stirred under anaerobic conditions. By this anaerobic treatment, the sludge releases phosphorus.

Next, in the anaerobic tank 10, the mixture of sludge and raw water subjected to the anaerobic treatment flows into the denitrification tank 12. A part of the aerobic treatment liquid supplied from the aerobic tank 14 to the sedimentation tank 16 flows into the denitrification tank 12 as a circulating liquid. Further, the denitrification tank 12 is provided with a stirrer 24, and the mixed liquid from the anaerobic tank 10 and the circulating liquid from the aerobic tank 14 are mixed under the condition of facultative anaerobic (anoxic condition). . Here, the circulating liquid from the aerobic tank 14 contains nitric acid. Therefore, in the denitrification tank 12, a denitrification treatment for reducing nitric acid using organic matter in raw water as a hydrogen donor is performed. Thereby, the organic matter in the raw water is oxidized and removed, and the nitrate nitrogen in the aerobic treatment liquid is removed.

The mixed liquid in the denitrification tank 12 flows into the aerobic tank 14. A diffuser member 32 connected to an aeration air pipe 30 is disposed at the bottom of the aerobic tank 14, and the inside of the tank is aerated. The aerobic tank 14 is divided by a partition wall 34 into a front-stage aeration unit 36 and a rear-stage aeration unit 38, and a microorganism carrier 40 is arranged above the diffusing member 32 of the rear-stage aeration unit 38. Furthermore, the latter aeration unit 3
A cleaning air ejection member 42 is arranged below the microbial carrier 40 along the air diffusion member 32. Cleaning air is supplied to the cleaning air ejection member 42 via a cleaning air pipe 44. Further, the diffusion member 32 has a porous diffusion plate or the like, and supplies the supplied aerated air as fine bubbles into the liquid in the tank. On the other hand, the cleaning air ejection member 4
Numeral 2 is provided with an opening in a pipe, and ejects a relatively large-diameter bubble from the opening. Further, the amount of air jetted from the cleaning air jetting member 42 is set to be larger than the corresponding amount of air from the air diffusing member 32, thereby cleaning the microorganism carrier 40.

As described above, aeration air is supplied to the aerobic tank 14, so that the inside of the tank is maintained under aerobic conditions, where oxidation of organic substances and oxidation of organic nitrogen and ammonia nitrogen are performed. That is, nitration (including nitritation) is performed. In particular, a microorganism carrier 40 is disposed in the rear aeration unit 38. Therefore, the microorganisms are held in the microorganism carrier 40, the microorganisms in the tank are maintained at a high concentration, and an effective nitrification treatment can be performed.

In particular, in this embodiment, the microorganism carrier 4
As 0, a number of materials 40a in the form of a pipe made of a plastic net material as shown in FIG. The microbial carrier 40 has a high porosity, and an air diffusion member 32 is disposed below the microbial carrier 40, so that air and the liquid in the tank flow through the voids of the microbial carrier 40. As a result, the microorganisms held in the microorganism carrier 40 and the liquid in the tank are effectively brought into contact with each other, oxygen is supplied to the microorganisms, and an effective nitrification treatment is performed.

The microorganism carrier 40 is not necessarily limited to that shown in FIG. 2, and various microorganism carriers such as those shown in Japanese Patent Application Laid-Open No. 9-10793 can be used.

In addition, air is not normally supplied to the cleaning air jetting member 42. Then, a relatively large amount of air is periodically supplied thereto, whereby the microorganism carrier 4 is supplied.
Separation of sludge from zero is promoted, and accumulation of excessive microorganisms on the microorganism carrier 40 is prevented.

A part of the processing liquid from the aerobic tank 14 is circulated to the denitrification tank 12 and the other part flows into the settling tank 16. The sedimentation tank 16 is placed in an aerobic tank 14 in a substantially stationary state.
The solid matter (sludge) in the treatment liquid is settled and separated. And
The supernatant water from which solids have been removed is discharged as treated water.
On the other hand, part of the settled sludge settled at the bottom of the settling tank 16 is returned to the anaerobic tank 10 as returned sludge, and the other part is pulled out of the system as surplus sludge.

Next, a configuration for cleaning the microorganism carrier 40 will be described with reference to FIG. FIG. 3 is a diagram showing a configuration example of the air piping in the aerobic tank 14. First, the aeration air piping 30 is connected to the aeration blower 50, and the aeration air from the aeration blower 50 is used as the aeration air. The air is supplied to the air diffusing member 32 through the pipe 30, and aeration is performed from here. The aeration in the tank by the aeration air is basically performed continuously.

On the other hand, the cleaning air pipe 44 is connected to a cleaning blower 54 via a plurality of cleaning air switching valves 52. The cleaning is performed periodically at a predetermined time interval.
Each one is opened sequentially. Therefore, the cleaning air ejection member 42
The cleaning air is jetted in order from the one corresponding to one of the cleaning air switching valves 52. In the illustrated example, five cleaning air switching valves 52 are provided. As a result, the cleaning air jetting member 42 is divided into five blocks, and the cleaning air is jetted sequentially from each block. As a result, the microorganism carriers 40 located above the cleaning air jetting member 42 of each block are sequentially air-cleaned.

