JPH10128366A - Method for treating waste water using microorganism-immobilized carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating waste water using microorganism- immobilized carriers which can inexpensively and stably suppress the clogging of a screen caused by the carriers. SOLUTION: In a method for treating waste water using microorganism- immobilized carriers 4 wherein the carriers 4 are fed into a waste water treating tank 3 wherein a screen 5 is provided for preventing them from flowing out and waste water treatment is performed while aeration for feeding oxygen to microorganisms immobilized on the carriers 4 is performed, the carriers 4 whose specific gravity is lower than that of the waste water to be treated are used and the screen is installed on the bottom part of the waste water treating tank 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment method using a microorganism-immobilized carrier, and more particularly to a wastewater treatment method provided with a screen so that the microorganism-immobilized carrier does not flow out of a wastewater treatment tank.

[0002]

2. Description of the Related Art In a method for biologically purifying organic and inorganic substances in sewage and industrial wastewater, microorganisms are fixed on a particulate carrier made of an organic polymer substance or an inorganic substance and polluted under aerobic conditions. There is a method using a microorganism-immobilized carrier for decomposing and removing a substance. This method has a high treatment capacity because it can maintain a high concentration of microorganisms useful for treating wastewater such as nitrifying bacteria, as compared with the activated sludge method or the like, but has the following problems.

[0003] That is, the wastewater treatment tank is provided with a screen having a mesh width that does not allow the carrier to pass through on the outlet side or on both the outlet side and the inlet side in order to prevent the microorganism-immobilized carrier from flowing out. The carrier adheres and causes clogging of the screen, thereby increasing the permeation resistance of the water flow and impeding continuous wastewater treatment.

[0004] In order to suppress clogging of the screen due to the carrier, reference 1 [Department: "Characteristics and application examples of resin-based fluidized bed bioreactor", PPM, vol. 24, no. 1
1 (1993)], a screen is arranged perpendicular to the liquid surface of a wastewater treatment tank, and air diffusers are provided on the front and rear sides of the screen. Has been proposed.

FIG. 6 schematically shows a wastewater treatment method using a microorganism-immobilized carrier described in Reference 1. In FIG.
Denotes waste water, 2 denotes treated water, 3 denotes a waste water treatment tank, 4 denotes a carrier, 5 denotes a screen, 6 denotes an air diffuser, 7 denotes an air diffuser for blowing air bubbles to the screen surface, and 8 denotes a partition wall.

Since the screen 5 is provided at the upper part of the wastewater treatment tank 3 using the carrier 4 having a specific gravity larger than the specific gravity of the wastewater 1, the carrier 4 is accumulated at the lower part of the wastewater treatment tank 3 and adheres to the screen 5. It has become difficult.

However, since air is diffused from the air diffuser 6 provided at the bottom of the wastewater treatment tank 3 for supplying oxygen to the microorganisms, the carrier 4 accumulated at the lower part of the wastewater treatment tank 3 is directed upward by the air diffuser. The gas flow soars upward and easily adheres to the screen 5. Therefore, even if the air diffusing device 7 that can blow air bubbles to the screen surface is provided on the front side or the front and rear side of the screen 5, clogging of the screen cannot be sufficiently suppressed.

[0008] Reference 2 [edited by Japan Sewerage Business Development Department: "Report on Evaluation of Nitrification-Promoted Modified Circulation Method" Pegasus "Using Encapsulated Immobilized Carrier" (1993.6)] states that a screen is wastewater. A method has been proposed in which an oblique device is disposed obliquely to the liquid surface of the processing tank and an air diffuser for blowing air bubbles to the screen surface is provided on the front side of the screen.
As in the case of Document 1, since a carrier having a specific gravity larger than the specific gravity of the wastewater is used, clogging of the screen cannot be sufficiently suppressed.

Therefore, the actual situation is to enlarge the screen or scrape off the carrier adhered to the screen surface with a brush or the like as described in JP-A-6-238290.

Japanese Unexamined Patent Publication No. 57-122997 also discloses a wastewater treatment method using a carrier having a specific gravity smaller than the specific gravity of the wastewater.

[0011]

However, both the enlargement of the screen and the method described in JP-A-6-238290 lead to a significant increase in equipment costs.

Further, the method described in JP-A-57-122997 does not relate to a wastewater treatment method performed by providing a screen.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a wastewater treatment method using a microorganism-immobilized carrier, which can inexpensively and stably suppress clogging of a screen by the carrier. Aim.

