JPH10272484A - Wastewater treatment equipment - Google Patents

Abstract

(57) [Problem] To provide a wastewater treatment apparatus capable of preventing a screen from being clogged without increasing equipment cost and destroying a carrier. SOLUTION: In a wastewater treatment apparatus having a reaction tank filled with a microorganism-immobilized carrier 3 and provided with a screen 4 on a treated water outlet side, wastewater treatment satisfying the following conditions: apparatus. (B) The screen 4
Is 3 mm or more. (B) When the shape of the microorganism-immobilized carrier 3 is a cylinder and the inner diameter of the cylinder is Di and the outer diameter is Do, W / Do ≦ 3/4 and 0.5 ≦
Di / Do ≦ 0.8.

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 Document 1 [edited by Japan Sewer Business Development Department:
"Report on the Evaluation of a Modified Digestion-Promoting Circulation Method" Pegasus "Using Entrapped Immobilized Carriers" (1993.6)] and Reference 2 [Toshinori Kyosai: The 30th Annual Meeting of the Japan Society on Water Environment (1996) .11) P. 67-93], as a method of treating wastewater for biologically removing pollutants in wastewater, a reaction vessel is filled with a carrier, and the carrier is filled with microorganisms that decompose and remove the pollutants. There is a method of carrying it. By using this method, the concentration of microorganisms in the reaction tank can be increased as compared with the conventional activated sludge method, so that the reaction tank can be downsized and the equipment cost can be greatly reduced.

[0003] Usually, the carrier is formed of a resin such as polypropylene, and has a shape of a sphere, a cube or a cylinder having a minimum outer diameter of 1 to 30 mm. (Total volume of the carrier present per unit volume of the tank). Here, the shortest outer diameter of the carrier refers to the shortest length of a straight line connecting two points on the outer surface of the carrier, which is symmetrical with respect to a plurality of mirror target surfaces of the carrier. For a sphere, the diameter of the sphere, for a cube, the side length, for a rectangular parallelepiped, the shortest side length, and for a cylinder, the outer diameter of the cross-sectional circle is the shortest outer diameter.

[0004] However, the method using this carrier has the following problems. That is, on the treated water outlet side of the reaction tank,
1 to 1.5 m mesh width so that the carrier does not flow out of the reaction tank
Although a screen of m is provided, a carrier carrying microorganisms adheres to the surface of the screen and closes the screen, making continuous wastewater treatment impossible.

[0005] In order to prevent the screen from being clogged, there has been proposed a method of scraping off the carrier adhered to the screen surface using a brush as described in JP-A-6-238390.

[0006]

However, scraping off the mechanically attached carrier using a brush not only increases the equipment cost but also sometimes destroys the resin carrier.

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 capable of preventing a screen from being clogged without increasing equipment costs or destroying a carrier. .

[0008]

The object of the present invention is to provide a wastewater treatment apparatus having a reaction tank filled with a microorganism-immobilized carrier and provided with a screen on the treated water outlet side, which satisfies the following conditions. It is solved by a wastewater treatment device characterized by the following. (A) The width W of the screen is 3 mm or more. (B) When the shape of the microorganism-immobilized carrier is a cylinder and the inner diameter of the cylinder is Di and the outer diameter is Do, W / Do ≦
3/4, and 0.5 ≦ Di / Do ≦ 0.8.

The present inventors examined the closing behavior of the screen due to the carrier adhesion by changing the mesh width of the screen, the size and the shape of the carrier in various ways using the existing wastewater treatment apparatus. At this time, the filling rate of the carrier is fixed at 10%, and the treated wastewater is treated as wastewater (COD:
45mg / L, NH ₄ over N: 26mg / L, L is liter).

FIG. 3 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.

The present results are obtained when a cylindrical carrier is used. If the mesh width W of the screen is set to 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. Recognize. A small water level difference before and after the screen means that no blockage has occurred in the screen. Similar results were obtained when spherical or cubic carriers were used.

FIG. 4 shows the relationship between (screen width W) / (minimum outer diameter D of the carrier) and the number of carriers per unit area of the screen biting into the screen.

The results are obtained when the flow velocity through the screen is kept constant at 120 m / hr using a spherical, cubic, or cylindrical carrier. If W / D ≦ 3/4, any shape can be used. As for the carrier, no carrier caught in the screen was observed, indicating that the screen was not blocked. The shortest outer diameter D is the outer diameter Do when the carrier is a cylinder.

When the width of the screen is 3 mm or more, W / D
≦ 3/4 means that D ≧ 4 mm,
Since the volume of the carrier is inevitably increased, the surface area per unit volume of the carrier is reduced, and the treatment capacity of wastewater is reduced.

As a method for preventing a decrease in processing capacity due to an increase in volume, the packing ratio of the carrier may be increased, or the total surface area of the carrier may be secured by using a hollow carrier. But,
In the former case, the cost of the carrier is increased and the fluidity of the carrier is reduced. Therefore, it is necessary to use a hollow carrier which is easily affected by water and has excellent fluidity.

In the case of a hollow carrier, a cylindrical shape is the simplest in terms of manufacturing so as to satisfy the relationship with the mesh width of the screen, and is advantageous in terms of cost. At this time, if the ratio Di / Do is less than 0.5, the surface area of the carrier cannot be sufficiently ensured. If the ratio exceeds 0.8, the strength of the carrier is remarkably reduced, so that 0.5 ≦ Di / Do ≦
Must be 0.8.

When such a hollow carrier is used, the dead space occupied by the carrier itself can be reduced, which is advantageous from the viewpoint of securing a reaction volume in the treatment tank.

