JPH10272485A - Wastewater treatment equipment - Google Patents

Abstract

(57) [Problem] To provide a wastewater treatment apparatus using a microorganism-immobilized carrier capable of preventing screen clogging without increasing the size of equipment. SOLUTION: In a wastewater treatment apparatus having a reaction tank filled with a microorganism-immobilized carrier and having a screen on the treated water outlet side, the mesh width of the screen is set to W, and the shortest outer diameter of the microorganism-immobilized carrier is set to W. D / W / D ≦ 3 /
4. An apparatus for treating wastewater, wherein the relationship of W ≧ 3 mm is satisfied at least in the reaction tank located on the most upstream side with respect to the flow of treated water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment apparatus for biologically treating wastewater using a microorganism-immobilized carrier (hereinafter, simply referred to as a carrier).

[0002]

2. Description of the Related Art As a method of treating wastewater for biologically removing sludge material in wastewater, there is a method in which a reaction vessel is filled with a carrier, and a microorganism for decomposing and removing the sludge material is carried on the carrier. . By using this method, the concentration of microorganisms in the reaction tank can be made higher than in the conventional activated sludge method, so not only can the reaction tank be reduced in size and the equipment cost can be significantly reduced,
Processing time can also be reduced. Also, JP-A-7-256
No. 291, a plurality of reaction vessels filled with a carrier are provided,
A method for reducing the size of each reaction tank and further improving the processing efficiency has also been proposed.

However, the method using a carrier has the following problems. In other words, a screen is provided on the treated water outlet side of the reaction tank so that the carrier does not flow out of the reaction tank. Wastewater treatment becomes impossible. In particular, in a reaction tank located on the most upstream side with respect to the flow of wastewater in a treatment apparatus having a plurality of reaction tanks, the load of the sludge substance on the carrier is large, so that the screen is likely to be clogged.

In order to prevent screen clogging,
Reference 1 [bureau: “Characteristics and application examples of resin-based fluidized bed bioreactor”, PPM, vol. 24, no. 11 (199
3)] and Reference 2 [edited by the Japan Sewerage Business Development Department: “Report on Evaluation of a Modified Digestion-Promoting Circulation Method“ Pegasus ”Using Entrapped Immobilized Carriers” (1993.6)] A method is disclosed in which an air diffuser is provided and air bubbles are sprayed on the screen surface to prevent the carrier from adhering.

[0005] However, since this is not enough, there have been proposed methods of increasing the size of the screen or scraping off the carrier adhered to the screen surface using a brush as described in JP-A-6-238290. I have.

[0006]

However, increasing the size of the screen or providing a brush all leads to an increase in the size of the equipment, and goes against the downsizing of the equipment, which is the greatest merit of using a carrier. Will do.

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 apparatus using a carrier capable of preventing screen clogging without increasing the size of equipment. I do.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to provide a wastewater treatment apparatus having a reaction tank in which a carrier is filled and a screen is provided on the treated water outlet side, wherein the mesh width of the screen is W, When the outer diameter is D, W / D ≦ 3 /
4, and a relation of W ≧ 3 mm is satisfied at least in the reaction tank located on the most upstream side with respect to the flow of the treated water.

In a wastewater treatment apparatus having a reaction tank provided with a carrier and a screen provided on the treated water outlet side, the shortest outer diameter is usually 1 to 30 mm in the form of a sphere, a cube, or a hollow cylinder. Is filled at a filling rate of about 10% (total volume of the carriers present per unit volume of the reaction tank), and a screen having a mesh width of 1 to 1.5 mm is used. Here, the shortest outer diameter of the carrier means the following. In other words, the currently used carrier has a shape having a plurality of mirror-symmetric surfaces, but the length of a straight line connecting two points on the outer surface of the carrier which is symmetrical with respect to the mirror-target surface. Means the shortest length. The diameter of a sphere in a sphere, the length of a side in a cube, the length of the shortest side in a rectangular parallelepiped, the outer diameter of a cross-section of a hollow cylinder if the axis of the cylinder is longer than the outer diameter of the cross-section,
When the length of the shaft is shorter than the outer diameter of the sectional circle, the length of the shaft becomes the shortest outer diameter.