By such air cleaning, the microorganism carrier 4
0 is partially washed sequentially to remove and remove excess sludge. Here, the cleaning air blows out bubbles having a higher linear velocity than a normal aeration state. That is, the cleaning air supplied to each block of the cleaning air ejection member needs to be larger than the normal aeration air amount supplied to the block, and for example, is preferably about twice.

By supplying the cleaning air partially sequentially, the cleaning blower can be made relatively small while the linear velocity of the cleaning air is maintained at a sufficiently high value.

Next, FIG. 4 shows another embodiment. In this embodiment, the aeration blower 50 is also used as an air source for cleaning the microorganism carrier 40 without installing a cleaning blower.

If the output of the aeration blower 50 is variable and the output has a margin, the cleaning air can be supplied by increasing the output of the aeration blower 50 during cleaning. However, in general, the aeration blower 50 is operated in a fixed amount. Therefore, the microorganism carrier 4
When cleaning 0, it is preferable to reduce or stop the ventilation to the usual aeration equipment.

That is, the cleaning air pipe 44 is connected to the aeration air pipe 30 from the aeration blower 50. A valve 52 is provided in the cleaning air pipe 44, and a valve 56 is provided in the aeration air pipe 30, so that the supply of air to both the pipes 44 and 30 can be individually turned on and off. And
Normally, all the valves 52 are closed and the diffusing member 3 is closed.
Air is blown out from 2 to aerate the inside of the tank. When cleaning the microorganism carrier 40, a part of the valve 56 provided in the aeration air pipe 30 is closed, and the valve 52 provided in the cleaning air pipe 44 is sequentially opened for each block. Thereby, air is sequentially jetted from the cleaning air jetting member 42,
The microorganism carrier 40 can be sequentially washed.

In the configuration shown in FIG.
Although a plurality of valves 56 are provided, a portion for obtaining aeration air instead of cleaning air is determined in advance, and one valve 56 may be provided to cut off air to the portion. Good. Further, the valve 56 provided in the aeration air pipe 30 does not have to be closed, and the amount of air may be reduced. Further, as described above, instead of controlling the valve 56, the air amount of the aeration blower 50 may be increased to thereby obtain the cleaning air.

As described above, the anaerobic tank 1 is cleaned by air cleaning.
0, a microorganism carrier 4 in an aerobic tank 14 of a biological nitrogen phosphorus removing apparatus having a denitrification layer 12, an aerobic tank 14, and a sedimentation tank 16.
When 0 is installed, sludge is prevented from excessively adhering to the level that inhibits nitrification activity on the microbial carrier 40, and the environment near the microbial carrier 40 is maintained in a state suitable for adhering nitrifying bacteria and inhabiting. Becomes possible.

Since the air for washing is partially and sequentially supplied to the microorganism carrier 40 at the time of the air washing, the amount of the air for washing at the time of washing can be relatively reduced, and the equipment is expensive. Can be prevented.

The washing time of the microorganism carrier 40 to which the sludge has adhered is 1 to 60 minutes per time, and the washing air amount is usually 1 to 10 times, preferably 1 to 5 times the air linear velocity at the time of aeration. Desirably.

The microorganism carrier 40 may be made of synthetic resin, natural fiber or the like, and may be in the form of a string, a mesh lattice, a honeycomb, or the like. In particular, when the cylindrical lattice-shaped microorganism carrier 40 as shown in FIG. 2 is used, the fluidity of the suspended sludge does not decrease, and the sludge attached to the microorganism carrier 40 can be easily separated.

"Design Example" The following shows a comparison between a case where the design is performed by the conventional method and a case where the design is performed based on the present invention, taking a sewage treatment facility as an example.

(Design Conditions) Planned daily maximum inflow: 10,000 m ³ / d Planned daily average inflow (Q _in ): 8,000 m ³ / d Inflow water quality BOD ₅ ( _{CBOD, in} ): 130 mg / L soluble _{BOD 5 (C S-BOD,} in): 88mg / L SS (C SS, in): 70mg / L TN (C TN, in): 36mg / L T-P: 3.2mg / L final sedimentation tank target quality of treated water _{BOD5 (C BOD, eff):} 10mg / L SS (C SS, eff): 5mg / L TN (C TN, eff): 12mg / L NO 2 + NO 3 (C NOX, eff ): 10 mg / L Organic nitrogen: 2 mg / L T-P: 1 mg / L Design water temperature: 13 ° C. MLSS (X): 3,000 mg / L (Aerobic tank capacity and shape) Aerobic tank required for the present invention Capacity 2 When 00m ^3, the effective depth of the aerobic tank 5 m, if the width is 8m, if the tank length of the flow direction and 51m,
The aerobic tank capacity required for the present invention can be secured.