[0014]

The object of the present invention is to introduce a microorganism-immobilized carrier into a wastewater treatment tank provided with a screen for preventing its outflow, and to supply oxygen to the microorganisms immobilized on the microorganism-immobilized carrier. In a wastewater treatment method using a microorganism-immobilized carrier to treat wastewater while performing aeration for,
The problem is solved by a wastewater treatment method using a microorganism-immobilized carrier having the following characteristics. (A) using a microorganism-immobilized carrier whose specific gravity is smaller than the specific gravity of the wastewater to be treated, and (b) installing the screen below the wastewater treatment tank.

Here, the lower part of the wastewater treatment tank described in (b) above depends on the specific gravity of the microorganism-immobilized carrier to be used, but in a place facing the screen without disturbing the inside of the tank by aeration or the like. It means a position where there is almost no microorganism-immobilized carrier.

By using a microorganism-immobilized carrier whose specific gravity is smaller than the specific gravity of the wastewater to be treated, and installing the screen at the lower part of the wastewater treatment tank, the carrier is accumulated at the upper part of the wastewater treatment tank and is placed at a place facing the screen. Is almost nonexistent.
For this reason, it is difficult for the carrier to adhere to the screen. In addition, since the carrier is more easily accumulated on the upper part of the wastewater treatment tank by the upward gas flow generated by the aeration for supplying oxygen to the microorganisms from the bottom of the wastewater treatment tank, clogging of the screen by the carrier is almost completely suppressed. it can.

The specific gravity of the microorganism-immobilized carrier may be smaller than the specific gravity (approximately 1) of the wastewater. However, if the specific gravity is as close as possible to 1, the carrier will not float or settle, so that it will also be present at a location facing the screen. . Therefore, the specific gravity of the carrier is desirably 0.995 or less. Also, 0.97
When the amount is less than the above, the fluidity of the carrier becomes small and a fixed bed is easily formed in the vicinity of the liquid level, so that it may become impossible to perform a sufficient wastewater treatment.

If the microorganism-immobilized carrier has a hollow shape, the surface area per unit volume of the carrier can be made larger than that of a sphere or a cube, so that the carrier filling rate of the wastewater treatment tank can be reduced. Therefore, the number of carriers present at a location facing the screen can be further reduced, which is more effective in suppressing clogging of the screen. Furthermore, since the size of the hollow carrier can be larger than that of the sphere or cubic carrier, the mesh width of the screen can be increased and a large flow of water can be passed. Therefore, the size of the screen can be further reduced. Such a carrier can be easily produced by using polypropylene having a specific gravity of less than 1 and excellent corrosion resistance as a main component.

Since a carrier having a specific gravity of less than 1 has the property of floating, if the screen is provided perpendicular to the liquid surface of the wastewater treatment tank, the carrier can be more effectively prevented from adhering to the screen.

At this time, it is more effective if air is diffused at the front side of the screen to blow air bubbles on the screen surface, since the carrier adhered by the air bubbles is easily peeled off.

Further, if the screen is provided obliquely or parallel to the liquid surface of the wastewater treatment tank and the front side of the screen, that is, the upstream side with respect to the water flow is on the liquid surface side of the wastewater treatment tank, the carrier is not covered by the screen. Since the buoyancy acts to separate the carrier, the carrier is less likely to adhere to the screen than when the carrier is provided perpendicular to the liquid surface described above.

In this case, it is more effective for the above-mentioned reason to diffuse air for blowing bubbles on the screen surface on the rear surface side of the screen, that is, on the downstream side with respect to the water flow.

The method of the present invention is a method in which the carrier is unlikely to adhere to the screen in the first place. Therefore, it is sufficiently effective that the air is not intermittently blown to the screen surface but is intermittently performed. For example, when the flow velocity of the treated water passing through the screen fluctuates, the air only needs to be diffused when the carrier having the maximum flow velocity is most likely to adhere to the screen. Also, by performing such intermittent diffusion, energy can be saved as compared with the case of continuous diffusion.

In the method of the present invention, it is only necessary to change the type of carrier and the position of the screen, and no special equipment is required.

[0025]

FIG. 1 schematically shows an embodiment of the present invention. In FIG. 1, 1 is waste water, 2 is treated water, 3 is a waste water treatment tank, 4 is a carrier, 5 is a screen, 6 is an air diffuser,
7 is an air diffuser for blowing air bubbles on the screen surface,
8 represents a partition wall. In the following figures, the same numbers represent the same as those in FIG.