The present inventors divide the reaction tank consisting of a single tank into two parts, an upstream side and a downstream side, with respect to the flow of the treated water, and make the mesh width W of the screen provided in the upstream side reaction tank equal to the width of the screen provided in the upstream side. Shortest outer diameter D of the spherical, cubic, or hollow cylindrical carrier filled in the reactor
We examined what conditions could prevent screen clogging. At this time, in the reaction vessel on the downstream side, the shortest outer diameter of the carrier was 3 mm, and its filling rate was 10 mm.
%, The mesh width of the screen was 1.2 mm, which was the condition employed in the conventional reaction layer. The packing ratio of the carrier in the upstream reaction tank was kept constant at 10%. The treated wastewater is wastewater treated at an urban sewage treatment plant (T-BOD: 120m
g / l, TN: 32 mg / l, NH-N: 26 mg /
l).

FIG. 4 shows the relationship between (screen width W) / (shortest outer diameter D of the carrier) and the number of carriers per unit area of the screen that is engaged in the screen of the upstream reaction tank.

This result shows that the flow velocity through the screen is 120 m /
hr, but if W / D ≦ 3/4,
No carrier caught in the screen was observed in any of the carrier shapes, indicating that the screen was not clogged.

Therefore, the screen width of the screen is set to (3 ×
D) / 4 or less can prevent the clogging of the screen. However, when the screen width is small, when the flow rate through the screen is increased in order to increase the processing efficiency, the effect of obstructing the water flow by the screen itself appears, In this case, the pressure difference is large and the screen is broken. In addition, the water level at the outlet side of the treated water usually needs to be constant (river water level, etc.), so the water level at the front of the screen must rise, so a wastewater supply port is installed at a high place to pump up the wastewater. And energy and equipment costs increase.
Therefore, the extent to which the mesh width of the screen can be reduced was investigated by changing the flow velocity through the screen. At this time,
The conditions for the downstream reaction tank were the same as those described above, a carrier satisfying the shortest outer diameter D = (4 × W) / 3 was used for the upstream reaction tank, and FIG. 4 was obtained for other conditions. The conditions were the same.

FIG. 5 shows the effect of the screen width W on the relationship between the water level difference before and after the screen and the flow velocity through the screen.

If the mesh width W of the screen is 3 mm or more, the difference in water level before and after the screen can be suppressed even if the flow velocity through the screen is increased. Therefore, breakage of the screen can be prevented, and there is no need to provide a wastewater supply port at a high place. Although the results are obtained when a spherical carrier is used, substantially the same results were obtained when a cubic or hollow cylindrical carrier was used.

In both cases of FIGS. 4 and 5, in the downstream reaction tank, the water level difference before and after the screen was suppressed to 15 mm or less, which was a practically acceptable level.

From the above results, (screen width W)
If / (the shortest outer diameter D of the carrier) ≦ 3/4 and the mesh width W of the screen is 3 mm or more, clogging of the screen and destruction of the screen during processing can be prevented, and the wastewater supply port is disposed at a high place. Is no longer necessary.

When W / D ≦ 3/4 and W ≧ 3 mm, D ≧ 4 mm must be satisfied, and the volume of the carrier is inevitably increased, so that the surface area per unit volume of the carrier is decreased. Therefore, depending on the degree, the treatment capacity of the wastewater may decrease, but the filling rate of the carrier is increased,
This can be prevented by changing the shape and increasing the surface area.

In order to maintain the fluidity in the reaction tank and to secure a surface area enough to prevent a decrease in processing capacity,
The shortest outer diameter of the carrier is preferably 100 mm or less.