That is, 5 × 8 × 51 = 2,040 (m
³ )

This is divided into three tanks, and one tank has a tank length of 17 m. Of the tanks divided into three tanks,
The tank shall be provided with a lattice-shaped microorganism carrier. A diffuser for aeration is usually arranged at the bottom of the aerobic tank, and an air pipe for washing is also installed at the bottom of the two tanks after the microorganism carrier is installed.

As shown in FIG. 5, in the first tank, there is no microbial carrier, no washing air piping, and only aeration piping.
In the third tank, a microorganism carrier is arranged, and an aeration pipe and a cleaning air pipe are arranged.

(Selection of Blower) Under the above conditions, the amount of air required for normal aeration was determined by calculation, and the required amount of air was 105,000 Nm ³ / d. In order to obtain the required air amount of 105,000 Nm ³ / d, a model with the following capacity is usually selected for the blower for aeration.

Normal blower for aeration: 80 (Nm ³ / mi)
n) 80 × 60 × 24 = 115,200 (Nm ³ / d) On the other hand, at the time of washing the microorganism carrier, the ventilation is performed at a linear velocity twice that of the normal aeration. The linear air velocity during normal aeration is as follows.

Aerobic tank bottom area: 8 × 51 = 408 (m ² ) Air linear velocity during normal aeration: 105,000 {408} 2
60 (m / d) Hereinafter, a cleaning blower is selected for each cleaning air supply method.

When all the microorganism carriers are washed at the same time (conventional method): The bottom area of the microorganism carrier filled portion: 8 × 17 × 2 = 272
(M ² ) Required air volume for washing: 260 × 272 × 2 = 141,4
40 (Nm ³ / d) Blower selected: 100 (Nm ³ / min) 100 × 60 × 24 = 144,000 (Nm ³ / d) When the microorganism carrier is washed sequentially (in the present invention) The microorganisms to be washed at one time Make the carrier 1/8 of the whole. Bottom area of microbial carrier packed part to be washed: 8 × 17 × 2 ÷ 8 =
34 (m ² ) Air required for washing: 260 × 34 × 2 = 17,680
(Nm ³ / d) Blower selected: 15 (Nm ³ / min) 15 × 60 × 24 = 21,600 (Nm ³ / d) When washing is performed by a blower for normal aeration (the present invention) Microorganisms to be washed at one time Make the carrier 1/8 of the whole. The required air amount is the same as the value obtained above, and is 17,680.
(Nm ³ / d). Assuming that this amount of air is normally supplied by an aeration blower, the following is obtained.

Normal aeration Required air volume: 105,000
(Nm ³ / d) Required air volume during washing: 17,680 (Nm ³ / d) Required air volume Total: 122,680 (Nm ³ / d) Blower selected (normal blower for aeration): 90 (Nm ³ / mi)
n) 90 × 60 × 24 = 129,600 (Nm ³ / d) The above calculation results are summarized in Table 1, and it has been confirmed that the present invention can significantly reduce equipment cost.

[0046]

[Table 1]

[0047]

As described above, according to the present invention,
Since the air cleaning of the microbial carrier in the aerobic tank can be partially performed sequentially, the capacity of the cleaning blower can be reduced, or the cleaning blower can be omitted, and the cleaning can be performed using the aeration blower. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of an apparatus according to an embodiment.

FIG. 2 is a view showing a material of a microorganism carrier.

FIG. 3 is a diagram illustrating a configuration example of an air pipe of an aerobic tank when a cleaning blower is provided.

FIG. 4 is a configuration example of an air pipe of an aerobic tank when a cleaning blower is not provided.

FIG. 5 is a diagram showing a shape of an aerobic tank in a design example.

[Explanation of symbols]

10 anaerobic tank, 12 denitrification tank, 14 aerobic tank, 16 sedimentation tank, 22, 24 stirrer, 30 aerated air piping, 32
Diffuser member, 40 microorganism carrier, 42 cleaning air jetting member, 44 cleaning air pipe, 50 aeration blower, 52,
56 valves, 54 cleaning blowers.

Claims (2)

[Claims] 1. The raw water circulates in the order of an anaerobic tank, a denitrification tank, an aerobic tank, and a sedimentation tank, the sludge settled in the sedimentation tank is returned to the anaerobic tank, and the mixed solution in the aerobic tank is circulated to the denitrification tank. In the biological denitrification and dephosphorization apparatus for performing the denitrification and dephosphorization treatment, a microorganism carrier disposed in the aerobic tank and adhering and holding microorganisms is provided in the aerobic tank, and aeration is performed. An aeration air pipe for ejecting air; a washing air pipe provided below the microorganism carrier in the aerobic tank and intermittently ejecting washing air to wash the microorganism carrier; A biological denitrification / dephosphorization apparatus, comprising: a switching means for partially supplying cleaning air to a pipe and sequentially switching a supply section. 2. The apparatus according to claim 1, wherein the aeration air supplied to the aeration air pipe and the cleaning air supplied to the cleaning air pipe use air branched from a single air supply source. A biological denitrification dephosphorization apparatus characterized by the above-mentioned.