In this wastewater treatment equipment, a screen 5 is provided at a lower portion of a wastewater treatment tank 3 provided with an air diffuser 6 for supplying oxygen to microorganisms at the bottom thereof, perpendicular to the liquid surface. In the wastewater treatment tank 3, a carrier 4 having a specific gravity smaller than the wastewater 1
, And most of the carriers 4 are present at the top of the screen 5. Also, at the bottom of the screen 5,
An air diffuser 7 for blowing air bubbles to the screen surface is provided on the front side.

The wastewater 1 is supplied to the wastewater treatment tank 3, and the wastewater is treated while diffusing with the diffuser 6. Since the carrier 4 having a floating property is pushed up by the upward gas flow due to the aeration, the carrier 4 does not exist at the place facing the screen 5. Therefore, clogging of the screen 5 does not occur. At this time, it is more effective if air is continuously or intermittently diffused by the air diffuser 7 for blowing air bubbles on the screen surface provided on the front side of the screen 5.

FIG. 2 schematically shows another embodiment of the present invention. In this case, the screen 5 is provided in such a manner that the screen 5 is provided in parallel with the liquid surface of the wastewater treatment tank 3 and the front side of the screen 5, that is, the upstream side with respect to the water flow is the liquid surface side of the wastewater treatment tank 3. By arranging the screen 5 in this manner, the carrier 4 having the property of floating is arranged on the screen 5.
Hard to adhere to Further, an air diffuser 7 for blowing air bubbles on a screen surface provided on the rear side of the screen 5.
When the air is diffused, an upward gas flow is generated from the rear side of the screen 5, which is more effective.

FIG. 3 schematically shows another embodiment of the present invention. In this case, the screen 5 is provided obliquely with respect to the liquid surface of the wastewater treatment tank 3 and the front side of the screen 5, that is, the upstream side with respect to the water flow is provided on the liquid surface side of the wastewater treatment tank 3. 1 and 2, the carrier 4 hardly adheres to the screen 5. Further, it is more effective if air is diffused by the air diffuser 7 for blowing air bubbles to the screen surface provided on the rear side of the screen 5.

FIG. 4 schematically shows an embodiment of a screen provided with an air diffuser on the rear side. In FIG. 4, reference numeral 9 denotes a diffuser header, and reference numeral 10 denotes a projection. (A) is an example in which a plurality of diffuser headers 9 are provided on the rear side of the screen 5, and (b) is an example in which a plurality of projections 10 are provided on the screen 5.

The structure of the screen provided with the air diffuser on the rear side is made in this manner, so that the screen 5 of the carrier 4 is formed.
Can be more completely prevented.

The packing ratio of the microorganism-immobilized carrier is preferably 1 to 40% based on the true volume of the carrier, but the length is 2 to 8%.
In the case where a hollow cylindrical polypropylene having an outer diameter of about 2 to 8 mm is used as a main component, the filling rate is more preferably 3 to 15% based on the true volume.

Although the water depth of the wastewater treatment tank is generally about 5 m, the method of the present invention can be applied to an aeration tank having a water depth of 10 to 20 m, which is called a deep aeration method.

The wastewater treatment tank may be provided with a plurality of screens. In this case, the screens are provided in any combination of vertical, oblique, and parallel to the liquid level of the wastewater treatment tank.

The wastewater treatment tank does not need to be one stage, but may be multistage. In this case, the screen of each tank may be provided in any manner perpendicular, oblique, or parallel to the liquid level of the wastewater treatment tank.

The method of the present invention in which a screen is provided at the lower part of a wastewater treatment tank using a microorganism-immobilized carrier having a specific gravity smaller than the specific gravity of wastewater is used not only under aerobic conditions in which dissolved oxygen is present but also in the absence of dissolved oxygen. It can also be applied to oxygen conditions and microaerobic conditions where dissolved oxygen is present in trace amounts. In this case, in order to reduce the amount of dissolved oxygen, it is necessary to use large air bubbles for blowing air bubbles to the screen surface or to diffuse gas with a low oxygen concentration gas. Alternatively, a pump may be provided in the wastewater treatment tank to generate a water flow without spraying air bubbles to the screen surface to prevent the carrier from adhering to the screen.

[0037]

EXAMPLE In a treatment tank having an effective water depth of 4.5 m, a width of 1 m and a depth of 3 m, immobilization of microorganisms in the form of a hollow cylinder having an outer diameter of 4 mm, an inner diameter of 3 mm, and a length of 5 mm made of polypropylene with a specific gravity of 0.98 was used. The carrier is charged at a true volume based filling rate of 5%,
A wedge wire type screen having a mesh width of 2.5 mm and an effective area of 0.5 m ² is placed at the bottom of the treatment tank, perpendicularly to the wastewater level as shown in FIG. 1 (Example A of the present invention), or as shown in FIG. Wastewater treatment was performed by providing the liquid surface parallel to the liquid surface (Example B of the present invention), and the relationship between the flow rate through the screen (wastewater supply amount) and the water level difference between the front and rear surfaces of the screen was investigated. The air was diffused at a flow rate of 150 L / min (L represents liter; the same applies hereinafter) by an air diffuser provided at the center bottom of the processing tank to supply oxygen to the microorganisms. In addition, in Example A of the present invention, the air diffused to the screen was 30 L / min on the front side of the screen.
In the present invention example B, the air diffusion rate was 30 L / min on the rear side of the screen.