[0020]

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is waste water, 2 is treated water, 3 is the screen of the (most) upstream reaction tank, 4 is the screen of the downstream reaction tank, 5
Denotes a carrier in the (most) upstream reaction tank, 6 denotes a carrier in the downstream reaction tank, 7 denotes an air diffuser, and 8 denotes a blower. In the following figures, the same numbers represent the same as those in FIG.

A single-layer reaction tank having a mechanism for supplying oxygen to microorganisms by a diffuser 7 provided at the bottom by a blower 8 is separated into two tanks, an upstream side and a downstream side, with respect to the flow of treated water. A screen 3 having a mesh width W is newly provided in the reaction tank, and is changed to a carrier 5 having the shortest outer diameter D different from that before separation.
At this time, the screen 4 having the same conventional mesh width and the carrier 6 having the shortest outer diameter are used in the downstream reaction tank.

Thus, the upstream reaction tank is provided, and the mesh width W of the screen 3 and the shortest outer diameter D of the support 5 in this tank where the load of the sludge substance is large on the support are W / D ≦ 3/4 and W
If the adjustment is made so as to be ≧ 3 mm, clogging of the screen does not occur not only in the upstream reaction tank but also in the downstream reaction tank.

FIG. 2 shows another embodiment of the present invention.
In the case where a plurality of reaction tanks are provided, also in this case, the mesh width W of the screen 3 and the shortest outer diameter D of the carrier 5 of the most upstream reaction tank are W.
By adjusting so as to satisfy / D ≦ 3/4 and W ≧ 3 mm, clogging of the screen can be prevented.

FIG. 3 shows still another embodiment of the present invention. In the figure, 9 is a stirrer, 10 is a final sedimentation basin, 11 is returned sludge, and 12 is circulating water.

This is a wastewater treatment apparatus which comprises a reaction vessel filled with a plurality of carriers in which a reaction vessel not filled with carriers is provided at a preceding stage, and which can be recycled. Since there is a reaction tank in the first stage, clogging is less likely than in the above two cases,
Also in this case, the mesh width W of the screen 3 of the reaction tank on the most upstream side.
And the shortest outer diameter D of the carrier 5 is W / D ≦ 3/4 and W ≧ 3 m
By adjusting so as to satisfy m, clogging of the screen can be prevented.

In any case, the mesh width of the screen in the downstream reaction tank and the shortest outer diameter of the carrier may be the same as the mesh width of the screen in the most upstream reaction tank and the shortest outer diameter of the carrier. . Since the processing capacity tends to decrease because the size of the carrier is increased in all the layers, it is necessary to optimize the packing ratio and shape of the carrier.

[0027]

Since the present invention is constructed as described above, it is possible to provide a wastewater treatment apparatus using a carrier capable of preventing screen clogging without increasing the size of the equipment.

[Brief description of the drawings]

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

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

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

FIG. 4 is a diagram showing a relationship between (screen mesh width) / (shortest outer diameter of carrier) and the number of carriers per unit area of the screen biting into the screen.

FIG. 5 is a diagram showing the influence of the mesh width of the screen on the relationship between the water level difference before and after the screen and the flow velocity through the screen.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Wastewater 2 Treated water 3 Screen of upstream reaction layer 4 Screen of downstream reaction layer 5 Carrier of upstream reaction layer 6 Carrier of downstream reaction layer 7 Air diffuser 8 Blower 9 Stirrer 10 Final sedimentation tank 11 Returned sludge 12 Circulating water

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

Claims (1)

[Claims] 1. A wastewater treatment apparatus having a reaction tank filled with a microorganism-immobilized carrier and having a screen on the treated water outlet side, wherein the screen width is W, the shortest outer diameter of the microorganism-immobilized carrier. Is D, W / D ≦ 3 /
4. An apparatus for treating wastewater, wherein the relation of W ≧ 3 mm is satisfied at least in the reaction tank located at the most upstream side with respect to the flow of wastewater.