[0018]

FIG. 1 shows an embodiment of a wastewater treatment apparatus according to the present invention. In the figure, 1 is waste water, 2 is treated water, 3 is a carrier, 4 is a screen, 5 is an air diffuser, and 6 is a blower. In the following figures, the same numbers represent the same as those in FIG.

The reactor 3 is filled with a carrier 3, and a screen 4 is provided on the treated water outlet side. The reactor 3 comprises a single reaction tank. This is a wastewater treatment device having a mechanism for performing wastewater treatment.

The wastewater 1 is treated water 2 by removing pollutants by the wastewater treatment apparatus.
i, a cylindrical shape having an outer diameter Do is used, the mesh width W of the screen 4 is set to 3 mm or more, and W / Do ≦ 3/4;
By adjusting to satisfy 5 ≦ Di / Do ≦ 0.8,
No reduction in processing capacity or screen clogging occurs.

FIG. 2 shows another embodiment of the wastewater treatment apparatus according to the present invention. In the figure, 7 is the final sedimentation basin, 8 is the returned sludge, 9 is the agitator, and 10 is the circulating water.

In the first stage, there is one reaction tank in which the carrier 3 is not filled.
A tank is provided, comprising two reaction tanks filled with the carrier 3,
Moreover, it is a wastewater treatment device having a mechanism capable of performing recirculation treatment.

The wastewater 1 is treated as wastewater 2 by removing pollutants by the wastewater treatment apparatus. The sludge from the final sedimentation basin 7 is sent to the preceding reaction tank together with the circulating water 10 as return sludge 8, and is renewed. Reprocessed with wastewater. Although the screen is less likely to be clogged than in the case of FIG. 1 due to the presence of the reaction tank in the former stage, in this case, too, the carrier 3 is a cylindrical one, the mesh width W of the screen 4 is 3 mm or more, and W
If the adjustment is made so as to satisfy / Do ≦ 3/4 and 0.5 ≦ Di / Do ≦ 0.8, the processing capacity is not reduced and the screen is not blocked.

If the outer diameter Do of the cylindrical carrier is too large, the fluidity may decrease, so that the Do is preferably 100 mm or less.

As the carrier, a resin such as polypropylene, polyethylene, polystyrene, polyvinyl chloride, waste plastic, or a mixture of two or more of these resins molded into a cylinder can be used. Further, such a resin may be formed into a foam, talc, activated carbon, various ceramics, or the like may be added to the resin, or irregularities may be formed on the cylindrical surface.

[0026]

EXAMPLE A wastewater treatment apparatus shown in FIG. 1 was filled with a cylindrical and cubic polypropylene carrier having the size shown in Table 1 at a filling rate of 10%, and a wedge wire type having a wire width of 1.5 mm was used. A stainless steel screen adjusted to 3/4 of the shortest outer diameter of the carrier shown in Table 1 was installed on the treated water discharge side, and the first sedimentation tank overflow (TB) of the municipal sewage treatment plant was installed.
OD: 13045 mg / L, COD: 45 mg / L, N
H ₄ -N: 33 mg / L, L is liter), and the degree of blockage of the screen was evaluated based on the difference in water level before and after the screen, and the processing capacity was evaluated based on the removal rates of COD and NH ₄ -N. The retention time of the treated water was kept constant at 2 hr, the flow rate through the screen was kept constant at 120 m / hr, and the air was diffused so that the dissolved oxygen concentration became 3 to 4 mg / L (L is liter).

The results are shown in Table 1. When the screen width and the carrier shape are within the range of the present invention, the difference in water level before and after the screen is small and the screen is not blocked, and the removal rate of COD and NH ₄ -N is high and the processing ability is excellent. You can see that there is.

On the other hand, when the shortest outer diameter of the carrier is 3 mm,
Since the mesh width of the screen is 3/4 of the shortest outer diameter of the carrier, the mesh width of the screen is out of the range of the present invention as 2.25 mm, so that the difference in water level before and after the screen exceeds 50 mm,
Screen blockage occurs. At this time, since the carrier is small, the total surface area can be sufficiently ensured, so that the COD removal rate is 90% or more and the NH ₄ —N removal rate is 84% or more, and there is no problem in the processing ability.

When the shortest outer diameter of the carrier is 6, 10 mm, the mesh width of the screen is 4.5, 7.5 mm, respectively.
And within the scope of the present invention, the screen is not blocked, but when the carrier shape is out of the scope of the present invention as in the case of a cube or a cylinder having a Di / Do of 0.3, the COD removal rate, NH _{The 4} -N removal rate is reduced, causing a problem in processing capacity.

[0030]

[Table 1]

[0031]

Since the present invention is constructed as described above, it is possible to provide a wastewater treatment apparatus which can prevent the screen from being clogged without increasing the equipment cost and destroying the carrier.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a wastewater treatment apparatus according to the present invention.

FIG. 2 is a diagram showing another embodiment of the wastewater treatment apparatus according to the present invention.

FIG. 3 is a diagram showing the influence of the screen width W on the relationship between the front-rear water level difference between the screen and the flow velocity through the screen.

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

[Explanation of symbols]

 Reference Signs List 1 wastewater 2 treated water 3 carrier 4 screen 5 air diffuser 6 blower 7 final sedimentation tank 8 return sludge 9 stirrer 10 circulating water

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 wastewater treatment apparatus satisfies the following conditions: . (A) The width W of the screen is 3 mm or more. (B) When the shape of the microorganism-immobilized carrier is a cylinder and the inner diameter of the cylinder is Di and the outer diameter is Do, W / Do ≦
3/4, and 0.5 ≦ Di / Do ≦ 0.8.