For comparison, a similar investigation was carried out using a polypropylene carrier having a specific gravity of 1.02 and a mesh width of 2.0.
As shown in FIG. 6, a wedge wire type screen having an area of 5 mm and an effective area of 1 m ² was provided on the upper part of the treatment tank perpendicular to the liquid level of the wastewater. At this time, the air was diffused to the screen at a rate of 30 L / min on the front and rear surfaces of the screen.

FIG. 5 shows the results. In both cases A and B of the present invention, the water level difference between the front and rear surfaces of the screen increases with an increase in the flow velocity through the screen, but the rate of increase with respect to the flow velocity is smaller than in the conventional example. Further, at any of the screen passing velocities, the water level difference of the invention examples A and B is less than 1/2 of the water level difference of the conventional example even though the effective area of the screen is as small as 1/2.

From the above, it can be seen that the clogging of the screen by the carrier is greatly improved by the method of the present invention.

[0041]

As described above, the present invention is constructed as described above, so that it is possible to provide a wastewater treatment method using a microorganism-immobilized carrier, which can inexpensively and stably suppress the clogging of the screen by the carrier.

Further, according to the wastewater treatment method of the present invention, since the screen is not clogged, the size of the screen can be further reduced, and the construction cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing one embodiment of the present invention.

FIG. 2 is a diagram schematically showing another embodiment of the present invention.

FIG. 3 is a diagram schematically showing another embodiment of the present invention.

FIG. 4 is a view schematically showing one embodiment of a screen provided with an air diffuser on the rear surface side.

FIG. 5 is a diagram illustrating a relationship between a screen passing velocity and a water level difference between front and rear surfaces of the screen.

FIG. 6 is a diagram schematically showing a wastewater treatment method using a microorganism-immobilized carrier described in Document 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 wastewater 2 treated water 3 wastewater treatment tank 4 carrier 5 screen 6 air diffuser 7 air diffuser for blowing air bubbles on screen surface 8 partition wall 9 air diffuser header 10 protrusion

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toyoshi Sawada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (8)

[Claims] 1. A microorganism-immobilized carrier is charged into a wastewater treatment tank provided with a screen for preventing the outflow thereof, and the wastewater is discharged while performing aeration for supplying oxygen to the microorganisms immobilized on the microorganism-immobilized carrier. A wastewater treatment method using a microorganism-immobilized carrier to be treated, the method comprising using a microorganism-immobilized carrier having the following characteristics. (A) using a microorganism-immobilized carrier whose specific gravity is smaller than the specific gravity of the wastewater to be treated, and (b) installing the screen below the wastewater treatment tank. 2. The specific gravity of the microorganism-immobilized carrier is 0.97.
The wastewater treatment method using the microorganism-immobilized carrier according to claim 1, wherein the concentration is from 0.995 to 0.995. 3. The method for treating wastewater using a microorganism-immobilized carrier according to claim 1, wherein the microorganism-immobilized carrier is a hollow material mainly composed of polypropylene. 4. The wastewater treatment using the microorganism-immobilized carrier according to any one of claims 1 to 3, wherein the screen is provided perpendicular to a liquid surface of the wastewater treatment tank. Method. 5. The wastewater treatment method using a microorganism-immobilized carrier according to claim 4, wherein air is diffused on the front side of the screen to blow air bubbles onto the screen surface. 6. The screen is provided obliquely or parallel to the liquid level of the wastewater treatment tank, and the front side of the screen, that is, the upstream side with respect to the water flow is on the liquid level side of the wastewater treatment tank. A wastewater treatment method using the microorganism-immobilized carrier according to any one of claims 1 to 3. 7. The wastewater treatment method using the microorganism-immobilized carrier according to claim 6, wherein air is diffused to blow air bubbles on the screen surface on the rear surface side of the screen, that is, on the downstream side of the water flow. . 8. The method for treating wastewater using a microorganism-immobilized carrier according to claim 5, wherein the aeration for blowing air bubbles on the screen surface is performed intermittently.